Program

Saptarshi Das​

Penn State University​

2D Materials for 3D Integration, Advanced Logic, and More

In this talk, I will explore the intersection of artificial intelligence (AI), advanced materials, and novel computing architectures, focusing on the development of bio-inspired circuits for neuromorphic and edge sensing applications. By leveraging the unique properties of two-dimensional (2D) materials, such as MoS2, WSe2, and graphene, I will demonstrate their potential in enabling energy-efficient, scalable, and highly adaptable circuits that emulate biological neural systems. These circuits are particularly well-suited for edge computing and sensing tasks, where compactness and power efficiency are critical. One example of this approach is leveraging AI and machine learning (ML) to enhance the performance of graphene-based electronic tongue for food safety, environmental monitoring, and healthcare applications (Nature, 634, 572–578, 2024). Furthermore, we have demonstrated bio-inspired computing paradigms that replicate complex biological processes, including auditory processing in barn owls, collision avoidance in locusts, probabilistic computing in dragonflies, and multisensory integration in octopuses. By combining 2D materials with bio-inspired principles, we are paving the way for compact, functionally diverse integrated circuits that harness the power of neuromorphic processing. Finally, beyond bio-inspired circuit design, I will delve into the transformative potential of monolithic 3D integration using emerging 2D field-effect transistors (FETs). Our recent breakthroughs in wafer-scale 2-tier and 3-tier 3D integration with MoS2 and WSe2 FETs have enabled the realization of multifunctional circuits, paving the way for the next generation of logic and memory devices (Nature, 625, 276-281, 2024). These advancements are critical for overcoming the limitations of conventional scaling and unlocking new possibilities in high-density, low-power electronics, particularly for mimicking the three-dimensional structure of the brain.

Zhengtang Luo​

Hong Kong University of Science and Technology

Synthesis and optoelectronic properties of two-dimensional transition metal dichalcogenides

The unique properties and potential of two-dimensional (2D) transition metal dichalcogenides (TMDs) materials have garnered significant attention in the field of optoelectronics. Among the various methods used for their synthesis and growth, chemical vapor deposition (CVD) stands out as a widely employed technique. Recently, we have explored different strategies to synthesize 2D materials and heterostructures through CVD method, with the aim of enhancing their functionality for advanced photodetection applications. These synthesis approaches of 2D TMDs encompass the low-temperature growth and thermally-assisted tellurization method. Additionally, we have investigated defect engineering of 2D materials for single photon emitters, as well as the fabrication of pristine homojunctions and mixed-dimensional heterostructures for self-powered photodetectors. These endeavors have shed light on the mechanisms underlying CVD synthesis of 2D TMDs and their applications in advanced optoelectronics. Consequently, they have significantly contributed to our understanding of optoelectronics and the integration of 2D materials into advanced image sensing technologies.

Chul-Ho Lee​

Seoul National University

Van der Waals gate stack engineering for high-performance 2D electronics

Gate stack engineering has been pivotal for aggressive scaling in modern CMOS technologies, enabling high-performance and low-power transistors through superior interface quality and precise electrostatic control. However, achieving these requirements in 2D semiconductor-based devices remains challenging due to difficulties in forming high-quality gate dielectrics. In this talk, recent progress and key issues in gate stack engineering for 2D transistors will be discussed. Specifically, a gate-dielectric-less van der Waals Schottky-gated metal-semiconductor field-effect transistor (MESFET) utilizing pinning-free metal gates, and metal-oxide-semiconductor FETs (MOSFETs) and ferroelectric-based Fe-FETs employing interlayer-assisted dielectric integration will be presented.

Alexander Holleitner​

Technical University of Munich​

Bosonic and fermionic interactions in coherent interlayer exciton ensembles

Heterostructures made from 2D transition-metal dichalcogenides are known as ideal platforms to explore exciton ensembles ranging from localized moiré excitons to degenerate interlayer exciton ensembles with an extended spatial coherence at cryogenic temperatures.

We highlight luminescence experiments on the bosonic and fermionic interactions in such degenerate exciton ensembles in the milli-Kelvin regime.

We thank J. Figueiredo, M. Troue, M. Richter, H. Lambers, T. Taniguchi, K. Watanabe, U. Wurstbauer, and A. Knorr for a very fruitful collaboration on the physics of interlayer excitons and the DFG for financial support via HO 3324 / 16 and the excellence cluster MCQST (EXS-2111).

Peng Zhou​

Fudan University

Post-Moore Era Electronic Devices and Integration

The development of integrated circuits in the post-Moore era is most likely to follow paths based on new materials, novel devices, and Beyond CMOS architectures. Two-dimensional semiconductor materials represented by MoS₂ and WSe₂, featuring atomic monolayer stability, extreme high mobility, higher integration density, and low power consumption, have emerged as potentially disruptive materials and were incorporated into the International Roadmap for Devices and Systems (IRDS) in 2017. We has conducted in-depth studies on transistor structure design, source-drain contact optimization, and dielectric engineering improvement. Two-thirds of the developed complete 2D integration process demonstrates compatibility with silicon-based technology. Through independent innovation, we have established proprietary processes and achieved the world’s largest-scale logic function verification using 2D semiconductors. The RISC-V chip named “WUJI” integrates 5,900 transistors. By leveraging existing domestic semiconductor manufacturing equipment, the team has achieved deep integration with silicon-based industrial chains and CMOS processes, accelerating the industrialization of 2D semiconductors. Concurrently, innovations in device physics mechanisms continue to advance high-speed non-volatile flash memory technology. By combining 2D Dirac band structures with ballistic transport characteristics, the Gaussian length of 2D channels can be modulated to achieve super-injection of channel charges into storage layers. This super-injection mechanism fundamentally differs from conventional field-assisted injection in flash memory: while traditional injection exhibits maximum injection thresholds, super-injection enables theoretically unlimited charge injection. A quasi-2D Poisson model was developed to theoretically predict this phenomenon. The fabricated “PoX” picosecond flash memory demonstrates record-breaking sub-1-nanosecond (400 picoseconds) programming/erasing speeds, surpassing even the fastest volatile SRAM technology at equivalent technology nodes. The 2D super-injection mechanism elevates non-volatile memory speeds to approach the ~1T theoretical limit, indicating a paradigm shift that will redefine the boundaries of existing memory technologies.

Kibum Kang​

Korea Advanced Institute of Science & Technology​

2D Semiconductor MOCVD Growth Advancements for the Angstrom Era Targeting Industrial Fabrication​

In the past decade, there have been dramatic breakthroughs in 2D semiconductor transistor technology, with academia presenting numerous solutions to address critical challenges in improving growth quality and device performance. As the industry transitions into the Angstrom era of semiconductor processes, these atomically thin materials have the potential to achieve transistor body thicknesses below 1 nm—unattainable with conventional semiconductors such as silicon or GaAs—offering markedly enhanced short-channel immunity, minimized short-channel effects, maximized gate control, low subthreshold swing, and reduced power supply voltage (Vdd). Recognizing these advantages, major foundries are strategically planning to integrate 2D semiconductor thin films into commercial fabrication flows by the mid-2030s, laying the groundwork for next-generation 2D Complementary FETs (C-FET) beyond silicon CFET technology and enabling ultra-thin channels on insulators for efficient 3D stacking and high-performance logic in back-end-of-line (BEOL) applications. Moreover, emerging concepts—such as channel-on-glass—promise high-performance transistors for advanced packaging, transparent electronics, displays, and micro LED systems.

This presentation highlights our achievements in scalable, low-temperature metal-organic chemical vapor deposition (MOCVD) for transition metal dichalcogenides (TMDs), with a particular focus on developing processes suitable for industrial adoption. We discuss the evolution from NaCl-assisted MOCVD methods (Gen #1) to gas-source additive precursor techniques (Gen #2), hybrid approaches (Gen #3) aimed at optimizing thermal budget control at temperatures as low as 400°C, and the latest MOCVD systems (Gen #4) that achieve single-crystal TMD growth on amorphous substrates. We also examine transfer-free fabrication of MoS₂ and WSe₂ transistor arrays, a key technology that has remained challenging to implement until now. By bringing together innovations in materials synthesis and device integration, this work provides a clear pathway for adopting 2D semiconductors in future electronic systems and introduces our efforts to overcome the remaining hurdles in transitioning from lab-scale demonstrations to large-scale industrial manufacturing.

Alexey Chernikov​

TU Dresden​

Manipulation and transport of excitons in 2D semiconductors and antiferromagnets

Two-dimensional transition metal dichalcogenides offer an excellent platform to study non-linear dynamics of tightly-bound exciton quasiparticles. The properties of the excitons and their optical response change drastically in the presence of free charges, leading to emergence of many-body states described as trions or Fermi polarons. The physics of such Bose-Fermi quasiparticle mixtures have attracted a lot of interest in the scientific community and motivated the development of methods to control them on ultrafast time-scales. In addition, excitons were recently demonstrated to play central role also for magnetic 2D materials, with open questions regarding exciton mobility and its relation to the magnetic order, from both fundamental and technological perspectives. The first part of the talk will be focused on the use of intense THz pulses to transiently modify light-emission of exciton-electron ensembles in monolayer semiconductors. We demonstrate a near complete, THz-induced trion-to-exciton conversion by monitoring time resolved photoluminescence after optical excitation. It offers new pathways to manipulate exciton-electron mixtures, triggering a non-linear optical response by low-energy photons on picosecond timescales. In the second part, I will discuss exciton transport in the layered semiconducting antiferromagnet CrSBr. Strong influence of the magnetic order on the exciton propagation will be discussed including rapid, non-linear exciton expansion in ultra-thin layers as well as contraction of the exciton clouds at low temperatures. These results are particularly interesting in the context of magnetic control of exciton transport and the consequences of coupling optical excitations to the magnetic order.

Roman Gorbachev​

University of Manchester​

Ultra-clean van der Waals heterostructures

Layer-by-layer assembly of van der Waals (vdW) heterostructures underpins new discoveries in solid state physics, material science and chemistry. Despite successes, all current assembly techniques use polymeric supports which limit their cleanliness, ultimate electronic performance, and potential for optoelectronic applications. In the first part of the talk, I will introduce a polymer-free platform for heterostructure assembly using re-usable flexible silicon nitride membranes. This approach enables production of heterostructures with interfaces free from interlayer contamination and correspondingly excellent optoelectronic behaviour. In addition, eliminating polymeric supports allows new possibilities for vdW heterostructure fabrication: assembly at temperatures up to 600°C, and in different environments including ultra-high vacuum and liquid submersion. In the second part, I will discuss how this new technology affects twisted bilayer TMDs in the regime of small twist angles. Here I will cover the atomic reconstruction: formation of ferroelectric domains in TMDs with different thicknesses and explore how their atomic structure can be characterised using multi-slice electron ptychography. I will also show our recent results on ferroelectric tunnelling junctions and their string dependence on the pre-existing domain network. In the last, conclusive part I will discuss the challenges the field is facing, using devices based on twisted 2D interfaces as an example. I will show the importance of nanofabrication in the context of twistronics and offer avenues for future development of nanofabrication pathways.

Kosuke Nagashio​

The University of Tokyo

Towards the Development of Wafer-Scale Integration Using 2D Materials

Over the past decade, significant efforts have been dedicated to fabricating transistors using large-area MOCVD-grown MoS₂ on sapphire substrates. Despite these advances, the key challenge remains the lower mobility compared to that achieved with powder-source CVD. In this talk, we will present the latest progress in MOCVD growth techniques and the corresponding device performance improvements.

Theresia Knobloch​

TU Wien

Overcoming Gate Stack Challenges in Ultra-Scaled 2D Transistors​

As in nanosheet field-effect-transistors (FETs) the thickness of the silicon channels is approaching sub-5 nm, the mobility degrades due to increased scattering and pronounced short channel effects are observed. One possible solution to allow for continued transistor scaling is to use two-dimensional (2D) semiconductors such as transition-metal dichalcogenides (TMDs) as channels. However, identifying a suitable gate stack is critical for realizing high-performance 2D FETs. While most 2D prototype devices rely on conventional gate oxides, including HfO2 or Al2O3, as they can be readily deposited using atomic layer deposition, the interface formed between TMDs and amorphous oxides is highly defective, thereby degrading the device performance and reliability and increasing the thermal resistance of the gate stack. In recent years, a large variety of novel insulators have been suggested, including native oxides to 2D materials like Bi2SeO5, fluorides like CaF2, and transferred 3D crystals like SrTiO3. A suitable gate insulator needs to provide excellent gate control, suppress gate leakage, reduce remote phonon scattering and minimize interface trap densities. In addition, the gate stack must offer a minimal overall thermal resistance to ensure adequate heat dissipation and must provide good reliability. For device integration, the insulator growth technique must be compatible with a fabrication flow of stacked complementary 2D nanosheet architectures. In this talk, we will give a comprehensive overview of insulators suggested to be used as the gate stack in scaled 2D FETs, and will highlight the most critical related challenges. These challenges include the device performance, evaluated for a realistic operation scenario according to the International Roadmap for Semiconductor Devices and Systems, as well as device reliability and good heat management. We will outline how through comprehensive experiments, advanced modeling, and collaborative efforts, the research community can converge on robust solutions to overcome gate stack challenges in ultra-scaled 2D transistors.

Yu-Jung Lu​

Academia Sinica

Polariton-Mediated Ultrafast Energy Transfer in a van der Waals Superlattice​

Exciton-polariton dynamics in two-dimensional (2D) transition metal dichalcogenide (TMD) materials have attracted considerable attention across various scientific disciplines due to their fundamental significance and potential applications in optoelectronics. However, practical implementation has been hindered by the challenge of maintaining stable and long-range polariton propagation. In this work, we present an innovative material platform featuring extensive monolayer WS2/Al2O3 superlattices coupled to a waveguide mode designed to host exciton-polaritons with operation at room temperature. Time-resolved transient absorption spectra show picosecond nonlinear energy transfer phenomena between upper and lower polariton states, clarifying the dynamic behavior within this quantum realm. Interestingly, the nonlinear energy-transfer dynamics of the two polariton states show that equilibrium occurs at an optimal probe delay time of 2 ps, and we observed a population inversion behavior between the UP and LP states. In particular, 25-fold all-optical modulation was achieved by varying the photoexcited carrier densities. These results indicate that self-hybridized polaritons can strongly interact with each other in the nonlinear excitation regime, leading to unique energy transfer, which has implications for a wide range of nonlinear, ultrafast optical devices in the visible frequency range. This research not only advances our fundamental understanding of polariton dynamics but also promotes the development of innovative technologies that harness these fascinating quantum phenomena. The detailed mechanisms and potential applications of 2D-based nanodevices will be further explored in our presentation.

Reference [1] Tzu-Yu Peng#, Jason Lynch#, Jing-Wei Yang, Yen-Yu Wang, Xing-Hao Lee, Ben R. Conran, Clifford. McAleese, Deep Jariwala, and Yu-Jung Lu, Polariton-Mediated Ultrafast Energy Transfer in a van der Waals Superlattice. ACS Nano (2025) DOI: 10.1021/acsnano.4c16649 [2] Hao-Yu Lan, Yu-Hung Hsieh, Zong-Yi Chiao, Deep Jariwala, Min-Hsiung Shih, Ta-Jen Yen, Ortwin Hess, Yu-Jung Lu, Gate-Tunable Plasmon-Enhanced Photodetection in a Monolayer MoS2 Phototransistor with Ultrahigh Photoresponsivity. Nano Lett. 21, 3083–3091 (2021) [3] Jui-Han Fu, Jiacheng Min, Che-Kang Chang, Chien-Chih Tseng, Qingxiao Wang, Hayato Sugisaki, Chenyang Li, Yu-Ming Chang, Ibrahim Alnami, Wei-Ren Syong, Ci Lin, Feier Fang, Lv Zhao, Chao-Sung Lai, Wei-Sheng Chiu, Wen-Hao Chang, Yu-Jung Lu, Kaimin Shih, Lain-Jong Li, Yi Wan, Yumeng Shi, Vincent Tung. Orientated Lateral Growth of Two-Dimensional Materials on C-plane Sapphire. Nature Nanotech. 18, 1289–1294 (2023) [4]Wei-Ren Syong, Jui-Han Fu, Yu-Hsin Kuo, Yu-Cheng Chu, Mariam Hakami, Tzu-Yu Peng, Jason Lynch, Deep Jariwala, Vincent Tung, and Yu-Jung Lu, Enhancing Photogating Gain in Scalable MoS2 Plasmonic Photodetectors via Resonant Plasmonic Metasurfaces. ACS Nano 18, 5446–5456 (2024).

Thuc Hue Ly​

City University of Hong Kong​

State-of-The-Art Processing of 2D Materials ​

The scalable fabrication and integration of 2D devices require large-area synthesis and the state-of-the-art post-synthesis processing of 2D layers. Current challenges in processing 2D materials include: (1) Difficult to transfer the 2D materials without causing damage and contamination. (2) Challenges in effectively cleaning 2D materials. (3) Stress easily applied during processing, which can alter the phases and structures of 2D materials. (4) The patterning process for 2D materials is sophisticated, unrepeatable and non-reversible. To address these challenges, we have recently developed several innovative techniques: (i) We developed novel ice-aided transfer and ice-stamp transfer methods, in which water (ice) is the sole medium in the entire process. The adhesion between various 2D materials and ice can be precisely controlled by temperature. This controlled adhesion enables the transfer of ultrahigh-quality and exceptionally clean 2D flakes and continuous films, applicable across a wide range of substrates. (ii) Furthermore, beyond transfer, ice can also be utilized to clean the surfaces of 2D materials at higher temperatures. (iii) We can precisely control phases during transfer by relaxation of the growth strain on the substrate. For example, in 2D In2Se3, the intriguing ferroelectric phases can be obtained and show great promise for future neuromorphic computing. (iv) We developed a novel reversible, optical method for precise patterning of 2D ReS2 materials, utilizing redox surface reactions. This technique allows for micrometer-scale patterning of 2D materials. (v) We also developed an atomic scale phase patterning technique by direct electron beam writing in 2D ReS2, achieving precision down to sub-1 nm. These state-of-the-art techniques enable the creation of unprecedented ultraclean and ultra-precise 2D structures and device performances, contributing significantly to the forthcoming technological revolutions associated with 2D materials.

Gwan-Hyoung Lee​

Seoul National University

A Novel Approach to Grow Wafer-scale Single Crystal Transition Metal Dichalcogenides: Hypotaxy

With the great interest in two-dimensional (2D) semiconductors for advanced electronics beyond silicon, significant developments have been achieved in the synthesis of transition metal dichalcogenides (TMDs). Highly crystalline TMDs have been epitaxially grown on limited types of crystalline substrate by chemical vapor deposition (CVD). This process, however, necessitates subsequent transfer onto a desired substrate for device fabrication, posing challenges in thickness and scalability control. In this talk, we report the hypotaxy of wafer-scale single crystal TMDs, enabling downward growth of these films through overlying 2D template even on amorphous or lattice-mismatched substrates, while preserving interlayer crystalline alignment with the 2D template. By sulfurizing or selenizing a pre-deposited metal film covered by graphene, TMD nuclei form with crystalline alignment with the graphene nanopores that are generated during the process. These aligned TMD nuclei coalesce as the graphene is gradually removed, resulting in the fabrication of a single crystal TMD film. Our method allows for precise control of MoS2 thickness, ranging from monolayer to several hundred layers, on various substrates. Employing wafer-scale single crystal graphene template fosters the growth of 4-inch single crystal MoS2. The hypotaxially grown single crystal monolayer MoS2 shows remarkably high in-plane thermal conductivity (~120 W/mK) and carrier mobility (~87 cm^2/Vs) with high uniformity in a wafer scale. Additionally, by preforming nanopores in graphene via oxygen plasma treatment, the MoS2 can be hypotaxially grown at lower temperature of 400oC, aligning with back-end-of-line (BEOL) semiconductor process. This hypotaxy approach also extends to other TMDs, such as MoSe2, WS2, and WSe2, utilizing the same growth mechanism. Our work shows a novel way to overcome the substrate constraints inherent in conventional epitaxial growth and to fabricate wafer-scale single crystal TMDs on arbitrary substrates, required for monolithic 3D integration.

Yan Wang​

University of Cambridge

Dielectrics for 2D Semiconductors​

Atomically thin (or two-dimensional, 2D) transition metal dichalcogenide (TMD) semiconductors possess ideal attributes for meeting industry scaling targets for transistor channel technology. The realization of ultra-scaled field effect transistors (FETs) will require industry compatible gate dielectrics with very low equivalent oxide thickness (EOT) values. Dielectric substrates such as SiO2, Al2O3 and HfO2 unintentionally dope 2D TMDs and create interfacial defect states that lead to non-ideal FET characteristics – such as variable threshold voltage. Here we show that zirconium oxide (ZrO2) forms an ultra-clean and inert interface with MoS2. Our detailed soft and hard X-ray photoelectron spectroscopy (XPS) analysis reveals that SiO2 and HfO2 substrates introduce significant doping of MoS2 while ZrO2 exhibits no measurable interactions with MoS2. Because of the ultra-clean MoS2/ZrO2 dielectric interface, MoS2 FETs using ZrO2 as dielectric show extremely stable and positive threshold voltage, low subthreshold swing, and high ON currents. Furthermore, we demonstrate that the ultra-clean interface between ZrO2 and monolayer MoS2 enables effective modulation of the threshold voltage in top gate FETs by gate metal work function engineering.

Maciej Koperski​

National University of Singapore​

Electrically excited arrays of single photon emitters in monolayer WSe2: effects of electric and magnetic fields​

Electrically excited arrays of single photon emitters in monolayer WSe2: effects of electric and magnetic fields

Maciej Koperski

Materials Science and Engineering Department, National University of Singapore Institute for Functional Intelligent Materials, National University of Singapore

Deposition of a monolayer transition metal dichalcogenides on an array of nanopillars has been demonstrated to create single photon emitters spatially localized in the nanoscale. We developed a protocol to lift such altered 2D layers from the pillars and integrate them into light-emitting devices realized as vertical tunneling junctions. The device-integrated monolayers preserved the single photon emission, despite no observable morphology deformation being detected via atomic force microscopy. These results point to the conclusion that the single photon emitters originate from the creation of defects rather than strain modulation of the band gap.

The integration of WSe2 monolayer hosting arrays of single photon emitters into the tunneling devices, studied under the influence of the magnetic field, demonstrates the tunability of the properties of the single photon emitters. Stark and Zeeman effects can be used to control the emission energy, while the light polarization properties modified by a magnetic field enable altering the state of the quantum emitter on a Bloch sphere.

References [1] J. Howarth, K. Vaklinova, M. Grzeszczyk, G. Baldi, L. Hague, M. Potemski, K. S. Novoselov, A. Kozikov, M. Koperski, Electroluminescent vertical tunneling junctions based on WSe2 monolayer quantum emitter arrays: Exploring tunability with electric and magnetic fields, Proceedings of the National Academy of Sciences 117 (24), 13214-13219 (2024). [2] D. Litvinov, A. Wu, M. Barbosa, K. Vaklinova, M. Grzeszczyk, G. Baldi, M. Zhu, M. Koperski, Single photon sources and single electron transistors in two-dimensional materials, Materials Science and Engineering: R: Reports 163, 100928 (2025). [3] L. Loh, J. Wang, M. Grzeszczyk, M. Koperski, G. Eda, Towards quantum light-emitting devices based on van der Waals materials, Nature Reviews Electrical Engineering, 1, 815–829 (2024). [4] M. Koperski, K. Nogajewski, A. Arora, V. Cherkez, P. Mallet, J.-Y. Veuillen, J. Marcus, P. Kossacki, M. Potemski, Single photon emitters in exfoliated WSe2 structures, Nature Nanotechnology 10 (6), 503-506 (2015). [5] M. Koperski, M. R. Molas, A. Arora, K. Nogajewski, M. Bartos, J. Wyzula, D. Vaclavkova, P. Kossacki, M. Potemski, Orbital, spin and valley contributions to Zeeman splitting of excitonic resonances in MoSe2, WSe2 and WS2 Monolayers, 2D Materials 6 (1), 015001 (2018). [6] K. Walczyk, G. Krasucki, K. Olkowska-Pucko, Z. Chen, T. Taniguchi, K. Watanabe, A. Babiński, M. Koperski, M. R. Molas, N. Zawadzka, Optical response of WSe2-based vertical tunneling junction, Solid State Communications 396, 115756 (2025). [7] L. Loh, Y. W. Ho, F. Xuan, A. G. del Águila, Y. Chen, S. Y. Wong, J. Zhang, Z. Wang, K. Watanabe, T. Taniguchi, P. J. Pigram, M. Bosman, S. Y. Quek, M. Koperski, G. Eda, Nb impurity-bound excitons as quantum emitters in monolayer WS2, Nature Communications 15 (1), 10035 (2024).

Feng Miao​

Nanjing University

2D Materials for Physical Computing

The continuous enhancement of computational power is crucial for driving societal progress. Currently, this improvement heavily relies on the integration of transistors. As this integration level nears its limit, marking the end of Moore’s Law, the growth in hardware computational power has slowed and been struggling to meet the exponential data processing needs of the AI era. This presents a significant challenge. To overcome it, we need to explore entirely new computing approaches to process information. Unlike traditional digital computing, which relies on abstract symbolic representation and operates at the CMOS circuit level, physical computing processes information at the device level by leveraging material-specific physical processes, thus offering ongoing improvements in computational power. Two-dimensional (2D) materials, with their atomic-layer thickness, enable precise control of physical properties using external fields, creating a superior platform for future physical computing. In this talk, I will show how 2D materials open up unprecedented opportunities for harnessing new physics to advance physical computing. I’ll begin by presenting our findings on Wigner crystals and ferroelectricity in graphene moiré systems and discuss how these properties can be applied to build basic solid-state quantum simulators [1], moiré synaptic transistors [2], and noise-resistant neuromorphic devices [3]. I will also show how adjusting the interface potential barrier in heterostructures composed of 2D materials can lead to the development of reconfigurable retinomorphic sensors [4-6], visual motion perceptrons [7], and in-sensor dynamic computing [8]. Finally, I will present our initial explorations on new physical computing schemes [9-10] and share our vision of future physical computing.

References [1] Nature 609, 479 (2022). [2] Chinese Physics Letters 40, 117201 (2023). [3] Nature Nanotechnology 19, 962 (2024). [4] Science Advances 6, eaba6173 (2020). [5] Nature Electronics 5, 248 (2022). [6] National Science Review 8, nwaa172 (2021). [7] Science Advances 9, eadi4083(2023). [8] Nature Electronics 7, 225 (2024). [9] Nature Nanotechnology 16, 1079 (2021). [10] Nature Electronics 6, 381 (2023).

Benjamin Groven​

IMEC

Opportunities of halogen-based gas-phase reactants​ during chemical vapor deposition of transition metal dichalcogenides​

Historically, halogen-based gas-phase reactants prove indispensable to enable selective epitaxial growth of mainstream group-IV semiconductors for nanoelectronic applications [1]. Here, we review how a chlorine gas (Cl2) co-reactant modulates the growth behavior during the chemical vapor deposition of future two-dimensional transitional metal dichalcogenide (TMD) semiconductors. Such co-reactant assists to overcome three critical manufacturing roadblocks for TMDs: (i) it promotes metal precursor diffusivity and reduces TMD nucleation density below 0.01 µm-2 at low deposition temperature of 300°C; (ii) opens a deposition selectivity window; and (iii) enables monolayer thickness control [2,3]. [1] J. Bloem et al., J. Crys. Growth 1980 (DOI: 10.1016/0022-0248(80)90002-0) [2] B. Groven et al., submitted 2024 (DOI: 10.21203/rs.3.rs-4504047/v1) [3] Y. Shi et al., IEDM 2021 (DOI: 10.1109/IEDM19574.2021.9720676)

Akshay Rao​

University of Cambridge

Photoredox phase engineering of transition metal dichalcogenides​

Crystallographic phase engineering plays an important part in the precise control of the physical and electronic properties of materials. In two-dimensional transition metal dichalcogenides (2D TMDs), phase engineering using chemical lithiation with the organometallization agent n-butyllithium (n-BuLi), to convert the semiconducting 2H (trigonal) to the metallic 1T (octahedral) phase, has been widely explored for applications in areas such as transistors, catalysis and batteries. Although this chemical phase engineering can be performed at ambient temperatures and pressures, the underlying mechanisms are poorly understood, and the use of n-BuLi raises notable safety concerns. Here we optically visualize the archetypical phase transition from the 2H to the 1T phase in mono- and bilayer 2D TMDs and discover that this reaction can be accelerated by up to six orders of magnitude using low-power illumination at 455 nm. We identify that the above-gap illumination improves the rate-limiting charge-transfer kinetics through a photoredox process. We use this method to achieve rapid and high-quality phase engineering of TMDs and demonstrate that this methodology can be harnessed to inscribe arbitrary phase patterns with diffraction-limited edge resolution into few-layer TMDs. Finally, we replace pyrophoric n-BuLi with safer polycyclic aromatic organolithiation agents and show that their performance exceeds that of n-BuLi as a phase transition agent. Our work opens opportunities for exploring the in situ characterization of electrochemical processes and paves the way for sustainably scaling up materials and devices by photoredox phase engineering.

Saurabh Lodha​

IIT Bombay

2D TMD Transistors for Neuromorphic Engineering​

Luminescence thermometry has gained considerable attention for applications in biotechnology, nanoelectronics, and nanophotonics, areas where conventional thermometric techniques are ineffective. Here, we demonstrate exciton-phonon-based luminescence thermometry using monolayer WS₂ as a noninvasive, high-spatial-resolution platform. Our experiments reveal that monolayer WS₂ achieves an average relative sensitivity above 4%/K over the 300–425 K range, placing it among the most sensitive materials reported to date. We also derive an analytical expression for relative sensitivity, providing a quantitative framework for performance evaluation.

We examine the condition for resonant enhancement of the upconversion signal by matching the difference between the incident photon energy and the material’s band gap energy to an integer multiple of the optical phonon energy. Monolayer WS₂ exhibits high absolute and relative sensitivity, strong reproducibility, and ease of fabrication, making it a promising alternative to rare-earth-doped materials and quantum dots. This work highlights the utility of upconversion photoluminescence in monolayer TMDs for extremely-sensitive temperature monitoring.

Paolo Samorì

University of Strasbourg

The molecular approach to multifunctional 2D electronics

The remarkable characteristics of 2D materials can be further refined, expanded, and improved by integrating them with specifically designed molecules, utilizing principles of supramolecular chemistry. By leveraging the extensive range of molecules that can be tailored and synthesized with specific functionalities, it becomes possible to engineer 2D materials with adaptable physical and chemical characteristics. This approach enables the creation of novel functionalities, aiming to develop multifunctional hybrid systems suited for electronic applications beyond CMOS technology, in line with the “more than Moore” strategy of functional diversification.[1] In my lecture I will present our recent findings on the use of chemical approaches to develop flexible pressure sensors with enhanced characteristics and complex multi-responsive opto-electronic devices capable to emulate brain-like logic operations. On the one hand, by tuning of the employed materials, structural design, and functionality, we have realized graphene-based pressure sensors displaying high sensitivity (742.3 kPa-1) with a linear response extended over a widest window exceeding 800 kPa. Such pressure sensors are endowed with a voltage-controlled highly precise inherent correction of thermal drifts to ultimately enable reliable sensing applications across varying environmental conditions. [2] On the other hand, we demonstrate that the asymmetric interfacing of 2D semiconductors with stimuli responsive molecules and (bio)polymers enabling dipole modulation at the interface with the semiconductor or acting as reservoir of ion that are controllably released offers a precise tool to achieve high control over the dynamic doping. When such organic-inorganic hybrid van der Waals heterostructures are integrated in field-effect transistors, synaptic plasticity including sensory, short-term, and long-term memory operation can be emulated, paving the way for environmental-friendly neuromorphic computing and energy-efficient 2D optoelectronics. By combining the best of two worlds, the interfacing of 2D materials with the infinite arsenal of functional molecules available on our planet represents a versatile strategy to harness multifunctionality and boost performance in 2D material-based hybrid devices, towards disruptive technologies addressing global challenges in electronics, sensing, and energy-related applications.[3]

[1] Chem. Rev., 2022, 122, 50 [2] Adv. Mater. 2025 in press (DOI: 10.1002/adma.202503867) [3] (a) Adv. Mater. 2024, 36, 2307359; (b) Adv. Funct. Mater. 2025 in press (DOI: 10.1002/adfm.202509607)

Daniel Rhodes

University of Wisconsin-Madison​

Progress toward the growth of high mobility TMDs​

For many years, the quality of semiconducting transition metal dichalcogenides (TMDs) has remained substantially poor. Despite several different approaches to modifying growth parameters, monolayer TMDs grown by chemical vapor processes have remained limited to mobilities of just a few thousand cm2/Vs at cryogenic temperatures. The carrier mobilities in TMDs are limited by both charged defects (typically around 0.1% to 1% of all atomic sites) and isovalent defects (~1% to 5% of all atomic sites), compared to hBN and graphene which have point defect densities of just .0001% of all atomic sites and mobilities that are primarily limited by edge disorder. In recent years, a promising synthesis route has been identified for producing high-quality transition metal selenides and tellurides using excess chalcogen as a flux. Published results have shown that defect densities can be reduced to .001% and .1% for charged and isovalent defects, respectively. This reduction in defects shows considerable improvement in carrier mobility for monolayer WSe2, with measured hole mobilities of nearly 70,000 cm2/Vs. While this chalcogen self-flux method has improved TMDs considerably, the residual defect densities still remain relatively high compared to state-of-the-art semiconductors. Additionally, this method is not compatible for growth of higher vapor pressure TMDs, like MoS2 and WS2, which are target materials for the semiconducting industry. In this talk, I will discuss some of insights we have gained over the years into the limitations of reducing point defect densities further in transition metal selenides and tellurides and our understanding of how different growth parameters integrated into the self-flux approach change the defect densities. I will also discuss new growth methods that we have developed to overcome the challenges associated with growing high-quality transition metal sulfides.

Hua Zhang​

City University of Hong Kong

Phase Engineering of Nanomaterials (PEN)

In this talk, I will summarize the recent research on phase engineering of nanomaterials (PEN) in my group, particularly focusing on the rational design and synthesis of novel nanomaterials with unconventional phases for various promising applications. For example, by using wet-chemical methods, for the first time, we have successfully prepared novel Au nanostructures (e.g., the hexagonal-close packed (hcp) 2H-Au nanosheets, 4H-Au nanoribbons, and 4H/fcc and fcc/2H/fcc heterophase Au nanorods), epitaxially grown metal nanostructures on the aforementioned unconventional Au nanostructures and 2H-Pd nanoparticles, and amorphous/crystalline heterophase Pd, PdCu, Rh and Rh alloy nanosheets. By using gas-solid reactions, metastable 1T’-phase group VI transition metal dichalcogenides (TMDs), e.g., WS2, WSe2, MoS2, MoSe2, WS2xSe2(1-x) and MoS2xSe2(1-x), have been prepared. Impressively, the 1T’-MoS2-supported single-atomically dispersed Pt (s-Pt) atoms with Pt loading up to 10 wt% exhibit superior performance in hydrogen evolution reaction. Importantly, 1T’-TMD monolayers can be stabilized on 4H-Au nanowires, which have been used for ultrasensitive SERS detection. Moreover, the salt-assisted 2H-to-1T’ phase transformation of TMDs have been achieved, and the phase transformation of TMDs during our developed electrochemical Li-intercalation process has been observed. Impressively, the lithiation-induced amorphization of Pd3P2S8 has been achieved. Currently, my group focuses on the investigation of (crystal) phase-dependent physicochemical properties, functions and applications in catalysis, (opto-)electronic devices, clean energy, chemical and biosensors, surface enhanced Raman scattering, photothermal therapy, etc., which we believe are quite unique and very important not only in fundamental studies, but also in future practical applications. Importantly, the concepts of phase engineering of nanomaterials (PEN), crystal-phase heterostructures, and heterophase materials are proposed.

Kausik Majumdar​

Indian Institute of Science

Quadrupolar exciton trapped in super-moiré potential

Moiré-trapped interlayer exciton in hetero-bilayers offers a rich platform to explore interaction-driven novel quantum phenomena. Extending the number of layers to three and beyond leads to highly intriguing multi-polar exciton - a state created by superposition of vertically aligned phase-coherent excitons. However, their experimental realisation remains challenging due to unintentional twist-angle mismatch among the layers. Here we propose that the super-moiré effect in a hetero-trilayer creates periodic pockets of aligned atomic registries. This facilitates the formation of quadrupolar excitons trapped in such super-moiré pockets. Using nearly-aligned WS2-WSe2-WS2 hetero-stack, we demonstrate the signature of interaction between multiple confined levels of the top and bottom moiré interfaces, creating hybridized symmetric (and bright) and anti-symmetric (and dark) quadrupolar states. A vertical electric field results in the spectral movement of the upper-moiré confined levels with respect to the lower-moiré confined levels. This leads to the observation of the anti-crossing between the multiple confined quadrupolar states. We also show that the electric field can brighten the anti-symmetric branch through tuning the electron-hole overlap. The results underscore the critical role of super-moiré effect in quadrupolar excitons.

Mark Hersam​

Northwestern University​

Chemically Functionalized 2D Materials for Quantum Photonic Science and Technology

Layered two-dimensional (2D) materials interact primarily via van der Waals (vdW) bonding, which has created opportunities for heterostructures that are not constrained by epitaxial lattice matching [1]. However, since any passivated surface interacts with another via non-covalent forces, vdW heterostructures are not limited to 2D materials alone. In particular, 2D materials can be integrated with a diverse range of other materials, including those of different dimensionality, to form mixed-dimensional vdW heterostructures [2]. Furthermore, chemical functionalization allows tailoring of the properties of 2D materials and the degree of coupling across heterointerfaces [3]. In this talk, the prospects of mixed-dimensional heterostructures for quantum photonic science and technology will be discussed with a focus on how chemical functionalization can manipulate and enhance single-photon emission in strained 2D transition metal dichalcogenides [4]. In addition to technological implications, this talk will explore fundamental issues including band alignment, doping, trap states, and charge/energy transfer across heterointerfaces [5].

[1] S. Hadke, et al., Chemical Reviews, 125, 835 (2025). [2] M. I. B. Utama, et al., MRS Bulletin, 48, 905 (2023). [3] J. T. Gish, et al., Nature Electronics, 7, 336 (2024). [4] M. I. B. Utama, et al., Nature Communications, 14, 2193 (2023). [5] S. V. Rangnekar, et al., ACS Nano, 17, 17516 (2023).

Suyeon Cho​

EWHA Womans University

2D Amorphous Solids for Sub-Nanometer Scale Devices

Amorphous solids are a type of condensed matter characterized by the absence of long-range order in their lattice structure. However, they still exhibit short- or medium-range order, which contributes to their versatile local and global electronic and chemical properties. Recently, 2D amorphous solids have gained attention for their exceptional mechanical and electronic features, which are unattainable in conventional crystalline materials. This talk highlights the physical properties of ultrathin 2D amorphous solids, which are formed through covalent bonding and feature polyhedron structures with shared edges and corners. Two notable examples of 2D amorphous solids include honeycomb-structured nanosheets with mixed hybrid orbitals and layered materials with reduced coordination numbers of the elements. We provide an in-depth discussion of (1) the phase transition between crystalline and amorphous phases in 2D solids, (2) advanced synthetic methods for producing high-quality amorphous films with precise thickness control, and (3) the potential applications of sub-nanometer scale 2D amorphous solids. Lastly, we explore their potential to revolutionize the design of highly versatile electronic devices at sub-nanometer scales.

Radha Boya​

The University of Manchester

Programmable memristors with two-dimensional nanofluidic channels

Nanofluidic memristors, obtained by confining aqueous salt electrolyte within nanoscale channels, offer low energy consumption and the ability to mimic biological learning. Theoretically, four different types of memristors are possible, differentiated by their hysteresis loop direction. Here, we show that by varying electrolyte composition, pH, applied voltage frequency, channel material and height, all four memristor types can emerge in nanofluidic systems. We observed two hitherto unidentified memristor types in 2D nanochannels and investigated their molecular origins. We investigate the impact of temperature on ionic mobility and memristors’ characteristics. We show that our channels display both volatile and non-volatile memory, including short-term depression akin to synapses, with signal recovery over time.

References:

1. A. Ismail, G-H Nam, A. Lokhandwala, S. V. Pandey, K. V. Saurav, Y. You, H. Jyothilal, S. Goutham, R. Sajja, A. Keerthi, B. Radha*, “Programmable memristors with two-dimensional nanofluidic channels”, Nature Communications (2025), in press.
2. P. Robin,† T. Emmerich,† A. Ismail,† A. Nigues, Y. You, G.-H. Nam, A. Keerthi, A. Siria, A.K. Geim, B. Radha, L. Bocquet, “Long-term memory and synapse-like dynamics of ionic carriers in two-dimensional nanofluidic channels”, Science (2023), 379, 161

Thomas J. Kempa​

Johns Hopkins University

Quantum Emission from Confined Excitons in a 2D Semiconductor–MOF Heterostructure

Van der Waals heterostructures (vdWHs) of vertically stacked 2D atomic crystals have been used to elicit intriguing phenomena that arise from strong electronic correlations spawned at the heterointerface. However, vdWHs containing heterointerfaces between these 2D atomic crystal lattices and molecular assemblies are emerging as equally intriguing platforms through which new properties can be harnessed for energy conversion, photodetection, spin-selective charge injection, and quantum emission. In particular, we have developed a unique approach, which we call “lattice embossing,” whereby proximity coupling a 2D metal-organic framework (MOF) to a 2D semiconductor can lead to intriguing quantum emission features. Crucially, the exciton confinement giving rise to this effect can be precisely tuned, because the MOF periodicity, symmetry, and band topology can be tailored through chemical synthesis. Here, I describe key spectroscopic results that attest to the extraordinary spectral purity, dynamics, and character of the emission from the quantum confined excitons. Notably, the resulting quantum light is precisely defined in space and can be switched on demand by inducing a phase change of the MOF lattice. I conclude by highlighting how such 2D atomic crystal–MOF heterostructures could be exciting platforms for controlling excitons, spins, phonons and even strain tensors. Ultimately, the vast array of chemical, electronic, magnetic, and mechanical potentials that such heterostructures can support will open unique opportunities in optics, sensing, and information processing.

Andrew J. Mannix​

Stanford University

Chemical and Mechanical Strategies for Optimizing 2D Semiconductors

High-quality synthesis and low-resistance contacts continue to be critical bottlenecks in scaling WS₂ and WSe₂ for electronic and quantum devices. In this talk, I will present our progress toward chemical strategies that enhance crystal quality during growth and introduce dopants to lower contact resistance. We developed a hybrid metal–organic chemical vapor deposition (HyMOCVD) process that enables tunable WS₂ films with precise doping, alloying, and growth-promoting additives, alongside confined-space, polytype-selective synthesis of ferroelectric 3R-phase TMDCs on dielectrics. A systematic survey of growth promoter salts reveals a common etching mechanism that underlies their enhancement of grain size. Contact interface mechanics also strongly influence device performance: we demonstrate that strain induced by Ni electrodes boosts WS₂ transistor on-current by 2.7× and reduces contact resistance by 78%. For p-type WSe₂, a straightforward chloroform doping approach yields a 100× increase in current, on/off ratios >10¹⁰, contact resistance as low as 2.5 kΩ, and long-term stability. These chemical and mechanical strategies unveil new pathways to achieve high-performance 2D semiconductor devices.

Stephan Hofmann​

University of Cambridge

Accelerated Process Discovery for 2D materials

The technological potential of low dimensional materials, from graphene, h-BN to transition metal dichalcogenides (TMDs), hinges on scalable process capability for controlled and effective heterogeneous integration. Process development largely still follows an Edisonian trial-and-error approach, blind and constraint by conventional reactors. This is not only wasteful and frustratingly slow, but hinders scientific breakthroughs in crystal growth and innovation in new deposition technology. This talk will focus on our cross-correlative operando and high-throughput approaches to accelerate process discovery. We show operando spectroscopic imaging ellipsometry and scanning electron microscopy with machine-learning assisted analysis and parameter space exploration for salt-assisted WS2 layer CVD and TMD oxidation phenomena, and how direct kinetic process data can open data driven approaches to advance the required understanding of underpinning mechanisms.

Klaas-Jan Tielrooij​

Eindhoven University of Technology

Watching charges and heat diffuse in 2D TMDs​

Understanding the flow of charges and heat is crucial for a host of applications. This is certainly also the case for 2D TMDs, which are projected to play a role as channel material in future chips, among others. At the moment, these transport dynamics are not yet fully understood.

We have addressed this challenge using spatiotemporal microscopy [1,2] to “watch” how charges and heat spread out in space as a function of time. In this technique, ultrashort pump pulses create an excitation and ultrashort probe pulses, with a variable delay in time and a variable pump-probe spatial offset, map out how transport of this excitation occurs in space and time. This technique provides nanometer spatial and femtosecond temporal resolution. Depending on the considered timescale, the transported excitation corresponds either to electronic charge or to phononic heat. We have specifically studied how these processes depend on the flake thickness down to the monolayer, all at room temperature.

In the case of charge transport [3], we observe several sequential transport regimes, including a counter-intuitive one with effective negative diffusion. The observed transport phenomena are governed by the interplay between quasi-free charges, excitons, and defects. A microscopic model, developed by Roberto Rosati and Ermin Malic, accurately describes the observed charge transport phenomena.

In the case of heat transport [4], we observe the occurrence of highly viscous heat transport with ultra-low heat diffusivities for the thinnest flakes. A mesoscopic model based on ab initio input parameters, developed by Jordi Tur-Prats, Albert Beardo and Xavier Alvarez, explains these observations as representing a novel regime of non-diffusive heat transport.

The identification of these charge and heat transport mechanisms will aid the design of electronic and optoelectronic applications based on ultra-thin layered semiconductors.

[1] S. Varghese et al, Rev. Sci. Instr. 94 (2023), 034903 [2] G.D. Brinatti Vazquez et al, Adv. Electron. Mater. 10 (2024), 2300584 [3] G. Lo Gerfo Morganti et al. accepted for publication in Nat. Commun. [4] S. Varghese et al. to be submitted

Kazunari Matsuda​

Kyoto University

Recent progress of optical science using moiré excitonic states in van der Waals heterostructure

Atomically thin low-dimensional semiconductors, such as two-dimensional (2D) transition metal dichalogenides, and their heterostructures have intensively studied from viewpoint of fundamental physics and optical applications [1-6]. The optically excitonic states in the moiré potential (moirés exciton) provide the platform for studying novel optical physics of 2D materials, and their heterostructure. Here, I will talk about the selected topics of recent progress of optical physics toward quantum optics and applications using moirés excitons in artificial van der Waals heterostructures [4,6]. [1] Y. Miyauchi, S. Konabe, K. Matsuda, et al., Nat. Commun. 9 (2018) 2598. [2] Y. Zhang, K. Matsuda, et al., Adv. Mater. 34 (2022) 2200301. [3] K. Shinokita, K. Matsuda, et al., ACS Nano 16 (2022) 16862. [4] H. Wang, K. Matsuda, et al., Nat. Commun. 15 (2024) 4905. [5] H. Kim, K. Matsuda, et al., ACS Nano 19 (2025) 322. [6] S. Asada, K. Matsuda, et al., Nat. Commun. in press.

Andrea C. Ferrari​

University of Cambridge

Light Scattering And Emission From Layered Materials Heterostructures

Layered materials are taking centre stage in the ever-increasing research effort to develop material platforms for quantum technologies. We are at the dawn of the era of layered quantum materials. Their optical, electronic, magnetic, thermal and mechanical properties make them attractive for most aspects of this global pursuit. Layered materials have already shown potential as scalable components, including quantum light sources, photon detectors and nanoscale sensors, and have enabled research of new phases of matter within the broader field of quantum simulations. I will discuss opportunities and challenges faced by layered materials within the landscape of material platforms for quantum technologies, with focus on applications that rely on light–matter interfaces.

Xiuju Song​

Zhejiang University

Data-driven Synthesis Prediction of Transition Metal Dichalcognides via Machine Learning

Transition metal dichalcogenides (TMDs) have emerged as a promising class of materials for next-generation electronics, optoelectronics, and energy storage due to their unique layered structures and tuneable properties. However, the traditional trial-and-error approach to synthesizing TMDs is time-consuming and resource-intensive, hindering rapid material discovery. Machine learning (ML), as a cutting-edge AI technology, provides transformative capabilities to disrupt traditional empirical approaches in materials research. Harnessing data-driven methods to mine hidden experimental insights enables accurate structure–property modelling, heterostructure and van der Waals stack engineering, defect and doping analysis, and rapid screening and discovery of novel TMDs—ultimately streamlining the design of high-performance TMDs materials and devices. In this work, we propose a data-driven ML framework to predict the synthesis results of TMDs by analysing historical synthesis data and material properties. We employ feature engineering to extract critical synthesis parameters and train supervised learning models, including XGboost and neural networks, to correlate process conditions with resulting material characteristics. The model’s performance is validated against experimental results, demonstrating high accuracy in predicting domain size and crystalline quality. By integrating explainable AI, we elucidate key factors governing successful synthesis, enabling rational design of TMDs. This approach paves the way for accelerated discovery of novel TMDs with tailored functionalities.

Heejun Yang​

Korea Advanced Institute of Science & Technology

Atomic-scale thermopower in 2D TMDs and graphene

Thermoelectricity (i.e., thermopower generation) has been investigated mainly on the macroscopic scale despite its origin being linked to materials’ local electronic band structure. Recently, the microscopic origins of thermopower have gained attention in the design of novel and efficient thermoelectric devices. In particular, distinct origins for thermopower have been expected with low-dimensional, strongly correlated, and topological materials. In this presentation, I will demonstrate our findings on thermoelectric puddles(1),(2), phonon puddles(3), and thermal biasing effects to break the atomic lattice symmetry(4) in variously stacked graphene and 1T-TaS2, using our Scanning ThermoElectric Microscopy (SThEM). Based on the sensitive probe of the local density of states’ derivatives in SThEM, harnessing atomic-scale thermopower can be achieved above room temperature, distinguished from conventional low-temperature studies with scanning tunneling microscopy.

References

1. Nano Letters 19, 61 (2018), Coherent Thermoelectric Power from Graphene Quantum Dots
2. ACS Nano 15, 5397 (2021), Harnessing Thermoelectric Puddles via the Stacking Order and Electronic Screening in Graphene
3. Nature Communications 13, 4516 (2022), Atomic-scale thermopower in charge density wave states
4. Nature Communications 16, 1879 (2025), Thermal biasing for lattice symmetry breaking and topological edge state imaging

Su-Hyun Gong​

Korea University

Light manipulation using 2D semiconductor multilayers

The emergence of 2D materials stimulated intensive research on both electronic and photonic applications. Especially, transition metal dichalcogenides (TMDs) provided an excellent platform for photonic applications due to their strong light-exciton interaction. However, multilayered TMDs have attracted far less attention than TMD monolayers because they become indirect bandgap materials. Here I will present that multilayered TMD itself is a good platform for controlling light-matter interaction without integrating an external photonic structure. A TMD multilayer can be utilized for a passive optical structure because it possesses a high dielectric constant. We believe our results show potential for the TMD-based nanophotonics offering a small mode volume but with a lower loss compared to the surface plasmon polaritons.

Yang Chai

The Hong Kong Polytechnic University

Two-dimensional materials electron devices with semimetals

Over the past decades, the development of 2D electron devices has made significant progress. However, achieving low-resistance contacts to p-type semiconductors remains a major challenge. Semimetals can form low-resistance contacts with semiconductors by suppressing metal-induced gap states (MIGS). While researchers have successfully achieved ultralow contact resistance for n-type 2D semiconductors using bismuth, p-type 2D semiconductors still present substantial difficulties. We introduce an ultrathin selenium (Se) interfacial layer—the element with the highest work function in the periodic table—to reduce the Schottky barrier height. The band hybridization between the Se layer and the gold electrode induces a semiconductor-to-semimetal transition at the contact interface. This transition suppresses MIGS formation in the semiconductor due to the low density of states near the Fermi level. By leveraging this high effective work function and band-hybridized semimetallic contact in p-type WSe₂ transistors, we achieve a significant reduction in contact resistance. In addition, we demonstrate topological semimetal with protected Fermi-arc surface states for highly scalable, conductive, and reliable interconnects. As the thickness of topological semimetals decreases from bulk crystal to nanoscale, its resistivity also decreases, showing high scaling potential. The room-temperature resistivity of nanoscale topological semimetal exhibits 10 times lower than the resistivity of Cu with the same thickness.

Yanfeng Zhang

Peking University

Direct synthesis and property modulations of 2D transition-metal chalcogenides via interface intercalation, defect engineering, layer thickness

The direct synthesis and property modulations of 2D transition-metal chalcogenides (TMDCs) via interface modulation, defects and layer thickness, etc., have attracted a lot of attentions in developing more intriguing properties and applications. Intercalation of native metal atoms in the van der Waals (vdW) gaps of 2D layered TMDCs is promising to afford intriguing properties. Herein, we report the direct synthesis of one-unit cell thick kagome-structured Co-telluride (Co9Te16) on Gr/SiC(0001) via the molecular beam epitaxy (MBE) route, and clarify its formation mechanism, and the possible flat band states from Co-intercalation in 1T-CoTe2 layers, by in situ scanning tunneling microscopy/spectroscopy (STM/STS) combined with density functional theory (DFT) calculations. A ferrimagnetic order is also predicted in kagome-Co9Te16. This work should provide a novel route for the direct synthesis of ultrathin kagome materials via a metal self-intercalation route. We also report the direct preparation of monolayer 1D-defect-induced Co4Te7 superlattices on lattice-matched SrTiO3(001) via MBE, and the explorations of the atomic structure and the novel electronic states around EF. This work should offer valuable insights into the engineering of periodic 1D-defect patterns in 2D TMDCs materials. We also report the successful synthesis of ultrathin h-GaTe layers on the graphene/SiC(0001) substrate, the identification of the layer-dependent vdW quantum well states (QWSs) by onsite STM/STS and their origins by DFT calculations, and the widely tunable band gaps. This work should deepen our understanding on the electronic tunability of 2D III−VI semiconductors by thickness and defect engineering.

Lilia Xie

Princeton University

Anomalous Hall effect from inter-superlattice scattering in an intercalated transition metal dichalcogenide

Superlattice formation dictates the physical properties of many materials, including the nature of the ground state in magnetic materials. Chemical composition is commonly considered to be the primary determinant of superlattice identity, especially in intercalation compounds. Here, we find that kinetic control of superlattice growth leads to the coexistence of disparate domains within a compositionally “perfect” single crystal of an intercalated transition metal dichalcogenide. We demonstrate that Cr1/4TaS2 is a bulk noncollinear antiferromagnet in which scattering between bulk and minority superlattice domains engenders complex magnetotransport below the Néel temperature, including an anomalous Hall effect. We characterize the magnetic phases in different domains, image their nanoscale morphology, and propose a mechanism for nucleation and growth. These results provide a blueprint for the deliberate engineering of macroscopic transport responses via microscopic patterning of magnetic exchange interactions in superlattice domains.

Sunmin Ryu

POSTECH

Unequivocal Orientational Imaging of 2D Crystals by Interferometric Second-Harmonic Generation Spectroscopy

Optical imaging of the orientational domains of various 2D crystals will be crucial in understanding their growth and characterizing their properties. Optical second-harmonic generation (SHG) spectroscopy has been successful for 2D crystals with high rotational symmetry, which defies orientational polarimetry based on linear spectroscopy. However, the method fails to differentiate two antiparallel domains of monolayer transition metal dichalcogenides (TMDs), let alone identify them individually. In this talk, I will introduce interferometric SHG polarimetry [1], which enables unequivocal orientation imaging by resolving both issues. By employing dual-polarization spectral phase interferometry and related mathematical analysis [2], the SHG amplitude and phase are simultaneously measured, allowing for the reconstruction of the orientation of TMDs [2] and hexagonal BN [3] without the aforementioned ambiguity. Furthermore, the two antiparallel domains were crystallographically identified using a phase reference [4], a task that would typically require atomic-resolution microscopy. The method was also extended to single-shot optical measurements of the stacking angle of heterobilayer TMDs [2]. The interferometric SHG spectroscopy demonstrated in these studies highlights the potential of interferometric parametric generation through atom-thick nonlinear optical materials.

References

[1] W. Kim, J. Y. Ahn, J. Oh, J. H. Shim and S. Ryu, “Second-Harmonic Young’s Interference in Atom-Thin Heterocrystals”, Nano Lett. 20, 8825 (2020) [2] J. Oh, W. Kim, G. Jeong and S. Ryu, “Polarization-Resolved Interferometric Second-Harmonic Generation”, in preparation [3] Y. Lee, J. Oh and S. Ryu, “Nonlinear Crystallographic and Structural Imaging of Chemically Synthesized 2D Hexagonal Boron Nitride”, in preparation [4] J. Kim, Y. Lee, W. Kim, J. Oh and S. Ryu, “Unequivocal orientation determination of 2D crystals by differential phase second-harmonic generation polarimetry”, in preparation

Xidong Duan

Hunan University

Gate-driven band modulation hyperdoping for high-performance p-type two-dimensional semiconductors

Conventional semiconductor processes such as lattice substitution doping (e.g., ion implantation) are prone to high-energy damage, while surface adsorbate-induced charge transfer doping typically involves aggressive chemical treatments, introduction of surface impurities, and chemical stability issues, making them unsuitable for atomically thin two-dimensional(2D) semiconductors.

We have developed a gate-tunable hyperdoping method for p-type 2D semiconductors. The research team constructed a type-III band-aligned van der Waals heterostructure (vdWHs) using monolayer tin disulfide (1L-SnS2) and bilayer tungsten diselenide (2L-WSe2). The back-gate bias voltage (Vgs) can effectively modulate the interlayer charge transfer doping, achieving hyperdoping beyond the typical dielectric breakdown limit of maximum electrostatic doping, and obtaining an ultra-high 2D hole concentration of up to 1.49×1014 cm−2. The high hole concentration enables p-type 2D transistors to exhibit outstanding performance, with the lowest source-drain contact resistance (RC) as low as 0.041 kΩ·μm and the highest on-state current density (Ion) reaching 2.30 mA/μm. These are world records reported in the literature.

Yasumitsu Miyata

National Institute for Materials Science

Quantitative defect analysis in CVD-grown monolayer WS₂

Transition metal dichalcogenides (TMDs) are promising next-generation semiconductors due to their atomically thin structures and excellent transport properties. Quantification and control of point defects are crucial to understand their physical properties and enable device applications. However, the relationship between synthesis conditions and defect density remains poorly understood. Here, we study point defects in monolayer WSe₂ grown under different chemical vapor deposition (CVD) conditions using conductive atomic force microscopy (C-AFM). We find that the use of salt as a growth promoter significantly increases the concentration of transition metal impurities. This suggests that the promoter modulates the supply of unintended metallic impurities from the precursors. We also discuss the origin of defects and their effect on material properties, supported by scanning transmission electron microscopy (STEM) and scanning tunneling microscopy (STM) observations.

Lili Wang

Tsinghua University

Interface engineered charge orders and pairing modulations

The quantum states of electrons in a crystal are governed by the symmetries of the system. The high-temperature superconductivity sets in upon reduced asymmetry (suppressed magneticity/nematicity) and reaches optimum at the quantum critical point of the symmetry-breaking order with intensified quantum fluctuations. The monolayer FeSe on SrTiO3(001) serves as a unique platform for the direct spectroscopic probe of the exotic pairing state and the interplay with charge orders. We prepared dual-TiO2-δ-terminated SrTiO3(001) surfaces with (√13 × √13), c(4 × 2) and (2 × 2) reconstructions and identified various charge orders with universally broken rotational symmetry. Intriguingly, the monolayer FeSe thereon exhibit multiple charge orders and pairing modulations. Our atomically resolved spectroscopy characterization disclosed the out-of-plane Se-Fe-Se triple layer gradient and inequivalent Fe sublattices with contrasting density of states between on and off TiO5□, which gives global spatial pairing modulations featured by particle-hole asymmetry. These results disclose delicate atomic-scale correlations between pairing and lattice-electronic coupling in the Bardeen-Cooper-Schrieffer to Bose-Einstein condensation crossover regime, providing insights into understanding the pairing mechanism of multiorbital superconductivity.

Keywords: FeSe/SrTiO3(001), interface structure, oxygen vacancy, charge order, pairing modulation

References:

1. Ding et al., Atomic-site-dependent pairing gap in monolayer FeSe/SrTiO3(001)-(√13 × √13), Nano Lett. 24, 8445 (2024).
2. Ding et al., Unidirectional charge orders induced by oxygen vacancies on SrTiO3(001), ACS Nano 18, 17786 (2024).
3. Ding et al., Sublattice dichotomy in monolayer FeSe superconductor, arXiv: 2406.15239.

Alexander Tartakovskii

University of Sheffield

Nanophotonics and strong light-matter interaction with multilayer van der Waals materials

The field of nanophotonics requires high quality materials for fabrication of resonant structures that can confine light down to the nanoscale. Recently, layered materials, studied mostly for the unique properties in their atomically thin form and often referred to as “van der Waals materials” for the forces holding atomic planes in bulk crystals, have been introduced as alternative dielectric building blocks for nanophotonics. Compared to Si or III-V semiconductors, these layered materials exhibit higher refractive indices; far larger birefringence values; transparency in the visible and near-infrared; out-of-plane van der Waals adhesive forces. These properties have allowed a variety of photonic structure and device demonstrations for which the use of van der Waals materials either improved performance or enabled previously inaccessible phenomena. Here I will present our recent work on various nanophotonic structures based on van der Waals materials that can be broadly divided into 0D, 1D and 2D systems and can be used for Purcell enhancement, quantum and topological nanophotonics, nonlinear optics, and strong light-matter coupling.

Ageeth Bol

University of Michigan

Towards low-resistance p-type contacts to 2D transition metal dichalcogenides using plasma-enhanced atomic layer deposition

One major limitation of 2D transition metal dichalcogenide (TMD) based FETs is the high contact resistance between metallic electrodes and semiconducting channels, particularly for p-type contacts. In this presentation I will address how PEALD of p-type TMDs can be used to improve this contact resistance. First, I will go over controlled doping strategies to form p-type 2D TMD contact materials using PEALD, with an emphasis on Nb Doped WS2. Our recent results show contact resistance values as low as 0.30 ± 0.26 kΩ·μm between Pd and PEALD NbxW1-xS2, demonstrating that low resistance contacts between metal and p-type TMDs are possible. Then, I will discuss reducing unintentional p-doping introduced during PEALD of TMDs. PEALD TMDs typically contain some level of hydrogen impurities that leads to unintentional p-doping. We have shown that these impurities can be reduced by introducing an Ar plasma C step in the standard PEALD TMD process. Finally, the use of remote plasmas in PEALD for contact deposition can lead to the creation of undesired impurities and defects in the 2D TMD channel, possibly impacting electronic behavior. I will present some first insights into the defects that are created during PEALD on 2DTMDs and how we can reduce the number of plasma-induced impurities and defects

Hiroki Ago

Kyushu University

Lattice-guided, dense arrays of TMD nanoribbons and their applications

TMDs exhibit unique properties and potential applications when reduced to 1D nanoribbons, owing to quantum confinement and high edge densities. However, effective growth methods for self-aligned TMD nanoribbons are still lacking. Here, a versatile approach for lattice-guided growth of dense, aligned MoS2 nanoribbons arrays via chemical vapor deposition (CVD) on anisotropic sapphire substrates is presented [1]. This method enables the synthesis of nanoribbons with widths below 10 nm without tailored surface steps. The MoS2 nanoribbons are aligned parallel to the zigzag direction and allow to grow and MoS2-WS2 hetero-nanoribbons. The 1D nature of the nanoribbons was asserted by the observation of Coulomb blockade at low temperatures. More importantly, pronounced catalytic activity was observed at the edges of the nanoribbons, indicating their promise for efficient catalysis. User-friendly, UV tape transfer is also presented [2]. Finally, I will introduce the national project, “Science of 2.5D materials”, supported by the Japanese government [2,3].

References [1] Z. Ma et al., Sci. Adv., 11, eadr8046 (2025). [2] M. Nakatani et al., Nat. Electron. 7, 119 (2024). [3] H. Ago et al., Sci. Tech. Adv. Mater. (STAM), 23, 275 (2022). [4] H. Ago et al., NPG Asia Mater., 16: 31 (2024).

Adina Luican-Mayer

University of Ottawa

Scanning Probe Microscopy of Twisted 2D TMDs

By spanning the full range of twist angles between two-dimensional (2D) layers, one can observe the formation of long-range moire lattices or in-plane reconstructions into energetically favorable patterns. In this talk, I will discuss both phenomena in twisted transition metal dichalcogenides (TMDs) and graphene, as investigated through scanning tunneling microscopy (STM). In the first part of the talk, I will discuss the demonstration of reversible local response of domain wall networks in ferroelectric interfaces of marginally twisted WS2 bilayers. Moreover, in the case of twisted WS2 bilayers close to 60°, we observe signatures of at bands and study the infuence of atomic relaxation on their band structure. In the second part of the talk, I will discuss recent results exploring complex moire patterns in twisted multilayer graphene.

Goki Eda

National University of Singapore

Probing broken symmetry with nonlinear optics

One of the defining characteristics of van der Waals materials is their exceptional versatility for symmetry manipulation. Strain and stacking order have been widely explored to engineer crystallographic symmetry and achieve properties otherwise absent in pristine materials. Magnetic van der Waals materials further offer opportunities to investigate the interplay between time-reversal symmetry and crystallographic symmetry, making them a rich platform for studying condensed matter phenomena and developing novel device functionalities. This talk will focus on two second-order nonlinear optical phenomena – second harmonic generation (SHG) and shift current generation – in van der Waals materials. First, I will discuss our recent work on probing magnetic order in chromium thiophosphate (CrPS₄), a non-centrosymmetric layered A-type antiferromagnetic material, using SHG. Our polarization-resolved SHG analysis reveals sensitivity to the Néel vector direction rather than the net magnetization [1]. In the second part, I will present our ongoing investigation of shift current in strain-engineered monolayer MoS₂, where the influence of exciton effects remains a topic with open questions. Interestingly, our photocurrent spectra uncover a series of resonances that can be attributed to both bright and dark excitons [2]. I will conclude by addressing open questions and highlighting emerging opportunities in the field.

[1] Ho et al. “Imaging the Néel Vector in Few-Layer CrPS4 with Second-Harmonic Generation” 25, 5624 (2025). [2] Chen et al. “Exciton shift current in monolayer MoS2” In preparation.

Key words: Nonlinear optics, excitons, optoelectronics

Andrew Graves

Pennsylvania State University

MOCVD of Epitaxial WSe₂: From Growth Dynamics to Substitutional p-Type Doping

Among the most exciting applications of transition metal dichalcogenides (TMDs) is their integration into next-generation scaled electronics where conventional silicon-based approaches face fundamental limitations. In addition to their superior electrostatics at atomic thickness, their 2D nature enables novel, high-density device architectures.¹ Of the TMDs, tungsten diselenide (WSe₂) has emerged as a particularly promising candidate for complementary metal–oxide–semiconductor (CMOS) technologies due to its intrinsic p-type conductivity. However, to harness this potential for practical electronics, synthesis approaches must deliver high crystalline quality, uniformity over large areas, and compatibility with existing semiconductor manufacturing infrastructure. Metal–organic chemical vapor deposition (MOCVD) satisfies these criteria, offering scalable growth of uniform 2D films on industry-relevant substrates. Furthermore, by tuning growth conditions to promote epitaxial alignment with the substrate, MOCVD enables the formation of high-quality, wafer-scale, nominally single-crystalline films that can be transferred to device platforms with minimal degradation. In this work, we present a comprehensive study of WSe₂ film growth and report initial efforts of substitutional p-type doping, two interrelated challenges that must be addressed to realize CMOS-compatible 2D device platforms. Building on previous work,² we demonstrate a two-step MOCVD process for growing 2-inch WSe₂ films on c-plane sapphire using a nitrogen carrier gas. This approach employs a low-temperature nucleation step (~850 °C) followed by higher-temperature lateral growth (~1000 °C). In situ and ex situ analyses reveal a continuous and dynamic phase transition from the metallic 1T to the semiconducting 2H polymorph during growth. We examine how synthesis parameters, such as nucleation temperature, govern this transformation. These insights not only inform the thermodynamic and kinetic underpinnings of WSe₂ growth but begin to lay the groundwork for deterministic phase engineering in WSe₂ by MOCVD. To monitor film evolution in real time, we implement in situ spectroscopic ellipsometry (SE), expanding on previous work modeling TMD surface coverage.³ Post-growth characterization—including in-plane X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS)—provides a detailed picture of crystalline quality, epitaxial alignment, nucleation density, domain coverage, and phase composition. These tools enable a deeper mechanistic understanding of growth and underscore the value of real-time optical monitoring. Despite the promise of WSe₂ as a native p-type material, further enhancement of its hole conductivity is necessary to match the performance of n-type TMDs like MoS₂. To address this, we explore substitutional p-type doping via two strategies: in situ phosphine (PH₃) treatment during MOCVD and ex situ annealing under nitric oxide (NO). Structural and chemical changes are tracked using Raman, PL, and XPS, while field-effect transistor (FET) measurements assess the resulting electrical performance. Notably, NO-doped films exhibit over three orders of magnitude improvement in on-state current, complete suppression of the n-branch, and elimination of FET hysteresis—highlighting the potential of ex situ doping for achieving high-performance p-type behavior in WSe₂. Collectively, these efforts represent a coherent strategy for advancing WSe₂ growth and doping at the wafer scale, paving the way toward its integration into scalable, CMOS-compatible 2D electronic systems. ______________ References

1. Jayachandran, D., Pendurthi, R., Sadaf, M.U.K. et al. Three-dimensional integration of two-dimensional field-effect transistors. Nature 625, 276–281 (2024). https://doi.org/10.1038/s41586-023-06860-5
2. Zhu, H., Nayir, N., Choudhury, T.H. et al. Step engineering for nucleation and domain orientation control in WSe₂ epitaxy on c-plane sapphire. Nat. Nanotechnol. 18, 1295–1302 (2023). https://doi.org/10.1038/s41565-023-01456-6
3. Houser, E., McKnight, T.V., Redwing, J.M., Peiris, F.C. Modeling the coverage of MoS₂ and WS₂ thin films using in-situ spectroscopic ellipsometry. J. Cryst. Growth 640, 127741 (2024). https://doi.org/10.1016/j.jcrysgro.2024.127741

Vincent Tung

The University of Tokyo

EPITAXY GROWTH OF P-TYPE 2D SEMICONDUCTORS

The rise of two-dimensional (2D) semiconductors represents the next wave of innovation in semiconductor technology, offering new opportunities for scaling channel materials and rethinking device architectures beyond the limits of bulk silicon CMOS. However, despite considerable progress in n-type 2D materials, such as MoS₂ and WS₂, the development of high-performance p-type counterparts remains significantly underdeveloped. This imbalance presents a critical bottleneck, as the lack of robust p-type 2D semiconductors hinders the realization of complementary logic circuits and limits the overall performance gain relative to silicon CMOS. A key challenge in identifying suitable p-type 2D semiconductors lies in the inherent difficulty of achieving stable valence band alignment, sufficient hole mobility, and reliable contact formation without introducing Fermi-level pinning or unintentional doping. Moreover, the performance of 2D devices is often compromised by degraded semiconductor/dielectric and semiconductor/electrode interfaces, especially when harsh fabrication steps or transfer processes are involved. These interfaces, though only a few atoms thick, play a decisive role in governing charge transport, threshold voltage stability, and scalability. In this talk, I will present our recent efforts in addressing these challenges by focusing on the synthesis and integration of p-type 2D semiconductors, particularly under low-temperature conditions. Emphasis will be placed on strategies for the direct growth of these materials on insulating substrates, thereby preserving electronically clean and atomically well-defined interfaces. This approach offers a practical pathway toward realizing high-performance complementary 2D logic while maintaining compatibility with back-end-of-line (BEOL) process constraints.

Priya Mahadevan

S.N. Bose National Centre for Basic Sciences

Do we understand the untwisted limit of the transition metal dichalcogenides?

The semiconducting nature of the Mo and W based transition metal dichalcogenides have brought these materials into the limelight. Twisted heterostructures involving these materials have been found to show unusual phenomena under various perturbations. These suggest the presence of strongly correlated states in these materials, an aspect that one does not expect upon doping holes into a semiconductor. While a lot of effort has gone into understanding the exotic ground states found at the twisted limit, in this talk I will present aspects of the untwisted limit that are not well understood. The discussion of the crystal field splitting of the TM d levels has been used to explain the origin of the semiconducting state. However, we are talking of systems with band gaps in the range of 1.5 – 2 eV, which have a level reversal of the transition metal d character of the band extrema at the symmetry points Gamma and K. The minimal model required to capture the low energy electronic structure will be presented, in addition to some consequences.

Ursula Wurstbauer

University of Münster

Optical signatures of inhomogeneities and moiré minibands in van der Waals bilayers

Two-dimensional (2D) materials are atomically thin crystals characterized by strong in-plane bonds and weak van der Waals (vdW) coupling between adjacent layers allowing to assemble vdW stacks. Heterobilayers of transition-metal dichalcogenides such as MoSe2/WSe2 host dense ensembles of interlayer excitons potentially forming a coherent many-body state at low temperature [1,2]. Twisted homobilayers such as tWSe2 are prone to the formation of moiré minibands. Both, the formation of moiré minibands as well as the potential landscape for interlayer excitons are significantly impacted by lattice reconstruction and lateral inhomogeneities of the moiré lattice constant referred to as twist-disorder.

We unravel the formation of moiré lattices and local twist disorder for tWSe2 by lateral force microscopy in ambient with atomic resolution. From a statistical study of several tWSe2 bilayers we identify areas with a large variation in twist angle up to 1° within less than a micrometer distance, but also areas with low twist disorder These findings with µ-Raman spectroscopy and identify optical signatures that allow the identification of the mean twist angle, but also areas with high and low twist angle disorder by this fast and versatile method [4].

Next, the formation of moiré minibands in tWSe2 is studied by their collective electronic inter moiré miniband excitations (IMBE) by means of low-temperature resonant inelastic light scattering spectroscopy (RILS). We access a series of RILS modes showing a peculiar dependence on twist angle and temperature [4]. These observations demonstrate the potential to study correlated electron phases by RILS that is a well-established powerful method to study low-dimensional interacting electronic systems [5] as well as (exotic) correlated phases as we recently demonstrated by the observation of chiral graviton modes in the fractional quantum Hall liquid [6].

Acknowledgements We acknowledge fruitful collaboration with Rami Dana, Julian Klein, Frances M. Ross, Dante Kennes and Tim Wehling. Financial support is provided by the DFG via the SPP 2244 and grants WU 637/ 7-2 and 8-1.

References [1] M. Troue et al., Phys. Rev. Lett. 131, 036902 (2023). [2] M. Brotons-Gisbert et al. MRS Bulletin 49, 914–931 (2024). [3] N. L. Bathen et al. in preparation. [4] N. Saigal et al. (2024) Phys. Rev. Lett. 133, 046902 (2024). [5] U. Wurstbauer et al. Solid State commun. 400, 115889 (2025).

Deji Akinwande

University of Texas at Austin

The quantum limits of contact resistance, benchmarking and ballistic transport in 2D field-effect transistors

In advanced two-dimensional (2D) field-effect transistors (FETs), charge transport is approaching dissipation-less ballistic transport and is limited by the interfacial contact resistance between the contact electrode and the 2D semiconducting channel. Here we discuss the total contact resistance (2Rc) of different types of monolayer molybdenum disulfide (MoS2) contact and the benchmarking near the quantum resistance contact (Rcq) limit and discuss the prospects of ballistic transport.

Cinzia Casiraghi

University of Manchester

Printed TMDs-based electronics on paper: from high-performance photodetectors to synapsis-like devices

Flexible electronics currently depend on complex, resource-intensive fabrication methods, use of rare metals, nanomaterials with limited stability, and polymeric substrates that contribute to plastic waste. Paper is an alternative substrate to traditional plastic and silicon-based materials, enabling to reduce electronic waste and environmental impact. However, the development of paper-based electronics remain challenging due to the poor compatibility of paper with commonly used materials and chemicals, its high surface roughness, sensitivity to moisture, and mechanical fragility. Our group has recently developed biocompatible and water-based conductive, semiconductive and insulating 2-Dimensional (2D) material inks that are suitable for the fabrication of fully printed devices on paper substrate. [1-3] In this talk I will give examples of printed devices that exploit transition-metal dichalcogenides (TMDs) inks. First, I will show an analog MoS2 based memristor, metal-free and fully printed on paper, with volatile resistive switching, low energy consumption (~0.17 nJ), high cycle endurance (over 10,000 cycles on paper), excellent thermal stability and great stability under ambient conditions (lasting over 100 days), able to perform all basic synaptic bio-functionalities. [4] Finally, I will show a fully printed photodetector exploiting a printable ReS2 ink, able to outperform all previous 2D material-based ink photodetectors made on paper. [5]

1. McManus et al, Nature Nano, 12, 343 (2017)
2. Peng et al, Materials Horiz. (2023), DOI: 10.1039/D3MH01224G
3. Conti et al, Nature comms, 11, 1 (2020)
4. Peng et al, under review
5. Zhao et al, under review

Stuart Parkin

Max Planck Institute of Microstructure Physics

2D van der Waals oligatomic layers for spintronics

2D van der Waals (vdw) layers are highly interesting for spintronic phenomena and devices. For example, vdw layers allow for the exploration of exotic magnetism in the 2D limit including the first 2D spin glass1. vdw layers also allow for novel ultrathin tunnel barriers for both magnetic tunnel junctions (MTJs) and Josephson junctions (JJs). Recently, we have demonstrated an all-antiferromagnetic tunnel junction that is formed from two bilayers of the van der Waals antiferromagnet CrSBr that are twisted at a non-zero angle. These junctions exhibit two (or more) non-volatile states in zero magnetic field with very large tunneling magnetoresistance values exceeding 1,000 %2. The tunneling magnetoresistance varies monotonically with the twist angle. Moreover, the antiferromagnetic electrodes have zero stray magnetic fields that is an essential criterion for applications in spintronic memory and logic. On the other hand, Josephson junctions that are formed from two superconducting electrodes separated by a weak link are of great interest for superconducting devices. We discuss a novel intrinsic Josephson Diode effect that is exhibited by lateral and vertical Josephson junctions with weak links formed from several vdw materials including NiTe23, PtTe24 and WTe25. The superconducting critical current density shows large asymmetries for current flowing in opposite directions of up to 80%. Such an effect could have important applications (beyond superconducting logic) as a novel magnetic field detector at cryogenic temperatures, for example, to “read” magnetic domain walls in a cryogenic racetrack memory6* .

• Funded by European Research Council Advanced Grant “SUPERMINT” (2022-2027). References (1) Pal, B.; Gopi, A. K.; Guan, Y.; Wang, R.; Chakraborty, A.; Tiwari, K.; Mathew, A.; Srivastava, A. K.; Zhang, W.; Kostanovski, I.; et al. Realization of a Spin Glass in a two-dimensional van der Waals material. Science (under review) 2025. (2) Chen, Y.; Samanta, K.; Shahed, N. A.; Zhang, H.; Fang, C.; Ernst, A.; Tsymbal, E. Y.; Parkin, S. S. P. Twist-assisted all-antiferromagnetic tunnel junction in the atomic limit. Nature 2024, 632, 1045-1051. (3) Pal, B.; Chakraborty, A.; Sivakumar, P. K.; Davydova, M.; Gopi, A. K.; Pandeya, A. K.; Krieger, J. A.; Zhang, Y.; Date, M.; Ju, S.; et al. Josephson diode effect from Cooper pair momentum in a topological semimetal. Nat. Phys. 2022, 18, 1228-1233. (4) Sivakumar, P. K.; Ahari, M. T.; Kim, J.-K.; Wu, Y.; Dixit, A.; Coster, G. J. d.; Pandeya, A. K.; Gilbert, M. J.; Parkin, S. S. P. Long-range Phase Coherence and Second Order φ_0-Josephson Effect in a Dirac Semimetal 1T-PtTe2 Comm. Phys. 2024, 7, 354. (5) Kim, J.-K.; Jeon, K.-R.; Sivakumar, P. K.; Jeon, J.; Koerner, C.; Woltersdorf, G.; Parkin, S. S. P. Intrinsic supercurrent non-reciprocity coupled to the crystal structure of a van der Waals Josephson barrier. Nat. Commun. 2024, 15, 1120. (6) Jeon, J.-C.; Migliorini, A.; Yoon, J.; Jeong, J.; Parkin, S. S. P. Multi-core memristor from electrically readable nanoscopic racetracks. Science 2024, 386, 315-322. －2－

Zakaria Al Balushi

UC Berkeley and Lawrence Berkeley National Labs

Direct Heterogeneous Integration of TMDs via Spin-on Molecular Chemistry

Two-dimensional (2D) semiconductors, such as molybdenum disulfide (MoS2), are emerging as key materials for next-generation electronics, addressing challenges in the miniaturization of silicon-based technologies. Despite progress in scaling-up 2D materials, integrating them into functional devices remains challenging, particularly in the context of three-dimensional integration. Here, we present a scalable method for growing high-quality mono- to few-layer MoS2 on large wafers using a spin-on precursor, molybdenum ethyl xanthate. This approach facilitates the formation of a metastable amorphous molybdenum trisulfide phase, which we can then be leveraged for direct heterogeneous integration. We thoroughly investigate the growth dynamics and associated versatile features using comprehensive characterization, reactive force-field molecular dynamics simulations, and Density Functional Theory. Our method allows precise control over film thickness, grain size, and defect density, yielding wafer-scale monolayer MoS2 with reliable optical properties comparable to as-exfoliated samples. Additionally, we achieve area-selective formation of MoS2 and the direct deposition of sub-5 nm high-k oxides using atomic layer deposition, without the need for seeding or surface functionalization. This process enables the fabrication of complex superlattice structures, top-gated FETs, and memristor devices, all from a single-source chemistry. Our findings highlight the versatility of spin-on metal xanthate chemistries for the synthesis and integration of transition metal dichalcogenides, paving the way for advanced nanoscale fabrication processes and enhancing the commercial viability of 2D materials in electronics.

Mario Lanza

National University of Singapore

Quantum tunnelling across gate dielectrics for transistors with 2D channels

In this presentation I will discuss the different articles that have studied quantum tunnelling (and leakage current in general) across different gate dielectrics for transistors with 2D channels, with special emphasis on monolayer and few-layers-thick hexagonal boron nitride (hBN). I will discuss several experimental factors related to fabrication and characterization protocols that can have big implications in the values of quantum tunnelling current observed, as well as the reliability of the claims presented in the literature. Finally, I will give my opinion on whether hBN could be a good dielectric for transistors with 2D channels.

Joohoon Kang

Sungkyunkwan University

Van der Waals 3D Assembly of 2D Nanomaterials for Scalable Electronics

Two-dimensional (2D) nanomaterials have received great attention as potential building blocks for use in fundamental elements of (opto)electronic applications due to their diverse and remarkable electronic and optical properties. However, such fundamental demonstrations cannot be directly applied to practical applications because of scalable synthesis of high-quality nanomaterials and their proper assembly. In this presentation, I will demonstrate wafer-scale van der Waals assembly of 2D materials, which are exfoliated via a molecular intercalation-assisted electrochemical exfoliation method. The resulting materials with distinct electronic properties including metal, semiconductor, and insulator, can be assembled into various (opto)electronic devices such as transistors, diodes, logic gates, and photodetectors. Also, such solution-based approach further enables inkjet printing-based device fabrications without conventional lithography.

Ahmet Avsar

National University of Singapore

Unconventional Spin Transport in Two-Dimensional Quantum Materials

Two-dimensional (2D) quantum materials present a fertile ground for exploring unconventional spin transport phenomena beyond conventional approaches. In this talk, I will present two examples where tailored 2D systems exhibit enhanced and unexpected spin phenomena. In graphene based spin valves, we observe enhanced spin polarization reaching up to 60%, alongside a pronounced spin anisotropy induced by a Moiré potential. In the second part, I will discuss spin transport in a magnetic topological insulator where we uncover highly tunable spin-polarized transport localized at the hinges—a surprising result linked to its higher-order topological nature. Remarkably, despite strong spin-orbit coupling and intrinsic magnetism, we detect robust spin polarization up to 75%. These findings underscore the potential of engineered 2D quantum materials for advancing spintronic technologies through new symmetry-protected and topologically robust spin transport regimes.

Seoung-Ki Lee

Pusan National University

Crystallinity Control of MoS₂ through Solution-Based Synthesis Methods

Solution-based synthesis has attracted sustained interest as a versatile approach for engineering two-dimensional (2D) transition metal dichalcogenides (TMDs), due to its potential to expand material functionality and enable novel structural designs. A critical aspect of this approach lies in the phase transition from liquid precursors to solid-state crystals, during which nucleation and growth must be precisely regulated to achieve desirable crystallinity and morphology. In this study, a synthesis strategy based on the (NH₄)₂MoS₄ precursor is employed to modulate the crystalline structure and morphology of MoS₂. Laser-induced photothermal processing facilitates the formation of nanocrystalline MoS₂ films with uniformly distributed grain domains through localized and rapid thermal decomposition. By controlling the degree of localized thermal accumulation, the grain size can be tuned, with domains reaching sizes on the order of several tens of micrometers. As an alternative strategy, a precipitation-driven synthesis route is developed to fabricate MoS₂ wires consisting of crystallographic layers that are vertically stacked along the longitudinal direction. Based on these solution-processed and crystallinity-controlled structures, potential applications in electronics, optoelectronics, and electrochemical systems will also be discussed.

Deep Jariwala

University of Pennsylvania

Are Excitons in 2D Materials useful?

The isolation of stable atomically thin two-dimensional (2D) materials on arbitrary substrates has led to a revolution in solid state physics and semiconductor device research over the past decade. A variety of other 2D materials (including semiconductors) with varying properties have been isolated raising the prospects for devices assembled by van der Waals forces. Particularly, these van der Waals bonded semiconductors exhibit strong excitonic resonances and large optical dielectric constants as compared to bulk 3D semiconductors. While they are a fertile ground for fundamental investigations, a pressing question remains: Do excitons make these materials any more useful ?
First, I will focus on the subject of strong light-matter coupling in excitonic 2D semiconductors, namely chalcogenides of Mo and W. Visible spectrum band-gaps with strong excitonic absorption makes transition metal dichalcogenides (TMDCs) of molybdenum and tungsten as attractive candidates for investigating strong light-matter interaction formation of hybrid states. We will present our recent work on the light trapping in multi-layer TMDCs when coupled to reflective substrates. Next, I will show the extension of these results to superlattices of excitonic chalcogenides, as well as metal organic chalcogenolates as new class of hybrid 2D chalcogenides. These hybrid multilayers and materials offer a unique opportunity to tailor the light-dispersion in the strong to ultra-strong coupling regime. Finally, if time permits, I will discuss the physics of strong light-matter coupling and it’s applications in phase modulator devices, photovoltaic devices. Our results highlight the vast opportunities available to tailor light-matter interactions and building practical devices with 2D semiconductors. I will conclude with a broad vision and prospects for 2D and 1D materials in the future of semiconductor opto-electronics and photonics.

Jonathan N. Coleman

Trinity College Dublin

Quantifying the factors limiting charge transport in printed nanosheet networks

Solution-processable two-dimensional (2D) materials present significant opportunities for printed electronics, enabling devices such as transistors, capacitors, diodes, and integrated circuits. However, achieving state-of-the-art performance requires advancements in both nanosheet processing and printing methodologies. A critical challenge lies in optimizing the electrical properties of nanosheet networks, particularly by reducing inter-nanosheet junction resistance, which often dominates charge transport limitations. For instance, in printed transistors based on 2H-MoS₂, junction resistance plays a pivotal role in determining network mobility. To maximize mobility, junctions must exhibit resistance (RJ) lower than that of individual nanosheets (RNS), necessitating a deeper understanding of the factors governing nanosheet network conduction. In this talk, I will present a series of approaches to investigate the impact of nanosheet dimensions and network morphology on junction resistance, mobility, and overall conductivity. I will first introduce conduction models for nanosheet networks and demonstrate their use in extracting RJ and RNS. I will then discuss two experimental techniques that allow simultaneous measurement of both resistances as a function of temperature, revealing distinct inter- and intra-nanosheet conduction mechanisms in MoS₂ and graphene networks. Furthermore, I will examine the role of nanosheet aspect ratio in determining junction resistance, highlighting how network morphology influences transport properties. This analysis provides concrete guidelines for minimizing junction resistance and enhancing network mobility. Finally, I will address the impact of network disorder on measured junction resistance, presenting a framework that combines experimental data with theoretical modeling to account for these effects and optimize device performance. This work advances our understanding of charge transport in printed 2D materials and provides key strategies for engineering high-mobility nanosheet networks, paving the way for next-generation printed electronic devices.

Yuki M. Itahashi

The University of Tokyo

Superconducting diode effect in a van der Waals superconductor​ ​

Rectification in superconductors is one of the quantum phenomena reflecting crystal symmetry and superconducting properties. In this work, we report a second harmonic nonreciprocal transport and superconducting diode effect in a van der Waals layered trigonal superconductor PbTaSe2. Especially, we realized the rectification without application of external magnetic field. The current directional and magnetic field dependence of the rectification effect is consistent with the crystal symmetry, indicating the important role of crystal symmetry.

Claudia Backes

University of Kassel

Characterisation of solution-processed MoS2 nanosheets by MIR and FIR​ vibrational spectroscopy​

Characterisation of the exact chemical composition of solution-processed and functionalised 2D materials is still a challenging task. Typically, a combination of Raman spectroscopy, XPS, TGA-MS and electron-microscopy based EDX is used. Some reports also complement this portfolio with IR vibrational spectrocopy in the MIR range which is suitable to detect organic functionalities which are physisorbed or chemisorbed on the surface. However, any quantitative information is lacking and a distinction between physisorption (of e.g. solvent) and covalently-grafted moieties is hardly possible. In this talk, we address this by systematic studies of solution-processed and/or functionalised MoS2 nanosheets as model substance, where we extend the spectroscopic range to the FIR, where Mo-S vibrations can be discerned. This is possible through diffuse-reflectance Fourier transform IR spectroscopy (DRIFT) in CsI matrix. The spectra in the FIR show characteristic changes with nanosheet thickness as confirmed by theory. Through normalisation to the Mo-S vibrations, it is possible to obtain semi-quantitative information on the amount of organic molecules associated with the MoS2 surface. We first develop washing procedures to remove as much physisorbed solvent and surfactant after exfoliation and size selection as possible. We find that small molecule surfactants such as sodium cholate can be removed to below the detection limit after three centrifugation-based washing steps with water and isopropanol, while the solvent NMP cannot be removed this way. An analysis of the vibrational modes provides evidence of covalent grafting of sono-chemically produced degradation products for samples produced by sonication with a flathead sonic tip in NMP. Polymeric adsorbates such as PVP commonly used as stabiliser in electrochemical exfoliation are also challenging to remove, but washing protocols could be elaborated. The purified nanosheets are then subjected to functionalisation with diazonium salts to investigate the reactivity of nanosheets produced by different exfoliation strategies in the liquid phase. We find the binding motif to be a combination of covalent attachment to sulfur, as well as defect functionalisation, regardless of the production method. Instead, the extent of covalent and defect functionalisation is dependent on the reactivity of the diazonium salt. Our work demonstrates that DRIFT can aid the controlled chemical modification of the 2D material surface enabling the production of samples with controlled doping and purity. Further, it is a powerful tool to clarify reaction mechanisms and identify unintentional chemical modification.

Yi Wan

National University of Singapore

Atomic-Scale Insights into Mastering Epitaxial Growth of 2D Transition Metal Dichalcogenides

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged as promising candidates to overcome the limitations of silicon-based electronics, offering a viable pathway to extend Moore’s Law and drive innovations in very-large-scale integration (VLSI) technology. Their intrinsic atomic thinness, tunable bandgaps, and excellent electrostatic control make them attractive for applications ranging from logic transistors to optoelectronics and flexible devices. However, the presence of grain boundaries in polycrystalline TMD films introduces one-dimensional (1D) defects that act as carrier scattering centers, degrading device mobility, reliability, and uniformity. To fully leverage the unique properties of TMDs in scalable electronic and optoelectronic platforms, the realization of wafer-scale single-crystal films is essential.

In this talk, I will present our recent progress toward atomic-scale control of TMD epitaxy, with a focus on MoS2 and WSe2. I will discuss our mechanistic insights into the roles of substrate step edges, interfacial reconstruction, and ultrathin surface decoration layers—such as oxide buffers—in directing unidirectional domain alignment. These engineered pathways enable orientation-controlled nucleation and the suppression of grain boundaries. Our work establishes a unified strategy for mastering 2D TMD epitaxy through atomic-scale substrate and interface engineering, paving the way for high-performance, wafer-scale 2D electronics.

Zhiyuan Zeng

City University of Hong Kong

Li⁺ intercalation chemistry in 2D materials: scalable preparation, mechanism study and applications

Intercalation of atoms, ions, and molecules is an effective means of tuning the properties of two-dimensional materials, while in situ imaging and spectroscopy provide powerful tools for deciphering intercalation dynamics and mechanisms.1,2 Firstly, we developed a lithium ion battery intercalation & exfoliation method with detailed experimental procedures for the mass production of 11 2D transition metal dichalcogenides (TMDs) and inorganic nanosheets, such as MoS2, WS2, TiS2, TaS2, ZrS2, graphene, h-BN, NbSe2, WSe2, Sb2Se3 and Bi2Te3, among them 3 TMDs achieved mono- or double layer yield > 90%.3 The Li insertion can be monitored and finely controlled in the battery testing system, so that the galvanostatic discharge process is stopped at a proper Li content to avoid decomposition of the intercalated compounds. Secondly, we discovered that small current and high cut-off voltage (0.005 A g-1, 0.9 V) produces pure 2H WS2 bilayers. while large current and low cut-off voltage (0.02 A g-1, 0.7 V) leads to 1T’ WS2 monolayers.4 For lithium intercalation mechanism, the state-of-the-art In-Situ Liquid Phase TEM is an ideal technique for identifying the phase changes during intercalation process.5 Combining with in-situ XAS, XRD and Raman, etc, the underlying lithium intercalation mechanism in TMDs were elucidated to achieve scalable production. For water decontamination, our metallic 1T/1T′ phase 2D TMDs (MoS2, WS2, TaS2, TiS2) nanosheets exhibited exceptional Pb2+ removal capacity (up to 758 mg∙g-1) with treatment capacity of 55 L-water/g-adsorbent for feeding Pb2+ concentration of 1 mg∙L-1, which is 1-3 orders of magnitude higher than other 2D materials and commercial activated carbon, holding great potential as Point-of-use (POU) devices.6 Then, a one-step covalent functionalization of MoS2 nanosheets was used for membrane fabrication, which exhibits rejection rates of >90% and >80% for various dyes and NaCl in reverse osmosis (RO).7 After that, we found that 1Tʹ-MoS2 electrode demonstrates exceptional volumetric desalination capacity of 65.1 mgNaCl cm-3 in capacitive deionization.8

References: [1] R. Yang†, L. Mei†, Z. Lin†, et al., D. Voiry, Q. Lu, J. Li, Z. Y. Zeng, Nat. Rev. Chem., 2024, 8, 410. [2] R. Yang, et al., H. S. Shin, D. Voiry, Q. Lu, J. Li, Z. Y. Zeng, Nat. Synth., 2023, 2, 101-118. [3] R. Yang, L. Mei, et al., H. S. Shin, D. Voiry, Z.Y. Zeng, Nat. Protoc., 2022, 17, 358-377. [4] L. Mei, et al., J. Li, X. Yu, Z. Y. Zeng, Nat. Synth., 2024, DOI: 10.1038/s44160-024-00679-2. [5] R. Yang, L. Mei, Y. Fan, Q. Zhang, H. G. Liao, J. Yang, J. Li, Z. Y. Zeng, Nat. Protoc., 2023, 18, 555-578. [6] L. Mei, M. Sun, R. Yang, et al., B. Huang, L. Gu, D. Voiry, Z. Y. Zeng, Nat. Commun., 2024, 15, 7770. [7] L. Mei, et al., C. Y. Tang, D. Voiry, H. Wang, A. B. Farimani, Z. Y. Zeng, Adv. Mater., 2022, 34, 2201416. [8] T. Ying, Y. Xiong, H. Peng, et al., C. Y. Tang, J. Fan, Z. Y. Zeng, Adv. Mater., 2024, 36, 2403385.

Soumya Sarkar

University of Southampton

Clean contacts for 2D spintronic and ferroelectric memory devices

Ferroic devices based on two-dimensional (2D) materials offer scalable solutions for high-density, non-volatile memory at advanced technology nodes. However, realising their full potential requires overcoming challenges related to device yield, reliability, and performance.[1] One critical challenge is to achieve clean metal contacts for 2D spintronic and ferroelectric memory devices. Here, we demonstrate how clean ferromagnetic van der Waals (vdW) contacts of indium and cobalt can enable spin-injection in graphene at room temperature, resulting in magnetoresistance over 15 times higher than defective contacts with pure cobalt.[2] By leveraging spin tunneling through the vdW gap, we eliminate the unreliable step of depositing ultrathin dielectric tunnel barriers on 2D surfaces, improving device yield. Non-local spin transport is observed at room temperature. We also show that clean contacts improve the electroresistance of ferroelectric diodes (FeDs) based on vdW heterostructures of CuInP2S6 (CIPS, <10 nm thick) and graphene, achieving ON/OFF ratios around 106, rectification ratios above 2500, low read/write voltages of 0.5/2V and a maximum output current density of 100 A/cm2.[3] The improved performance can be attributed to due to the absence of interface defects which allows effective modulation of the average barrier height upon polarisation switching. In addition, the stabilisation of intermediate net polarisation states in CIPS leads to multi-bit data retention at room temperature. Combined with its two-terminal self-selecting design, FeDs based on vdW heterostructures provide a viable approach for high-density compute-in-memory applications.[4] References

1. Yan Wang, Soumya Sarkar, Han Yan, Manish Chhowalla, “Perspectives on critical challenges in two-dimensional transition metal dichalcogenides for electronics” Nature Electronics, 2024, 7 (8), 638-645.
2. Soumya Sarkar, Saeyoung Oh, Peter J. Newton, Yang Li, Han Yan, Hu Young Jeong, Yan Wang, Manish Chhowalla “Spin injection in graphene using ferromagnetic indium-cobalt van der Waals contacts” Nature Electronics, 2025, 1-7.
3. Soumya Sarkar, Zirun Han, Maheera Abdul Ghani, Nives Strkalj, Jung Ho Kim, Yan Wang, Deep Jariwala, Manish Chhowalla “Multistate ferroelectric diodes with high electroresistance based on van der Waals heterostructures” Nano Letters, 2024, 24 (42), 13232-13237.
4. Soumya Sarkar, Xiwen Liu, Deep Jariwala, “Can a ferroelectric diode be a selector-less, universal, non-volatile memory?” (Arxiv, preprint online), 2025.

Yasir J Noori

University of Southampton

Can Electrochemical Deposition Grow TMDs?

Growing heterostructures of 2D materials in a scalable fashion remains a major obstacle that needs to be overcome before these materials can make an impact in industries. Electrochemical deposition is a scalable and widely adopted technique in the semiconductor industry. In our group, we have been pushing electrochemical deposition to grow vertical and planar heterostructures based on MoS2, WS2, WSe2, and graphene [1-5]. We used novel electrode designs to electrochemically deposit TMDs heterostructures selectively in micro and nanostructures at large scales and over insulating substrates, opening new doors towards utilising this technique for device applications such as light emitters and detectors. This talk will summarise the state-of-the-art in this approach and identify the key challenges that remain to be addressed.

Figure 1: (a) Schematic representations of the vertical electrochemical growth of MoS2 and (b) WS2 over graphene. (c) Electrochemical growth of MoS2, WS2 and WSe2 in planar TMD heterostructures.

References

1. P. N. Bartlett, C. H. de Groot, et al. “Molecular Precursors for the Electrodeposition of 2D-layered metal chalcogenides” Nature Reviews Chemistry, 2025, 9, 88-101.

2. Yasir J Noori, Shibin Thomas, et. al. “Electrodeposited WS2 monolayers on patterned graphene”, IOP 2D Materials, 2022, 9, 1, 015025.

3. Nema M Abdelazim, Yasir J Noori, et. al., “Lateral growth of MoS2 2D material semiconductor over an insulator via electrodeposition”, Advanced Electronic Materials, 2021, 7, 9, 2100419.

4. Yasir J Noori, Shibin Thomas, et. al. “Large-area electrodeposition of few-layer MoS2 on graphene for 2D material heterostructures”, ACS Applied Materials & Interfaces, 2020, 12, 44, 49786.

5. Shibin Thomas, Victoria K Greenacre, et. al., “Electrodeposition of 2D layered tungsten diselenide thin films using a single source precursor” Journal of Materials Chemistry C, 2024, 12, 47, 19191-19199

Salim El-Kazzi

AIXTRON

Monolayer control of 2D materials on 300 mm Si-CMOS Platforms

Two-dimensional (2D) materials are already meeting the high-performance benchmarks set for them. For instance, academic institutions and research centers have demonstrated transistors that exceed the International Roadmap for Devices and Systems (IRDS) targets for next-generation logic devices. However, the 2D materials community still faces significant challenges in scaling these breakthroughs to industry-standard 200 mm and 300 mm wafers. This difficulty arises largely because, for the first time, the silicon industry is attempting to control single-layer materials at the wafer scale - materials that primarily interact via van der Waals forces and must endure harsh processing conditions such as high temperatures, inter-wafer transfers, and oxide depositions. In this talk, we demonstrate how a versatile and robust 2D deposition technique is crucial to addressing these challenges. Specifically, we highlight how the AIXTRON CCS 2D reactor is enabling the research community to advance in this field. We focus on how in-situ monitoring of precursors, growth behavior, and advanced characterization techniques are helping researchers resolve reliability issues and consistently produce high-quality 2D layers. The presentation concludes by outlining the key areas the community must address to pave the way for integrating 2D materials into the silicon industry.

Seong-Ju Hwang

Yonsei University

Interface- and defect-engineering of 2D nanostructured metal compounds

Highly anisotropic 2D nanosheets of layered metal compounds (metal oxides, layered double hydroxides, metal chalcogenides, metal carbides, metal nitrides, and carbon nitrides) have evoked great deal of research activity because of their outstanding performances as functional materials. A great diversity in the chemical compositions, crystal structures, and defect structures of inorganic nanosheets provides this class of materials with a wide spectrum of physical properties and functionalities. The inorganic nanosheets can be used as powerful building blocks for exploring high performance hybrid catalysts. Since the crystal defect and interfacial interaction have profound influence on the electrochemical and catalytic activity of hybrid materials, the energy functionalities of 2D metal compound-based nanohybrids can be greatly enhanced by defect- and interface-engineering. In this talk, several classes of 2D metal compound nanosheets and their nanohybrids applicable for renewable energy technology will be presented together with the discussion about the relationship between chemical bonding nature and functionalities. The crucial role of interface/defect engineering in optimizing the energy performances of 2D nanosheet-based metal compounds will be highlighted.

Saroj P. Dash

Chalmers University of Technology

Spin on 2D Quantum Matter

Exploring spin, orbital, and topological properties of two-dimensional (2D) quantum materials represents a new platform for realizing novel quantum and spin-based phenomena and device applications. We showed that the unique band structure and lower crystal symmetries of WTe2 and TaIrTe4 can provide an unconventional spin-polarized current [1] and out-of-plane spin-orbit torque [2] needed for field-free magnetization switching. On the other hand, 2D magnets are promising owing to their tunable magnetic properties. We reported above room temperature 2D magnet-based spin-valve devices in heterostructure with graphene [3,4]. We further utilized such 2D magnets with co-existence of ferromagnetic and anti-ferromagnetic orders with intrinsic exchange bias in the system, giving rise to a canted magnetism [5]. Such canted magnetism of 2D magnets helps in achieving field-free magnetization switching with conventional spin orbit materials such as Pt [5,6]. Combining such 2D quantum materials in van der Waals heterostructures can offer a promising platform for efficient control of magnetization dynamics for non-volatile spin-based memory. Recently, we demonstrated energy-efficient field-free spin-orbit torque (SOT) switching and tunable magnetization dynamics in 2D heterostructure comprising out-of-plane magnet Fe3GaTe2 and topological Weyl semimetal TaIrTe4 [7]. In TaIrTe4/Fe3GaTe2 devices, an energy-efficient and deterministic field-free SOT magnetization switching is achieved at room temperature with a very low current density [7]. These results establish that 2D heterostructures provide a promising route to energy-efficient, field-free, and tunable SOT-based spintronic memory devices. References [1] B. Zhao et al, Saroj Dash, Advanced Materials 32, 2000818 (2020). [2] L. Binasal et al, Saroj Dash, Nature Communications 15 (1), 4649 (2024). [3] B. Zhao et al, Saroj Dash, Advanced Materials, 2209113 (2023). [4] R. Ngaloy et al, Saroj Dash, ACS Nano 2024, 18, 7, 5240 (2024). [5] B. Zhao et al, Saroj Dash, ArXiv, https://doi.org/10.48550/arXiv.2308.13408 [6] B. Zhao et al, Saroj Dash, ACS Nano 2025, https://doi.org/10.1021/acsnano.4c16826 [7] L. Pandey et al, Saroj Dash, Arxiv, https://doi.org/10.48550/arXiv.2408.13095

Alicia Forment-Aliaga

University of Valencia

Tuning and Probing 2D Materials

The emergence of new functionalities in two-dimensional materials (2Dms) can be driven by their chemical modification using a diverse array of molecules and clusters. In pursuit of this goal, our work has focused on the functionalization of transition metal chalcogenides with bistable molecular systems such as spin crossover complexes, chiral molecules, and polyoxometalates, among others.(1,2)

Taking this approach a step further, we have explored innovative strategies to achieve asymmetric functionalization, enabling the creation of Janus 2D materials. By modifying each side of the 2D material differently, we unlock the potential for emergent properties that surpass those of the parent material. In this context, we present the liquid-phase fabrication strategy we are currently developing to produce these Janus 2D systems, offering a versatile pathway toward the tailored design of multifunctional materials.(3)

Finally, we aim to address the challenge of characterizing functionalized 2D materials, as conventional spectroscopic techniques—such as Raman, IR, and XPS—often suffer from limited sensitivity and spatial resolution. In contrast, Scanning Probe Microscopy (SPM) enables nanoscale analysis with high lateral resolution. Beyond topography, SPM can probe mechanical properties, offering insights into surface chemistry. Here, we show that adhesion mapping via SPM provides a simple, reliable method to distinguish between bare and functionalized regions. Notably, adhesion values are independent of layer thickness, confirming their surface-specific nature and highlighting the utility of this approach for chemical characterization of 2Dms.(4)

(1) R. Torres-Cavanillas, M. Morant-Giner, et al. Nat. Chem. 2021, 13, 1101–1109 (2) M. Guillen-Soler, N. Vassilyeva et al. Adv. Sustainable Syst. 2023, 2300607 (3) N. Vassilyeva, A. Forment-Aliaga, E. Coronado Small 2024, 2406599 (4) I. Bortons-Alcazar et al. ACS Appl. Mater. Interfaces 2024, 16, 19711−19719

Hyeon-Jin Shin

Gwangju Institute of Science and Technology

Enabling 3D Logic with 2D Materials: Advances in CFETs and Interconnect Systems

As digital transformation accelerates, the volume of generated data is growing exponentially, placing increasing demands on semiconductor devices for higher performance and lower power consumption. However, conventional silicon-based transistors are approaching their physical and performance scaling limits. To address these challenges, innovation in materials, device architectures, and fabrication processes is essential [1]. Two-dimensional materials (2DMs), with their atomically thin channels and excellent electrostatic control, have emerged as promising candidates to overcome these limitations. In particular, semiconducting 2D materials such as MoS₂ offer reliable performance at deeply scaled channel lengths, making them well-suited for future logic applications [2]. Among the most promising device architectures is the 2D material-based Multibridge Channel Complementary Field-Effect Transistor (2DM-MBC CFET), which enables high integration density, energy efficiency, and a reduced footprint [1]. In this talk, we will present the current state-of-the-art, key challenges, and remaining tasks for the industrialization of 2DM-MBC CFETs [3]. Furthermore, to enable efficient signal transport between vertically stacked transistors, we will also discuss the development of novel interconnect systems [4].

Reference [1] S. H. Shin. H.-J. Shin* et al., “2D Materials in Logic Technology: Power Efficiency and Scalability in 2DM-MBC CFET” Nano. Lett. 25 (18), 7224–7233, 2025 [2] Y. Liu, H.-J. Shin et. al., “Promises and prospects of two-dimensional transistors” Nature, 591 (7848), 43-53, 2021 [3] H. H. Yoon, H.-J. Shin* et. al., “Enabling the Angstrom Era: 2D Material-Based Multi-Bridge-Channel Complementary Field Effect Transistors” In revision [4] H. Kim, H.-J. Shin* et. al., “Future Interconnect Materials for Highly Integrated Semiconductor Devices” In revision

Ute Kaiser

Universität Ulm

Tailoring and Quantifying Defect Sturctures in 2D TMDs and TMPTs for Functional Nano-Devices

Reducing power consumption enormously while enabling efficient nano catalysis, high-performance batteries, and quantum technologies is a central challenge in nanoscience. As Nature Reviews Materials highlights, “nanostructured electrocatalysts with tunable activity and selectivity” are key to catalytic efficiency¹. Likewise, Nature Nanotechnology notes that “nanoparticles require shorter distances for electron transport, leading to higher conductivity and greater power density”². Such applications demand extreme miniaturization, reproducible fabrication, and atomic-level control of material properties. Two-dimensional materials, particularly transition metal dichalcogenides (TMDs), offer unique advantages here due to their highly tunable electronic, optical, and magnetic characteristics. However, in few-layer stacks, especially in devices with an active middle layer, assessing and engineering the relevant atomic defect structures remains a major hurdle. While single atomic defects such as chalcogen vacancies can be created and imaged using the unique low-voltage Cc/Cs-corrected high-resolution transmission electron microscopy (HRTEM)3-5, the projection nature of TEM poses intrinsic challenges: in few-layer TMDs, multiple atoms align along the beam direction, making it difficult to identify defect positions in the hidden middle layers. In this work, we present a method to extract subtle intensity variations in HRTEM images, allowing us to identify and quantify defect structures even within the central layer of trilayer MoS₂. Our results reveal a significantly reduced beam damage cross-section in the middle layer, which has critical implications for device reliability and performance6. Furthermore, we demonstrate first correlation between optical and transport measurements with high-resolution electron microscopy characterization at the same location identifying point-like defects in MoS₂ and WS₂ samples. This is enabled by employing a reversible transfer technique after HRTEM characterization6. Our results show a clear correlation between electron dose, defect density, and changes in transport, photoluminescence and Raman response — thus paving the way for non-invasive, automatable quality control via optical methods in future7,8. Finally, we report on the formation of new phases within host-TMPTs and TMDs induced by electron irradiation and/or external treatment. In detail, we observe the emergence of MnS-like phases from various TMPTs with first-principles calculations suggesting potential ferromagnetic behavior in specific crystal orientations9, as well as the formation of the 1T’ phase from 1H MoTe211,12 and Mo₆S₆ chain formation within MoS₂. Together, these results represent a step forward towards the long-term goal of correlating macroscopic device functionality with atomically resolved defect structures in 2D materials. Our approach opens the door for targeted defect engineering and comprehensive structure–property correlations — key prerequisites for the integration of TMDs in real-world nanoscale devices.

[1] Z. W. She et al. Nat. Rev. Mater. 2, 17046 (2017). [2] J. Liu et al. Nat. Nanotechnol. 9, 1031–1039 (2014). [3] U. Kaiser et al., Ultramicroscopy, 111, 8, 1239 (2011). [4] S. Kretschmer, et al, Nano Lett. 20, 2865 (2020). [5] M. Linck, et al. PRL 117, 076101 (2016). [6] M. Quincke, et al. Nano Letters 24,10496 (2024). [7] M. Quincke, et al. ACS App. Nano Mat. 5 11429 (2022). [8] N. Moses Badlyan, M. Quincke, et al.,Nanotechnology 35 435001(2024). [9] A. Storm, J. Köster, et al. ACS Nano 17 4250 (2023). [10] J. Köster, A. Storm et al., J. of Phys. Chem. C 126 15446 (2022). [11] V. O. Khaustov, et al., ACS Applied Nano Materials 7 18094 (2023). [12] V. O. Khaustov, et al. 2D Materials 12 025025 (2025). [13] J. Köster et al., J. Phys. Chem. C 125 13601 (2021).

Arindam Ghosh

Indian Institute of Science

Devices with marginally-misoriented twisted bilayers of TMDC

Over the past few years, the twisted bilayers of two-dimensional materials have become a new resource for fundamental discoveries as well as device applications. Many of these functionalities rely on controlled breaking of structural symmetry that results in new regimes of electron-electron as well as electron-light interactions. At near-parallel orientation, for example, twisted bilayers of transition metal dichalcogenides (TMDC) exhibit interlayer charge transfer-driven out-of-plane ferroelectricity. In this talk, I shall show some recent results from devices that consist of a twisted bilayer of TMDC in the van der Waals heterostructure for electronic and optoelectronic applications [1,2]. I shall show the evidence of non-local transport and formation of memories with graphene and twisted TMDC heterostructures, as well as extremely sensitive opto-electronics where the optically induced interlayer charge transfer is driven by internal electric fields. These advances will hopefully establish the twisted bilayers of TMDC firmly in the device application space. [1] Sett et al. Nano Letters 24, 9245 (2025) [2] Gill et al. (2025, under review)

Kian Ping Loh

National Unversity of Singapore

Electrocatalysis on 1T'-molybdenum disulfide

I would like to introduce 1T-MoS2 as an interesting platform for loading single atom catalysts (SAC). Identifying a substrate that provides strong anchoring of two different types of single atom catalysts (SACs) while enabling their dynamic re-configuration into binuclear dual atom catalyst (DAC) is crucial for attaining good performance in electrochemical synthesis, but remains relatively unexplored. In this study, we demonstrate that the electrochemical desulfurization of MoS2 produces abundant 1 Tʹ domains that facilitate the high loading of Cu (7.9 wt%) and Pt (6.7 wt%) to form DACs. By using operando X-ray absorption spectroscopy and first-principles calculations, we revealed the dynamic, reversible configuration between single atom state (Pt and Cu) and DAC state (Cu-Pt) by applying a voltage near hydrogen evolution reaction during electrochemical reactions [1]. As a proof of principle, we demonstrate that the Cu-Pt DACs induced by electric field showed superior performance for the selective hydrogenation of alkynes as compared to mono-elemental Cu or Pt catalysts.

In another study, we demonstrate that 1T′-enriched lithiated molybdenum disulfide is a highly powerful reducing agent, which can be exploited for the in-situ reduction of metal ions within the inner planes of lithiated molybdenum disulfide to form a zero valent metal-intercalated molybdenum disulfide [2]. The confinement of platinum nanoparticles within the molybdenum disulfide layered structure leads to enhanced hydrogen evolution reaction activity and stability compared to catalysts dispersed on carbon support. We discovered that by hydrogenating the intercalated Li to form lithium hydride (LiH), unprecedented long-term (>3 months) air stability of the 1T′ phase can be achieved. Most importantly, this passivation method has wide applicability for other alkali metals and TMDs [3].

References

[1] Wu, J., Chen, Z., Yang, K. Kian Ping Loh* et al. Electric bias-induced reversible configuration of single and heteronuclear dual-atom catalysts on 1Tʹ-MoS2. Naure Nanotechnology (2025). https://doi.org/10.1038/s41565-025-01934-z

[2] Chen, Z., Leng, K., Zhao, X. Kian Ping Loh* et al. Interface confined hydrogen evolution reaction in zero valent metal nanoparticles-intercalated molybdenum disulfide. Nat Commun 8, 14548 (2017). https://doi.org/10.1038/ncomms14548

[3] Chemical Stabilization of 1T′ Phase Transition Metal Dichalcogenides with Giant Optical Kerr Nonlinearity Sherman J. R. Tan, Kian Ping Loh*, Journal of the American Chemical Society 2017, 139, 6, 2504-2511

Tibor Grasser

TU Wien

Benchmarking Insulators for Devices Based on 2D Materials

Despite remarkable advances in 2D electronic devices, their predicted performance potential remains largely untapped. A key limiting factor is the lack of scalable insulators that integrate with 2D materials as seamlessly as SiO₂ does with silicon. Identifying suitable insulators for 2D nanoelectronics is a critical and complex challenge. This issue is particularly pressing as the scaling of transistors toward sub-10 nm channel lengths demands gate insulators with sub-1 nm equivalent oxide thicknesses (EOT). To enable competitive device performance, these insulators must meet stringent requirements, including (i) low gate leakage currents, (ii) a low density of interface traps, (iii) a low density of border traps within the insulator, and (iv) high dielectric strength.

Over the past decade, a wide range of insulating materials has been proposed, underscoring the need for early and systematic screening. However, benchmarking these insulators presents several challenges. First, experimentally available samples often suffer from non-optimized fabrication processes and do not match the quality of commercial SiO₂ and HfO₂. Second, these materials typically fall short of the aggressive EOT targets required for future technologies, complicating direct comparisons. Third, theoretical predictions via atomistic simulations are hindered by uncertainties in the crystal structures of many candidates and by the strong dependence of defect characteristics on processing conditions.

In this talk, I will present our combined experimental and theoretical approach aimed at separating processing-related limitations from the intrinsic potential of novel insulator materials. This strategy enables a more reliable assessment of their suitability for achieving sub-1 nm EOT values in next-generation 2D devices.

Nasim Alem

The Pennsylvania State University

Investigation of Luminescence in 2D Quantum Heterostructures Using Advanced Electron Microscopy Imaging and Spectroscopy

Scanning/Transmission electron microscopy (S/TEM) imaging and spectroscopy is unique among material characterization methods in that it allows for direct imaging of atomic structure and defects as well as their local physical and electronic properties. With the invention and development of aberration correctors, and fast and sensitive detectors over the last 15 years, advanced electron microscopy now possesses the ability to image individual atoms and directly identify their chemistry and structure with sub-Ångstrom precision. The unprecedented spatial and energy resolution of STEM, in combination with Electron energy loss spectroscopy (EELS) and Cathodoluminescence (CL) techniques has further enabled us to detect variations in the absorption and emission characteristics of materials at the nanoscale regime and correlate them with the local structure and chemistry. Furthermore, recent advances in data-driven analysis and machine learning (ML) algorithms have allowed extraction of meaningful information from electron microscopy data sets. In this talk, we will present our recent studies on the local electronic/atomic structure and light emission characteristics in in-plane monolayer 2D transition metal dichalcogenide (TMD) Mo(S,Se)2 quantum dots embedded in W(S,Se)2 matrix using STEM-EELS-CL. Our studies uncover evidence of quantum confinement as well as emission of interface excitons in the dot sizes ranging from a couple of nanometers to a few tens of nanometers. This talk will also present our recent efforts in understanding the underlying physics of defect formation and heteroepitaxy in the large family of 2D vertical TMD heterostructures, which is the key in the large-scale synthesis of 2D based heterostructure devices.

Jiong Zhao

The Hong Kong Polytechnic University

The dynamic phase and atomic structures in 2D ferroelectric materials

The development of electronic devices is currently facing significant challenges—key issues include how to further reduce device size, improve computational speed, enhance the integration of storage and computing units, and reduce energy consumption. In recent years, a new paradigm has been proposed that goes beyond the traditional von Neumann architecture: in-memory computing architectures. Among these, two-dimensional (2D) ferroelectric materials, with their miniaturized dimensions, high speed, high sensitivity, and room-temperature ferroelectric order with stable memory functionality, have emerged as ideal candidates for next-generation in-memory computing devices. Additionally, the phase transitions that readily occur in 2D materials may provide greater flexibility in manipulating non-volatile memory. Thus, 2D multiphase ferroelectric materials offer a highly promising solution to these critical challenges.

In this presentation, we will elucidate the physical origins of 2D ferroelectric order and ferroelectric phase transitions, and discuss how to control/manipulate phase transitions and ferroelectric polarization in 2D materials to construct novel devices. We employ various in situ transmission electron microscopy (TEM) techniques, particularly in situ mechanical manipulation, in situ mechanical testing, in situ electrical testing, in situ heating, and in situ electron-beam control, to comprehensively investigate the ferroelectric properties of 2D chalcogenides. These 2D ferroelectric materials exhibit unique topological, mechanical, electrical, and other fascinating physical properties. Through our research, we have successfully established direct correlations between atomic-scale structures and device performance, thereby deepening the understanding of 2D functional materials and advancing their practical applications.

Yasufumi Takahashi

Nagoya University

Electrochemical imaging of hydrogen evolution reaction sites on two-dimensional materials

MoS₂ is a promising non-precious catalyst for the hydrogen evolution reaction (HER), but identifying active sites remains challenging. Using scanning electrochemical cell microscopy (SECCM), we visualized heterogeneous HER activity on MoS₂ and its heterostructures, revealing relationships with layer number and aging. SECCM also identified active sites in MoSSe nanoscrolls and SnS₂ nanosheets, demonstrating its power in characterizing local catalytic properties of 2D materials.

John Robertson

University of Cambridge

Vt control in MoS₂ and Si FETs and recent proposed layered Semiconductors and Hi K Insulators

We explain how the n,p polarity and threshold voltage (Vt) control of Si-based and thus MoS2 FETs is controlled in terms of the charge neutrality level (CNL) of electropositive (eg Y2O3) and electronegative (Al2O3) oxides rather than their oxygen areal density as previously believed [1]. We then study recent suggestions of alternative layered semiconductors and high K insulators such as Bi2O2Se and Bi2SeO5 [2].

1. R Cao, H Guo, JW Luo, J Robertson, ACS App Elec Mater 7 721 (2025)

2. J Tang et al, Nature Mater 24 519 (2025)

Yimo Han

Rice University

Revealing Strain, Stacking, and Switching of van der Waals Materials by Advanced Electron Microscopy

Van der Waals (vdW) materials exhibit highly versatile properties, making them promising candidates for future applications in electronics, optoelectronics, and quantum computing. The local structure, including strain, stacking order, and interlayer sliding, plays a critical role in dictating these properties by influencing domain structure, charge transport, and even topological states. In this presentation, we demonstrate how 4D-STEM is utilized to investigate strain, stacking, and in-situ switching in two-dimensional (2D) vdW ferroelectrics (FEs). Specifically, we examine group IV monochalcogenide thin flakes grown by physical vapor deposition (PVD), which exhibit spontaneous in-plane polarization and giant nonlinear optical effects. These materials are at the forefront of nanoelectronic innovation, with their unique structure enabling polarization that is intricately linked to both in-plane lattice strain and out-of-plane stacking order, directly influencing their electronic properties. To probe these effects, we developed a novel 4D-STEM approach that simultaneously resolves strain and stacking order in vdW SnSe. Using electron ptychography, we achieved layer-by-layer mapping of the stacking order, revealing the coexistence of antiferroelectric (AFE) and FE phases that form unique AFE-FE domain walls. Furthermore, by applying an external electric field in in-situ switching studies, we identified two primary pathways for AFE-to-FE switching, both involving interlayer sliding and polarization switching. This systematic study of vdW FEs provides critical insights into their fundamental behavior, paving the way for their engineering and integration into nanoelectronic devices.

Ritesh Agarwal

University of Pennsylvania

Unconventional amorphization in layered ferroic materials from multimodal coupling of fields to competing orders

In layered ferroic systems, many competing orders exist which lead to novel properties. These systems are typically metastable with multiple competing states very close to the ground state. Characterization of their ground states and the effect of external stimuli on their structure and properties is required to understand the complex role of multiple competing orders in stabilizing their structures. We will discuss our efforts towards understanding the structure-property relationships in ferroic In2Se3 by using a suite of structural and optoelectronic microscopy probes. We also observed an energy-efficient, unconventional long-range solid-state amorphization in a new ferroic β″-phase of In2Se3 nanowires via the application of a direct current. The complex interplay of the applied electric field, current flow parallel to the van der Waals layers and piezoelectric stress, results in the formation of interlayer sliding defects and in-plane polarization rotation induced disorder in this layered material. Upon reaching a critical limit of the electrically induced disorder, the structure becomes frustrated and locally collapses into an amorphous phase, and this phenomenon is replicated over a much larger microscopic lengthscales through acoustic jerks. Our work demonstrates new multimodal coupling mechanisms of the ferroic order in materials to the externally applied electric field, current, and internally generated stress and can be useful to design new materials and low-power devices. Our initial efforts towards understanding the role of quantum geometry in determining the unique properties of complex materials will also be discussed.

Bilu Liu

Tsinghua University

Mass production of 2D electrocatalysts for industrial relevant high-current-density water electrolysis

Graphene and 2D materials possessing large surface area, tunable electronic and chemical properties, and can be massively produced at low cost. There are important class of materials for various catalysis. In this talk, I will introduce our works in the mass production of 2D materials by top-down exfoliation method. Then, I will talk about the use of such massively produced 2D materials in large current density electrolysis including fundamental understanding of the process, interfacial engineering, and electrolyzer performance at industrial relevant high current density (>2 A/cm2).

Zdeněk Sofer

University of Chemistry and Technology Prague

Controlled doping and solid solutions of TMDCH and layered chalcogen-halogenides

Doping of transition metal dichalcogenides is crucial for modulating electronic properties such as carrier type and concentration. Although these materials are typically native n-type semiconductors, incorporation of transition metals—such as V, Nb, Ta, Ti, Zr, and Hf—can induce p-type or ambipolar behaviour, while rhenium doping significantly enhances n-type conductivity. Moreover, the formation of solid solutions in TMDCH further enables tuning of both electronic and structural properties. Chemical vapor transport (CVT) has proven to be an effective method for growing bulk TMDCH and other two-dimensional materials. In this work, we demonstrate scalable crystal growth on the kilogram scale, as well as high-quality, low-defect TMDCH films produced via flux methods. We also showcase electrochemical exfoliation and printed device fabrication from large-scale TMDCH, achieving high-mobility p-type and n-type films. Finally, we present novel mixed chalcogen-halogenides including CrSBr, its doping and structural analogues. High-k layered compounds prepared by both flux growth and CVT will be demonstrated for application in devices.

Pablo Ares

Autonomous University of Madrid

Magnetic Field Screening of graphene, graphene oxide and MoS₂

2D materials offer exciting possibilities for integration into nanoscale devices, particularly in applications requiring precise control of magnetic fields. In this work, we use Magnetic Force Microscopy (MFM) to investigate how graphene, graphene oxide (GO), and MoS₂ interact with the magnetic fields of the underlying nanostructures. We find that graphene exhibits a weak but measurable overall screening effect (~0.5% per layer), while GO and MoS₂ show negligible interaction with the magnetic field [1]. This suggests that graphene could be employed for controlled magnetic field modulation, whereas GO and MoS₂ provide minimal interference with magnetic functionalities. These results highlight the potential of 2D materials to provide effective protection while minimally affecting the underlying magnetic functionalities, whic is important in spintronics, data storage, and other advanced magnetic nanodevices, where precise tuning of magnetic interactions is crucial.

[1] D. A. Aldave et al., Magnetic Field Screening of 2D Materials Revealed by Magnetic Force Microscopy. Adv. Electron. Mater. 2025, 11, 2400607.

Jagoda Sławińska

University of Groningen

Ferroelectricity and charge-spin interconversion in TMDs

Transition metal dichalcogenides (TMDs) are promising materials for spintronics due to their strong spin-orbit coupling, topological features, and symmetry-driven properties. In addition, there are several materials capable of hosting ferroelectricity. In this talk, I will present theoretical results demonstrating ferroelectric switching of charge-spin conversion, unconventional configurations of spin Hall effect, and persistent spin textures that may enhance spin lifetimes. These functionalities are relevant for memory and logic-in-memory applications, where efficient charge-spin interconversion and/or long spin lifetime are essential. Using symmetry analysis and first-principles calculations, we explore how these spin-related effects can be realized and tuned in both two- and three-dimensional TMDs. Our findings highlight the potential of TMDs for electrically controlled spintronic devices.

P. James Schuck

Comlumbia University

Nonlinear and quantum vad der Waals photonics in 2D semiconductors

I will discuss our recent results demonstrating exceptional nonlinear optical frequency conversion in transition metal dichalcogenides (TMDs). By fabricating nano-photonic elements such as waveguides, metasurfaces, and periodically poled stacks, we achieve macroscopic frequency conversion efficiencies over microscopic distances, 10 − 100× smaller than current systems with similar performances. Further, we report the broadband generation of entangled photon pairs at telecom wavelength via quasi-phase-matched spontaneous parametric down-conversion, showing the highest coincidence-to-accidental-ratio (CAR) ever demonstrated in a vdW material. Work by us an others is now opening the new and unexplored field of phase-matched nonlinear optics with microscopic van der Waals crystals, unlocking applications that require simple, ultra-compact technologies such as on-chip entangled photon-pair sources for integrated quantum circuitry and sensing.

Takhee Lee

Seoul National University

Remote Surface-Charge-Transfer Doping on 2D Materials Field Effect Transistors

Efficient doping for modulating electrical properties of two-dimensional (2D) transition metal dichalcogenide (TMDC) semiconductors is essential for meeting the versatile requirements for electronic and optoelectronic devices applications. In this talk, I will present our group’s research work on surface-charge-transfer doping (SCTD) of molecules in 2D TMDC field effect transistors (FETs). In particular, I will explain the effects of molecular SCTD on the charge transport properties of WSe2 using three p-type molecular dopants (F4-TCNQ, magic blue, and Mo(tfd-COCF3)3) [2]. The temperature dependent transport measurements show that the dopant counterions on WSe2 surface can induce Coulomb scattering in WSe2 channel and the degree of scattering is significantly dependent on the dopant. Then, I will explain a remote SCTD method by inserting a h-BN layer between MoS2 and n-type molecular dopant (benzyl viologen) [2]. A quantitative analysis in remotely doped FET devices supports an effective suppression of the dopant-induced scattering relative to the conventional direct SCTD method. Our study of the SCTD method on 2D TMDC FETs can be a promising method for material-level tailoring of electrical and optoelectronic devices based on TMDCs.

References [1]. J.-K. Kim et al., Adv. Mater. 33, 2101598 (2021). [2]. J. Jang et al., Sci. Adv. 8, eabn3181 (2022).

Mingsheng Xu

Zhejiang University

Wafer-Scale 2D Cr-Based Layered Materials with Room-Temperature Magnetic Properties

The pursuit of high Curie temperature ferromagnets in 2D materials at room temperature has garnered significant interest for potential spintronic applications [1]. However, the controllable synthesis of 2D magnetic materials remains to be challenge. Here, we present our studies on 2D Cr-based layered materials such as CrS2 and CrTe2. We report for the first time the synthesis of 2D layered CrS2 down to the monolayer via the chemical vapor deposition (CVD) method, its phase structures and physical properties. We show that the monolayer 2H-CrS2 is a direct bandgap semiconductor with a gap of approximately 0.95 eV predicted by the PBE functional, while the 1T- and 1T’-CrS2 are metallic and semi-metallic with approximately 10 meV gap, respectively. Furthermore, 2H CrS2 exhibits nonmagnetic semiconducting properties while for ferromagnetic spin configuration, the 1T and 1T’ CrS2 show magnetic characteristics [2,3]. Further, we report the fine controllable synthesis of wafer-scale 1T-CrTe2 films on a SiO2/Si substrate at temperatures below 400 ºC [4]. Magnetic hysteresis measurements reveal that the synthesized 1T-CrTe2 films exhibit perpendicular magnetic anisotropy along with distinct step-like magnetic transitions. We find that 1T-CrTe2 is susceptible to oxygen adsorption even in ambient conditions and thus have effect on the magnetic properties.

Keywords: Chemical vapor deposition, synthesis, CrS2, CrTe2, magnetism, electronics

References [1] Yahya Khan, Sk. Md. Obaidulla, Mohammad Rezwan Habib, Anabil Gayen, Tao Liang, Xuefeng Wang, and Mingsheng Xu, Recent breakthroughs in two-dimensional van der Waals magnetic materials and emerging applications, Nano Today 34, 100902 (2020). [2] Mohammad Rezwan Habib, Shengping Wang, Weijia Wang, Han Xiao, Sk Md Obaidulla, Anabil Gayen, Yahya Khan, Hongzheng Chen, Mingsheng Xu, Electronic properties of polymorphic two dimensional layered chromium disulphide, Nanoscale 11, 20213 (2019). [3] Han Xiao, Wenzhuo Zhuang, Leyi Loh, Tao Liang, Anabil Gayen, Peng Ye, Michel Bosman, Goki Eda, Xuefeng Wang, Mingsheng Xu, Van der Waals epitaxial growth of 2D layered room-temperature ferromagnetic CrS2, Adv. Mater. Interfaces 9, 2201353 (2022). [4] Jiwei Liu, Cong Wang, Yuwei Wang, Jianbin Xu, Wei Ji, Mingsheng Xu, Deren Yang, Si-CMOS compatible synthesis of wafer-scale 1T-CrTe2 with step-like magnetic transition, Adv. Mater. 37, 2414845 (2025).

Daniel Lau

The Hong Kong Polytechnic University

Multiferroicity in self-intercalated 2D chromium telluride

Two-dimensional (2D) multiferroic materials, combining ferroelectricity and ferromagnetism, are highly sought after for next-generation, low-power spintronic devices. Yet, their realization remains challenging due to the inherent incompatibility of these properties. Here, we unveil a novel multiferroic phase in 2D chromium chalcogenide, featuring robust out-of-plane ferroelectricity at room temperature and ferromagnetism with a Curie temperature of 220 K. Using scanning transmission electron microscopy, we directly visualize long-range ferroelectric order driven by ionic displacement of self-intercalated atoms. Remarkably, this material also hosts a non-collinear spin structure, yielding colossal anomalous Hall conductivity and a large Hall angle. Our findings open new avenues for the design of 2D multiferroics and pave the way for advanced, energy-efficient spintronic applications.

Jong-Hyun Ahn

Yonsei University

Neural Implantable Sensor Arrays Based on 2D Materials for Brain Monitoring and Stimulation

Two-dimensional (2D) materials, such as MoS₂ and graphene, exhibit remarkable mechanical flexibility and electrical properties. Using these characteristics, they can be precisely integrated with organs featuring complex surfaces, such as the human brain, enabling the measurement of diverse signals, including intracranial pressure, temperature, and electrocorticography (ECoG) signals. These capabilities offer promising applications in the diagnosis of various brain disorders. In this presentation, we introduce a novel implantable multimodal sensor array designed for minimally invasive neural monitoring and stimulation. This sensor array is engineered to be injected through a small cranial opening, where it naturally expands to establish a conformal contact with the cortical surface. It incorporates graphene-based multi-channel electrodes for neural recording and electrical stimulation, alongside MoS₂-based sensors for monitoring intracranial temperature and pressure. The mesh-like structural design utilizes elastic restoring force to facilitate expansion upon deployment. Experimental results demonstrate that, upon injection into a rabbit’s brain, the sensor array effectively detects epileptic discharges on the cortical surface and mitigates them via targeted electrical stimulation. Simultaneously, it provides continuous monitoring of intracranial temperature, pressure, and ECoG signals. This innovative approach presents significant potential for the implantation of various functional neuroelectronic devices through minimally invasive surgical techniques.

David Estrada

Boise State University

Scalable manufacturing of transition metal dichalcogenide thin films

The rapidly evolving field of 2-dimensional (2D) materials continues to open new avenues for fundamental and applied research across numerous disciplines [1]. Recent advances in the synthesis of 2D and layered material inks and thin films have expanded the design space for 2D-enabled sensors, energy storage, transistors, and other applications. Formulating stable inks that meet the rheological requirements of materials jetting platforms presents significant challenges, necessitating careful solvent selection to optimize surface tension, viscosity, and chemical compatibility for reliable TMD film deposition [2-5]. Here we highlight our recent progress on 2D and layered material inks, including aerosol jet printing of ternary TMD alloys of NbTaS2 [6]. While additive manufacturing techniques offer promising solutions for sensors, thin-film electronics, and energy storage devices, current methods are not yet capable of producing films with the quality required for high-performance nanoelectronics. To address this challenge, our team has initiated investigations into direct epitaxial growth methods, such as metal-organic chemical vapor deposition (MOCVD), for scalable multi-wafer synthesis of TMDs on sapphire substrates .This portion of the talk will present our recent insights into WS₂ nucleation and film growth on sapphire using tungsten hexacarbonyl and hydrogen sulfide precursors in an AIXTRON 2D Close Coupled Showerhead MOCVD 3 × 2 reactor, with in situ photoreflectometry monitoring. We will also briefly highlight our process for patterning TMD films directly on sapphire, eliminating the need to transfer films for device fabrication. These results provide fundamental understanding of the structure-property-processing relationships governing 2D TMD thin-film synthesis and contribute to the advancement of scalable MOCVD-based multi-wafer growth techniques.

This material is based on research sponsored, in part, by Air Force Research Laboratory under agreement number FA8650-20-2-5506, as conducted through the flexible hybrid electronics manufacturing innovation institute, NextFlex. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of Air Force Research Laboratory or the U.S. Government.

[1] Lin, Yu-Chuan, et al. “Recent advances in 2D material theory, synthesis, properties, and applications.” ACS Nano 17.11 (2023): 9694-9747. [2] McKibben, Nicholas, et al. “Formulation and aerosol jet printing of nickel nanoparticle ink for high-temperature microelectronic applications and patterned graphene growth.” ACS Applied Electronic Materials 6.2 (2024): 748-760. [3] Rajabi Kouchi, Fereshteh, et al. “Synthesis and Formulation of Ternary Transition Metal Dichalcogenide Alloys for Additive Electronic Manufacturing.” Electrochemical Society Meeting Abstracts 243. No. 16. The Electrochemical Society, Inc., 2023. [4] Valayil Varghese, Tony, et al. “Multijet gold nanoparticle inks for additive manufacturing of printed and wearable electronics.” ACS Materials Au 4.1 (2023): 65-73. [5] Hollar, Courtney, et al. “High‐performance flexible bismuth telluride thin film from solution processed colloidal nanoplates.” Advanced Materials Technologies 5.11 (2020): 2000600. [6] Manzi, Jacob, et al. “Plasma-jet printing of colloidal thermoelectric Bi2Te3 nanoflakes for flexible energy harvesting.” Nanoscale 15.14 (2023): 6596-6606. [7] Curtis, Michael, et al. “Assessment of wafer scale MoS2 atomic layers grown by metal–organic chemical vapor deposition using organo-metal, organo-sulfide, and H2S precursors.” RSC Advances 14.31 (2024): 22618-22626.

Prasana Sahoo

Indian Institute of Technology Kharagpur

Engineering Excitons in 2D Lateral Heterostructures for Reconfigurable Optoelectronics

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have enabled the exploration of exotic quantum phenomena with promising applications.¹ Among various architectures, lateral heterostructures (LHS) — accessible only via direct synthesis — offer a unique solid-state platform for engineering the confinement and transport of carriers and excitons across 1D junctions. We’ll present our recent advances in CVD-grown, multi-junction 2D LHS exhibiting high optical and electronic quality.² Electrical transport studies reveal diode-like rectification and gate-controlled, spectrally tunable electroluminescence. Temperature-dependent photoluminescence uncovers the dynamics of neutral excitons, trions, and quantum emitters, highlighting the role of intrinsic defects and interfacial charge modulation.3 We further demonstrate multimodal excitonic transistor behavior in bilayer LHS FETs, enabling reconfigurable trion-to-exciton conversion.4 By tuning bias and excitation energy, we access a regime of polarity-reversible photoconductivity, making these devices ideal for multifunctional optoelectronic systems. Recent moiré-engineering efforts through vertical stacking of LHS (MoS₂–WS₂ and MoSe₂–WSe₂) have unlocked quadruple moiré pockets with twist-angle (θ) control from 0° to 60°, allowing programmable modulation of excitons and phonons.5 Aligned and near-aligned angles exhibit a giant enhancement in second harmonic generation. Our findings showcase 2D LHS and their moiré superlattices as scalable, tunable platforms for spectral photodetection, exciton-based logic, and on-chip quantum photonic circuits. [1] S. Chakraborty et al. iScience 25, 103942 (2022) [2] P. K. Sahoo et al., Nature, 553, 63–67 (2018) [3] B. Kundu et al. Nano Lett. 24, 14615–14624 (2024). [4] B. Kundu et al. arXiv:2411.01257 [5] S. Chakraborty et al., arXiv:2505.01188

Ye Wang

University of Manchester

Chiral 2D Materials: dimensionality tuning and quantum applications

Chiral materials, characterized by their lack of mirror symmetry, play a central role in fields ranging from stereochemistry to spintronics and photonics. Recent advances have brought this concept into the realm of two-dimensional (2D) materials, where chirality can be engineered and tuned with unprecedented precision. In this talk, I will present our recent efforts to induce and control chirality in 2D systems through molecular functionalization and dimensionality tuning. By coupling achiral 2D layers with chiral molecules, we demonstrate robust spin-selective transport and enhanced optical activity. I will also highlight our development of highly sensitive, miniaturized detectors for circularly polarized light using chiral 2D heterostructures—offering tunable spectral response and relevance for emerging quantum photonic technologies. These findings point to new strategies for designing low-dimensional quantum systems with tailored chiroptical functionalities.

U. Chandni

Indian Institute of Science

Transport in twisted bilayer graphene/WSe₂ hybrids and asymmetrical-I-Vs in MoS₂ van der Waals field effect transistors

This talk is divided into two parts. In the first part, I will summarize our recent efforts in combining twisted bilayer graphene (tBLG) with WSe2 layers to explore a variety of correlated phases. The formation of extremely flat bands at certain ‘magic’ angles in twisted bilayers of graphene has led to the observation of correlated insulating states and superconductivity and other exotic states such as Chern insulators, orbital ferromagnets, and nematic phases. The dielectric environment of tBLG plays an important role in controlling electronic correlations within these flat bands. In this talk, I shall highlight various facets of many-body correlations that we have explored using a combination of magneto-transport, thermoelectric measurements and planar tunneling, in moire graphene in close proximity with WSe2 layers, that introduces a finite spin-orbit coupling. In the second part of the talk, I shall highlight some curious observations seen in MoS2 van der Waals field effect transistors. We report a reproducible asymmetry in monolayer and multilayer MoS2 devices, unaffected by source-drain orientations. The results reveal that gate proximity, dielectric layers, and interfacial effects contribute to this behaviour, suggesting that factors beyond Schottky barriers contribute to the phenomena. This highlights the influence of gate materials and device architectures on the transport properties of 2D materials.

Akshay Singh

Indian Institute of Science

Wafer-scale growth of 2D magnets, and creating single photon emitters in 2D semiconductors

Two-dimensional magnetic materials (2D-MM) are critical for spintronic and quantum devices, but large-area growth remains unsolved. First, I will discuss the development of a generalized vapour deposition approach of synthesizing wafer-scale, epitaxial 2D-MM (CrCl₃) films. To achieve this milestone for air-sensitive 2D-MM, we demonstrate several innovations concerning light management during synthesis, carrier-gas purity, and precursor delivery. We also uncover the atomic-scale origin of substrate-dependent growth via state-of-the-art machine learning-enabled simulations. Selective-area synthesis and large-scale transfer of these 2D-MM are shown, which will enable spintronic devices. In the second part of the talk, I will briefly discuss our group’s work on creating single photon emitters in monolayer MoS2 by just using ultralow electron beam accelerating voltages (< 5 kV). We understand the physical origin of these peaks and their spin nature, and also find long-term spectral stability.

References

[1] Kumar, V. et al., arxiv:2505.16627, 2025

[2] Dash, A.K., et al., Advanced Functional Materials, 2421684, 2025]

Ki Kang Kim

Sungkyunkwan University

Synthesis and Anisotropic Vibrational Properties of High-Quality Violet Phosphorus for Optoelectronic Applications

Violet phosphorus (VP), a stable and semiconducting allotrope of phosphorus, has recently emerged as a promising two-dimensional (2D) material due to its tunable bandgap, anisotropic structure, and high ambient stability. In this work, we demonstrate the scalable synthesis of high-quality single-crystal VP using a lead-free Sn–Bi binary metal flux method, achieving lateral sizes up to 5 mm. The optimized flux conditions suppress nucleation via the formation of SnP₃, leading to enhanced crystal quality confirmed by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy.

Furthermore, the anisotropic interlayer vibrational properties of VP were investigated through low-frequency polarized Raman spectroscopy. Clear observation of shear (S) and layer-breathing (LB) modes reveals strong layer-dependent behavior and symmetry evolution between odd and even layers. These findings not only elucidate the unique lattice dynamics of VP but also provide essential insight into its interlayer coupling strength.

A phototransistor fabricated from the synthesized VP crystals exhibited ultrahigh responsivity (4.87 × 10⁴ A/W), detectivity (1.68 × 10¹⁵ cm·Hz⁰․⁵·W⁻¹), and sub-millisecond response time, outperforming most reported 2D photodetectors. Our combined study on synthesis, vibrational properties, and device performance establishes VP as a viable platform for future optoelectronic and quantum applications.

Soo Min Kim

Sookmyung Women's University​

Wafer-Scale Single-Crystal hBN​: Scalable Growth Strategies for Quantum and 2D Electronic Applications​

Hexagonal boron nitride (hBN) is a key material for next-generation 2D technologies, serving as an atomically flat insulator, tunneling barrier, and platform for quantum emitters. Despite its significance, the wafer-scale synthesis of single-crystal (SC) hBN remains a major challenge due to random nucleation, grain boundary formation, and non-uniform layer stacking.

This presentation highlights recent advances in the growth of large-area SC hBN films using tailored chemical vapor deposition (CVD) approaches. Strategies such as epitaxial alignment, surface engineering, and substrate-mediated control will be discussed, which collectively suppress grain formation and enable high-crystallinity growth of both monolayer and multilayer SC hBN. These scalable techniques provide a foundation for integrating SC hBN into van der Waals heterostructures, quantum photonics, and high-performance 2D electronic devices.

Deepnarayan Biswas

Diamond Light Source

State-of-the-art photoelectron spectroscopy facilities at Diamond Light Source for studying 2D materials and devices

Understanding the electronic and structural properties of two-dimensional (2D) materials is crucial for tailoring their behaviour in novel heterostructures and enabling the development of next-generation devices. At Diamond Light Source, the I05 and I09 beamlines provide state-of-the-art photoelectron facilities tailored for such investigations.

The I05 beamline specializes in ultraviolet (UV) high-resolution angle-resolved photoelectron spectroscopy (ARPES) and micro-ARPES, enabling detailed mapping of electronic band structures with sub-micron spatial resolution. The I09 beamline offers complementary capabilities, including soft and hard X-ray (110 eV – 10+ kV) photoelectron spectroscopies, x-ray absorption spectroscopy, soft X-ray ARPES and X-ray standing wave (XSW) techniques. This makes it ideal for studying electronic structures of buried layers or interfaces and depth dependence of chemical and electronic profiles of heterostructures and devices. Using XSW, one can also determine element specific structures with sub-angstrom resolution.

Together, these advanced techniques provide a comprehensive toolkit for probing the electronic, chemical, and structural properties of 2D materials and devices. In this talk, I will showcase a few recent studies performed at these facilities, demonstrating their critical role in advancing our understanding of 2D materials and their potential for next-generation technologies.

Min-Kyu Joo

Sookmyung Women's University

Electrically Reconfigurable Conducting Channel in 2D vdW Heterostructures

Two-dimensional van der Waals heterostructures are promising for neuromorphic computing, multi-threshold logic, and reconfigurable analog/RF applications. However, electrically driven conducting-channel redistribution in multilayer stacks remains underexplored. In this presentation, I will discuss bias-dependent gm-curve shape variations in four device platforms: monolayer graphene/MoS₂ junction FETs, multilayer WSe₂/MoS₂ heterostructures, and few-layer ReS₂ and WSe₂ devices. Transconductance is a key metric in field-effect transistors, directly dictating voltage-to-current conversion efficiency, gain bandwidth, and noise performance. While conventional devices exhibit a single gm peak marking the onset of channel conduction, the emergence of multi-peak gm profiles unlocks entirely new functionalities. By engineering two distinct gm maxima through gate and drain bias tuning, we demonstrate programmable discrete current steps in the output characteristics, which correspond to sequential migration of the conduction centroid between different channel layers. This in situ channel reconfiguration, evidenced by dual-peak gm, is realized within a single transistor, enabling multi-threshold activation functions without structural modification.

Tanushree H. Choudhury

Indian Institute of Technology Bombay

Impact of in-situ oxygen incorporation in WS2

Composition control of transition metal dichalcogenides has attracted tremendous attention for tailoring and controlling the electrical properties1. Dopants like oxygen, introduced by ex-situ treatments and in-situ incorporation, significantly impact electronic, optical, and catalytic properties by introducing and passivating defect states, modifying charge carrier dynamics, and enhancing reactivity. Theoretically, it has been shown that substitutional oxygen doping can alter the band gap and absorption spectra of MoS22. Ex-situ oxygen incorporation gives mixed results, as significant damage can occur. Limited studies of in-situ oxygen doping show an enhanced mobility for 16% oxygen doping/alloying in MoS23.

In-situ incorporation of oxygen gas provides a means to vary the concentration of oxygen and the sequence of incorporation. In this work, we systematically explore the impact of the varying amount of oxygen and the sequence of exposure for WS2. We introduce oxygen (5-28%) along with carrier gas (argon), while the growth of WS2 is achieved using WO3 and S. Flow rates higher than 28% oxygen cause complete etching of the WS2 domains. Atomic force microscopy, Raman, and photoluminescence (PL) spectroscopy were used to investigate the effect on growth morphology and optical properties. As the concentration of oxygen is increased, the excitonic peak shifts towards lower energy, while the Raman spectra remain unaffected. X-ray photoelectron spectroscopy confirms the change in the oxidation state of tungsten, confirming oxygen incorporation. It is also interesting to note that the sequence of oxygen incorporation had a significant effect on the properties of WS2. For instance, when oxygen is introduced before ramping the temperature, no growth is observed. Introducing the oxygen at different stages during the growth modulates the PL spectra across the triangular domains. Temperature and power-dependent Raman and PL measurements will be used to explain the optical properties. The growth mechanism and variation in the optical properties will be discussed.

References:

1. Singh, A. K. et al. Review of strategies toward the development of alloy two-dimensional (2D) transition metal dichalcogenides. iScience 24, 103532 (2021).
2. Kong, L.J., Liu, G.H. and Qiang, L., 2016. Electronic and optical properties of O-doped monolayer MoS2. Computational Materials Science, 111, pp.416-423.
3. Tang, J., Wei, Z., Wang, Q., Wang, Y., Han, B., Li, X., Huang, B., Liao, M., Liu, J., Li, N. and Zhao, Y., 2020. In situ oxygen doping of monolayer MoS2 for novel electronics. Small, 16(42), p.2004276.

Jiang Pu

Tokyo Institute of Technology

Strain effects in monolayer semiconductor and heterostructure devices

Monolayer semiconductors, such as transition metal dichalcogenides (TMDCs), have excellent mechanical strength and can greatly modulate their crystal structure and electronic properties by strain effects. For example, while typical inorganic semiconductors suffer structural destruction by strain of ~ 1%, TMDCs are stable even against strains of up to 10%. In fact, optical modulation due to band-gap changes caused by strains has been demonstrated, and the improvement of transistor performance due to band-curvature tuning has also been theoretically predicted. In addition to these typical strain effects, the crystal structure can be directly modulated, which is expected to lead to quantum functionalities derived from symmetry modulation. Therefore, the strain effects of TMDCs can be a powerful approach to develop functional electronic and optoelectronic devices. In this talk, we introduce three functional devices based on the strain effects of TMDCs and their heterostructures. First, we fabricated monolayer transistors with intentional compressive and tensile strain, and demonstrated the control and improvement of transistor characteristics due to band gap/curvature tuning. Next, we prepared strained monolayer light-emitting devices, and realized the electrical control of room-temperature chiral light emission, which is arising from crystal symmetry modulation and electronic structure evolution. This strain-induced symmetry breaking can also be realized at a TMDC in-plane heterostructure interface, as well as demonstrating robust chiral light emission at the heterointerface. Finally, we can extend the strain effects to van der Waals heterostructures, and proposed the structural and symmetry control of the moiré pattern.

Ziliang Ye

The University of British Columbia

Non-volatile Tuning of 2D Excitons in Rhombohedral MoS₂ Through Sliding Ferroelectricity

The tunability in the stacking degree of freedom of 2D van der Waals materials provides a new and powerful approach to engineer their physical properties. Sliding ferroelectricity is one such example where an electric field can couple to a stacking-dependent out-of-plane polarization, driving one layer of atoms to move relative to its neighbors, as previously reported in artificially stacked boron nitrides and transition metal dichalcogenides. In this talk, I will show that such a hysteretic phenomenon can occur in chemically synthesized rhombohedral molybdenum disulfide (3R-MoS2), a polytype in which each MoS2 layer is stacked in parallel naturally. Besides the uniform crystal orientation, each layer in the 3R polytype is coherently shifted by one-third of the unit cell in the same direction, leading to a uniform polarization and an intrinsic bulk photovoltaic effect that can accumulate over multiple layers. On the other hand, sliding between layers can occur under shear force during sample preparation, creating a variety of domains of different stacking with a power-law size distribution. When the externally applied electric field overcomes the local pinning, some of these pre-existing domain walls can be released for propagation, switching the polarization in a large portion of the flake. Such atomic-scale motion can induce significant changes in the optical properties of atomically thin MoS2 through strong excitonic resonances in the visible range, revealing interesting details about the switching pathway in sliding ferroelectricity. The large optical reflectance change associated with the stacking switch can happen on the sub-nanosecond timescale, making it promising to be implemented in non-volatile optical memories with high performance.

Miao-Ling Lin

Chinese Academy of Sciences

Interplay of Phonon and Optical Cavity Effects in Layered Semiconductor Materials

In this talk, I will show that layered semiconductor materials can act as naturally occurring and induce spatial variations in the photon field inside LSMs, and a phonon cavity to match the photon wave vector with quantized standing-wave vectors of layer-breathing phonons along the out-of-plane axis. The two effects result in spatially modulated electron-photon and electron-phonon interactions and the observation of Raman forbidden layer-breathing modes (LBMs). A spatial interference model of pht-phn coupling mediated by the corresponding one-dimensional periodic electronic states is presented to describe the intensity of Raman-inactive LBMs dependent on LBM standing-wave vectors, LSM layer number, excitation wavelength, and the underlying substrate. Our work reveals the impact of spatial coherence of photon and phonon fields on phonon excitation via photon or phonon cavity engineering.

Chunsen Liu

Fudan University

The speed boundary of memory: a sub-nanosecond flash memory​

With the rapid development of artificial intelligence, the speed of information access determines the upper limit of computing ability. The access speed limits of information storage have become a fundamental scientific issue in integrated circuit research today. Current volatile memory technologies (where data is lost upon power loss) boast speeds approaching transistor switching time, representing the current pinnacle of information accessibility. In contrast, while non-volatile memories such as flash memory offer significant power-efficiency advantages, their electric-field-assisted programming speeds remain far below transistor switching speed. This report focuses on overcoming these speed limitations in charge-based non-volatile memory, bringing its programming speed up to transistor-level benchmarks and redefining the boundary of modern memory technologies with this breakthrough.

Wooyoung Shim

Yonsei University

Ion transport within van der Waals crystals

The force-flux relationship is a fundamental concept in explaining mass transport under a driving force in non-equilibrium conditions. This relationship is captured by the Onsager relation, which describes how gradients in concentration, temperature, and voltage drive the transport of mass, heat, and charge, while also considering cross-effects. In this presentation, I will explore how ion transport driven by a voltage gradient varies depending on the diffusion medium, and how this transport can be harnessed in various technological applications. Specifically, I will focus on layered materials with van der Waals gaps, which facilitate ion movement along pathways with low diffusion energy barriers. These materials hold significant potential in semiconductors, metals, and insulators, where they could serve as memory devices, switching devices, and ion-sieving membranes.

References

1. “Memristive InAs-based semiconductors with anisotropic ion transport” Kim, T., W. & Shim, W.* and coworkers, Advanced Materials (2025)
2. “Anomalous in-plane electrical anisotropy in elemental metal nanosheets” Kim, T. & Shim, W.* and coworkers, Nature Synthesis 4, 31 (2025)
3. “Cation-eutaxy enabled III-V-derived van der Waals crystals as memristive semiconductors” Bae, J., Won, J. & Shim, W.* and coworkers, Nature Materials 23, 1402 (2024)
4. “Polytypic two-dimensional FeAs with high anisotropy” Won, J. & Shim, W.* and coworkers, Nano Letters 23, 23 (2023)
5. “Nontypical Wulff-shaped silicon nanosheets with high catalytic activity” Lee, M. & Shim, W.* and coworkers, J. Am. Chem. Soc. 145, 22620 (2023)
6. “Layered Aluminum for electromagnetic wave absorber with near-zero reflection” Kim, T. & Shim, W.* and coworkers, Nano Letters 21, 1132 (2021)
7. “Neuromorphic van der Waals crystals for substantial energy generation” Kim, S. & Shim, W.* and coworkers, Nature Communications 12, 47 (2021)

Archana Raja

Lawrence Berkeley National Laboratory

Painting potential landscapes on an atomically thin canvas

Atomically thin van der Waals crystals like graphene and transition metal dichalcogenides allow for the creation of arbitrary, atomically precise interfaces simply by stacking disparate monolayers without the constraints of covalent bonding or epitaxy. By leveraging the environmental sensitivity of interactions at the ultra- thin, two-dimensional (2D) limit, we can “paint” potential energy landscapes to create and control the electronic structure and excitations in these systems. We have characterized and discovered phenomena in such 2D potential landscapes from the atom scale to the application scale using multimodal photon and electron-based spectroscopies.

In this talk, I will discuss stories from our joint experimental and theoretical work on the prototypical 2D semiconductor interface of monolayer WS 2 and monolayer WSe 2 . In part one, we use ultrafast electron diffraction to reveal the role of layer-hybridized electronic states for controlling energy and charge transport across atomically sharp junctions [1]. In part two, we align the registry of the two layers and use electron energy loss spectroscopy to directly visualize the real space localization of excitonic states within a single moiré unit cell [2], opening the possibility of engineering excitonic superlattices with nanometer precision. In the third and final part, I will discuss the transport of energy across such a superlattice potential using interlayer excitons [3]. We uncover unexpected trends in the temperature dependent exciton diffusivity, which suggests that the moiré potential landscape is dynamic down to very low temperatures

[1] A. Sood, J. Haber, A. Raja et al. “Bidirectional phonon emission in two- dimensional heterostructures triggered by ultrafast charge transfer,” Nature Nanotechnology 18 (1), 29-35 (2023) [2] S. Susarla, M. H. Naik, A. Raja et al. “Hyperspectral imaging of excitons within a moiré unit-cell with a sub-nanometer electron probe,” Science 378 (6625), 1235-1239 (2022) [3] A. Rossi, J. Zipfel, I.Maity*, A. Raja et al. “Anomalous interlayer exciton diffusion in WS 2 /WSe 2 moiré heterostructure,” ACS Nano 18 (28), 18202-18210 (2024)

Yue Wang

University of York

Ultrasensitive luminescence thermometry based on monolayer WS₂

Luminescence thermometry has gained considerable attention for applications in biotechnology, nanoelectronics, and nanophotonics, areas where conventional thermometric techniques are ineffective. Here, we demonstrate exciton-phonon-based luminescence thermometry using monolayer WS₂ as a noninvasive, high-spatial-resolution platform. Our experiments reveal that monolayer WS₂ achieves an average relative sensitivity above 4%/K over the 300–425 K range, placing it among the most sensitive materials reported to date. We also derive an analytical expression for relative sensitivity, providing a quantitative framework for performance evaluation.

We examine the condition for resonant enhancement of the upconversion signal by matching the difference between the incident photon energy and the material’s band gap energy to an integer multiple of the optical phonon energy. Monolayer WS₂ exhibits high absolute and relative sensitivity, strong reproducibility, and ease of fabrication, making it a promising alternative to rare-earth-doped materials and quantum dots. This work highlights the utility of upconversion photoluminescence in monolayer TMDs for extremely-sensitive temperature monitoring.

Antonija Grubišić-Čabo

University of Groningen

Twist Angle Effects on the Electronic Structure of WS2 and Graphene

Twisted bilayer materials, such as graphene and transition metal dichalcogenides like WS2, have attracted significant attention due to their rich emergent properties. Despite their promise for uncovering novel physical phenomena, making them at scales large enough for detailed spectroscopic analysis remains a challenge. As a result, direct measurements of their electronic structures using angle-resolved photoemission spectroscopy (ARPES) have been limited. In this talk, I will present recent nanoscale ARPES measurements on twisted bilayer WS2 with a twist angle of 4.4°, and twisted bilayer graphene with a 2.4° twist angle. For WS2, comparison with density functional theory (DFT) calculations along key symmetry directions reveals unexpected effects due to structural relaxation. In graphene, we observe clear signatures of modifications to the electronic structure at the M point, well below the Fermi level, which is possibly a consequence of the twisting. These results shed new light on the complex behavior of twisted bilayer materials and suggest promising directions for future research.

Christopher Muratore

University of Dayton

Meeting tomorrow’s medical diagnostic industry needs with scaled processes for 2D electronic biosensor production

Working closely with a major industrial medical diagnostics manufacturer for four years to transition self-administered diagnostics technology from an optical to electronic platform required novel 2D material synthesis and device fabrication approaches to address emerging healthcare challenges. Fabrication of 2D electronic devices on a flexible substrate enabled high-throughput device production in a roll-to-roll process followed by application of capture agents for specific biomarker detection using existing production equipment and established practices for packaging and storing sensor devices. All materials were selected with easy recycling in mind to ease the waste stream burden for products with high numbers of anticipated regular users. To simplify fabrication processes, doped p-type 2D molybdenum disulfide materials with subthreshold swing occurring near 0V were engineered to eliminate the need for an external gate electrode. For rapid production, laser patterning of device electrodes and laser annealing of amorphous MoS2 material applied at room temperature we developed. Processes to control engineer substrate surface morphology after contact patterning ranging from ultra-low roughness (<0.5 nm) to allow application of 2D materials to intentionally roughened surfaces to control flow over the sensor surface were developed. Strategies to overcome challenges of meeting requirements to qualify devices as quantitative diagnostics are addressed.

Yukiko Yamada-Takamura

Japan Advanced Institute of Science and Technology

Polymorphism in monochalcogenides : trigonal-antiprismatic phases in GaSe

III-VI monochalcogenides, GaSe, GaS, and InSe, are known to exist in layered structures with each layer crystallized in trigonal-prismatic (P) structure with 2 adjacent atomic layers of metal sandwiched in between 2 atomic layers of chalcogen. They have several polytypes which varies in the van der Waals stacking of the layers, but, unlike transition metal dichalcogenides, discussion on polymorphs having different intralayer structure is scarce. Recently, we found a new polymorph which we named “trigonal-antiprismatic (AP)” phase in GaSe films epitaxially grown on Ge(111) substrates from vapor phase by observing cross sections using scanning transmission electron microscope [1]. First-principles electronic structure calculations revealed that AP phase becomes more stable compared to the P phase at large lattice constants [2], which suggests that the AP phase may have been stabilized due to epitaxial tensile strain. [1] T. Yonezawa, et al., Surface and Interface Analysis 51, 95-99 (2019). [2] H. Nitta, et al., Physical Review B 102, 235407 (2020).

Cecilia Mattevi​

Imperial College London​

Engineering Synthetic 2D Magnetic Materials for Energy-Efficient Computing

The discovery of long-range magnetic order in atomically thin two-dimensional (2D) materials is a new emerging field promising for future applications in ultra-compact low-power spintronics, miniaturized memory technologies, neuromorphic computing etc. The family of 2D magnets is rapidly expanding and the van der Waals and non-van der Waals chalcogenides of chromium are emerging as air stable magnetic materials with magnetism at room temperatures. In this talk, I will present our work on the MOCVD (metal organic chemical vapour deposition) of different crystal phases of chromium di-chalcogenides atomically thin crystals deposited onto different epitaxial substrates. The synthesis precision, represented by the phase selectivity, is achieved by the combination of the kinetic control of the synthesis and the chemistry of the chosen precursors. We demonstrate that different polymorphs exhibit distinct magnetic properties and integrate 2D chromium dichalcogenides into memory device building blocks.

Stela Canulescu

Technical University of Denmark

Shape-driven light harvesting in TMD nanostructures

Transitional metal dichalcogenides (TMDs) exhibit unique physical properties, such as switchable metallic and sliding ferroelectricity. Even more exciting phenomena can be induced by exploiting inversion symmetry in TMDs. However, TMDs, including MoS2 and WS2. typically adopt a 2H stacking orientation in bulk, which is centrosymmetric and limits their application in light-harvesting technologies. In this talk, I will explore how engineering non-centrosymmetric structures in TMDs can enable unconventional light-harvesting mechanisms, specifically through the bulk photovoltaic effect (BPVE). BPVE refers to photocurrent generation in a single-phase homogeneous material that lacks inversion symmetry when illuminated uniformly. This process is fundamentally different from traditional photovoltaic effects, which rely on homo- or hetero-PN junctions for charge separation. BPVE offers several advantages over conventional photovoltaic cells, including generating photocurrent without needing a PN junction, enabling more straightforward and robust device designs. Unlike conventional photovoltaic principles, where charge separation is driven by a built-in electric field, BPVE relies on the coherent evolution of electron and hole wavefunctions, known as the shift current. As a result, charge carrier separation does not depend on the electric field, and the maximum attainable open-circuit voltage (VOC) is not limited by the band gap, making BPVE an attractive approach for light harvesting. However, identifying materials that can effectively exploit BPVE remains a key challenge in the field. Our research demonstrates that non-centrosymmetric structures in TMDs can be engineered by applying strain, inducing disorder, or controlling stacking sequences such as the 3R phase. Specifically, we explore two approaches for growing TMD nanoribbons, focusing on MoS2 and WS2. In the first approach, we use a bottom-up method involving ultra-thin oxide precursors grown by Pulsed Laser Deposition (PLD) and alkali metal halides to synthesize horizontally aligned MoS2 nanoribbons. These nanoribbons form through the reaction between MoO3-x and NaF in a sulfur-rich environment, where vapor-liquid-solid (VLS) growth converts oxide films into MoS2 nanoribbons. This method yields highly crystalline, epitaxially grown nanoribbons with non-centrosymmetric 3R stacking, providing significant advantages over conventional fabrication methods like chemical vapor deposition (CVD). The MoS2 nanoribbons exhibit strong second-order nonlinear responses, including second harmonic generation (SHG) and shift current. Notably, these nanoribbons demonstrate a short-circuit current density (Jsc) of 104 mA/cm² at an illumination intensity of 10⁵ W/cm²—among the highest reported for TMD-based materials—and an open-circuit voltage (VOC) of 200 mV. The second approach involves fabricating WS2 nanoribbons using a bottom-up method that starts with mechanically exfoliated WS2 flakes. These flakes are patterned into nanoribbons through electron beam lithography followed by plasma etching. While the as-patterned WS2 flakes do not exhibit a photocurrent under light illumination, the nanoribbons show consistent shift current responses that depend on the width of the nanostructure. We hypothesize that defect-induced disorder may play a role in generating the shift current in these nanoribbons. In conclusion, we will discuss the potential of engineered non-centrosymmetric TMDs for efficient light harvesting and the challenges and opportunities in harnessing BPVE for future energy applications.

Seongil Im

Yonsei University

Ultrafast Vertical Schottky Diodes Utilizing 2D-layered van der Waals Materials for GHz RF Applications

The first and most applications of two dimensional (2D) semiconductors have been much oriented to using the lateral in-plane mobility. Plain field effect transistors are the representatives of the 2D electron devices, but we this time more focus on second category of device applications such as vertical diode or barristor action with thick 2D-layered TMDs, since we found that somewhat unique important applications are possible in such a vertical devices. Here, we have demonstrated vertical Schottky diodes, which has relatively large contact area and low contact resistance, aiming at high cutoff frequencies. ITO/60 nm-thick p-WSe2 (with bottom Pt Ohmic) and Pt/160 nm-thick n-MoSe2 (with graphene/Au Ohmic) Schottky diodes are those. The p-type Schottky diode showed 27 GHz (5G use) but n-type diode with graphene demonstrated 220 GHz cutoff in maximum performance. We attribute these excellences to least contact resistance and contact capacitance based on graphene-induced quantum capacitance. In the meeting, even further results will be discussed with n-MoSe2 Schottky diodes in the meeting, since we have also developed another type of n-MoSe2 Schottky diodes. The diodes now contain air gap (instead of graphene) at the MoSe2/Au interface, and it shows cutoff frequencies approaching to maximum ~400 GHz.

Sanjay Benura

San Diego State University

Quantum Light Emission in 2D Materials

Two-dimensional (2D) materials such as hexagonal boron nitride (hBN) and twisted heterostructures of 2D semiconductors have emerged as promising platforms for quantum light emission across a broad spectral range. These materials support unique optically active atomic or molecular defects such as deep-level emitters in hBN and host excitons trapped in moiré potentials in twist-engineered heterostructures, enabling non-classical light generation. Our research aims to create and control scalable quantum emitters that operate at room temperature and can be directly and seamlessly integrated into on-chip photonic circuits for applications in optical quantum information science and technology. Guided by the hypothesis that deep defect levels in atomically thin hBN are decoupled from the material’s fundamental electronic bands, we explore the formation of robust quantum systems rooted in defect engineering. In this talk, I will present our group’s recent progress in the design and realization of quantum spin defects in wafer-scale hBN, along with detailed photophysical characterization, including emission energies, single-photon emission behavior, and excited-state lifetimes. I will also discuss our efforts in constructing van der Waals heterostructures with 2D semiconductors to uncover new sources of quantum light enabled by moiré engineering.

Fang Liu

Stanford University

Large-Area Moiré Structures for Exploring Ultrafast Dynamics and Thermodynamic Behavior

Two-dimensional (2D) materials and their twisted heterostructures hold immense promise for electronic, optoelectronic, and electrochemical applications. However, exploration of high-quality heterostructures has largely been limited to microscopic-sized flakes. To address this, we have developed scalable and controllable top-down processes to convert a variety of van der Waals (vdW) single crystals into twisted moiré superlattices with high yield, high uniformity, excellent quality, and macroscopic dimensions ranging from millimeters to centimeters. The macroscopic sizes of these materials have enabled new discoveries including ultrafast thermal exchange at bilayer interfaces, rapid tuning of moiré superlattice structures under photoexcitation, and identification of significantly reduced Debye temperature for the deformed monolayers in the moiré superlattice compared to isolated monolayers. The advances in producing large-scale monolayers and moiré structures represent a significant step toward the mass production and commercialization of 2D twistronic devices.

Jianbin Xu

The Chinese University of Hong Kong

Progress in Light-Matter Interplay in 2D Materials from the Near-Infrared and Beyond

Comprehensive understandings of optoelectronic properties and phenomena at hetero-interfaces and in atomically-thin films play a crucial role for high-performance device design and fabrication. Manipulation of the interplay between matter and photonic structure yields numerous opportunities in fundamental understandings and practical applications. In this presentation, we will present a systematic view of 2D materials in photonics and optoelectronics. In particularly, we will introduce our understanding of the Fano-type asymmetry deviated from the Rabi-type asymmetry in the exciton-plasmon hybrid system. Then we will demonstrate the manipulation of the polarization and direction of the photoluminescence from the metaphotonic structures composed of transition metal dichalcogenides (TMDCs). Meanwhile, we will also present other photonic structures coupled with 2D materials to realize unique photonic and optoelectronic properties.

Yang Xu

Zhejiang University

Graphene/Silicon Heterostructures for Integrated Nanotechnology

Two-dimensional (2D) materials and their heterostructures represent a rapidly expanding class of materials, offering exciting features in exponentially growing areas of physics, and engineering. Low-power consumption, high operating speeds, and efficient energy conversion are the primary requirements for the next-generation electronic and optoelectronic devices, where 2D materials made their mark as the potential materials to resolve the limitations of silicon electronics. Developing device schemes by integrating 2D and 3D (bulk) materials enables us to continue the benefits of matured Si-based technology, while exploiting the novel features of low-dimensional materials. This lecture aims to provide a comprehensive understanding of the role of 2D-3D hybrid systems in emerging applications with functionalities superior to those of individual materials. This lecture also discusses how the intrinsic charge generation and transport features of 2D heterostructures can be integrated with Si technology to overcome the existing technological limitations and develop unique electronic and optoelectronic devices. The challenges and opportunities regarding the back-end-of-line integration of 2D materials with Si CMOS technologies will be discussed. Recent developments of graphene/Si heterojunction devices will also be presented. These devices, combining the benefits of graphene and Si, demonstrate their potential applications for post-Moore’s nanotechnology.

Keywords: 2D/3D integration, Optoelectronic devices; Silicon nanotechnology

Jieun Yang

Kyung Hee University

Helium Ion Irradiation-Induced Defect Formation and Structural Analysis in Trilayer Hexagonal Boron Nitride

Hexagonal boron nitride (hBN), a two-dimensional material, is recognized as a promising platform for quantum emitters due to its optically active defects. However, ion implantation, while providing a controllable method for defect engineering, can also introduce luminescent centers in the substrate, potentially interfering with the intrinsic emission from hBN. In this study, we employ low-energy, ultra-low dose helium ion beams to introduce point defects in trilayer hBN, effectively minimizing substrate-related effects. Atomic resolution STEM analysis of pristine trilayer hBN is used to confirm the intrinsic defect structure, establishing a baseline for interpreting the observed optical response. Our findings highlight a method for isolating intrinsic defect emissions in hBN by precisely adjusting ion implantation parameters, and demonstrate a direct correlation between defect structures and their optical responses.

Seunguk Song

Sungkyunkwan University

Transistors integrated with 2D semiconductor channels and ferroelectric Sc-doped AlN

The integration of ferroelectric materials with two-dimensional (2D) semiconductors offers a compelling platform for next-generation low-power and multifunctional electronics. In particular, scandium-doped aluminum nitride (AlScN), with its large remnant polarization (~80-115 μC/cm2), enables strong electrostatic coupling and nonvolatile charge control in 2D-channel devices. Here, we demonstrate high-performance MoS2/AlScN ferroelectric field-effect transistors (FeFETs) using indium (In) contacts, achieving high on-state current (~300 μA/μm at Vds = 3 V) and an exceptional on/off current ratio (~2 × 107). The combination of high polarization and efficient charge injection also enables reliable multi-level conductance states, advancing the prospects for embedded memory applications. Furthermore, WSe2-based FeFETs exhibit tunable polarity (n-type, p-type, or ambipolar) via contact engineering, along with a large memory window (~6 V) and robust switching characteristics, highlighting their versatility for emerging logic-in-memory and content-addressable memory architectures. Complementing these advances, we also realize AlScN-based negative capacitance field-effect transistors (NCFETs) with MoS2 channels, achieving sub-thermionic subthreshold swing (~30.7 mV/dec). Incorporation of an interfacial dielectric such as HfOx effectively suppresses hysteresis and enhances device stability, offering a practical route to ultra-low-power logic applications. Taken together, these results establish AlScN as a highly versatile and scalable ferroelectric platform for enabling energy-efficient 2D electronic and memory technologies.

Hae Yeon Lee

Rice University

Manipulating Optical Emission from hBN and monolayer TMDs Using Cathodoluminescence Spectroscopy with High Spatial Resolution

Controlling light emission from materials is the basis in optoelectronics and photonics. With its wide band gap and single photon emissions across a broad spectral range, hexagonal boron nitride (hBN) has emerged as a highly promising material platform for these applications. However, there are challenges in investigating hBN using only laser excitation: analyzing band-edge emission of hBN is challenging due to the need for high energy deep ultraviolet (DUV) excitation, and sub-band gap localized emissions are difficult to study because of the diffraction limit. Here, we use cathodoluminescence (CL) spectroscopy within an electron microscope (both STEM and SEM) to overcome those challenges and offer high spatial resolution. Moreover, the electron microscopy images that are obtained alongside the optical spectral map enable accurate understanding of structure-property relationships. We will demonstrate multiple strategies for manipulating hBN’s optical emission by (i) tuning the twist angle and (ii) applying local strain. First, we will show how the intensity and wavelength of emissions can be continuously tuned by varying twist angles between two hBN layers. The twist angles in heterostructures are analyzed using diffraction patterns and atomic-resolved STEM images. Second, we will demonstrate that applying strain locally induces new sub-band gap emissions due to carbon doping, which is promising for single photon emission. Additionally, we will present how CL can characterize TMD monolayers, revealing spatially confined trion emission within ~20 nm region. The CL map can be directly correlated with EELS to elucidate the origin of the localized emission. This presentation will highlight cathodoluminescence as a powerful complement to photoluminescence, overcoming its limitations, and propose novel strategies to control and characterize optical properties of vdW heterostructure. These insights offer exciting potential for quantum information technologies and optoelectronic applications.

Jinkyoung Yoo

Los Alamos National Lab

Postprocessing to fabricate disorders in two-dimensional semiconductors

Heterostructuring can deliver and tune physical properties of various 2D transition metal dichalcogenide (TMD) s have been extensively studied. Depending on Fermi level alignment, electron transfer occurs between different 2D materials or vice versa. In such heterostructures, one 2D layer serves as a fast channel for excited carriers, enhancing the separation of electron-hole pairs. This leads to tunable electrical and optical properties—such as electron-hole recombination rates and optical absorption—not achievable by either material alone. Additionally, defect engineering offers further control over the properties of 2D materials. Generating defects such as dislocations, nanopores and vacancies, it is able to control electronic, optical and magnetic properties by tuning excitonic states and band structure. Proton irradiation is one method used for defect engineering, capable of inducing changes in defect geometry, phase transformation, and crystallinity. Nanopores generated by proton irradiation in exfoliated ML WS₂ have been shown to enhance exciton-to-trion conversion without affecting material homogeneity or crystallinity, by creating in-gap states favorable for trion formation. Building on these methods, we demonstrate property changes in proton-irradiated ML graphene and ML TMD heterostructures. The ML materials are prepared by mechanical exfoliation, and transferred onto a SiO2 substrate to form a heterostructure by staking ML WS2 on ML graphene. Atomic force microscopy is used to confirm the staked bilayer structure through topographical images. Raman spectroscopy and photoluminescence measurements are performed to investigate property changes and carrier transfer of ML graphene and ML WS2 before and after heterostructuring and proton irradiation. Transmission electronic microscopy is also employed to analyze the defect structures generated by proton irradiation. Our results show that the properties of semiconductors can be controlled through heterostructuring with graphene, and defect introduction via proton irradiation. This presents a promising route to achieving desirable properties for applications.