Poster Program

Kamal Kumar Paul

University of Cambridge

High-efficiency WSe2 photovoltaics enabled by ultra-clean van der Waals contacts

Layered transition metal dichalcogenide (TMD) semiconductors have garnered significant interest for photovoltaic applications owing to their excellent light absorption and efficient charge carrier transport properties. Among them, tungsten diselenide (WSe₂) stands out as a particularly promising absorber material. Nevertheless, its performance has been largely constrained by defective metal–semiconductor interfaces, which have limited power conversion efficiencies (PCEs) to approximately 6–7%. Here, we demonstrate highly stable WSe₂ solar cells achieving a record power conversion efficiency (PCE) of ~11%, enabled by ultra-clean indium/gold (In/Au) van der Waals (vdW) contacts. A novel grid-patterned top electrode design enables near-ideal diode behavior with an exceptional on/off ratio of 10⁹. The devices exhibit strong photovoltaic performance, with an open-circuit voltage of ~575 mV and short-circuit current density approaching the theoretical limit. Near-unity external quantum efficiency across the 500–830 nm range further confirms the excellent carrier collection. These results highlight the importance of clean vdW contacts in realizing high-efficiency WSe₂ photovoltaics and open avenues for continued optimization.

Jiwon Lee

Kyung Hee University

Growth of Two-dimensional FeS via Chemical Vapor Deposition

Two-dimensional(2D) ferroelectric materials, e.g. indium selenide, have attracted significant attention due to their unique properties, such as immunity to depolarization field and potential applications, such as high mobility transistors and non-volatile memory. However, large-scale growth of indium selenide film is still challenging, primarily due to stringent reaction conditions. In this study, we successfully synthesized centimeter-scale ultrathin, ferroelectric indium selenide film with phase controllability using the hypotaxy method. This method involves the downward growth of single crystal film beneath a graphene template, maintaining van der Waals crystalline alignment with the graphene. The grown indium selenide exhibits high crystallinity and robust in-plane and out-of-plane ferroelectricity at room temperature. Our findings suggest that incorporating indium selenide into ferroelectric semiconductor field-effect transistors(FeS-FETs) can lead to fabrication of the devices with high electron mobility and enhanced non-volatile memory performance.

Yi Hu

The Hong Kong Polytechnic University

Interface-Enhanced Growth of 2D Interlayer Heterostructure Wafers from Low Sulfurization-Activity Metals

Two-dimensional (2D) van der Waals (vdW) heterostructures have garnered significant interest in the scientific community due to the extraordinary interlayer coupling and sharp band alignment.1,2 The wafer-scale preparation of those heterostructure are fundamental for further practical applications, but is still hindered, particularly for metals with low sulfidation activity such as hafnium.3 The single Hf metal film is hard to be sulfurized or selenized due to its low reactivity, showing a limited increase in thickness after selenization and a dirty surface due to the step-by-step metal film preparation and multiple selenization processes. Here, we develop a one-pot preparation of wafer-scale HfSe2/WSe2 heterostructures via an interfacially enhanced selenization way. By depositing a W layer (high sulfidation activity) over a Hf layer, followed by a one-pot selenization process, the chemical bonding between Hf and Se atoms is enhanced through interfacial Se diffusion and a confined lattice reaction. The resulting vdW heterostructures demonstrate strong interfacial coupling, showing significant charge transfer, enhanced piezoelectricity and Si-compatible transistor integration. This interface-enhanced selenization may provide valuable insights into the fabrication of wafer-scale interlayer heterostructures involving metals with low sulfidation activity, as well as the development of high-density integrated circuits.

Simon Leitner

Montanuniversitaet Leoben

Comparative Reliability Study of hBN and Fluorophlogopite as Gate Dielectrics for MoS2-Based 2D FETs

The stability and reliability of two-dimensional (2D) field-effect transistors (FETs) is critically influenced by the choice of gate dielectric. 2D dielectrics have demonstrated considerable promise, due to their atomically flat interface, which is free of dangling bonds and their thin, crystalline nature. Hexagonal boron nitride (hBN) is widely regarded as the standard material for this category due to its long-established presence in the field, substantial band gap and high thermal conductivity. Conversely, naturally occurring layered silicates such as mica, talc and chlorite, along with synthetic variants such as fluorophlogopite are gaining attention due to their abundance, mechanical resilience, and tuneable properties.

The present work presents a comparative study of hBN and fluorophlogopite as gate dielectrics in back-gated MoS₂-based FETs. Preliminary results show that fluorophlogopite exhibits approximately twice the dielectric strength of hBN, underscoring its promise for high-field operation. In addition, clear shifts in threshold voltage and notable changes in hysteresis behavior point to differences in charge trapping and defect dynamics between the two dielectrics.

To investigate these effects in greater detail, we apply a combination of bias temperature instability (BTI) measurements, transfer hysteresis analysis, and complementary C–V and I–V characterization to extract trap densities and evaluate degradation behavior. These findings contribute to mapping the defect landscape and reliability of each dielectric and are expected to offer practical benchmarks for the evaluation of emerging 2D-compatible insulators in next-generation FETs.

Mengyao Su

The Hong Kong Polytechnic University

Atomic-Scale Atlas of Stacking Polymorphs in Bilayer MoTe2

Yutong Xiang

Fudan University

Sub-nanosecond flash memory enabled by charge super injection

Highly efficient data-driven computing requires non-volatile memory with program speeds below one nanosecond to match the computing frequency. Flash memory, the dominant non-volatile memory technology, offers a simple single transistor structure and reliable storage capability. However, its program speed is limited by the low efficiency of the electric-field-assisted program, preventing it from breaking the sub-one nanosecond bottleneck. Here, we report a two-dimensional (2D) Dirac graphene-channel flash memory based on a charge super injection mechanism, supporting both electron and hole channel-to-gate injection. The Dirac channel flash shows a program speed of 400 picoseconds, non-volatile storage and robust endurance over 5.5×106 cycles. Our developed quasi-2D model reveals a channel thickness modulated horizontal electric field (Ey) distribution effect, indicating that the thin-body channel can improve the Ey-assisted program efficiency. We also find that the injection behaviour in the Dirac material exhibits monotonic characteristics, in contrast to the non-monotonic behaviour observed in the 2D semiconductor WSe2. This work demonstrates that the speed of non-volatile flash memory can outperform the fastest volatile static random-access memory (SRAM) with the same channel length, redefining the speed boundary of charge-based memory technologies.

Lingqi Li

National University of Singapore

Energy-Efficient Spiking Neural Network (SNN)-in-Logic Architectures Enabled by Scalable MoS2-Ferroelectric HZO Reconfigurable Dual-Gate Transistors

The increasing demand for efficient processing of large data sets presents critical energy challenges in modern electronics. In this work, we present a unified architecture that integrates high-performance von Neumann logic with Spiking Neural Networks (SNNs) for energy-efficient neuromorphic computing. Central to this approach is an all-in-one reconfigurable field-effect transistor (RFET) based on large-scale, back-end-of-line (BEOL)-compatible dual-gate MoS₂ transistors incorporating ferroelectric Hafnium Zirconium Oxide (HZO) layers. This RFET platform supports both logic computation and neuromorphic SNN functionalities within a single device. This resulting SNN-in-Logic system enables dynamic logic pruning for optimized data selection, achieving up to 90% energy reduction in real-world workloads, such as traffic simulations. Beyond energy savings, the proposed architecture offers enhanced scalability and circuit design versatility, addressing the needs of data-intensive, resource-constrained environments. This work manifests the first demonstration of an integrated logic-SNN architecture using 2D ferroelectric transistors, paving the way for next-generation neuromorphic computing systems.

Andrew Pannone

The Pennsylvania State University

Hardware acceleration of reconfigurable dendritic computation

Neuromorphic algorithms often define artificial neurons as simple computational elements, where the soma performs a thresholding operation on summed synaptic inputs, neglecting the crucial role of dendrites in filtering and preprocessing information. Recent advancements indicate that the incorporation of dendritic stages into artificial neural networks (ANNs) has the potential to significantly decrease the number of trainable parameters required to reach a target accuracy. Therefore, the development of hardware components that implement dendritic functions on-chip will increase ANN performance by facilitating energy efficient network operations. In this study, we demonstrate the hardware realization of non-monotonic dendritic activation functions using a programmable complementary metal-oxide-semiconductor (CMOS) circuit based on the heterogeneous integration of n-type MoS2 and p-type WSe2 memtransistors. The reconfigurable dendritic circuit is combined with a resistor network to act as a single layer neural network capable of performing all 16 two-input Boolean functions, notably including non-linearly separable functions that normally require at least one hidden layer. When utilized in ANNs, deep convolutional neural networks (CNNs), graph convolutional networks (GCNs), and reinforcement learning (RL) frameworks we found that dendritic activation accelerates learning, reduces the required number of hidden layers to reach a target accuracy, helps to facilitate the retention of network accuracy at larger depths, and achieves a higher reward in fewer episodes. These benefits minimize hardware requirements and energy consumption, highlighting the potential of dendritic computation to advance neuromorphic systems and create more efficient AI accelerators.

Changjun Park

Ulsan National Institute of Science and Technology (UNIST)

Enhanced Performance of 2D Transistors via van der Waals Integration of High-k Crystalline Dielectrics

Two-dimensional (2D) semiconductors are being widely considered as a channel solution toward device scaling owing to their atomically-thin-thickness and dangling-bond-free characteristics. Despite those potentials, 2D Field-effect Transistors (FETs) have yet to achieve optimal performances, largely due to the lack of best-tailored dielectric integration. For example, the integration of routinely used amorphous high-k dielectrics often results in poor interface quality, limiting the charge carrier mobility. Meanwhile, van der Waals (vdW) insulators such as h-BN exhibit low dielectric constants, leading to insufficient gate controllability. Herein, our work presents the vdW integration of high-k crystalline dielectric, so as to achieve both improved the interface quality and electrostatic control in 2D FETs. Through the vdW assembly of MoS2 with crystalline lanthanum oxychloride (LaOCl), we achieved enhanced gate controllability, reduced hysteresis, and minimized mobility degradation, enabling high-performance 2D electronics. On the basis of these advantages, we demonstrate the low power Complementary Metal-Oxide-Semiconductor (CMOS) logic as the future application of the LaOCl integrated 2D FETs.

Lan-Anh Nguyen

Sungkyunkwan University

Electrical Spin-Flip Switching in Layered Diluted Magnetic Semiconductors at Room Temperature

Efficient magnetic switching is a cornerstone for advancing spintronics, particularly for energy-efficient data storage and memory devices. Here, we report the electrical switching of spin-flips in V-doped WSe2 multilayers, a van der Waals (vdW)-layered diluted magnetic semiconductor (DMS), and demonstrate ultralow-power switching operation at room temperature. Our study reveals unique linear magnetoresistance and parabolic magnetoresistance states, where electrical modulation induces transitions between interlayered ferromagnetic, ferrimagnetic, and antiferromagnetic configurations. We identify an unconventional linear magnetoresistance hysteresis characterized by electrically driven spin flip/flop switching, distinct from conventional random network disorder or linear band-dispersion mechanisms. Applying an electrical voltage across vertical vdW-layered V-doped WSe2 multilayers generates the spin currents at room temperature, driving spin-flip transitions from ferromagnetic to antiferromagnetic states due to a strong spin-transfer torque effect. Notably, the critical current density reaches an ultralow value of ∼10-1 A/cm2, accompanied by pico-watt power consumption, a record-low spin current density by a six-order-of-magnitude improvement over conventional spintronic devices. These findings establish the V-doped WSe2 multilayer device as a transformative platform for ultralow-power spintronics, underscoring the potential of vdW-layered DMS systems for next-generation energy-efficient spintronic technologies.

Debottam Daw

Sungkyunkwan University

Overcoming mobility limits in 2D TMD monolayers

The persistent challenge of low carrier mobility in layered two-dimensional (2D) semiconductors has limited their applicability in next-generation transistors. In this work, we introduce a state-of-the-art hot-carrier field-effect transistor (HC-FET) architecture that leverages a ferroelectric substrate and in-plane polarization to achieve unprecedented carrier mobility over 4700 cm2V-1s-1 and 0.1 mA/𝛍m current density in monolayer MoS2, outperforming traditional FETs. The experimental findings, supported by robust theoretical framework, reveal that the hot-carrier mechanism effectively accelerates carriers by mitigating scattering from phonons and charged impurities, leading to improvements in mobility, current density, and subthreshold-swing. Our work elucidates the fundamental interplay between dielectric screening, in-plane polarization, and carrier transport, presenting a transformative pathway for performance improvements in future 2D transistors. Moreover, the HC-FET design is versatile and applicable across various TMD materials, opening potential avenues for scalable, ultra-fast, energy-efficient electronics.

Shibin Deng

Nankai University

Frozen Non-Equilibrium Dynamics of Exciton Mott Insulators in Moiré Superlattices

Moiré superlattices, such as those formed from transition metal dichalcogenide (TMDC) heterostructures, have emerged as an exciting platform for exploring quantum many-body physics. They are being touted as a potential solid-state complement to ultracold gases trapped in optical lattices for quantum simulations. A key open question is the coherence and dynamics of the quantum phases arising from photoexcited moiré excitons, particularly amid dissipation. Herein, we employ transient photoluminescence and ultrafast reflectance microscopy to image non-equilibrium exciton phase transitions. Counterintuitively, experimental results and theoretical simulations indicate that strong long-range dipolar repulsion between moiré excitons freezes the motion of the Mott insulator phase over 70 ns. In mixed electron-exciton lattices, reduced dipolar interactions show diminished freezing dynamics. These findings challenge the prevailing notion that repulsion disperses particles, whereas attraction binds them. The observed phenomenon of frozen dynamics due to strong repulsive interactions is characteristic of highly coherent systems, a feature previously realized exclusively in ultracold gases.

Xin Zhou

National University of Singapore

Multi Scale In Situ Visualization of Bias Induced Layer Sliding in MoTe2

Haoxuan Ding

Peking University

Scanning Tunneling Microscopy Study of Two-Dimensional Fe-, Co-, and Ni-based Magnetic Self-intercalated Transition Metal Dichalcogenides

In recent years, two-dimensional magnetic materials have become a research hotspot in condensed matter physics and materials science due to their unique physical properties and broad application prospects. The self-intercalation strategy, as a novel approach for modulating the properties of two-dimensional materials, has shown tremendous potential in the controlled preparation of Fe-, Co-, and Ni-based transition metal dichalcogenides (TMDCs), enabling stable magnetism above room temperature. However, systematic understanding of how self-intercalated structures modify electronic structures and induce magnetic ordering at the atomic scale, as well as the interfacial regulatory differences among various intercalating elements, remains elusive. This research utilizes scanning tunneling microscopy (STM) to systematically investigate the microstructure, electronic states, and magnetic characteristics of two-dimensional Fe-, Co-, and Ni-based magnetic self-intercalated TMDCs. Through molecular beam epitaxy (MBE) techniques to synthesize FexSey, CoxTey, NixTey and other systems, scanning tunneling microscopy/spectroscopy (STM/STS) is employed to analyze superlattice structures and local electronic states, revealing unique Kagome lattice and flat band features in CoxTey, and room-temperature ferromagnetism with distinct energy state distributions in FexSey. Applying spin-polarized scanning tunneling microscopy (SP-STM) to directly image the domain structures and spin orientations in self-intercalated materials will reveal how intercalated atoms induce long-range magnetic ordering by modifying electronic density of states and d-orbital hybridization. Theoretical calculations indicate that the d-electron configurations and intercalation positions of different transition metal elements significantly influence magnetic exchange interactions and magnetic anisotropy. This research will establish structure-property relationships between self-intercalated structures, electronic states, and magnetism at the atomic scale, providing new strategies to overcome performance limitations of traditional two-dimensional magnetic materials, with promising applications in spintronics, quantum computing, and other advanced fields.

References: [1]Cui, F.; He, K.; Wu, S.; Zhang, H.; Lu, Y.; Li, Z.; Hu, J.; Pan, S.; Zhu, L.; Huan, Y.; Li, B.; Duan, X.; Ji, Q.; Zhao, X.; Zhang, Y. Stoichiometry-Tunable Synthesis and Magnetic Property Exploration of Two-Dimensional Chromium Selenides. ACS Nano 2024, 18, 6276–6285. [2]Wu, Q.; Quan, W.; Pan, S.; Hu, J.; Zhang, Z.; Wang, J.; Zheng, F.; Zhang, Y. Atomically Thin Kagome-Structured Co9Te16 Achieved through Self-Intercalation and Its Flat Band Visualization. Nano Lett. 2024, 24 (25), 7672–7680. [3]Quan, W.; Lu, Y.; Wu, Q.; Shang, C.; Li, C.; Hu, J.; Wang, J.; Zhang, Z.; Zhou, S.; Zhao, J.; Ji, Q.; Zhang, Y. Spontaneous Line Defect-Induced Co4Te7 Superlattices on SrTiO3(001) Featuring Flat Bands. Adv. Funct. Mater. 2024, 34 (29). [4]Huan, Y. H.; Luo, T. T.; Han, X. C.; Ge, J.; Cui, F. F.; Zhu, L. J.; Hu, J. Y.; Zheng, F. P.; Zhao, X. X.; Wang, L. L.; Wang, J.; Zhang, Y. F. Composition-Controllable Syntheses and Property Modulations from 2D Ferromagnetic Fe5Se8 to Metallic Fe3Se4 Nanosheets. Adv. Mater. 2022, 35, 2207276. [5]Pan, S. Y.; Hong, M.; Zhu, L. J.; Quan, W. Z.; Zhang, Z. H.; Huan, Y. H.; Yang, P. F.; Cui, F. F.; Zhou, F.; Hu, J. Y.; Zheng, F. P.; Zhang, Y. F. On-Site Synthesis and Characterizations of Atomically-Thin Nickel Tellurides with Versatile Stoichiometric Phases through Self-Intercalation. ACS Nano 2022, 16, 11444–11454.

Hayeong Sung

Seoul National University

Modulation of Metal Work Functions by Quasi-van der Waals Recrystallization

Two-dimensional (2D) semiconductors with atomic thinness have been considered as promising semiconductor channels. However, conventional metal deposition on 2D semiconductors have shown high contact resistance due to Fermi energy level pinning. Furthermore, there have been limited numbers of reports for p-type contacts. To resolve this issue, various methods, such as van der Waals (vdW) contacts and edge contacts, have been explored. Here, we report modulation of metal work functions by quasi-van der Waals (qvdW) recrystallization. The metal work functions are strongly influenced by its crystalline orientation and crystallinity. As we previously reported, we enhanced crystallinity of metals and induce atomic flatness of the metal surface by annealing the deposited metal with contact to hexagonal boron nitride (hBN). In this work, we increase work function of deposited gold film Au by ~0.4 eV by encapsulation-annealing. The WSe2 transistors transferred on the recrystallized gold contacts show enhanced injection at the metal-semiconductor junctions and showed enhanced properties. Our work shows a method to modulate the metal work function by qvdW recrystallization and improves carrier injection from the contact electrode to 2D semiconductors.

References

1. X. Liu., M. S. Choi., E. Hwang., W. J. Yoo., & J. Sun, Adv. Mat., 34(15), 2108425 (2022).
2. Y. Lee., Y. Chang., H. Ryu., J. H. Kim., K. Watanabe., T. Taniguchi., … & G. H. Lee. ACS Appl. Mater. Interfaces, 15(4), 6092-6097 (2022).

Byeongchan Kim

Seoul National University

Strain-induced local polarity conversion in WSe2 for homojunction inverter applications

Two-dimensional (2D) materials are drawing significant attention as potential channel materials for next-generation transistors, owing to their atomically thin structure, excellent electrostatic control, and suitability for device scaling. Despite being intrinsic semiconductors, most 2D materials exhibit a strong unipolar behavior due to Fermi level pinning and contact asymmetries, making it challenging to realize complementary logic with a single material. As a result, conventional approaches to 2D complementary field-effect transistors (CFETs) often rely on the integration of distinct n-type and p-type semiconductors, introducing complexities in fabrication and material compatibility. Here, we present a strain engineering strategy that enables local modulation of carrier polarity within a single 2D semiconductor, allowing the realization of homojunction-based CFETs. By applying localized mechanical strain through a simple metal stressor deposition, we induce a transition from p-type to n-type conduction in the same 2D material-demonstrated here using WSe2 as a representative channel. Crucially, this technique requires no change in contact metal or chemical doping, offering a streamlined and CMOS-compatible fabrication process. This strain-driven approach opens a new pathway for constructing fully 2D inverters and logic devices using homogeneous materials, significantly simplifyng integration while maintaining electrical performance and scalability.

Sewoong Oh

Yonsei University

Patterned Nafion-Enabled Local Doping and Robust Contacts for High-Performance 2D WSe2 Electronics

Selective area doping and contact resistance (Rc) reduction remain critical challenges for advancing two-dimensional (2D) semiconductor electronics. Unlike conventional three-dimensional (3D) semiconductors that utilize ion implantation, achieving spatially controlled doping in 2D materials has been notably difficult. Moreover, maintaining low Rc under thermal and ambient conditions has rarely been demonstrated, highlighting the instability issues in 2D contacts. In this work, we present a novel doping strategy using ultrathin patterned Nafion as a medium for localized doping of p-type WSe₂. Electron-beam-defined Nafion regions significantly increase the hole concentration in WSe₂ by nearly two orders of magnitude, effectively transforming the material into a high-conductivity resistor suitable for circuit integration. Furthermore, when applied at the contact areas, Nafion reduces Rc to approximately 6 kΩ·μm, maintaining its performance for over two months in ambient air and withstanding thermal annealing at 200 °C in N₂. This approach offers a significant advancement in both selective area doping and long-term Rc stability, presenting a promising route for future 2D electronic applications.

Jibin N Sunil

University of Basel

Quantum transport in MoS2 electronic devices

Atomically thin semiconducting transition metal dichalcogenides (TMDCs) like MoS2 can form high mobility 2D electron systems. These systems are often optically active and are predicted to exhibit various novel electronic phases driven by electron-electron interactions. However, experimental progress is frequently hindered by technical challenges, such as highly resistive contacts. In this study, we report several fabrication techniques that achieve low contact resistances to MoS2. Utilizing these advancements, we demonstrate a series of fundamental experiments, including the observation of 2D Andreev bound states near superconducting contacts, and the quantized conductance in gate-defined constrictions (quantum point contact). In addition, we discuss preliminary optical experiments that underscore the potential of these materials for exploring new electronic phases.

Shun Feng

École Polytechnique Fédérale de Lausanne (EPFL)

Hybrid trion transistor based on a bilayer semiconductor

Layer-hybridized excitons in two-dimensional homobilayer structures enable the electrical tunability of their lifetimes, interactions, and micrometer-scale transport. However, the drag of hybrid excitons by in-plane electric fields akin to transistor-like action has not been demonstrated yet. In this work, we achieved the in-plane field dragged lateral transport of layer-hybridized trions (charged hybrid excitons) in bilayer WSe2, characterized by photoluminescence spectra and spatial imaging of hybrid trion emission. We exploit the vertical field induced switch of hybrid exciton transitions in this platform to enhance their lateral field-induced drag. Moreover, we unveil the different transport dynamics of positive and negative trions based on their mobilities. Our results, supported by microscopic theory, demonstrate the design and operating principles of ambipolar, three-terminal field-effect excitonic devices.

Yoonbeen Kang

Yonsei University

Operando Investigation of Sodium-Catalyzed MoS2 Growth: Diffusion Dynamics and Surface Interactions

The interactions between precursors and substrates, along with the diffusion behavior, are pivotal to the chemical vapor deposition (CVD) synthesis of transition metal dichalcogenides (TMCs). A thorough understanding of these mechanisms is essential for fabricating large-area, high-quality TMC films. However, the precise kinetics associated with diffusion and surface effects have not been extensively characterized. In this poster, we present real-time observations of MoS2 growth influenced by precursor/sodium droplet eutectic (SODE). Acting both as a catalyst and a precursor reservoir, SODE enables the transport of reactive species from the basal plane to the edge, facilitating growth via a conventional surface-mediated route. Interestingly, SODE tends to situate itself between MoS2 and SiO2, enhancing particle mobility and rotation. Kinetic investigations demonstrate that MoS2 exhibits significantly faster growth on its own basal plane compared to SiO2, underscoring the role of precursor diffusion in growth efficiency. These experimental findings are further substantiated by density functional theory (DFT) calculations, which validate the thermodynamic and kinetic trends. Notably, the extended diffusion length enabled by SODE—compared to growth without SODE—leads to a more uniform film formation, confirming the efficacy of this molten-metal-assisted method. Our findings provide a deeper understanding of precursor transport and surface interactions during TMC growth and suggest promising strategies for scalable and cost-efficient production of high-quality TMC materials.

Marios Matheou

Politecnico di Milano

Investigating the impact of substrate on atomic defects formation in CVD-grown WS2 monolayers using hyperspectral imaging

2D materials, and in particular atomically thin Transition Metal Dichalcogenides (TMDs), exhibit properties heavily influenced by atomic defects, significantly impacting their electronic and optical performance [1], [2]. Chemical Vapour Deposition (CVD) is a leading technique for synthesizing high- quality, large area TMD monolayers. Growth substrate properties like surface energy and lattice mismatch directly impact defect density and distribution in the formed TMD crystals [3]. Hyperspectral imaging is an ideal technique to characterize such samples, since it generates a spectral hypercube of light intensity as a function of spatial (x,y) and frequency (ω) coordinates over large areas with diffraction limited resolution [4]. In our work, we used a modified fiber-compatible epifluorescence microscope with a TWINS (Translating Wedge-based Identical pulses eNcoding System) common-path interferometer [5] for a wide-field wavelength resolved characterization of the photoluminescence (PL) produced by CVD- grown WS2 monolayers at room temperature (RT). Specifically, we characterized WS2 monolayers grown on a sapphire substrate and on an Al-rich sapphire substrate, then transferred on SiO2. In the former case, PL spectral peak position maps revealed well-defined regions of distinct spectral shifts. The redshift increases progressively from the edges towards the center of the flake, culminating in large, heavily redshifted areas at the core of the crystals. For TMDs grown on Al-rich sapphire substrate, we instead observed intense luminescence spots at the edges of the crystals. In this case, the PL peak wavelength pattern exhibits a more inhomogeneous distribution, with less pronounced redshift along the triangular crystal’s bisectors. Our study reveals significant differences in optical properties of WS2 monolayers grown on sapphire and Al-rich sapphire substrates, most probably related to different defect distributions. The Al-rich sapphire substrate might strongly influence the properties of grown materials by inducing the formation of Tungsten or Sulfur atomic defects in different positions of the crystals [6]. In combination with more advanced TEM, ARPES and XPS characterizations, these findings can be utilised for optimizing CVD growth conditions, in order to control the atomic defect density in TMD monolayers, thus tailoring their optical properties. Achieving such control on the single defect level will pave the way for their use in quantum computation and communication technologies.

[1] K. F. Mak and J. Shan, “Photonics and optoelectronics of 2D semiconductor transition metal dichalcogenides,” Nature Photonics, vol. 10, no. 4, pp. 216–226, 2016. [2] D. Jariwala, T. J. Marks, and M. C. Hersam, “Mixed-dimensional van der Waals heterostructures,” Nature Materials, vol. 16, no. 2, pp. 170–181, 2017. [3] Y. Gong et al., “Vertical and in-plane heterostructures from WS₂/MoS₂ monolayers,” Nature Materials, vol. 13, no. 12, pp. 1135–1142, 2014. [4] C. Trovatello et al., “Hyperspectral microscopy of two-dimensional semiconductors,” Optical Materials: X, vol. 14, no. 100145, 2022. [5] A. Perri et al., “Hyperspectral imaging with a TWINS birefringent interferometer,” Optics Express, vol. 27, no. 11, pp. 15956–15967, 2019. [6] H. Y. Jeong et al., “Heterogeneous defect domains in single-crystalline hexagonal WS₂,” Advanced Materials, vol. 29, no. 15, 2017.

Tsz Wing Tang

The Hong Kong University of Science and Technology (HKUST)

Structured-Defect Engineering of Hexagonal Boron Nitride for Identified Visible Single Photon Emitters

Michael Curtis

Boise State University

Multi-wafer TMD deposition process development leveraging in-situ process monitoring and machine learning on a close coupled showerhead MOCVD system.

In this work we present advancements that contribute to the maturation of MOCVD as a scalable technique for the growth of two-dimensional transition metal dichalcogenides (TMDs). Using a newly installed AIXTRON 2D CCS MOCVD system engineered for multi-wafer growth, we developed a process that leverages integrated in-situ monitoring tools including Epison 5 precursor concentration controllers and EpiTT photoreflectance for real-time feedback and control. Departing from baseline qualification recipes, we optimized a multistage growth process including sapphire substrate passivation via H₂S pretreatment and dynamic modulation of precursor ratios during lateral film growth[1], [2], [3]. These modifications, guided by in-situ process monitoring, enabled rapid convergence on conditions favorable for near uniform monolayer growth across 50 mm wafers. To accelerate nucleation optimization, we implemented a machine learning model trained on quantitative AFM-based defect analysis. This model provided predictive insight into nucleation behavior and allowed us to increase nucleation domain size by a factor of 4 and eliminate vertical growth almost entirely. Resulting TMD films exhibit high monolayer uniformity and material quality, confirmed by atomic force microscopy and temperature-dependent Raman and photoluminescence spectroscopy support an increase in inter-defect distance by a factor of 6[4]. These results demonstrate the effectiveness of combining in-situ monitoring, dynamic process control, and ML-guided feedback for reproducible and high-quality MOCVD growth of 2D materials. This work provides a preliminary foundation for further studies into industry relevant monolayer TMD deposition.

[1] H. Zhu et al., “Step engineering for nucleation and domain orientation control in WSe2 epitaxy on c-plane sapphire,” Nat Nanotechnol, vol. 18, no. 11, pp. 1295–1302, 2023, doi: 10.1038/s41565-023-01456-6. [2] X. Zhang et al., “Diffusion-Controlled Epitaxy of Large Area Coalesced WSe2 Monolayers on Sapphire,” Nano Lett, vol. 18, no. 2, pp. 1049–1056, Feb. 2018, doi: 10.1021/ACS.NANOLETT.7B04521/SUPPL_FILE/NL7B04521_SI_001.PDF. [3] S. Tang et al., “Migration-Enhanced Metal–Organic Chemical Vapor Deposition of Wafer-Scale Fully Coalesced WS2 and WSe2 Monolayers,” Cryst Growth Des, vol. 23, no. 3, pp. 1547–1558, Mar. 2023, doi: 10.1021/acs.cgd.2c01134. [4] A. McCreary et al., “Distinct photoluminescence and Raman spectroscopy signatures for identifying highly crystalline WS2 monolayers produced by different growth methods,” J Mater Res, vol. 31, no. 7, pp. 931–944, Apr. 2016, doi: 10.1557/jmr.2016.47.

Zara Taylor

University of Sheffield

Near-field and transmission characterisation of nanobeam waveguides made from multilayer transition metal dichalcogenides

Multilayer (quasi-bulk) semiconducting transition metal dichalcogenides (TMDs) have recently attracted strong interest as building blocks for advanced nanophotonic structures, following a decade of intense studies of intriguing optical and electronic properties observed in monolayers of these materials. In their multilayer form TMDs show considerable promise for nanophotonics thanks to their high refractive indices, large optical anisotropy, wide transparency windows reaching to the visible, and robust room temperature excitons providing scope for nonlinear optics. Adherence of TMD layers to any substrate via van der Waals forces is a further key enabler for the nanofabrication of complex photonic structures requiring heterointegration.

Here, we apply scattering-type Scanning Near-field Optical Microscopy (s-SNOM) in the visible and near-infrared spectral ranges to assess a prominent member of the TMD family tungsten disulphide (WS2) for applications in waveguiding. Recent ellipsometry measurements show that WS2 has a high refractive index exceeding 4 and extremely low absorption (10 times lower than silicon) in the wavelength range starting from 700 nm. This makes WS2 a promising material for waveguiding in the near-infrared, which we test in this work using methods complementary to and, potentially, more accurate than ellipsometry.

In s-SNOM, the interference between tip-backscattered light and in-plane propagating modes scattered by the crystal edge cause the formation of fringes sensitive to the crystal axes, excitation wavelength and TMD flake geometry. The high tunability of these fringes makes them an excellent probe of mode propagation and local refractive index properties. In this work, we study these fringe patterns to investigate energy loss mechanisms in quasi- bulk WS2 crystals. By comparing experimental s-SNOM data with finite-difference time- domain (FDTD) simulations of guided optical modes, we characterise confinement and attenuation of the fundamental TE and TM modes within the low-loss 650-1500nm wavelength range.

Our measurements on unpatterned flakes enable the identification and characterisation of dominant modes and their associated losses. We then design and fabricate nanobeam waveguides (200 nm height and 300 nm width) both with and without off-chip out-couplers for further characterisation with direct transmission and s-SNOM measurements, respectively. We identify and characterise the loss mechanisms now also including backscattering-induced losses on imperfections. Our results support WS₂ as a promising low-loss, high-index alternative to silicon within future short-wavelength nanophotonic applications.

Subhankar Debnath

Indian Institute of Information Technology Guwahati

Printed Optoelectronic Synapse based on CVD-grown Monolayer MoS2 with Ultralow Power Consumption and High Photoresponsivity

Optoelectronic synapses, which integrate photodetection and synaptic functions in a single platform, offer a promising approach to mimic the visual processing capabilities of the human brain. These devices facilitate simultaneous visual information perception, processing, and memorization, making them ideal for advanced artificial vision systems with applications in robotics, autonomous vehicles, medical imaging, and surveillance. Two-dimensional (2D) materials, such as monolayer molybdenum disulfide (MoS2), are particularly attractive for optoelectronic synaptic devices due to their excellent energy efficiency, high photoelectric conversion efficiency, and mechanical flexibility. Despite their advantages, the fabrication of 2D material-based devices has predominantly relied on lithography-based techniques, which are costly, require cleanroom facilities, and involve high-vacuum systems. These limitations hinder the scalability of these devices for practical applications. In this work, we present a novel approach for fabricating high-performance optoelectronic synaptic devices by utilizing monolayer MoS2 with controlled defects, grown via chemical vapor deposition (CVD), as the active material and employing a cost-effective printing technology for electrode fabrication. The inherent defects in CVD-grown monolayer MoS2, often considered as limitations, are effectively utilized in this work. These defects enable the trapping of photogenerated carriers, which plays a critical role in inducing synaptic characteristics. To the best of our knowledge, this is the first report to integrate CVD-grown monolayer MoS2 with printing technology for optoelectronic synaptic device fabrication. The printed device demonstrates exceptional photoelectric conversion with a peak responsivity of 10.3 A/W at 5 V external bias under 532 nm illumination. It exhibits robust synaptic behaviors, including excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), short-term memory (STM), long-term memory (LTM), and spike-timing-dependent plasticity (STDP). Remarkably, the device emulates human learning and forgetting processes with extraordinary energy efficiency, achieving 1.2 fJ energy consumption per synaptic event. An artificial neural network (ANN) was designed on the MATLAB platform, based on the learning characteristics of our device to evaluate its neuromorphic potential. The ANN achieved a recognition accuracy of 85.1% on the MNIST handwritten digit dataset. Thus, this work highlights the potential of defect-engineered 2D materials and printed technology for scalable, cost-effective, and energy-efficient neuromorphic applications, paving the way for next-generation artificial vision systems

Xin Li

Hunan University

Two-dimensional metallic alloy contacts with composition-tunable work functions

Heterostructures made using two-dimensional semiconducting transition metal dichalcogenides could be used to build next-generation electronic devices. However, their performance is limited by low-quality metal– semiconductor contacts, and it remains challenging to create contacts with variable work functions using metals or metallic transition metal dichalcogenides. Here we show that a one-step chemical vapour deposition method can be used to fabricate nanoplates of a two-dimensional metallic alloy VS2xSe2(1–x) (where 0 ≤ x ≤ 1), which has a continuously tunable band alignment. The work function of the alloy can vary from 4.79 ± 0.01 eV (VSe2, x = 0) to 4.64 ± 0.01 eV (VS2,x = 1.00). The van der Waals heterostructures of VS2xSe2(1–x) and p-type tungsten diselenide (WSe2) exhibit increased contact potential difference asx varies from 0 to 1, with transistors made using VSe2/WSe2 contacts showing a lower potential difference and better device performance than transistors with VSSe/WSe2 contacts, and in both cases, achieve better performance than devices with evaporated metal contacts. The contact potential difference in heterostructures of the alloy and n-type molybdenum disulfide can be turned from −71.5 mV (VSe2) to 0 mV (VSSe) to 59.3 mV (VS2)—that is, from Schottky to ohmic contacts—with the lowest-work-function (VS2) transistors showing the best performance.

Seo Hyeon Moon

Pusan National University

Highly Aligned MoS2 Nanowire Growth for van der Waals Junctions with Monolayer WSe2

Two-dimensional transition metal dichalcogenides (TMDs) generally have an MX₂ structure and, due to their layered structure, can be transformed into various forms of nanostructures. Among them, MoS₂ features a distinctive S-Mo-S sandwich-like structure, with interlayer bonding governed by van der Waals interactions, enabling facile structural modification. Although various morphologies such as thin films, nanospheres, and nanoflowers have been successfully synthesized, these structures are constrained by disordered grain orientation and undefined interfaces, limiting precise control over crystallographic and interfacial properties. In this study, we propose a MoS₂ wire structure with highly aligned crystallinity, synthesized via a solution-precipitation method. The resulting MoS₂ wires grow vertically along the longitudinal axis, showing clear crystallographic alignment and high structural quality. These features facilitate controlled interface design and support the fabrication of heterojunction devices. The wire morphology and lattice spacing were confirmed by SEM and TEM, with Raman spectroscopy supporting the layered structure. XRD revealed the preferred crystallographic growth direction. To construct a van der Waals (vdW) heterointerface, the synthesized MoS₂ wires were integrated with a monolayer WSe₂, enabling simultaneous vertical and lateral atomic contact at the interface. Cross-sectional TEM analysis was used to investigate the stacking sequence. The band alignment and type of the 1D MoS₂/2D WSe₂ heterojunction were determined by UPS analysis, and the PL results supported the interfacial charge transfer behavior. This work presents a strategic approach for designing highly aligned MoS₂ wire structures and fabricating well-defined vdW heterointerfaces, offering valuable insights for precise interface control and next-generation heterojunction device development.

Hai Phuong Duong

Sungkyunkwan University

Gate-tunable Bi-directional Photocurrent in Gr/WSe2/Gr/metal Homojunction for In-sensor Optoelectronic Computing

Endowed with high precision, reduced data transfer, and low power consumption, in-sensor optoelectronic computing has garnered significant attention in recent years. The rapid advancements in in-sensor image processing technology demand simplified device structures alongside the achievement of high-performance metrics. Herein, we demonstrate the gate-tunable bipolar photoresponse enabled through high-performance graphene (Gr)/WSe2/Gr/metal homojunction photodiode designed explicitly for in-sensor optoelectronic computing. By utilizing a selectively asymmetric bottom contact, with the semimetal Gr serving as the electrode, we manipulate the local carrier dynamics within the WSe2 channel under varying applied gate biases. This configuration reverses the built-in electric field, consequently inverting the direction of the drift photocurrent. Incorporating Gr/metal and Gr contact, chosen for their identical work functions and van der Waals interface properties, facilitates seamless switching between negative and positive photocurrents at gate biases near 0 V. The device demonstrates remarkable efficiency in minimizing dark current, achieving an ultra-high light on/off ratio of 108. Furthermore, it displays exceptional performance characteristics, including a high responsivity and external quantum efficiency. It also features an ultra-fast response speed of 1 μs and photodetection at 532 nm. Notably, the gate-tunable switching capability between negative and positive photocurrents, exhibiting a linear power dependence, is utilized to demonstrate 3 × 3 kernels in in-sensor image processing.

Yevhenii Rybalchenko

imec, KU Leuven

Anomalous mechanism of bilayer island formation during MOCVD growth of a monolayer MoS2 on sapphire

Synthetic two-dimensional transition metal dichalcogenides (MX2) with semiconducting properties are widely considered as a potential channel material in future transistors. One of the challenges in the deposition of MX2 thin films is achieving a layer-by-layer lateral epitaxial growth on macroscopic scale. Bilayer usually begins to nucleate before the full closure of the 1st monolayer (ML) MX2 due to the morphology of the commonly used growth template – sapphire substrate [1]. The 2nd ML islands tend to decrease electrostatic control of MX2 channels and introduce higher device-to-device variability [2]. A lot of progress has been made to limit the vertical MX2 growth by optimizing the growth parameters [1]. However, currently available research only considers bilayer nucleation on top of existing MX2 crystal. It is important to have a full understanding of different ways that bilayers can nucleate to suppress their negative effect on the electrical properties of the channel. Here we show an unusual mechanism for the bilayer MoS2 growth that occurs due to the sapphire substrate’s etching and leads to appearance of bilayer crystals encapsulated under a fully closed ML. In this work, MoS2 ML is deposited by metal-organic chemical vapor deposition (MOCVD) on c-plane sapphire substrate at 1000 ºC from Molybdenum hexacarbonyl (Mo(CO)6) and Hydrogen Sulfide (H2S) as precursors. Bilayers start to form before the full closure of the 1st ML, which results in ~ 20% coverage of the surface with 2nd ML islands. Interestingly, measurements in contact mode atomic force microscopy (AFM) show a difference in height between bilayers. Some of them are ~0.2 nm lower than the normal height of MoS2 ML. Exposing the sapphire surface uncovers the presence of cavities underneath the locations that were previously occupied by such bilayers. We ascribe the origin of these pits to the etching of sapphire surface during the MOCVD process. Kumagai et al. have shown that Al2O3 surface can react with H2 at high temperatures, thus, decomposing the former [3]. In this case, H2 is generated as a by-product during the MoS2 MOCVD process. The etched cavities seem to serve as an additional nucleation site for the growth of the MoS2 crystals. MoS2 within the etched pit and the cavity itself then grow simultaneously until the 1st ML closes on top of the crystal, thus preventing their access to the precursor gases. Cross-sectional transmission electron microscopy confirms that some bilayers are indeed encapsulated under the 1st ML (buried islands), while others grow normally – on top of it (2nd ML islands). Conductive AFM reveals the impact of the buried islands on the electrical conduction as they locally decrease current. Crystalline orientation of the bilayer does not dictate its conductivity as both kinds have the same crystalline orientation as the monolayer. Moreover, the interface with sapphire cavity cannot be the reason of buried islands’ low conductivity as (1) based on the cavities’ depth, surface terminations of the pit and the terrace outside of it are the same; (2) low-conductive islands are still present after transfer. Nevertheless, low conductivity can be clearly correlated to the MoS2 nucleation inside the cavity. Most of the low-conductive islands are much smaller than their counterparts with normal conductivity. There is likely a correlation between the size of the island and its properties as well. During the MOCVD growth, the Mo and S adatoms tend to laterally diffuse across the sapphire terrace until they find the most energetically favorable position. However, any interaction between adatoms and the buried MoS2 crystal becomes impossible once the top MoS2 layer covers it. Thus, it is possible that the low conductivity stems from a higher defectivity of buried islands caused by a limited supply of the precursors during growth. Here we report an unusual mechanism of the bilayer formation in MOCVD MoS2, which occurs via crystal nucleation inside the etched sapphire pits and its further encapsulation under the 1st closed ML. These buried islands tend to have low intrinsic electrical conductivity, which could negatively affect the performance of the channel in a transistor. Our results provide further insight into the essential features of the MOCVD growth of MoS2 thin films.

References [1] G. Jin et al., “Heteroepitaxial van der Waals semiconductor superlattices,” Nat. Nanotechnol., vol. 16, no. 10, pp. 1092–1098, Oct. 2021, doi: 10.1038/s41565-021-00942-z. [2] Y. Shi et al., “Superior electrostatic control in uniform monolayer MoS2 scaled transistors via in-situ surface smoothening,” in 2021 IEEE International Electron Devices Meeting (IEDM), Dec. 2021, p. 37.1.1-37.1.4. doi: 10.1109/IEDM19574.2021.9720676. [3] Y. Kumagai et al., “Formation of AlN on sapphire surfaces by high-temperature heating in a mixed flow of H2 and N2,” Journal of Crystal Growth, vol. 350, no. 1, pp. 60–65, Jul. 2012, doi: 10.1016/j.jcrysgro.2011.12.023.

Bin Han

University of Strasbourg

Molecular Welding Strategy for Grain Boundary Precise Repair in 2D Semiconductors

The industrialization of chips relies on the integration of field-effect transistors (FETs) on wafer-scale substrates, necessitating high-quality, large-area 2D semiconductors with uniformity and minimal defects. However, chemical vapor deposition (CVD) growth inevitably introduces grain boundaries (GBs), defects, and dislocations that degrade device performance. In particular, grain boundaries formed at the interface of differently oriented grains cause structural discontinuities, increase carrier scattering, introduce additional trap states, and reduce device stability and uniformity, posing a major challenge for high-quality transistor integration. Here, we report a molecular welding strategy for precise grain boundary repair in WS₂. Using a solvent-free post-treatment, 1,4-benzenedithiol (BDT) molecules covalently bridge abundant sulfur vacancies at the grain boundary, forming a conductive “bridge” that enhances carrier transport. This method significantly enhances photoluminescence intensity at the grain boundary, increases the transistor mobility by 200-fold, improves the on-state current by three orders of magnitude, and raises the on/off ratio by 10⁵. Additionally, the carrier concentration in the transistor channel is notably increased, while the trap density at the boundary is reduced to the level of the grain interior, and the repair effect remains stable over time. Beyond precise grain boundary repair, our approach effectively heals sulfur vacancy defects within the grains, improving overall charge transport and device uniformity, providing a reliable technological foundation for 2D semiconductor devices integration.

Kory Burns

University of Virginia

(Dis)order in the court: Probing Heterogeneities in TMDs with Vibrational EELS

Two-dimensional (2D) compound semiconductors and dielectrics exhibit a range of levels of disorder dependent on their stoichiometry, which can be engineered based on growth conditions, substrate interactions, or atom-by-atom modifications with charged projectiles. There is an entire framework of studies that builds upon research dedicated towards the associated properties with heterogeneities in films, but fail to make one-to-one correlations with the atomic arrangement of the lattice and the optical/infrared emissions. In this talk, we first use aberration-corrected scanning transmission electron microscopy (STEM) to visualize the atomic sites, then machine learning to map out the positions and relative displacement of the atoms in the vicinity of defects. Next, core-loss electron energy loss spectroscopy (EELS) is used to determine the global and local composition, as well as localized carbon and oxygen impurities to unveil their role in stabilizing strain0driven polymorph. Last, monochromated EELS inside an aberration-corrected STEM is used, which greatly reduces the energy distribution of the electron source to maximize the energy resolution without sacrificing too much spatial resolution. Accordingly, we map the high-frequency vibrational modes and exciton complexes in transition metal dichalcogenides (TMDs) using off-axis EELS to correlate the impact single atom modifications have on the vibrational and optical spectrum. Ultimately, we address applications ranging from quantum sensors to thermoelectric junction devices.

Soonhyo Kim

Pohang University of Science and Technology (POSTECH)

Leveraging Fermi-Level Pinning with Selenium Interlayers for High-Performance p-Type Contacts in 2D WSe2 Transistors

The development of high-performance p-type 2D transistors has been hindered by the lack of suitable contact engineering strategies that enable efficient hole injection. Conventional approaches, such as van der Waals (vdW) metal contacts and semimetallic electrodes, suffer from scalability limitations or an insufficient number of materials with deep work function energy levels required for p-type conduction. In this work, we demonstrate a novel contact engineering strategy that leverages a selenium (Se) interlayer to improve hole injection in p-type transition metal dichalcogenide (TMD) transistors. Rather than eliminating Fermi-level pinning, we utilize it to realign the Fermi level at the metal–semiconductor interface, thereby enhancing p-type conduction. Electrical measurements reveal that selenium interlayer contacts significantly improve device performance, increasing the average field-effect mobility from 24 to 107 cm²/(V·s) and the on-current density from 8.5 to 55 μA/μm, with maximum values reaching 119 cm²/(V·s) and 60 μA/μm, respectively. The lack of direct doping effects from selenium further supports the hypothesis that Fermi-level pinning at the metal–selenium interface plays a critical role in contact optimization. This work introduces a simple and scalable method for enhancing p-type conduction in 2D transistors and provides new insights into leveraging Fermi-level pinning for contact engineering.

Sameer Kumar Mallik

Chalmers University of Technology

van der Waals Nanoribbon Memtransistors for Dynamic Analog Memory and Synaptic Metaplasticity

van der Waals Nanoribbon Memtransistors for Dynamic Analog Memory and Synaptic Metaplasticity Sameer Kumar Mallik,1 Md. Anamul Hoque,1 and Saroj P. Dash1 1Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296 Göteborg, Sweden Email: mallik@chalmers.se / Phone: +91-8984501382

Memtransistor devices are gaining attention as promising components for neuromorphic computing, offering advantages such as miniaturized design, rapid switching capabilities, multi-level data storage, and low-power analog processing, making them ideal for future computing architectures.1 Recent advancements in two-dimensional (2D) materials such as transition metal dichalcogenides (TMDs) have significantly broadened the scope of memristive systems, where additional electrostatic gate control tunes the device characteristics to achieve a wide range conductance regime for tunable synaptic learning and heterosynaptic plasticity.2 Herein, we demonstrate the planar nonvolatile memristive switching in ultra-scaled multichannel field-effect transistors (FET) using tungsten disulfide (WS2) nanoribbons showing tunable synaptic operations for development of future neuromorphic hardware elements.

WS2 flakes are initially exfoliated on the SiO2/Si(doped) substrate using the scotch-tape method, followed by nanopatterning using electron beam lithography. Then the flakes are physically etched with the CHF3 reactive ion etching process. Finally, crystallography-controlled anisotropic wet chemical etching of WS2 is performed in the mixture of hydrogen peroxide (H2O2) and ammonium hydroxide (NH4OH) to produce WS2 nanoribbons,4 featuring atomically sharp zigzag edges. Ti (20 nm)/Au (90 nm) contacts for drain/source electrodes are prepared using standard electron beam lithography, electron beam evaporation, followed by lift-off techniques. The planar memristive switching device is fabricated using multichannel nanoribbons of varying widths from 10 to 200 nm connected parallelly across drain-source electrodes. The devices show filament free memristive switching cycles with SET and RESET process at different gate bias. By applying repeated voltage cycles to emulate gradual SET and RESET processes, we also demonstrate analog memory behaviors in planar nanoribbon memristors. The retention measurements are also carried out at different SET and RESET voltages during the sweep cycles demonstrating the non-volatile nature of the planar memristive effects. Furthermore, we have performed the temperature dependence of the memristive switching ranging from 100 to 300 K. The memory window is observed to vary with temperature regardless of the switching ratio, explaining possible thermally activated trap states arising from the edges of the nanoribbons. The complex bio-inspired neuromorphic functionalities can be mimicked in such planar memristive devices by exploring various conductance regimes using volatile gate tunability of nanoribbon FETs. The non-volatile control of pulse switching operations at different gate voltages and long-term memory behaviors of biological neurons such as potentiation and depression are emulated with different read voltages by successive application of pulse voltages. The pulse conditions such as amplitude, width, and delay are crucial parameters to control the synaptic weight. Furthermore, in our proposed artificial synapse, we replicate short-term memory (STM) and long-term memory (LTM), which emerge from synaptic plasticity modulation. STM represents a temporary and weak enhancement of synaptic strength, lasting only seconds to minutes. However, repeated stimulation of STM leads to a lasting modification in synaptic weight, persisting from hours to months or even for a lifetime, known as LTM. In our device, we demonstrate STM, LTM, and their transition by modulating the number and frequency of pulse inputs. These meta materials provide unique opportunities to investigate filament-free tunable memristive switching characteristics. This work demonstrates further scaling of 2D TMDs for potential applications in bio-inspired neuromorphic functionalities, complex learning and cognitive dynamical information processing for the development of future in-memory computing architecture.

Reference [1] Mallik, S. K. et al. npj 2D Mater Appl 7, 63 (2023) [2] Yan, X. et al. Adv. Mater. 34, e2108025 (2022) [3] Hoque, Md. A. et al. NanoLett. 2025, 25, 1750−1757 [4] Munkhbat, B. et al. Nat. Commun. 2020, 11, 46

Jyun-Wei Huang

Academia Sinica

Gate-Tunable Carrier Dynamics and Conductivity of Photoexcited Monolayer MoS2 PhotoFETs with Conductive Nitride Gates

Monolayer transition metal dichalcogenides (TMDs) are promising for atomically thin devices in optoelectronic and photonic applications due to their excellent optical properties, including direct bandgaps and efficient exciton formation. However, achieving strong light-matter interaction in scalable monolayer TMDs remains challenging. In this work, we introduce conducting transition metal nitrides (TMNs) [1], specifically TiN and HfN, as reflective gate layers to enhance electrically tunable optical modulation efficiency in MoS₂-based phototransistors. The fabricated devices consist of a 100-nm sputtered TMN layer with an atomically smooth surface on p⁺-Si substrates, followed by a 30-nm Al₂O₃ gate dielectric and a dry-transferred scalable monolayer MoS₂ [2] with photolithographically defined source and drain contacts. Electrical characterization reveals a notable ~20 % greater threshold voltage difference between illuminated and dark conditions for TMN-gated devices compared to traditional silicon-gated counterparts while maintaining a high on-off current ratio (~10⁶) within a ±10 V operating range. Capacitance-voltage (C–V) measurements confirm a 10-fold increase in electron concentration for the TMN-gated structures. Pump-probe transient absorption spectroscopy was employed to investigate carrier dynamics [3], providing deeper insights into the working mechanism and facilitating optimization of the gated heterostructure design. The band alignment between TMNs (TiN: ~4.8–4.9 eV, HfN: 4.49 eV) and MoS₂ (4.47 eV) plays a crucial role in this study. These results highlight the advantages of scalable monolayer MoS₂ integrated with TMN gates, providing insights into carrier dynamics and suggesting promising applications as gate-tunable modulators with rapid switching for visible-light communication and dynamically tunable photonic devices.

References [1] 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)

[2] 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)

[3] 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 19, 8152-8161 (2025)

Achintya Dutta

KU Leuven

Hyperspatial Second-Harmonic Microscopy of Strain-Fields in 2D Semiconductors

Strain engineering in two-dimensional van der Waals semiconductors has emerged as a powerful approach for controlling exciton dynamics [1], opening potential pathways to excitonic quantum devices [2] and the exploration of hybrid exciton states [3]. This motivates the development of methods for local strain field analysis. Typically, strain is extracted via linear spectroscopy by measuring strain-induced shifts in exciton peak energies. However, these techniques do not provide quantitative information about local strain vectors, which is crucial for distinguishing uniaxial and biaxial contributions, resolving strain gradients, and evaluating circular or linear polarisation selection rules. These factors are essential for determining ideal conditions for launching spin-valley polarised exciton currents. Here, we demonstrate angle-resolved second-harmonic generation (SHG) microscopy combined with optical spectroscopy as a quantitative probe of spatially modulated strain in monolayer transition metal dichalcogenides. The strong SHG response, arising from broken inversion symmetry in this class of materials, is analysed using a photoelastic tensor model to extract local strain vectors from polarisation-dependent SHG intensity [4]. This method is applied to specific, highly directional strained geometries, including monolayers on rough diamond substrates relevant for experiments using THz radiation [5], and conceptually similar structures used for detecting directional exciton transport, with planned extensions towards voltage-tuneable strained nanodrums [3] and one-dimensional excitonic strain channels [1]. The SHG-derived strain maps for these samples are benchmarked against low-temperature spatially resolved PL, validating the strain magnitudes via exciton peak shifts. These results provide quantitative strain maps and corresponding exciton energy landscapes, enabling future studies on exciton transport and the development of devices that guide spin-valley encoded information in atomically thin materials.

References [1] F. Dirnberger, J. D. Ziegler, P. E. F. Junior et al., “Quasi-1D exciton channels in strain-engineered 2D materials”, Sci. Adv. 7, eabj3066 (2021). [2] A. R.-P. Montblanch, M. Barbone, I. Aharonovich et al., “Layered materials as a platform for quantum technologies”, Nat. Nanotech. 18, 555-571 (2023). [3] P. H. López, S. Heeg, C. Schattauer et al., “Strain control of hybridization between dark and localized excitons in a 2D semiconductor”, Nat. Comm. 13, 7691 (2022). [4] L. Mennel, M. M. Furchi, S. Wachter et al., “Optical imaging of strain in two-dimensional crystals”, Nat. Comm. 9, 516 (2018). [5] T. Venanzi, M. Cuccu, Raul Perea-Causin et al., “Ultrafast switching of trions in 2D materials by terahertz photons”, Nat. Photonics 18, 1344-1349 (2024).

Jheng Jie Lin

National Cheng Kung University

Selective area oxygen doping for improved performance p-type two dimensional WSe2 transistors

Despite recent advances, the contact resistance of p-type field-effect transistors (FETs) based on two-dimensional (2D) transition metal dichalcogenides (TMDs) remains higher than desired and must be reduced. We demonstrate a hybrid contact strategy that combines two leading approaches—transferred contacts and surface charge transfer doping via oxygen plasma oxidation—to significantly improve contact quality for p-type WSe2. By locally doping access regions adjacent to metal contacts embedded in hexagonal boron nitride (hBN), we preserve the pristine nature of the encapsulated WSe2 channel while enabling efficient hole injection. We observe a >30,000× reduction in contact resistance, reaching a minimum of 3.6 kΩ·μm, limited by the induced hole carrier density from plasma doping. Our devices exhibit negligible hysteresis from 10 to 300 K under back-gate operation, high reproducibility across multiple contacts and devices, and long-term atmospheric stability exceeding 50 days. This work outlines a route to reducing contact resistance in p-type TMD FETs while maintaining channel integrity and highlights the importance of enhancing hole doping strategies to achieve further improvements. We also investigate p–n junction-based devices on WSe2 using a surface oxidation and selective removal technique. Oxygen plasma treatment is used to significantly enhance the p-type behavior of WSe2, and subsequently, selective regions of the resulting tungsten oxide layer are removed by potassium hydroxide etching, allowing the underlying WSe2 to recover its intrinsic ambipolar characteristics. This approach allows for spatially controlled doping profiles and improves the surface cleanliness of treated regions. We thereby demonstrate a lateral p–n junction on few-layer WSe2 and demonstrate application for logic functions such as inverter operation.

Shreyasi Das

Indian Institute of Technology Bombay

Piezoelectric Stack Enabled Strain Tuning in WSe2/ReS2 Heterostructures

2D transition metal dichalcogenide (TMDs) heterostructure, given their tunable band alignments and efficient charge separation in atomically thin layers, finds immense applications for optoelectronics and quantum devices. Moreover, their remarkable elastic strength enables tuning optical and electrical properties through strain application. However, traditional strain modulation methods, like nanoindentation, flexible substrates, or patterned substrates, are inadequate for dynamic modulation in CMOS integrated devices. This study introduces a novel technique to dynamically modulate the rectification behavior and transistor parameters of a WSe₂/ReS₂ heterojunction using controllable strain from an integrated piezoelectric thin film stack. WSe₂ and ReS₂ are ambient stable TMDs exhibiting distinct ambipolar and n-type characteristics, respectively, forming a type-II band alignment. In this study, a 7-order rectification ratio modulation in the WSe₂/ReS₂ heterostructure is achieved along with significant modulation of field-effect parameters like 2x mobility enhancement and change in subthreshold slope from 184 mV/dec to 77.5 mV/dec by tuning bias applied across the piezo stack. The electrical gauge factor (EGF) for strain sensing showed values of -7031 V⁻¹ for compressive strain and 428 V⁻¹ for tensile strain.

The device architecture consists of few layer WSe₂ and few layer ReS₂ vertical p-n heterojunction on a piezo stack, a piezoelectric thin film sandwiched between two electrodes, where the top electrode also acts as the gate for the device. Piezoelectric force microscopy of the piezo film indicated a high piezoelectric coefficient (d₃₃) of 170 pm/V. The strain study on the individual WSe₂ and ReS₂ FETs agrees with the strain effect obtained in the heterostructure, substantiating the observations. This research highlights the ability to apply precise tensile and compressive strain to control electronic and optoelectronic properties in TMD heterostructures using a CMOS integrable piezo stack, paving the way for developing high-performance adaptive energy harvesters and photodetectors.

Giorgio Zambito

University of Genoa

Steering light within 2D TMD semiconductor layers

Two-dimensional (2D) Transition Metal Dichalcogenide (TMD) semiconductors have attracted diffuse interest due to their exceptional optoelectronic properties, enabling tunable photon emission and photoconversion response over a broadband spectrum. However, the inherent low photon absorption of the atomic layers demands for novel light coupling schemes that promote strong light coupling to the ultrathin 2D layers. To this end nanofabrication approaches compatible with the fragile 2D materials are required, as well as novel methods that can scale-up the active area of the 2D layers, that is typically limited at the micrometric scale. In this work the nanoscale reshaping of 2D TMDs layer is shown over large-area (cm2 scale), demonstrating superior photon harvesting properties and opening new perspectives in photonics [1-5]. In a first activity we developed a flat-optics scheme based on large-area 2D TMD semiconductor layers forming periodic nanogratings, based either onto few-layer MoS2 or onto van der Waals WS2-MoS2 heterostructures. These periodic nanogratings can effectively steer the light propagation within the 2D layers thanks to the excitation of Rayleigh photonic anomalies [2-4], that are easily tunable over a broadband Visible and Near-IR spectrum. These photonic anomalies promote a strong in-plane electromagnetic confinement and a broadband enhancement of the photon absorption within the ultrathin TMD layers, with strong impact in photonic and photoconversion applications. As an example, a photo to chemical energy conversion process have been recently boosted in flat-optics few-layer TMD semiconductors lying onto flexible templates, opening new possibilities for large-scale energy storage [4]. In a second activity the shape and/or the local strain of 2D TMD semiconductor layers have been tailored thanks to a novel thermal-Scanning Probe Lithography approach [6], thus observing strain-induced modulation of the optoelectronic response at the local scale. These results open new possibilities for locally tailoring the optoelectronic response and the photon emission in strained 2D TMD layers, with impact in nanophotonics, photoconversion and quantum technologies. References

1. C. Martella et al., Advanced Materials 30, 1705615, 2018.
2. M. Bhatnagar et al., Nanoscale, 12, 24385, 2020.
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Zongyuan Xin

The Hong Kong University of Science and Technology (HKUST)

Synthesis of One-dimensional Transition Metal Dichalcogenides by Chemical Vapor Deposition

As members of the two-dimensional (2D) layered materials, transition metal dichalcogenides (TMDs) have emerged as promising candidates for channel materials in next-generation transistors. Controlling dimensions represents a significant advancement in the development of nanomaterials with unique properties. This study explored the controlled synthesis of 1D MoSe₂ ribbons by optimizing chemical vapor deposition (CVD) parameters to achieve high-quality, uniform nanostructures. The prepared ribbons are hundreds of micrometers in length, with some ribbons measuring less than 100 nm in width. The ribbons were characterized as 2H-MoSe₂ using X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM). By systematically varying reaction parameters, this research revealed the unique role of H₂ in promoting anisotropic growth along different edges, supported theoretically by density functional theory (DFT) calculations. This growth method can be extended to synthesize other 1D TMDs. The findings provide insights into the mechanisms underlying the CVD synthesis process, highlighting the potential of 1D TMDs in advancing next-generation electronic devices.

Sanne Deijkers

Eindhoven University of Technology, imec

Metalorganic chemical vapor deposition growth behavior of MoS2 using di-tert-butyl sulfide as an organic sulfur precursor

2D transition metal dichalcogenides (TMDs), such as MoS2, have arisen as promising candidates to replace Si as the transistor in advanced integrated circuits. One of the most promising techniques for the large-scale fabrication of 2D TMDs is metalorganic chemical vapor deposition (MOCVD), which be ideal for direct growth on an oxide substrate. Despite numerous studies on MOCVD for TMDs, further understanding of the growth process is required to reach the desired quality of the deposited layers. In this work we have investigated the growth behavior of MoS2 on SiO2 using metalorganic precursor molybdenum hexacarbonyl (Mo(CO)6) and organic precursor di-tert-butyl sulfide (DTBS, ((CH3)3C)2S).

First, we investigated the effect of growth temperature in the range of 400-800 °C. Atomic force microscopy images revealed that the best results for the growth of 2D crystalline MoS2 grains were obtained at the temperature range from 600 to 700 °C. Below 600 °C no crystalline grains were visible, at 750 °C both 2D MoS2 grains and 3D Mo metal nuclei formed, and above 750 °C mainly Mo metal nuclei were observed. Even though no MoS2 grains were observed for growth temperatures below 600 °C, Rutherford backscattering spectroscopy measurements showed that Mo was present on the surface. This suggests that the relatively low temperature of 400 or 500 °C is insufficient to crystallize the deposited material. Additionally, MOCVD growth of 2D TMDs is strongly affected by the chalcogen to metal precursor ratio, which is expected to affect the metal precursor diffusion [1]. By varying the S/Mo precursor ratio from (4.4 ± 0.1)·103 to (20.9 ± 0.1)·103, a change in nucleation density was found from analyzing scanning electron microscopy images, while keeping the amount of deposited material constant. At higher S/Mo ratios nuclei are larger, and thus the nucleation density is lower, as a result of a larger diffusion length. In this contribution, we add to the understanding of 2D TMD deposition on SiO2 using an organic sulfur precursor, which enables further progress into the development of state-of-the-art nanoelectronics. [1] Wu et al., Appl. Phys. Lett. 123, 183101 (2023)

Jialong Wang

Peking University

Epitaxial Growth of Monolayer WS2 Single Crystals on Au(111) Toward Direct Surface-Enhanced Raman Spectroscopy Detection

The epitaxial growth of wafer-scale two-dimensional (2D) semiconducting transition metal dichalcogenides (STMDCs) single crystals is the key premise for their applications in next-generation electronics. Despite significant advancements, some fundamental factors affecting the epitaxy growth have not been fully uncovered, e.g., interface coupling strength, adlayer-substrate lattice matching, substrate step-edge guiding effects, etc. Herein, we develop a model system to tackle these issues concurrently, and realize the epitaxial growth of wafer-scale monolayer tungsten disulfide (WS2) single crystals on the Au(111) substrate. This epitaxial system is featured with good adlayer-substrate lattice matching, obvious step-edge-guiding effect for the unidirectionally aligned nucleation/growth, and relatively weaker interfacial interaction than that of monolayer MoS2/Au(111), as evidenced by the evolution of a uniform Moiré pattern and an intrinsic band gap, according to on-site scanning tunneling microscopy/spectroscopy (STM/STS) characterizations and density functional theory calculations. Intriguingly, the unidirectionally aligned monolayer WS2 domains along the Au(111) steps can behave as ultrasensitive templates for surface-enhanced Raman scattering detection of organic molecules, due to the obvious charge transfer occurred at substrate step edges. This work should hereby deepen our understanding of the epitaxy mechanism of 2D STMDCs on single-crystal substrates, and propel their wafer-scale production and applications in various cutting-edge fields.

Anton Minnekhanov

Emerging Technologies Research Center, XPANCEO

Giant Photorefractive Effect and Light-Induced Nanostructuring in van der Waals As2S3

Crystalline arsenic trisulfide (c-As2S3) is a layered van der Waals (vdW) material that is promising for next-generation nanophotonic devices due to its high refractive index (>3) and pronounced in-plane optical anisotropy (Δn ≈ 0.4).[1] While the amorphous form of As2S3 has been widely explored for its photorefractive properties,[2] the crystalline phase has remained understudied, in part due to challenges in controlled nanostructuring. Here, we show that light alone can act as a single, non-contact stimulus to modulate a wide range of properties in c-As2S3—optical, structural, and morphological—with high spatial precision. Under illumination, c-As2S3 exhibits a giant photorefractive effect across the UV–NIR spectrum, with refractive index modulation reaching Δn ≈ 0.1. This, together with intrinsic birefringence, enables reconfigurable waveguiding and dynamic photonic elements. Concurrently, light-induced thickness changes—ranging from thinning to expansion and eventually fast ablation—allow programmable reshaping of individual flakes depending on intensity. Using a low-power continuous-wave (CW) laser, we demonstrate direct-write nanostructuring with feature sizes down to 500 nm and resolution up to 50,000 PPI. The photochemical nature of the process avoids ablation and preserves material integrity. The resulting patterns are suitable for applications including optical data storage, metasurfaces, microlens arrays, and security features. The combination of broadband optical tunability, intensity-dependent geometry control, and high-resolution laser patterning defines c-As2S3 as a light-responsive vdW semiconductor with multifunctional potential. Its ability to unify multiple photonic functions via optical stimulus alone offers a scalable, TMD-compatible platform for 2D integrated optoelectronics.

[1] Slavich A. S. et al., Light Sci. Appl., 13 (2024) 68. [2] Ozols A., Saharovs Dm., Reinfelde M., J. Non-Cryst. Solids, 352 (2006) 2652–2656.

Hao Ou

Institute of Science Tokyo

Moiré Superlattice in Twisted Transition Metal Dichalcogenide Trilayers

Moiré superlattice forms when vertically stacking van der Waals materials. The study of moiré superlattice unveils many exotic low-dimensional phenomena, including strongly correlated electron behavior, unconventional superconductivity, and topological transport. The material system has manifested itself as a highly tunable platform for exploring new physics. When stacking two monolayer transition metal dichalcogenides (TMDCs), which lack inversion symmetry centers, the obtained moiré superlattice exhibits a two-dimensional array with alternatively polarized domains. Such a stacking-induced polarization opens a new gate for investigating the interfacial ferroelectricity/antiferroelectricity of the superlattice, and inspires the fabrication of next-generation non-volatile memory devices. Currently, most related studies focus on the moiré superlattice of twisted bilayer TMDCs, revealing a triangular lattice with polarized domain array. On the other hand, twisted multi-layer TMDCs could possibly exhibit moiré superlattice with more sophisticated domain structure, which probably leads to more exotic physical phenomena, such as multiple polarization states, stable external-field response, or robust electronic correlation, et al. thus deserving in-depth investigation.

In this work, we present the fabrication and observation of moiré superlattices in twisted trilayer WSe2. We controlled the twisted angle between adjacent layers during fabrication, to tune the moiré superlattice period and lattice relaxation. To observe the resulting superlattices, we employed the piezoresponse force microscope (PFM) to directly resolve the polarized domain structure. The observed moiré superlattice (trilayer superlattice) is shown to be the composition of the superlattices from two pairs of adjacent monolayers (bilayer superlattices). We present trilayer superlattices under two conditions: 1) one bilayer superlattice has a much longer period than the other, and 2) two bilayer superlattices have similar periods. For the first case, the trilayer superlattice shows a generally triangular structure with AA domains within AB/BA domains, due to the combination of relaxed and unrelaxed bilayer superlattices. For the second case, we found an approximately hexagonal lattice. This is the result of multiscale lattice relaxation, in which relaxation occurs in both atomic scale and moiré scale, when the two bilayer superlattices have similar periods. We analyzed the formation of the two types of trilayer superlattices and their domain structures. Our results reveal the huge potential of twisted multi-layer TMDCs as functional ferroelectric device applications based on van der Waals materials.

Srilagna Sahoo

Indian Institute of Technology Bombay

A Low Power Photo-sensitive Neuristor for Optogenetic Applications

Optogenetics is an emerging field of research that studies the control of cellular activity, specifically neuronal stimulation, utilizing a light source that can either excite or inhibit an individual or a group of neurons. Non-invasive, high spatial resolution of approximately 1 μm can be achieved with optical neuronal stimulation, in contrast to electrical stimulation. Two-dimensional (2D) material-based optoelectronic devices are promising due to their exceptional light-matter interaction properties, and the atomic thinness of 2D materials makes them ideal for scaled photo-transistors operating at low voltage. Inspired by optogenetics, we present a visible light-sensitive neuristor based on a few-layer single 2D semiconductor that emulates a highly photo- or light-sensitive Na ion channel consuming 15 fJ of energy per spike. A complete neuronal circuit has been simulated using the 45 nm CMOS technology node, incorporating the 2D photo-sensitive neuristor (PSN) as the Na ion channel. The energy consumption per spike (during both the spike and the integration period) for the entire circuit is 17 pJ. Due to its enhanced (1.5Í) firing rate compared to dark condition, the PSN can offer improved temporal precision and fidelity under light stimulation. However, there is a trade-off: the higher the firing rate, the more energy the PSN consumes. Fortunately, the spike-frequency adaptation (SFA) behavior of the PSN can mitigate this trade-off by reducing redundant spikes. Additionally, the post-inhibitory rebound (PIR) behavior exhibited by the PSN adds further versatility to this work by which light-stimulated fatigue (a reduction in spiking rate) can be alleviated.

Van Dam Do

Sungkyunkwan University

Sub-1 nm channel length for vertical transistors

A novel vertical field effect transistor (VFET) with a channel length of 0.65 nm, utilizing cross-stacked carbon nanotubes (CNTs) and a monolayer transition metal dichalcogenide (TMD) in between, offering exceptional performance improvements to sustain Moore’s Law. This CNT/monolayer TMD/CNT structure addresses the limitations of traditional graphene/monolayer TMD/metal VFETs, which suffer from low on/off ratios due to gate field screening and high off-state tunneling currents. The narrow junction formed by the CNTs and monolayer TMD drastically reduces tunneling currents, while the gate field, applied from the sidewall of the bottom CNT, efficiently modulates the ultra-short channel without field screening. The proposed VFET achieves superior performance metrics, including the highest on/off ratio (106), lower off-state current (10-13 A), and lower subthreshold swing (0.125 V.dec-1). The flexibility of the monolayer TMD ensures minimal air gap formation, enhancing electric field transmission and boosting device performance, resulting in a tenfold increase in current saturation and switching efficiency.

Brendan Healy

University of Warwick

Impact of Co-Reactants in Atomic Layer Deposition of High-k Dielectrics on Monolayer MoS2

The integration of single-layer transition metal dichalcogenides (TMDCs) in nanoscale electronic devices requires the deposition of high dielectric constant (high-κ) materials. Traditional thermal atomic layer deposition (ALD) is commonly used to deposit dielectrics on three-dimensional substrates. Owing to a chemically inert basal plane, ALD of high-κ materials on monolayer TMDCs is more challenging with direct thermal ALD with water (H2O) co-reactant often resulting in incomplete and non-uniform growth on atomically thin TMDCs. The development of alternative ALD processes for the realisation of dielectric layers on monolayer TMDCs is therefore important.

Here, we study oxygen (O2) plasma and ozone (O3) as co-reactants for the direct ALD of aluminium oxide (Al2O3) and hafnium dioxide (HfO2) on monolayer molybdenum disulfide (1L MoS2) films. By employing a robust characterisation process that combines atomic force microscopy (AFM), Raman/photoluminescence (PL) spectroscopy, and X-ray photoelectron spectroscopy (XPS), we reveal growth of high-κ dielectrics by plasma-enhanced ALD (PEALD) with O2 plasma oxidant damages the underlying 1L MoS2 via oxidation to molybdenum trioxide (MoO3). O3-based deposition is shown to be less damaging to 1L MoS2 and we demonstrate the growth of HfO2 via direct thermal ALD with O3 co-reactant. This work reveals the impact of ALD processes on 1L MoS2 during the growth of high-κ dielectrics, highlighting O3-based thermal ALD as a potential route for the integration of dielectric layers for optoelectronic device fabrication.

Oscar Palma Chaundler

The University of Sheffield

Topological Edge State Polaritons in hBN/WSe2 Double Grating Heterostructures

A large emerging class of layered so-called van der Waals (vdW) crystals has recently attracted attention as a viable nanophotonics platform. Materials from this class such as hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDs), so far extensively studied in a few-atomic-layer form, exhibit a wide range of properties suitable for photonics in their quasi-bulk form including variety of transparency windows extending into the visible, high refractive indices and large birefringence. Importantly, vdW materials can be easily stacked or attached to any substrate thanks to the out-of-plane van der Waals forces, a further key enabler for nanofabrication of complex photonic structures requiring heterointegration.

Here, we realise a topological photonic edge state at the boundary of two subwavelength gratings etched in an exfoliated hBN flake (30-100 nm thickness). The observed edge state is a photonic analogy of the celebrated Jackiw-Rebbi model describing a state that lies between two 1D media containing fermions with masses of opposite signs [1]. The studied hBN gratings are designed to have photonic band-structures with different topology, achieved by varying the filling factor (the relative thickness of the grating bars and grooves) leading to the band inversion (i.e. changing the sign of the “mass”), which can be probed in angle-resolved reflectance measurements. The experimental realisation of band inversion requires very accurate control of the refractive index contrast in the grating that we achieve by using “inverted” structures where an hBN grating is made first and then covered by an unetched hBN slab. Both the hBN flakes have precisely selected thicknesses creating an “inverted” grating with parameters unachievable by controlled depth etching of a single hBN flake. This approach also allows us to insert additional layers between the hBN grating and the top layer thus creating a photonic vdW heterostructure, in our case comprising a monolayer of semiconducting WSe 2 exhibiting excitons with a high oscillator strength. This allows us to observe the strong light matter interaction regime with formation of the edge state exciton-polaritons up to room temperature. We study nonlinear properties of such topological polaritons as a function of temperature both in photoluminescence and reflectance contrast under resonant excitation with a pulsed laser.

[1] R. Jackiw and C. Rebbi, Phys. Rev. D 13, 3398 (1976).

Nagendra Kamath

Indian Institute of Technology Mandi

Manipulating Valley Dynamics in MoS2 via Vanadium Doping

Two-dimensional transition metal dichalcogenides (TMDCs) exhibit valley-selective optical transitions, making them promising for valleytronic applications [1,2]. Controlling and manipulating the valley degree of freedom in TMDCs is essential for the development of valley-based electronics and optoelectronics [3]. Beyond the well-studied TMDCs such as MoX2 and WX2 (where X = S, Se, Te), alloying or substitutional doping has garnered interest due to the unique features that emerge from structural modifications [4]. Here, we investigate the helicity-resolved transient absorption response of monolayer MoS2 with a low concentration of vanadium (V- MoS2). Our results reveal that vanadium-induced defect states (VIDS) act as an additional valley, forming a three-valley system. Compared to pristine MoS2, which exhibits a valley depolarization time of ~0.5 ps, V-MoS2 demonstrates an extended valley lifetime of ~7 ps, indicating enhanced valley retention. Furthermore, intervalley scattering dynamics exhibit an energy transfer effect. When the B-exciton is pumped, excitons redistribute into the A-exciton valley while preserving spin polarization. This behaviour highlights the role of vanadium doping in modifying intervalley coupling and exciton dynamics. The findings provide an effective strategy for controlling valley lifetimes and intervalley dynamics, advancing spin-valleytronic applications.

References [1] Mak K F et al. The valley Hall effect in MoS2 transistors “Science” 344, 1489 (2014). [2] Soni A et al. Valley degree of freedom in two-dimensional van der Waals materials “J. Phys. D: Appl. Phys.” 55, 303003 (2022). [3] Schaibley J et al. Valleytronics in 2D materials “Nat. Rev. Mater.” 1, 16055 (2016) [4] Maity D et al. Tuning the valley depolarization dynamics in selenium and vanadium alloyed monolayer MoS2 “Phys. Rev. Mater.” 8, 064004 (2024).

Haofei Zheng

National University of Singapore

CMOS-compatible integration of ultrathin high-k HfOx on 2D semiconductors for high-performance dual-gate transistors

Atomically thin 2D semiconductors have emerged as promising as channel materials for next-generation low-power transistors. A critical step toward realizing their full potential lies in achieving uniform and ultrathin high-κ dielectrics on 2D materials via atomic layer deposition (ALD). However, the absence of dangling bonds on 2D material surfaces poses significant challenges for conformal deposition of high-κ oxides, particularly at sub-nanometer thicknesses. Here we report a CMOS-compatible approach for integrating sub-3 nm high-κ HfOx on molybdenum disulfide (MoS₂). The process begins with the deposition of an ultrathin Hf metal layer under ultrahigh vacuum, which is subsequently oxidized to form a uniform HfOx seeding layer. This layer facilitates the subsequent ALD of an additional HfOx film. Using this approach, dual-gate (DG) MoS₂ transistors are fabricated with a capacitance equivalent thickness (CET) of 0.7 nm, thereby meeting the IRDS target for the 1 nm technology node. These resulting devices exhibit excellent electrostatic control with a near-ideal subthreshold swing (SS) of 60 mV dec⁻¹. Additionally, short channel devices with approximately 80 nm gate lengths demonstrate a high on-current of 459 μA/μm at low operating voltages.

Moonchul Jung

Seoul National University

Vertically aligned MoS2 devices with sub-10 nm channel and 1D graphene contacts

Two-dimensional (2D) semiconductors are a promising channel material due to absence of short channel effect in nanochannel field-effect transistors (FETs). However, scaling down of device footprint, including the lengths of channel and contacts, remains challenging. Here, we demonstrate sub-10 nm nanochannel 2D devices with 1D graphene contacts. After stacking graphene/hBN/graphene heterostructure, MoS2 channel was fabricated on the side wall of etched stack, resulting in physical contact between edge of graphene and bottom surface of MoS2. As a result, MoS2 nanodevices with a channel length of sub-10 nm and a contact length of ~0.3 nm are fabricated. We achieved low contact resistance despite the reduced contact length, thus addressing a critical bottleneck in the scaling of 2D devices. Our work shows a novel approach to effectively mitigate the challenges associated with contact scaling in 2D devices.

Aferdita Xhameni

London Centre for Nanotechnology, University College London

Semiconductor-oxide heterostructure memristors for brain-inspired computing

We investigate the fabrication and characterisation of memristors based on a two-dimensional layered van-der-Waals semiconductor: hafnium disulfide (HfS2). By oxidising HfS2 crystals using a controlled dry thermal oxidation method, we fabricate oxide-semiconductor (HfOxSy/ HfS2) heterostructures which are integrated between metal contacts, forming vertical crossbar devices. When programmed with 80ns voltage pulses, our devices switch between non-volatile resistance states while maintaining an ON/ OFF ratio of 10^2. Crucially, HfOxSy/ HfS2 memristors switch resistance without requiring initialisation (electroforming) or over-current protection (current compliance), showing the potential of these devices to enable high efficiency and low latency in future memristive chips. We demonstrate the stability of our devices by testing the retention of multiple resistance states at 150oC for 10^4 s and we also observe unchanged resistance switching when devices are operated in vacuum (8.6mbar). To gain insight into their potential for machine learning applications, we characterise the devices with tailored potentiating and depressing pulsing schemes. Highly linear and symmetric conductance update with low cycle-to-cycle variation are observed, which are highly desirable for machine learning applications. From this data, we extract relevant performance parameters and achieve high accuracy inference for an image recognition task with a simulated crossbar array based on our devices, demonstrating the potential of this approach for fabricating memristive devices for machine learning and neuromorphic computing.

Iryna Kandybka

KU Leuven, imec

Area Selective Deposition of 2D WS2 by low temperature chemical vapor deposition

The area-selective deposition (ASD) of single-crystal semiconducting transition metal dichalcogenide (TMD) monolayers has significant potential in various cutting-edge applications, as it enables precise resist free patterning and material placement on substrates. Depositing TMD on predefined areas is important for constructing highly compact and efficient logic and memory devices. However, the methods to deposit high quality, grain boundary free TMD crystals must be developed in order to achieve the devices with the superior electronic properties. A selective deposition process of TMDs is needed at the back end of line temperatures below 400 °C to be compatible with the amorphous dielectrics. Typically, low deposition temperatures result in small 2D grains in the nanometer range. For instance, we observe that metal organic chemical vapour deposition (MOCVD) of tungsten disulfide (WS2) at 300 °C results in the 2D grains with the lateral dimensions of around 10 nm. Here we demonstrate that co-injecting Cl2 during the MOCVD of WS2 allows us to achieve large, up to micrometer-sized, WS2 crystals on SiO2 at deposition temperatures of 300 °C. Additionally, a selectivity window opens for Cl2 assisted MOCVD on dielectrics such as silicon oxide (SiO2), aluminum oxide (Al2O3) and hafnium oxide (HfO2). We show how selectivity towards SiO2 can be increased by adjusting Cl2 assisted MOCVD process parameters. Finally, we present concepts that enable coverage of the growth area by WS2 single crystals, required for the incorporation of 2D TMDs into the industrial processes.

Subir Ghosh

The Pennsylvania State University

A complementary two-dimensional material- based one instruction set computer

Silicon has driven semiconductor advances through miniaturization, but scaling challenges necessitate the exploration of new materials. Two-dimensional (2D) materials, with their atomic thickness and high carrier mobility, offer a promising alternative. Although significant progress has been made in wafer-scale growth, high-performance field-effect transistors and circuits based on 2D materials achieving complementary metal–oxide–semiconductor integration remains a challenge. Here, we present a 2D one instruction set computer based on complementary metal–oxide–semiconductor technology. We leverage the heterogeneous integration of large-area n-type MoS2 and p-type WSe2 field-effect transistors. By scaling the channel length, incorporating a high-κ gate dielectric and optimizing material growth and postprocessing, we tailored the threshold voltages for both n- and p-type 2D field-effect transistors, achieving high drive currents and reduced subthreshold leakage. This enabled circuit operation below 3 V with an operating frequency of up to 25 kHz, which was constrained by parasitic capacitances, along with ultra-low power consumption in the picowatt range and a switching energy as low as approximately 200 pJ. Finally, we projected the performance of the one instruction set computer and benchmarked it against state-of-the-art silicon technology using an industry-standard SPICE- compatible BSIM-BULK model, calibrated with experimental data and incorporating device-to-device variations. Although further advances are needed, this work marks a significant milestone in the application of 2D materials to microelectronics.

Yunxia Hu

The Hong Kong University of Science and Technology (HKUST)

Van der Waals-Integrated Self-Powered Image Sensors Based on Two-Dimensional Homojunctions

The van der Waals (vdWs) integration of two-dimensional (2D) provides a flexible strategy to construct multifunctional image sensors, exhibiting excellent and low-power consumption imaging functions. However, the multi-step device fabrication process usually introduces lattice mismatches and defects at the vdWs junction interfaces, which deteriorate device performance. Here we report van der Waals homojunctions consisting of 2H-MoTe2 with asymmetric thickness to eliminate heterogenous interfaces and thus obtain clean interfaces. The ability to tune the energy bands of 2H-MoTe2 continuously through layer engineering enables the creation of adjustable built-in electric field to realize self-powered photodetection. And the successful integration of 2H-MoTe2 homojunctions into an image sensor brings about zero-power consumption and near-infrared imaging functions. Addtionally, we propose a vdWs-integrated image sensor with crossbar architecture consisting of vertical 1T’/2H-MoTe2/ITO devices to realize self-powered imaging. The asymmetric electrode contacts for 2H-MoTe2 by combining Ohmic contact with 1T’-MoTe2 layers and Schottky contact with ITO electrodes contribute to the self-powered photodetection. These works open a new route to build image systems based on 2D materials, showing great opportunities in digital image systems with ultralow power consumption and excellent imaging functions.

Suman Kumar Chakraborty

Indian Institute of Technology Kharagpur

Multi-Moiré Networks Enabled Phonon and Exciton Renormalization in Engineered Two-Dimensional Lateral Hetero-Monolayers

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are emerging owing to their exotic physical, electro-optical properties and applications for next-generation optoelectronics and quantum technology. Combining different 2D TMDs into heterostructures with type-II band alignment can evoke new functionalities and provide new ways to manipulate their electronic, optical, magnetic and excitonic properties. Strong correlation and quasiparticle interactions provide new ways to control lattice and optical excitations. Though 2D heterostructures have been studied extensively in the past decades using mechanically exfoliated samples, understanding the light-matter interaction dynamics of directly synthesized 2D TMD heterostructures is still missing and needs further investigation. In this context, the chemical vapour deposition (CVD) method can provide flexibility in fabricating a wide range of 2D heterostructures with a balance between high quality, controllability, and cost-effectiveness [1]. Among others, the water-assisted one-pot CVD strategy is the most straightforward, robust, and highly controllable to grow electronic grade 2D lateral heterostructures (LHS) in situ with controlled thickness, layer number, and domain width using bulk TMDs as solid precursors in the presence of different carrier gases for the selective evaporation [2]. This heterostructure shows control over exciton density distribution, essential to designing excitonic devices [3]. Using this strategy and manipulating precursor to substrate distance, growth temperature, time, and adatoms flux, we have fabricated monolayer, bilayer, and trilayer multi-junction MoS2-WS2, MoSe2-WSe2 LHS. Using the dry transfer method, we have transferred MoS2-WS2 LHS onto other 2D HS. High-frequency and low-frequency Raman and photoluminescence spectroscopic measurements were carried out to understand the twist and material engineered moiré coupling driven lattice reconstruction to 2D heterostrain, interlayer interaction, optical characteristics, and charge transfer dynamics of these hybrid heterostructures. The stacking order-dependent formation of phonons, frequency to linewidth engineering, excitonic valley polarization renormalization, and second harmonic generation were investigated in detail. In addition to the TMD/TMD combination, 2D TMD/2D magnet heterostructures are also investigated, which shows a strong interplay of excitonic functionalities to magnetic ordering: exciton-magnon and spin-photon coupling.

Keywords: Multi-moiré, Lateral Hetero-monolayer, 2D semiconductors, Lattice relaxation, Heterostrain, Valley Polarization, Second Harmonic Generation.

Reference:

1. Chakraborty, S. K., et al. “Challenges and opportunities in 2D heterostructures for electronic and optoelectronic devices.” IScience 25.3 (2022): 103942.
2. Sahoo, Prasana K., et al. “One-pot growth of two-dimensional lateral heterostructures via sequential edge-epitaxy.” Nature 553.7686 (2018): 63-67.
3. Kundu, B. et al. Electrically Controlled Excitons, Charge Transfer Induced Trions, and Narrowband Emitters in MoSe2–WSe2 Lateral Heterostructure. Nano Lett. (2024) 24, 14615.

Mohamed Al Khalfioui

Université Côte d'Azur, CNRS, CRHEA

Investigation of 2D MoS2 Growth by Molecular Beam Epitaxy

Since the synthesis of graphene in 2004 [1], interest in two-dimensional (2D) materials has significantly increased, particularly focusing on transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2). These 2D materials offer exceptional electronic, mechanical, and optical properties at the atomic scale, and their bandgap is tunable depending on the number of layers [2], making them promising materials for advanced electronic, and optoelectronic devices. However, synthesizing high-quality 2D materials on an industrial scale remains a challenge. Although Chemical Vapor Deposition (CVD) and Pulsed Laser Deposition (PLD) offer more scalable alternatives, they encounter issues related to thickness uniformity and purity control. In this context, Molecular Beam Epitaxy (MBE) has emerged as a leading technique for growing TMDs (such as MoS2), thanks to its precise control over deposition parameters and the ability to monitor growth in situ using techniques such as Reflection High-Energy Electron Diffraction (RHEED). Our study demonstrates a growth of MoS2 layers on GaN/sapphire substrates [3] using Molecular Beam Epitaxy (MBE). Morphological characterization via Atomic Force Microscopy (AFM) revealed the formation of triangular MoS2 domains on the GaN surface. Raman spectroscopy analysis of the E12g and A1g modes showed distinct peak separations, confirming the formation of monolayer and bilayer MoS2 on the GaN substrate. High-Resolution Scanning Transmission Electron Microscopy (HR-STEM) was employed to investigate the interface between MoS2 and GaN.

References: [1] Novoselov K, et al. Electric field effect in atomically thin carbon films. Science 2004, 06 (5696), 666-669. [2] Splendiani A, et al. Emerging Photoluminescence in Monolayer MoS2. Nano Letters 2010, 10(4), 1271-1275. [3] Al Khalfioui, et al. Investigation of MoS2 growth on GaN/sapphire substrate using molecular beam epitaxy, Journal of Crystal Growth 652 (2025) 128047

Subham Mahanti

Indian Institute of Technology Bombay

Enhanced Avalanche Multiplication in Sub-micron WSe2 FETs via Asymmetric Schottky Contact Engineering

We demonstrate avalanche multiplication in sub-micron WSe₂ field-effect transistors (FETs) with asymmetric metal contacts, achieving a high multiplication factor (Mₘₐₓ ~ 10³) and low critical avalanche voltage (Vcr ~ 15 V) at room temperature. Devices were fabricated with platinum (Pt) and nickel (Ni) contacts to enable injection of electrons and holes, respectively, and were evaluated under four distinct configurations to study the influence of majority carrier type and Schottky barrier height. Avalanche multiplication is observed to be more pronounced when carrier injection occurs from the contact with a higher Schottky barrier—Pt for electrons and Ni for holes—suggesting that enhanced impact ionization arises from suppressed carrier injection and increased field asymmetry. The critical avalanche voltage remains nearly constant across varying gate biases, indicating that the observed current upturn originates from avalanche breakdown rather than ambipolar conduction. Under optical excitation, both Pt-e and Ni-h configurations exhibit strong photo response. Ionization rate analysis shows αₑ < αₕ, attributed to differences in effective mass, scattering rates, and band structure. This work presents the first direct comparison of avalanche behavior in WSe₂ devices based on both carrier type and contact metal, offering insight into contact-engineering strategies for next-generation, room-temperature 2D avalanche photodetectors.

Bora Kim

Daegu-Gyeongbuk Institute of Science and Technology (DGIST)

Selective Passivation of Wrinkle Defects in 1L-WSe2 Using TOPSe for Enhanced Optoelectronic Properties

Two-dimensional (2D) transition metal dichalcogenide monolayers (1L-TMDCs) have emerged as promising materials for next-generation electronic and optoelectronic devices. However, their practical applications are often hindered by structural defects, particularly one-dimensional (1D) line defects such as wrinkles and grain boundaries, which severely degrade their intrinsic optoelectronic properties. Despite efforts using small molecules and polymers, effective and selective passivation of line defects remains a critical challenge. In this work, we present a selective chemical passivation strategy for wrinkle defects in monolayer WSe2 (1L-WSe2) using trioctylphosphine selenide (TOPSe). Owing to the reduced steric hindrance and enhanced local electrostatic interactions, TOPSe preferentially reacts at wrinkled regions. Photoluminescence (PL) and femtosecond transient absorption microscopy (fs-TAM) measurements demonstrate that TOPSe treatment significantly reduces defect density at wrinkles, suppresses defect-related nonradiative recombination, and extends exciton lifetimes. Furthermore, Kelvin probe force microscopy (KPFM) shows increased local electron density at the passivated wrinkles, resulting in spatial homogenization of the conduction band and improved carrier transport in 1L-WSe2. Consequently, field-effect transistors (FETs) fabricated with TOPSe-treated 1L-WSe2 exhibit dramatic enhancement in device performance. These findings underscore the importance of line defect engineering in restoring the intrinsic optoelectronic properties of 1L-TMDCs and provide a novel approach for improving the performance of TMDC-based devices.

Yue Gong

Nanyang Technological University

Reconfigurable and Nonvolatile ferroelectric bulk photovoltaics based on 3R-WS2 for machine vision

Hardware implementation of reconfigurable and nonvolatile photoresponsivity is essential for advancing in-sensor computing for machine vision applications. However, existing reconfigurable photoresponsivity essentially depends on the photovoltaic effect of p-n junctions, which photoelectric efficiency is constrained by Shockley-Queisser limit and hinders the achievement of high-performance nonvolatile photoresponsivity. Here, we employ bulk photovoltaic effect of rhombohedral (3R) stacked/interlayer sliding tungsten disulfide (WS2) to surpass this limit and realize highly reconfigurable, nonvolatile photoresponsivity with a retinomorphic photovoltaic device. The device is composed of graphene/3R-WS2/graphene all van der Waals layered structure, demonstrating a wide range of nonvolatile reconfigurable photoresponsivity from positive to negative ( ± 0.92 A W−1) modulated by the polarization of 3R-WS2. Further, we integrate this system with a convolutional neural network to achieve high-accuracy (100%) color image recognition at σ = 0.3 noise level within six epochs. Our findings highlight the transformative potential of bulk photovoltaic effect-based devices for efficient machine vision systems.

Manavendra Pratap Singh

Indian Institute of Science

Anisotropic In-plane Thermal Conductivity of Freestanding Few Layer ReS2

Rhenium disulfide (ReS2) is a group VII layered semiconductor transition-metal dichalcogenide (TMDC). However, unlike other layered 2D materials, the initial study [1] indicated minimal effect of interlayer coupling on the optical, electrical, and vibrational properties. Recent studies also indicate strong and highly anisotropic responses of ReS2, which have applications in the control of optical fields [2,3]. Similar anisotropic behaviours have also been detected in the thermal characteristics of ReS2. Nonetheless, there are only a limited number of studies on the thermal conductivity of ReS2 [4,5]. Moreover, these studies focus on substrate-supported ReS2, where the substrate influences the thermal conductivity of ReS2. An extensive study on the thermal conductivity of freestanding ReS2, particularly for thicknesses below the 10 nm threshold, is currently lacking.

In this work, a few layers of ReS2 were prepared using mechanical exfoliation of bulk ReS2 crystals. Then, the selected ReS2 flake was transferred on a regular pattern of holes with diameters ~4 μm, which were created on SiO2/Si wafer using reactive ion etching. Linear polarization-dependent Raman measurements were performed to find the b-axis and cross b-axis of the flake. Using the temperature- and power-dependent Raman spectra taken along b-axis and cross b-axis, we calculated the anisotropic in-plane thermal conductivities. For the freestanding ReS2 flake, these thermal conductivities are observed to be 45.15 and 40.67 W/m-K along the b-axis and cross b-axis, respectively. The results presented here may open new avenues for the application of ReS2 as it will be a fantastic 2D material for thermoelectric applications.

References

1. Tongay, Sefaattin, et al., Nature communications, 5.1, 1-6 (2014).
2. Aslan, Burak, et al., Acs Photonics, 3.1, 96-101 (2015).
3. Webb, James L., et al., Physical Review B, 96.11, 115205 (2017).
4. Jang, Hyejin, et al. Advanced Materials, 29.35 (2017): 1700650.
5. Tahbaz, Sina, and Simone Pisana Journal of Physics: Materials, 7.1 (2024): 015014.

Manvi Verma

Indian Institute of Science

Digital Twin Enabled Modulation of Nucleation Density for Optimized 2D Material Synthesis

Chemical vapor deposition (CVD) is the leading technique for synthesizing single-crystalline two-dimensional (2D) materials[1], particularly for wafer-scale semiconductors and optoelectronic applications[2]. However, control of nucleation density[1] remains a fundamental challenge for large-area synthesis, as current methods generally lack a tunable experimental parameter to precisely control 2D nucleation. Moreover, CVD studies considering coupled mass, fluid, and heat transport profiles to infer the effect of process parameters on obtained growth are also critically missing.

We experimentally observe that a confined space substrate holder significantly modifies carrier gas velocity and 2D-MoS2 nucleation, leading to monolayer growth. To understand this intriguing observation and to quantitatively model the CVD process, we have created a hyper-realistic multiphysics computational fluid dynamics (CFD) based digital-twin of our CVD system[3]. Interestingly, space-confinement induced modifications in gas flow impact precursor delivery at the substrate, making precursor flux—a function of gas velocity, concentration, and gradients—the critical factor in controlling nucleation. Nucleation is suppressed by an order of magnitude in the space-confined region, experimentally verified by scanning electron microscopy, and supported by analytical calculations. Additionally, the digital twin predicts a significant time-lag between the set and actual growth temperature due to the substrate holder, which is nearly impossible to observe experimentally, and with immense implications on nucleation and growth. Our work offers a unique insight into controlling 2D material synthesis via precursor flux, especially on controlling the nucleation density. The digital-twin is independent of specific reactive species and enables predictive optimization of CVD process, offering a systematic pathway for large scale synthesis of 2D materials.

References [1] Dong Zhou et al., Cryst. Growth Des. 18 (2), 1012-1019 (2018). [2] Deep Jariwala et al., ACS Nano, 8 (2), 1102-1120 (2014). [3] Abhinav Sinha, Manvi Verma et al. (Preprint https://doi.org/10.21203/rs.3.rs-4957545/v1).

Jiwon Lee

Seoul National University

Large-Scale Growth of Indium Selenide with Phase Controllability

Two-dimensional(2D) ferroelectric materials, e.g. indium selenide, have attracted significant attention due to their unique properties, such as immunity to depolarization field and potential applications, such as high mobility transistors and non-volatile memory. However, large-scale growth of indium selenide film is still challenging, primarily due to stringent reaction conditions. In this study, we successfully synthesized centimeter-scale ultrathin, ferroelectric indium selenide film with phase controllability using the hypotaxy method. This method involves the downward growth of single crystal film beneath a graphene template, maintaining van der Waals crystalline alignment with the graphene. The grown indium selenide exhibits high crystallinity and robust in-plane and out-of-plane ferroelectricity at room temperature. Our findings suggest that incorporating indium selenide into ferroelectric semiconductor field-effect transistors(FeS-FETs) can lead to fabrication of the devices with high electron mobility and enhanced non-volatile memory performance.

Jaehyeok Lee

Seoul National University

Hypotaxial Growth of Ferroelectric Group-IV Monochalchogenides

Group-IV monochalcogenides (MXs, M = Ge or Sn; X = S or Se) are in-plane anisotropic two-dimensional (2D) materials featuring a puckered structure analogous to black phosphorus (BP) with alternating arrangement of metal and chalcogen atoms. In monolayer MXs, broken inversion symmetry and electronegativity differences between the constituent atoms induce in-plane ferroelectricity, positioning these materials as promising candidates for applications in bulk photovoltaic and synaptic devices. This ferroelectric property is particularly pronounced in monolayer or few-layer MXs, where the asymmetry in atomic structure is more distinct. Despite their unique properties, controlling thickness of MXs remains challenging due to their high interlayer binding energy. Here, we demonstrate growth of single-crystalline transition metal monochalcogenides (MXs), SnS, with high thickness controllability by our unique growth method, “hypotaxy.” (ref) In this experiment, we observed that SnS grew with orthorhombic structure and a thickness of around 15 nm aligned beneath the graphene. Our results demonstrate the feasibility of SnS growth through hypotaxy, and we aim to further refine this synthesis through additional experiments and process condition adjustments. This advancement will open opportunities for the development of diverse applications, such as photovoltaic and ferroelectric devices.

Abhay Agrawal

Chalmers University of Technology

Humidity-Enhanced NO2 Gas Sensing Using Atomically Sharp Edges in Multilayer MoS2

Ambient humidity remains a critical barrier in the realization of reliable NO₂ gas sensors operating at room temperature. In this work, multilayer MoS₂ structures with atomically precise zigzag edge terminations fabricated via electron beam lithography and followed by anisotropic wet etching are engineered to enable highly sensitive and selective NO₂ detection. The resulting sensors exhibit remarkable humidity tolerance at elevated temperatures and enhanced sensing performance at room temperature under ultraviolet (UV) illumination. Under UV exposure at 70% relative humidity, the device demonstrates a 33-fold increase in response and a sixfold improvement in recovery time when detecting 2.5 parts per billion (ppb) NO₂, relative to the performance under dry conditions (0% RH), yielding response values exceeding 1100%. The optimized platform achieves an estimated detection limit in the range of 4 to 400 parts per trillion (ppt). Density functional theory (DFT) calculations corroborate the critical role of MoS₂ edge sites in facilitating enhanced NO₂ adsorption and charge transfer. These findings underscore the potential of edge-engineered MoS₂ nanostructures for ultra-sensitive and selective NO₂ sensing in humid and complex environments, extending their applicability to real-world atmospheric monitoring.

Ajit Kumar Dash

Indian Institute of Science

Deterministic writing of single photon emitters via nanoindentation of monolayer TMDs on CMOS-compatible substrates.

Single photon emitters (SPEs) lie at the core of modern quantum technologies, including quantum communication, computing, and sensing. Defect and strain engineering of two-dimensional (2D) transition metal dichalcogenides (TMDs) can deterministically create SPEs ideal for quantum technology applications. SPEs can be written deterministically via atomic force microscopy (AFM) nanoindentation of monolayer TMDs on flexible polymer substrates [1]. However, polymer substrates are incompatible with CMOS technology and can modify SPE properties over time. Further, creating gated devices of SPEs on polymer substrates involves complex fabrication steps. This work [2] explores AFM nanoindentation of monolayer TMDs on SiO2/Si substrate (CMOS compatible) and studies the SPE nature of sharp bound exciton peaks originating from nanoindented sites. Then, we discuss the fabrication of gated devices of TMD-based SPEs on SiO2/Si substrate and study the evolution of SPEs with electrostatic doping. This technique is potentially applicable to other 2D semiconductors and would enable the integration of SPEs into practical quantum devices. [1] Rosenberger et al., ACS Nano, 13, 1, 904–912 (2019) [2] Dash, A.K., Jugade, S., Singh, A., et al. (manuscript under preparation)

Vilas Patil

Tyndall National Institute, University College Cork

Ambipolar Characteristic of TMDCs Field Effect Transistors

Due to their diverse structural, electri-cal, and optical characteristics, Group VI transi-tion metal dichalcogenides (TMDs) have been the focus of extensive study. These qualities may find use in electronics, spintronics, and optoelectronics. The chemical formula for sem-iconducting TMDs is MX2, where X is a chal-cogen and M is a transition metal (in the most well-known ones, M=Mo or W and X=S, Se, or Te). Molybdenum Ditelluride (MoTe2) has at-tracted significant interest in recent years be-cause to its distinct electrical characteristics and prospective use in nanoelectronics and op-toelectronics [1-3]. One major challenge in the field of 2D material-based electronic devices is the ability of achieving both n- and p-type de-vices, specifically required for complementary metal oxide semiconductor (CMOS) technolo-gy. Few layers of 2H MoTe2 flakes are ex-foliated on an 85nm SiO2/Si substrate using the scotch tape method followed by patterning source and drain Ni/Au metal electrodes (Fig. 1 inset). Through electrical characterization cor-related with theoretical simulations, this study evaluates the temperature-dependent electrical properties of MoTe2 back-gate field effect tran-sistors (FETs). Fig 1 demonstrates the transfer characteristic of the MoTe2 FET showing an ambipolar response, making this material very promising for CMOS technology. The ON cur-rent of the n-type device characteristic is slight-ly larger than the p-type device characteristic. The transfer curve showed significant hystere-sis, indicating a high trap state density at the MoTe2-SiO2 interface [4]. Atomistic-level in-sight into the carrier transport mechanism through the MoTe2 FETs, given the Schottky junction at the source and drain contact pads and MoTe2 channel interface, is gained through our density functional theory (DFT) calcula-tions. Our findings offer information on MoTe2’s temperature-dependent electrical char-acteristics, as well as its behaviour under vari-ous operating situations. Understanding these features is critical for the design and develop-ment of CMOS devices used in a variety of ap-plications, including high-temperature elec-tronics and thermoelectric devices.

Jean-Francois de Marneffe

imec vzw

Cleaning of Transition Metal Dichalcogenides using H2-based Transient Assisted Plasma Etching

Two-dimensional transition metal dichalcogenides (2D -TMDCs) such as WS2 and MoS2 materials have garnered significant interest as future channel materials in 2D materials-based devices, due to their high carrier mobility, great electrostatic gate control and tunable bandgaps (1-2 eV) [1]. The successful integration of TMDCs into CMOS processes is hindered by the presences of organic or polymeric contaminants on their surface, introduced by the material transfer and lithography steps. To address the issue of residual contaminants, scalable and efficient surface cleaning techniques must be developed. Plasma processing, a well-established industrial technology, has shown promise, especially with downstream plasma systems [2]. These systems effectively remove PMMA residues from surface while minimizing structural damage. However, precise process control is essential to maximize the selectivity towards WS2 and MoS2 monolayer and further reduce material degradation. In this study, poly (methyl methacrylate) (PMMA) films were spin coated onto monolayer WS2 and MoS2 surfaces, annealed at 160°C, above the glass transition temperature (110°C), and immersed in acetone for bulk PMMA removal. While this polymer cleaning method is common and widely used, trace residue in the nanometer range persists, badly contributing to the transport characteristics observed in TMDC-based devices.

In this work, PMMA-free TMDC surfaces were achieved by cleaning with transient-assisted plasma etching (TAPE) [3] and continuous wave (CW) plasma modes. Plasma conditions were optimized using various gas compositions, including argon (Ar), hydrogen (H₂), and ammonia (NH₃). The cleaning effectiveness and surface morphology were evaluated through Raman spectroscopy, photoluminescence (PL) and atomic force microscopy (AFM). Various plasma cleaning conditions were applied to WS₂ material, including TAPE Ar/H₂ at 1 and 5 Torr, CW Ar/H₂, CW H₂, and CW NH₃. TAPE mode at 1 Torr proved more effective in reducing PMMA residue (0.42 - 0.16 nm) and surface roughness. Interestingly, TAPE mode at higher pressure (5 Torr) showed less PMMA reduction (0.35 - 0.36 nm) and an unexpected increase in photoluminescence (PL) intensity, despite decreased surface roughness. This suggests that lower pressure yields a more efficient cleaning process in TAPE mode. Whereas CW H₂ plasma treatment effectively reduced PMMA thickness (<0.07 nm) but decreased PL intensity, indicating potential damage to the WS₂ surface. In contrast, CW NH₃ plasma preserved PL intensity, reduced PMMA to <0.1 nm, and maintained low roughness (Rq ~350 pm), providing effective cleaning without compromising material integrity.

[1] R. Younas, G. Zhou, and C. L. Hinkle, A perspective on the doping of transition metal dichalcogenides for ultra-scaled transistors: Challenges and opportunities, Appl Phys Lett 122, (2023). [2] D. Marinov et al., Reactive plasma cleaning and restoration of transition metal dichalcogenide monolayers, NPJ 2D Mater Appl 5, (2021). [3] A. Fathzadeh, P. Bezard, M. Darnon, I. Manders, T. Conard, I. Hoflijk, F. Lazzarino, and S. De Gendt, Transient-assisted plasma etching (TAPE): Concept, mechanism, and prospects, Journal of Vacuum Science & Technology A 42, (2024).

Babita Negi

RWTH Aachen University

High Gain Photodetection in Monolayer MoS2 over a wide temperature range

Molybdenum disulfide (MoS2), a two-dimensional (2D) transition metal dichalcogenide (TMDC), has recently been studied as a potential avalanche single photon detector because of its high impact ionization coefficient, especially in monolayers. Leveraging these properties, we demonstrate a monolayer (1L) MoS2 photodetector that achieves a detectivity of ~10^12 Jones and significant photocurrent gain of ~1.1×10^4. Notably, the device maintains its performance from room temperature down to 100 K. MoS2 films on sapphire were grown by metal-organic chemical vapor deposition (MOCVD) in an AIXTRON CCS® 2D R&D system using molybdenum hexacarbonyl (Mo(CO)6) and di-tert-butyl sulfide (S[C(CH3)]2 as precursors. The MoS2 monolayer films were transferred from sapphire onto a 90 nm SiO2/Si substrate through wet transfer. Interdigitated electrodes were defined by i-line photolithography and the unprotected MoS2 in the contact region was etched by tetrafluoromethane/oxygen (CF4/O2) reactive ion etching (RIE). Nickel/aluminum (Ni/Al) contacts of stack thickness 35/20 nm were formed by electron-beam evaporation, followed by lift-off to form the source & drain electrodes, with the edge contacts to the MoS2. Finally, the photoactive MoS2 channels were patterned by CF4/O2 RIE using another photoresist mask. Electrical characterization of the devices was performed under different temperatures using a cryogenic Lakeshore probe station under 10^(-6) mbar vacuum. A blue LED with a center wavelength ~460 nm was used as an illumination source. The output characteristics under dark conditions were probed at different back-gate voltages (Vgs), where a significant reduction in the dark current was observed under negative Vgs. It is attributed to a notable increase of the back-to-back Schottky barriers at the contacts. To further suppress the dark current, a constant Vgs = - 35 V was applied while the gate leakage current (Ig) was still at acceptable levels around 1 nA. The device was further measured at a gate voltage Vgs = -35 V across a temperature range from room temperature (293 K) to 100 K. We calculated the photoresponsive gain using the formula [G=(R.hc)⁄(q.λ.η)] by assuming a ~10% absorbance for monolayer MoS2. We observed that the gain persisted at least until 100 K, with a gain (G) of ~1.1×10^4 at room temperature. This is the highest gain for a MoS2 photodetector reported to date for the input light intensity range of 1 mW/cm^2. External responsivity (R) and detectivity (D) values of up to 400 A/W and 10^12 Jones were achieved at room temperature. These results show the potential of MoS2 for high-performance photodetectors with an optimal synergy between key parameters across a broad temperature range, potentially including avalanche photodetection. Our work paves the way further exploration of 2D TMDCs in low-temperature optoelectronic applications like photonic integrated circuits (PICs) for quantum computing. Keywords: MoS2, Photodetector, Gain

Alessandro Grillo

University of Manchester

All 2D Material Printed Diodes and Circuits on Paper for Sustainable Electronics

Sustainable electronics seek to minimize environmental impact by adopting eco-friendly materials, energy-efficient manufacturing methods, and recyclable components. However, many current strategies still rely on complex fabrication processes, scarce or unstable materials, and plastic substrates, raising sustainability concerns. Solution-processed two-dimensional (2D) materials offer a promising alternative: water-based and biocompatible conductive, semiconductive, and insulating inks can be produced through simple, scalable methods and printed directly onto biodegradable paper substrates. Despite this potential, the realization of fully printed 2D material-based diodes on paper remains a significant challenge.

In this work, we demonstrate the fabrication of fully printed 2D material diodes on paper substrates, employing Metal-Insulator-Semiconductor (MIS) architectures. Our approach utilizes water-based, biocompatible inks and ambient-condition processing, eliminating the need for high-vacuum techniques and precious metals. The resulting devices exhibit excellent electrical performance, including an on/off ratio exceeding two orders of magnitude and a forward current density of 1 mA/cm² at 1 V, along with mechanical robustness under 4% bending strain over 10,000 cycles. Furthermore, the diodes are successfully integrated into fully printed circuits on paper, incorporating 2D material-based resistors and capacitors. These results highlight a scalable and sustainable route toward environmentally friendly, disposable electronics.

Surabhi Suresh Nair

Khalifa University

Ultra Low Lattice Thermal Conductivity and Exceptional Thermoelectric Conversion Efficiency in Rippled MoS2

Molybdenum disulfide (MoS2) holds significant potential as a semiconductor for next-generation flexible thermoelectric modules, but its high thermal conductivity and low figure of merit have limited its commercial viability. In this study, we report a breakthrough, achieving a record-high n-type (p-type) thermoelectric figure of merit of 1.42 (1.25) at 1000 K, coupled with a thermoelectric conversion efficiency of 16% (14%) (along armchair direction), outperforming commercially available thermoelectric modules. Our first-principles calculations on rippled monolayer MoS2 show a transition from a direct to indirect band gap semiconductor at a rippling amplitude (r) of 1.0 and metal at r ≦3.0 Å. The maximum n-type Seebeck coefficient of 0.66 mV/K (0.59 mV/K) achieved along the armchair direction, at r = 0.5 Å (1.5 Å), at 1000 K is notable in the case of flexible thermoelectric materials. A high electrical conductivity contributes to an optimal power factor of 0.68 mW/mK2 along the armchair direction. The phonon dispersion reveals the dynamic stability of the system up to r = 1.5 Å. The forbidden gap between the acoustic and optical phonons branches reduces as r increases. An ultralow room temperature lattice thermal conductivity κl of 1.44 W/mK along the armchair direction is obtained at r=1.5 Å, which further reduces to 0.44 W/mK at 1000 K. The obtained value is 100 fold smaller than the room temperature κl of pristine monolayer MoS2 (144.60 W/mK). Our findings reveal a noteworthy n-type figure of merit (ZT) of 0.45 at 300 K (r = 1.50 Å) along the armchair direction, which is one order of magnitude more than the pristine monolayer MoS2. A significant thermoelectric conversion efficiency of 13%, taking a temperature gradient of 700 K, is obtained, outperforming Bi2Te3-based thermoelectric materials. These results highlight the potential of lattice distortions, which can be induced using bulged substrates, to drastically reduce the lattice thermal conductivity of MoS2 and other 2D materials, opening new possibilities for strain-engineered flexible electronic devices.

Xuerong Hu

University of Sheffield

Nanophotonic Structures made from Layered van der Waals Materials

Van der Waals materials have recently attracted intensive studies of their unique properties for nanophotonics. Compared with silicon, an attractive advantage of van der Waals materials is the flexibility of fabrication and easy integration with other systems, and possibilities of post-fabrication tuning. In addition, high refractive indices, attractive optical anisotropy phenomena, and low losses of van der Waals materials in the visible and near-infrared are critical for confining light to the photonic structures leading to stronger field and Purcell enhancement, which gives a promising platform to investigate the light-matter interaction phenomena and photonics applications. Here, we demonstrate high-performance nanophotonic structures using nanofabrication of thin-layer tungsten disulfide (WS2). Through mechanical exfoliation, thin (20-200 nm) films of WS2 can be deposited on Au, SiO2/Si and many other substrates. The common methods of electron-beam lithography (EBL) and chemical reactive ion etching (RIE) have been used for the fabrication processes. We found that high-performance structures can be formed when the designed structure is aligned with the crystal axis of WS2. Fig.(a-c) shows optical images in the bright and dark field as well as an SEM image of WS2 gratings on 300 nm SiO2/Si substrate, where we observed bound state in the continuum (BIC) optical modes using optical Fourier spectroscopy [Fig.(d)]. For WS2 nanopillar arrays on gold substrate, we realised perfect hexagonal pillars fabricated using “chemical” RIE etching [Fig.(e-g)]. We also realised WS2 topological photonic crystals on 1 µm SiO2/Si substrate [Fig.(i-j)] with triangle sides aligned with the crystal axis helping to achieve optimised triangle shapes. Here our highlight is observation of the topological edge state [Fig.(k)] and unidirectional light propagation. Our fabrication approach provides a way to achieve high-quality nanophotonic devices in a wide range of layered van der Waals materials.

Indrajeet Prasad

Indian Institute of Technology Goa

Measurements of absolute bandgap deformation-potentials of optically-bright bilayer WSe2

Gleb Tselikov

Emerging Technologies Research Center, XPANCEO

Tunable Laser Nanostructuring for van der Waals Materials

The emergence of layered van der Waals (vdW) materials, particularly two-dimensional transition metal dichalcogenides (2D TMDs), has unlocked transformative possibilities across energy, catalysis, nanophotonics, sensing, and biomedicine [1,2]. While advances in synthesis enable tailored compositions and properties, a critical bottleneck remains: the lack of a universal strategy to miniaturize and controllably tune the dimensional, morphological, and optical characteristics of vdW nanomaterials without compromising their intrinsic stability or composition in dispersed systems.
Here, we present a femtosecond laser-driven synthesis platform that addresses this challenge, enabling precise, scalable fabrication of colloidal nanoparticles (NPs) from vdW materials, with a focus on 2D TMDs. Our method achieves unparalleled control over NP morphology (10–150 nm), composition, and optical properties while preserving crystallinity and colloidal stability across >50 vdW systems. We demonstrate laser-generated nanostructures with various shapes, including fullerene-like, polygonal, and pyramidal geometries, alongside single-crystalline spherical MXenes and perovskite nanocubes. Molecular dynamics simulations reveal that cooling-rate-dependent heterogeneous/homogeneous nucleation governs crystallization, enabling tunable core-shell ratios and dimensions.
This breakthrough establishes femtosecond laser synthesis as a universal, versatile tool for engineering vdW-based nanostructures. By bridging the gap between scalable nanofabrication and property-specific design, our approach accelerates innovations in applications of vdW materials—from quantum emitters and nanophotonics to catalytic platforms—while opening avenues for unexplored functionalities in additive technologies. [1] Zotev, P. G. et al. Van der Waals Materials for Applications in Nanophotonics. Laser & Photonics Reviews 17, 2200957 (2023). [2] Oh, S.-H. et al. Nanophotonic biosensors harnessing van der Waals materials. Nature Communications 12, 1–18 (2021).

Daniel Gillard

University of Sheffield

Tuneable dark magneto-exciton-polaritons in CrSBr coupled to bound states in the continuum from a WS2 nanophotonic grating

Transition metal dichalcogenides (TMDCs) have been most commonly sought after due to their unique exciton properties in the monolayer regime. More recently, however, due to their naturally high refractive index and near-zero absorption at photon energies below the band-edge, along with ever-advancing fabrication and etching techniques, TMDCs have been frequently employed as a method of exploring the nanophotonic and topological playgrounds via etching of photonic crystals and lattices into large-area bulk TMDC flakes, raising a wide-ranging research topic with abundant exotic physical phenomena and photonic applications. Here we utilize a WS2 photonic grating to produce an optical bound state in the continuum (BIC). By coupling the photonic modes to the magneto-exciton of chromium sulfur bromide (CrSBr), we achieve a tuneable BIC polariton, with a Rabi splitting of 92 meV, inheriting an anisotropic B-field dependence from CrSBr, and vortex-like behaviour from the WS2 grating BIC. Combining these properties leads to B-field dependent non-linearity with stronger polariton-polariton interactions observed in the spin-aligned ferromagnetic regime at high fields, while limited interactions are observed in the low field antiferromagnetic regime.

Ashok Mondal

Sungkyunkwan University

Switching polariton screening in MoS2 microcavity towards polaritonics

Quasi-particle polaritons, blending light and matter, underpin advancements in photonics, optoelectronics, quantum computing, and the exploration of phenomena like Bose-Einstein condensation. Despite the known behaviors of exciton-polariton and trion-polariton in van der Waals transition metal dichalcogenides (TMDs), achieving electrical control over these polaritons remains a challenge, particularly for manipulating multiple polariton states and further tuning polariton screening in polaritonics. Here, We identify the electrical tuning of various polariton states within a monolayer of n-type MoS2 semiconductor, integrated within a microcavity and augmented with a transparent graphene gate-electrode, a hexagonal boron nitride insulator, and the MoS2 channel. We clearly observe photon-trion polaritons with distinct lower polariton branch (LPB) and upper polariton branch (UPB). This allows us to modulate the intensity and energy switchings via gate bias: at gate bias below threshold voltage, both polaritons are decoupled, and above threshold voltage, they are coupled to form LPB-UPB pair, and at high gate bias, complex polaritons (CPB) emerge due to polariton screening, a phenomenon consistent with Rabi splitting. We further identify distinct power fluence regimes in LPB, UPB, and CPB, which clearly featured a peculiar nonlinearity of a power exponents far exceeding one at intermediate power regime, well contrasted with conventional exciton dynamics. Our findings highlight the potential of electrically tunable polaritons in paving the way for next-generation photonic devices, quantum computing platforms, and studies into condensate phenomena.

Sebastian Buchberger

University of St Andrews

Investigating the influence of dielectric screening on the charge order instability in excitonic insulator candidate TiSe2

TiSe2 is a layered transition metal dichalcogenide, and it is long established that it exhibits an unconventional charge density wave (CDW) below a critical temperature of ~200K. However, the microscopic mechanism underlying this reconstructed ground state remains controversial [1,2,3]. In its normal state, TiSe2 exhibits a narrow indirect bandgap. Based on this electronic structure, the system was suggested to be an excitonic insulator, an exotic state in which the energy gain from the spontaneous formation of excitons drives the CDW transition [4]. However, since the electronic reconstruction is accompanied by a periodic lattice distortion, it was also argued that a less exotic structural mechanism may be responsible for the CDW. Thinning the material down to monolayer thickness provides new opportunities for testing these contradictory hypotheses. Assuming an excitonic mechanism, the charge ordered state should be highly sensitive to dielectric screening. To investigate this, we have developed the synthesis of high quality TiSe2 monolayers in epitaxial heterostructures with graphite, a highly screening metallic substrate, and with hexagonal boron nitride (hBN), the gold standard dielectric in the class of 2D materials. Due to the insulating nature of hBN, electronic structure measurements of the TiSe2/hBN heterostructure using angle resolved photoelectron spectroscopy (ARPES) are very challenging. However, by thinning the substrate down to a few 10 nanometres, we obtain high-quality μ-ARPES data on this TiSe2/hBN heterostructure. I will present the resulting temperature evolution of the CDW state in this system, and compare it to the reference system TiSe2/graphite to test the long-standing excitonic insulator claims in this material family. [1]PRL 99, 146403 (2007) [2]Nat.Mater. 13, 857 (2014) [3]PRB 103, 205108 (2021) [4]PRL 19, 439 (1967)

Jinying Wang

Nankai University

Spin torque in low-dimensional systems

To address the challenges of memory miniaturization and functionalization, we explore next-generation memory technologies based on quantum effects in low-dimensional systems. In collaboration with Intel, we employe density functional theory combined with the non-equilibrium Green‘s function method to systematically investigate two-dimensional (2D) bilayer heterostructures composed of 2D materials with strong spin–orbit coupling and 2D ferromagnets. We predict several 2D bilayer heterostructures, i.e., NbSe2/CrSe2, WTe2/CrSe2, MoTe2/VS2, exhibiting strong spin–orbit torque (SOT) effects and introduce a quality factor as a novel screening metric, which significantly accelerates the screening of high-torque candidates. This work provides key technical support for high-throughput screening and performance optimization of 2D heterojunctions (Small, 2024, 20, 2308965). We further extend the study of spin-torque effect to single-molecule systems, achieving preliminary microsecond-scale spin read/write operations and demonstrating non-volatile memory behavior.

Leonardo Cobelli

University of Padua

Weak Measurement of the Angular Goos-Hänchen Shift from a Monolayer MoS2 Immersed in a Dielectric Medium

Karolina Ciesiołkiewicz

Wrocław University of Science and Technology

Thermotransmittance spectroscopy of layered crystals using lab on fiber

Optical transmission is a key method for material characterization, allowing for simple determination of absorption spectra. Moreover, by introducing a modulated laser beam that evokes a perturbation in the material, photomodulated transmission spectra can be measured, which also enables the observation of optical transitions. Thinning vdWs crystals, such as MoS2, is often necessary to allow light transmission through higher-energy portions of the absorption spectrum, thereby revealing optical transitions A and B beyond the indirect absorption edge. However, this approach can be challenging. Optical fibers, through light confinement, offer here a solution by creating micro-laboratories that enable precise absorption measurements, even down to monolayers. In our study, we obtained the methodology of transferring TMDC materials on fiber tip and explored absorption properties of thin samples by observing excitons A and B. We also employed a backlight laser beam, which caused changes in absorption spectra through controlled heating, thereby providing insights into the effect of temperature variations within the sample. Furthermore, photomodulated transmission (PT) measurements using the lock-in technique were also conducted to observe the mentioned effects directly.

Seongmin Heo

Pohang University of Science and Technology (POSTECH)

Van der Waals Thin Film Transistors for Stretchable Electronics

With increasing demand for wearable devices, there is a critical need to transition from rigid electronics to soft, stretchable systems that closely adhere to human skin, enhancing comfort and usability. Stretchable displays, enabled by thin-film transistors (TFTs), are particularly promising as they offer skin-like flexibility, accommodating strains exceeding 50% while maintaining high electrical performance. Achieving this requires advanced materials and innovative fabrication processes. This study presents the development of stretchable TFT arrays utilizing van der Waals thin films based on two-dimensional (2D) transition metal dichalcogenides (TMDs). The research addresses crucial aspects such as manufacturing techniques, strategic material choices, and device architectures optimized for electronical and mechanical reliability. Additionally, essential design considerations including strain management, pixel integration, and robustness are explored to ensure stable device performance under mechanical deformation. These advancements demonstrate significant progress in stretchable display technology, paving the way for innovative wearable electronics and immersive augmented reality applications.

Ram Kumar

Indian Institute of Technology Kanpur

Strain induced structural changes and magnetic ordering in thin MoS2 flakes as a consequence of 1.5 MeV proton ion irradiation

Nohyoon Park

Daegu Gyeongbuk Institute of Science and Technology (DGIST)

Spatially Varying Excitonic Behavior in CVD-grown MoS2

Two-dimensional transition metal dichalcogenides (2D-TMDs) have attracted significant attention in electronics, photonics, and catalysis due to their remarkable mechanical, optical, and electronic properties. However, despite their striking physical and chemical properties and promise of a broad range of applications, fully unlocking their potential remains a challenge. One of the limitations is an incomplete understanding of their spatially varying excitonic behavior within atomically thin TMD flakes. In this study, we investigate the spatially varying exciton dynamics in CVD-grown monolayer MoS₂ using femtosecond transient absorption microscopy (fs-TAM). Interestingly, our results reveal distinct optical properties between the edge and interior regions of the flake. Region-selective transient absorption spectra showed that while both A and B exciton resonances appeared at both regions, their relative exciton band intensities varied markedly. At the edge of the flake, the A exciton band was dominant, with an amplitude 2.5 times greater than that of the B exciton. In contrast, at the interior of the flake, the A exciton band was substantially suppressed while the B exciton remained unchanged. This spatial varying exciton feature was further visualized in a false-color fs-TAM map at 650 nm, where the A exciton signal is localized to the edge and decays within 10 ps. These findings suggest that A and B excitons behave independently and are differentially affected by their local environments, with A excitons preferred at the flake edge. This region-dependent exciton behavior has significant implications for the design and optimization of TMD-based optoelectronic devices. Further studies into the structural and defect-related variations across the flake are necessary to uncover the origin of this spatial heterogeneity.

Sheng Pei

The Hong Kong University of Science and Technology (HKUST)

CVD-Grown Twisted Bilayer MoS2 for Tunable Non-liner Optics

Twisted bilayers transition metal dichalcogenide (TMDs) have an extra degree of freedom to modulate the properties of the material, leading to a variety of fascinating phenomena, which is called twistronics. The Moore superlattice caused by the twist angle leads to a unique electronic structure that provides an excellent platform for condensed matter physics studies. However, direct growth of twisted bilayers TMDs is challenging due to its thermodynamic unfavorable. Different from previously adopted two-step folding/tranfer method, here we propose a novel CVD method to control the twisted growth of the second layer MoS2 by altering the S/Mo ratio during the growth process, resulting in a series of twist angle in the range of 0-60°. Raman and photoluminescence spectroscopy show twist angle-dependent optical properties, and the Second Harmonic Generation is also altered by the symmetry breaking of the material. .This work presents a new insight into the direct growth of twisted TMDs and the application of nonlinear optics.

Beatriz Alba Sangrós

Institute of Molecular Science (ICMol), University of Valencia (UV)

Chiral functionalization of 2D materials

The induction of chirality in optically and electronically active materials is of great interest for applications in sensing and quantum information transmission. Two-dimensional (2D) materials, such as transition metal dichalcogenides (TMDs), exhibit exceptional electronic and optical properties but are inherently achiral. In particular, molybdenum disulfide (MoS₂) has attracted considerable interest due to its unique properties, including its direct bandgap semiconductor nature, high flexibility, and tunability. These characteristics significantly enhance its potential applications in optoelectronics and spintronics.[1] Due to their high aspect ratio and planar morphology, the preparation of chiral 2D nanomaterials could open new opportunities for the development of chiroptical sensors, materials for valleytronics, and other emerging applications. Moreover, chirality plays a fundamental role in numerous chemical and biological systems, making this research highly relevant to fields such as nanobiotechnology, nanomedicine, and nanotoxicology.[2], [3] Previous works have studied the possibility to achieve this kind of materials by functionalizing MoS2 with chiral molecules containing a thiol group such as penicillamine.[2], [3] In this work, we demonstrate the induction of chirality in monolayers of MoS₂ through functionalization with chiral molecules such as cysteine, a thiol-containing molecule. Liquid phase exfoliation of MoS₂ and the posterior functionalization with this chiral ligand in aqueous solution results in 2D nanosheets exhibiting strong circular dichroism signals.

REFERENCES: [1] W. Huang, L. Gan, H. Li, Y. Ma, and T. Zhai, “2D layered group IIIA metal chalcogenides: Synthesis, properties and applications in electronics and optoelectronics,” Royal Society of Chemistry, 2016. [2] F. Purcell-Milton et al., “Induction of Chirality in Two-Dimensional Nanomaterials: Chiral 2D MoS2 [3] Nanostructures,” ACS Nano, vol. 12, no. 2, pp. 954–964, Feb. 2018. Y. Wang, Y. Zhu, H. Yan, Y. Li, Y. Wang, and M. Chhowalla, “Chiral two-dimensional MoS2 by molecular functionalization as ultra-sensitive detectors for circularly polarized light,” 2024.

Yifu Chen

The Hong Kong University of Science and Technology (HKUST)

CVD Growth and Transformation of ZrS2 for High-k ZrO2 Dielectric Integration in 2D Electronics

This project focuses on developing high-κ zirconium dioxide (ZrO₂) dielectric layers via chemical vapor deposition (CVD) for integration with two-dimensional (2D) semiconductor devices. The research is divided into two main parts: (1) studying the CVD growth mechanisms of layered zirconium sulfide (ZrS₂), which serves as a template or precursor material, and (2) achieving controlled synthesis and structural engineering of ZrO₂ thin films through either direct CVD processes or in-situ oxidation of pre-grown ZrS₂. These efforts aim to establish a reliable route for producing high-quality ZrO₂ dielectrics compatible with 2D materials.

Gyu Lee

Yonsei University

Anomalous Au/n-MoSe2 Contact engineering for Both Schottky and Ohmic-like Device Operation

Two-dimensional materials such as graphene and transition metal dichalcogenides continue to attract interest due to their advantages for overcoming silicon systems scailng limits. Also their metal contact interfaces are being studied for superior performance devices. Here, we report our findings regarding interface dipole effects at Au/n-MoSe2 contact, that Bottom Au contact beneath n-MoSe2 shows Ohmic-like behavior while top Au contact apparently shows Schottky contact by sputtering damage. Ordered and disordered interface dipoles at the Au/n-MoSe2 contact explain such Ohmic-like and Schottky behavior respectively. We fabricate vertical Schottky diode form from Au/MoSe2/Au assembly and each contacts field effect transistors (FETs), so we report each contacts Schottky barrier difference with each contacts by low temperature measurements.

Henry Nameirakpam

Uppsala University

Realizing Large-Scale 2D Semiconducting Circuits on Diamond for Quantum Technology

Integrating molybdenum disulfide (MoS2) with diamond could lead to new device architectures for quantum processors. This work investigates the electrical transport properties of MoS2 directly grown on a single-crystal diamond substrate using ionic liquid gating. Our study demonstrates the first field-effect transistor (FET) of Chemical Vapor Deposition (CVD) grown MoS2 on (100) single-crystalline chemical vapor deposition (SC-CVD) diamond, marking a significant step towards integrating diamond technology with two-dimensional (2D) semiconductors. We achieved uniform, large-scale, and selective MoS2 growth on the diamond, potentially enabling advanced device fabrication. Our work addresses the key challenge of directly growing MoS2 on a functional substrate such as diamond, promising for next-generation quantum technologies.

Mahmoud M. H. Hammo

Technische Universität Dresden

Controllable Synthesis of CrCl3/MoS2 and NbS2/MoS2 van der Waals Heterostructures By CVT and CVD approaches

Controlling the layer-by-layer chemistry and structure of nanomaterials remains a crucial focus in nanoscience and nanoengineering. In particular, the integration of atomically thin MoS2 with either antiferromagnetic CrCl3 or metallic NbS2 two-dimensional materials offers exciting prospects for next-generation technologies. In this study, we employ two distinct synthesis approaches to fabricate high-quality van der Waals (vdW) heterostructures. First, we demonstrate the use of chemical vapor transport (CVT) as a novel route to synthesize high-crystalline CrCl3/MoS2 heterostructures on c-sapphire (0001) substrates. Notably, these heterostructures exhibit remarkable strain resistance, preserving their intrinsic properties. Second, we achieved the growth of highly crystalline NbS2/MoS2 vdW heterostructures on SiO2/Si substrates via atmospheric pressure chemical vapor deposition (APCVD). Each synthesis step is carefully optimized to control key parameters, including precursor amount, growth temperature, flow rate, and deposition time, ensuring precise layer formation. The resulting heterostructures exhibit sharp and well-defined crystal edges, indicative of high-quality interfaces. Raman spectroscopy, AFM and HRTEM confirm the monocrystalline character and precise structure of these layered nanomaterials, which their intrinsic properties are preserved. This can pave the way for next-generation applications, particularly in valleytronics, opto-spintronics, and quantum information processing.

Hancheng Ma

The Hong Kong University of Science and Technology (HKUST)

A Strategy for Transition Metal Chalcogenides Synthesis using Sequential Selenium Substitution

The direct synthesis of wafer-scale single-crystal transition metal dichalcogenides (TMDs) at relatively low temperatures and atmospheric pressure remains challenging, albeit the enormous potential applications as semiconductors. In this work, we demonstrate the feasibility of using single-crystal 2H-MoTe2 films as templates, followed by a sequential selenium substitution reaction to synthesize a variety of other TMDs and their heterostructure. We demonstrate the successful synthesis of vertical MoSe2/MoTe1.74Se0.26/MoSe2 heterostructure, as long completely with conversion to single-crystal 2H-MoSe2. We also demonstrate the synthesis of a MoTe2/MoSe2 lateral heterostructure with various substitution temperatures for Se substitution in 1T’ and 2H phase MoTe2. Computational results illustrate that Se substitution is likely to start at Te vacancy sites, where generated strain lowers the energy barrier for further substitution, leading to a chain reaction that propagates until the entire layer is selenized. The obtained MoSe2 shows a high hole mobility of 32 cm2 V−1 s−1, comparable to the 2.8–31.6 range from mechanically exfoliated samples. Consequently, this MoSe2-based photodetector shows a comparable responsivity of 41 mA W-1 under near-infrared (1060 nm) illumination. This controllable chalcogen substitution method provides a new way for large-scale synthesis of single-crystal TMDs and their heterostructures aimed at industrial applications.

Jun Wang

The Hong Kong University of Science and Technology (HKUST)

Direct Growth of Wafer-scale Epitaxially aligned Single-crystal 2D Transition Metal Dichalcognide Arrays

A critical challenge hindering the practical adoption of transition metal dichalcogenides (TMDs) in next-generation electronics is to achieve scalable, epitaxial single-crystal growth across wafer-scale substrates. To address this limitation, we present a direct growth in confined space for synthesizing aligned wafer-scale, single-crystal 2H-MoTe2 arrays. By precisely regulating pattern dimensions to control nucleation kinetics, we confine the nucleation process to a single site at the individual micro-pattern, leading to a single-crystal 2H-MoTe2 pattern. Notably, this synthesis strategy exhibits universal applicability across arbitrary pattern geometries and commercially viable substrates—including amorphous SiO2, crystalline silicon, and sapphire—due to its substrate-independent growth mechanism. Fabricated field-effect transistor (FET) arrays based on the synthesized 2H-MoTe2 demonstrate exceptional electrical uniformity with carrier mobility exceeding 50 cm2 V−1 s−1 and responsivity of 37.1 mA W-1. Our approach establish a new pathway for semiconductor chemisty that lead for the industrial application of TMD materials.

Zikun Tang

The Hong Kong Polytechnic University

The emergence of robust ferroelectricity and colossal anomalous hall effect in 2D chromium chalcogenide

Multiferroics exhibit both ferroelectricity and magnetism, breaking spatial inversion and time-reversal symmetries, leading to novel physical phenomena. Unlike fundamental interactions in particle physics, symmetry breaking in multiferroics occurs spontaneously at phase transitions and can be controlled. Advances in multiferroics have led to strong magnetoelectric responses, new materials, and potential applications in energy-efficient devices.

Chakradhar Sahoo

Aarhus University

Direct view of doping controlled band alignment across the lateral heterostructures

Deepa Thakur

Uppsala University

Sustainable Chemical Passivation of Two-dimensional Semiconductors for Optoelectronics

Navkiranjot Kaur Gill

Indian Institute of Science

Moire ferroelectricity-enhanced optoelectronic response in an all-2D van der Waals hybrid

Ferroelectricity in marginally twisted transition metal dichalcogenides (TMDCs) is a phenomenon emerging from electrical polarization in the moiré domain [1][2]. The artificial moiré superlattice comprises alternating MX and XM (M: metal, X: Chalcogen) triangular domains separated by shear strain solitons. These domains have broken mirror symmetry, which generates an out-of-plane electric dipole moment, which is opposite in direction in each domain, essentially giving rise to a moiré domain antiferromagnetic (MDAF) system in the moiré length scale. We investigate the optoelectronic potential of these near 0° twisted TMDCs, which have a ferroelectric domain network that can be tuned with an out-of-plane electric field and are remarkable light absorbers. In this work, we fabricate dual-gated Graphene-twisted WSe2 edge contacted heterostructure. These hybrids exhibit ultrahigh photoresponse, which we attribute to an additional electric field from the ferroelectric layer. Compared to non-ferroelectric 2H-WSe2 in edge-contacted geometry, these hybrids exhibit multifold increase in responsivity, and the responsivity values are of similar order to those of surface-contacted Gr-TMDCs photodetectors where the potential step at metal-Graphene interface helps with the charge transfer [3][4]. In addition to ultrahigh responsivity, the charge dynamics at the interface also get modified depending on the polarization of the ferroelectric layer. This work underlines the functionality of twisted WSe2 as a photosensitive layer and a ferroelectric layer, providing an additional electric field that modifies the charge dynamics and optoelectronic response in these Vander Waal hybrids. References [1] Weston, Astrid, et al. Nature nanotechnology 17.4 (2022): 390-395. [2] Wang, Xirui, et al. Nature nanotechnology 17.4 (2022): 367-371. [3] Roy, Kallol, et al. Nature nanotechnology 8.11 (2013): 826-830. [4] Lee, Eduardo JH, et al. Nature nanotechnology 3.8 (2008): 486-490.

Abhijith M B

Indian Institute of Technology Kharagpur

Dopant driven modulations and magnetic signatures in CVD grown Tungsten Selenide (WSe2)

Engineered 2D materials are at the vanguard in deploying structurally novel, property specific and application driven materials. 2D TMDC’s comprising of selenides of W, Mo, V, Nb have been known to exhibit interesting material phenomena like layer dependent optical properties, 2D magnetic ordering, superconductivity to name a few. CVD grown 2D materials are known for their production scalability, atomic layer thicknesses and pristine nature. Doping, widely prevalent in the silicon industry is a fascinating way to impart new attributes to chemical species. In-situ doping in CVD grown samples opens new avenues in engineering materials by tuning properties like structural phases, optical properties, electronic mobility and emergent magnetic traits. Here, we study dopant instigated changes in CVD grown WSe2 on introducing Nb in the system. The precursor evaporation dynamics that resonate in the crystallinity and quality of flakes is explored through vibrational mode shifts and varying FWHM, these subtle changes probed through Raman spectroscopy. STEM analysis investigates the intrinsic nature of the doping process. Magnetic studies point to emergent magnetic properties corresponding to weak ferromagnetic states superimposed over paramagnetism. Density functional theory calculations try to unearth the role of surface adsorbed dopants in magnetism. These findings strengthen our understanding of peculiar behaviors in materials and open possibilities of introducing novel properties in non-magnetic semiconducting materials.

Biswajeet Nayak

Indian Institute of Technology Kharagpur

Fabrication of electronic-grade 2D transition metal dichalcogenides via Chemical Vapor Deposition method

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are widely recognized for their exceptional electrical and optical properties, making them promising candidates for next-generation electronic and optoelectronic applications. Despite numerous proof-of-concept demonstrations, the synthesis of electronic-grade, large-area 2D TMDs with controlled thickness, uniformity, and doping remains a significant challenge. Persistent issues such as low carrier mobility, unintentional defects, and process variability continue to limit their practical integration. In this work, we fabricated large-area electronic grade WSe₂ and Nb-doped MoSe₂–WSe₂ lateral heterostructures using a water-assisted chemical vapor deposition (CVD). The growth process was meticulously optimized by tuning CVD process parameters and carrier gas composition to control domain size, crystalline quality, and layer thickness. Raman and photoluminescence spectroscopy confirm the high optical and structural quality of the synthesized heterostructures. Electrical transport measurements reveal that pristine WSe₂ exhibits robust p-type behaviour with Ion/off ratio of ~10 9. The Nb-doped MoSe₂ domain within the MoSe₂–WSe₂ lateral heterostructure demonstrates a transition from the previously reported n-type to ambipolar characteristics. Remarkably, this ambipolar behavior in the MoSe₂ domain can be effectively tuned by applying an external bias across the source and drain, offering dynamic control over carrier type and density. The intentional Nb doping in MoSe₂ enables precise modulation of electron concentration, yielding a lightly doped n⁻- region critical for forming clean junctions with adjacent p-type WSe₂, thereby enhancing charge separation efficiency. Our findings highlight the potential of such laterally integrated p–n⁻ junctions in 2D TMDs for the realization of high-performance, scalable optoelectronic devices, including photodetectors, diodes, and logic circuits. Furthermore, the optimization of metal contacts, tailored to each TMDs, significantly improves device performance, underscoring the crucial role of interface engineering in advancing 2D material-based device architectures.

Xiao Liu

University of Cambridge

Nanoscale tunable downscaling of 2D materials for electronics using atomic force microscopy

Field-effect transistors based on two-dimensional (2D) materials are widely considered as the building blocks of next-generation ultra-miniaturized electronics owing to their atomic thickness and electrical performance. However, they have yet to meet their potential due to the lack of reliable further downscaling fabrication and processing techniques at the nanoscale. Here, a method to scale down the size of 2D materials-based transistors to sub-10nm by atomic force microscopy (AFM) has been proposed. We utilize the extremely high precise positioning of AFM to tailor the surface of 2D materials under ambient conditions. Compared with the conventional patterning technologies: photo- and electron-beam lithography, this method has a higher ultimate resolution, as well as fewer defects, is contamination-free, as well as allowing in-situ device nanoscale modification and measurement.

Owen Wolley

University of Sheffield

Second harmonic generation enhancement through bound in the continuum states in 3R MoS2 gratings

Second harmonic generation enhancement through bound in the continuum states in 3R MoS2 gratings Owen Wolley1,, Xuerong Hu1, Yadong Wang1, Oscar Palma Chaundler1, Yue Wang2, Alexander I. Tartakovskii1, 1School of Mathematical and Physical Sciences, University of Sheffield, Sheffield, UK 2Department of Physics, University of York, York YO10 5DD, UK *owolley1@sheffield.ac.uk, *a.tartakovskii@sheffield.ac.uk Second harmonic generation (SHG), relying on second order nonlinear susceptibility c(2), requires a lack of inversion symmetry and a material with low optical losses. Combining strong nonlinearity with a high refractive index allows realisation of compact devices for SHG, as shown in our work. We employ 3R phase of molybdenum disulfide (MoS2), a high-refractive-index layered transition metal dichalcogenide (TMDs) from a class of so-called van der Waals crystals that recently emerged as promising materials for nanophotonics. In monolayer form, due to the lack of inversion symmetry, many TMDs show exceptionally high c(2), which is however not observed for most bulk TMDs as they are centrosymmetric crystals [1]. The non-centrosymmetric 3R MoS2 is a rare exception from this rule, representing a promising platform for nanophotonic structures with strongly enhanced c(2) [2]. We fabricate one-dimensional lattice structures (gratings) from exfoliated 3R MoS2 flakes (with thicknesses 30-120 nm) which host tuneable bound in the continuum states (BICs) and achieve giant enhancement (>300 fold) of the SHG signal of the grating structures resonantly excited into the BIC state compared to an unpatterned region of the flake. We observe the highest absolute SHG intensity when the BIC modes are tuned in resonance with the c(2) maximum of the material around 900 nm and show strong dependence of the maximum SHG signal on the orientation of the grating with respect to the crystal axes of the material. We further enhance the SHG signal by placing 3R MoS2 flakes on a silver mirror covered with 25-nm SiO2 thus allowing resonant enhancement of the signal at 450 nm and optimising the SHG signal collection above the grating. Our approach provides a promising route for enhancing optical nonlinear processes in van der Waals materials and highlights the potential of TMDs for applications in nonlinear nanophotonics.

References

1. Autere, A. et al. Nonlinear optics with 2D layered materials. Adv. Mater. 30, 1705963 (2018).
2. Shi, J. et al. 3R MoS2 with broken inversion symmetry: a promising ultrathin nonlinear optical device. Adv. Mater. 29, 1701486 (2017).

Justin Boddison-Chouinard

University of Ottawa, National Research Council Canada

Valley polarized transport in monolayer WSe2 quantum structures

Challenges associated with the quality of electrical contacts in semiconducting transition metal dichalcogenides have hampered the progress of transport studies, especially at low temperature and in the low carrier density regime.

In this poster, we present a device structure for achieving low resistive ohmic contacts that relies on the independent tunability of the carrier density in the contact region. We demonstrate that these low resistive ohmic contacts survive at temperatures as low as 10 mK and can successfully be used in transport measurements to probe a channel region down to the low carrier density regime.

We also present transport measurements of a gate-defined 1D channel in monolayer tungsten diselenide (WSe2)and discuss the origins of an unexpected valley-spin polarization at zero magnetic field.

Finally, we report magneto-transport measurements of a WSe2 heterostructure performed in perpendicular magnetic fields up to 8 T. We discuss the appearance of a Landau fan diagram in which we observe fully valley-spin polarized hole transport at low filling factors all the way down to a filling factor of ν = 1. Finally, we discuss the behaviour of the Landau fan diagram at higher densities, reflecting the spin-orbit coupling effects in monolayer WSe2.

Jinghan Shen

The Hong Kong University of Science and Technology (HKUST)

Sulfur-assisted metal doping in hexagonal boron nitride towards an insulator-to-semiconductor transition

Hexagonal boron nitride (hBN) is a versatile 2D material with exceptional properties such as high thermal conductivity, chemical stability, and mechanical strength. However, its large bandgap limits its practical applications in electronics and optoelectronics. In this study, we explore a novel approach to modulate the bandgap and conductivity of hBN through sulfur (S) and tin (Sn) doping. Using a chemical vapor deposition (CVD) method, we successfully transitioned hBN from an insulating to a semiconducting material. S-doping introduces donor states near the conduction band, enabling n-type conductivity, while Sn-doping creates impurity states closer to the Fermi level, resulting in p-type behavior. The co-doping mechanism was further analyzed through X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electrical performance measurements, showing significant changes in bonding characteristics and enhanced conductivity. Additionally, we investigate the impact of doping on the electronic structure of hBN, revealing how Sn-induced impurity states influence the material’s band structure. This research bridges the gap between theoretical predictions and experimental findings, offering new insights into heavy-element doping in hBN and paving the way for the development of high-mobility p-type transistors and n-type quantum emitters. Our findings suggest that sulfur and tin doping could significantly enhance the tunability of 2D materials for future electronic and optoelectronic devices.

Bhumit Luhar

Indian Institute of Technology Mandi

Room Temperature Defect-bound Excitons in V-doped WS2 Monolayers

Localized and defect-bound excitons in monolayer transition metal dichalcogenides are the subject of enormous interest and intense research due to their wide range of applications in sensors, quantum light-emitting diodes, and other quantum technologies. Impurity-induced in-gap states provide a platform for achieving the desired optical response from the two-dimensional TMDs. Previous reports emphasize that doped and disordered structures induce defect-bound excitonic emission. However, a distinct and prominent feature in photoluminescence had only been observed at cryogenic temperatures, and realizing it at room temperature remains challenging. Here, we report a non-trivial prominent defect-bound excitonic feature at room temperature ~120-130 meV below (~670 nm) the characteristic emission line in the V-doped WS2 monolayer. V-doping introduces gap states, causing the trapping of carriers and resulting in distinct emission lines apart from conventional emission. While optimizing the dopant concentration, the defect feature starts dominating the luminescence in spectral weight, which appears the same in amplitude. Further systematic investigations of PL unveil the rise and dynamics of defect-bound excitons with increasing dopant concentration. The investigation opens a path to realize distinct and stable defect-bound excitonic lines at room temperatures and demonstrates the use of chemically doped 2D materials for optoelectronic applications.

Manoj Kumar B

Birla Institute of Technology and Science (BITS)

Vertical p–n junction of MoS2 with h-BN Spacer for Enhanced Photocarrier Generation

Sudipta Majumder

Indian Institutes of Science Education and Research (IISER)

The Role of Defects in Achieving High Mobility in MoS2 Monolayers

Defects in semiconductors play a crucial role in modifying their electronic structure and transport properties. In transition metal dichalcogenides (TMDs), atomic chalcogen vacancies are among the most common intrinsic defects. While their influence on electrical transport has been widely explored, their precise role remains not fully understood. In this work, we investigate the impact of chalcogen vacancies in monolayer MoS2 grown by chemical vapor deposition, employing a combination of optical spectroscopy, low-temperature electrical transport measurements, scanning tunneling microscopy (STM), and first-principles density functional theory (DFT) calculations. We specifically focus on disulfur vacancies and demonstrate their significant role in modulating the electronic properties of MoS2. These vacancies introduce shallow donor states near the conduction band edge, which facilitate electron hopping conduction—a mechanism supported by both low-temperature transport data and spatially resolved STM measurements. DFT simulations further reveal that the defect-associated states are relatively delocalized, enabling n-type doping and enhanced conductivity. This defect-assisted transport mechanism accounts for the high field-effect mobility observed in these samples, often exceeding 100 cm² V⁻¹s⁻¹. Our results provide a clearer picture of how native defects influence charge transport in 2D materials and highlight the potential of defect engineering as a powerful strategy to tailor the performance of TMDs for electronic and optoelectronic applications.[1]

[1] Majumder, Sudipta, Sarika Lohkna, Vaibhav Walve, Rahul Chand, Gokul M. Anilkumar, Sooyeon Hwang, G. V. Pavan Kumar, Aparna Deshpande, Prasenjit Ghosh, and Atikur Rahman. “Unveiling the Correlation between Defects and High Mobility in MoS2 Monolayers.” ACS Applied Materials & Interfaces (2025).

Ye Joo Kwon

Sookmyung Women's University

Crystallinity and Layer-Controlled Growth of MoS2 Thin Films via Substrate Engineering

Jishnu Ghosh

Indian Institute of Science

Coexistence of Negative Differential Resistance and Resistive Switching in 2D FeS-FET

In2Se3 is recently discovered ferroelectric semiconductor which holds immense potential in nanoelectronics and allied applications. The inherent polarization property along with semiconductor nature made it a desired candidate for FeS-FET( Ferroelectric semiconductor field effect transistor) , FTJ( ferroelectric tunnel junction), Different semiconductor heterostructures and non-volatile memory applications. All these works exploited the polarization property of In2Se3 which can be altered by applying external electric field. Along with tuneable polarization property it also exists in different polymorphs (Alpha, Beta, Gamma) which makes it a good candidate for Phase Change Memory devices. In this work for the first time, we observed the Coexistence of Negative Differential Resistance and Resistive Switching mediated by Polarization Modulation of a In2Se3 based back-gated FeS-FET device. The observed NDR is also Gate tuneable and consistent in all temperature range. Since the discovery of the Esaki tunnelling diode, the negative differential resistance (NDR) effect has been widely applied in designing various devices such as logic switches, computer memory, and high-frequency oscillators. In addition to typical semiconductor-based tunnelling diodes vertically integrated two-dimensional (2D) layered van der Waals (VdW) heterostructures has also been used that involve the recently well-studied 2D transition metal dichalcogenides (TMDs) like MoS2-MoTe2, MoS2-WSe2, and MoS2-WSe2-graphene. However, to simplify the fabrication process and to have more practical applications in the future, it is better to possess the NDR effect at room temperature using a single type of material via a simple method. In this work we fabricated a planar transistor using Alpha phase Indium Selenide (2H- In2Se3) which is very much compatible with existing CMOS circuitry and process flow. Ferroelectric materials exhibit a spontaneous polarization in the absence of an external electric field. This polarization can be reoriented by ion displacement in the crystal, and polarization switching can be triggered by an external electrical field such that ferroelectric materials can have different conductance state. Our experiment shows that this NDR phenomenon occurs as an intermediate event during the switching process between two different conductance states. This polarization modulated NDR phenomenon is quite different from other NDR devices in terms of mechanism. The subtle atomic configuration of the central Se atom in Se-In-Se-In-Se sequence leads to emergence of ferroelectricity in In2Se3 and a unique correlation between the Out-Of-plane and In-Plane dipoles. In our back-gated architecture we explored this interlocking between the OOP and IP polarization to achieve NDR and Resistive Switching through a vast range of Gate and Drain voltages. Further High-resolution TEM studies reveal the detailing of polarization reversal process which includes Structural change of the material at different zones of the channel. To explore the possible changes in the microstructure TEM studies was done in Pristine sample as well as in samples after biasing with back-gate. A high density of stacking defects, along with Moire patterns were observed. Furthermore, Sliding between layers and dislocation of atoms were detected which could be associated with charged defects that couple to lateral electric field, providing a mechanism to drive polarization changes with Drain-Source biasing. Such defects alters both carrier concentration and mobility leading to change of conductance along the channel. We also observed a unique zipping and unzipping mechanism between Van der wall layers in channel region. Diverse electrical measurements at different ambient conditions along with TEM studies in this work will be helpful to understand the actual mechanism of polarization modulation and future application of In2Se3 based nanoelectronics devices.

Sunny Park

Sookmyung Women's University

Scalable synthesis of single-crystal Cu for high-quality 2D materials growth

You Peng

Peking University

Highly Stable Vertically Oriented 2H-NbS2 Nanosheets on Carbon Nanotube Films toward Superior Electrocatalytic Activity

2D metallic transition-metal dichalcogenides (MTMDCs) have attracted widespread research interest in the exploration of fundamental physical issues and energy-related fields. Although relatively high catalytic activity has been predicted theoretically in the new type MTMDCs-based electrocatalysts, their hydrogen evolution reaction (HER) performance is severely hampered by the insufficient catalytic stability due to structural degradation during long-time use and limited active sites in planar electrode structures. Herein, the scalable synthesis of vertically-oriented 2H-NbS2 nanosheets is reported on low-cost carbon nanotube (CNT) film substrates by a facile chemical vapor deposition route. The 3D vertically-oriented 2H-NbS2 nanosheets present abundant edge active sites and strong interface coupling with CNT thus possessing exceptional mechanical stability. These features impart the 3D nanosheets catalysts with remarkably low overpotentials of ≈55 mV at 10 mA cm−2 and ultra-high exchange current density of ≈1445 µA cm−2, and negligible performance degradation after 200 h operation at the large current density, which are superior to those of other TMDCs-based catalysts. This work hereby provides novel perspectives for the batch synthesis and application of 3D MTMDCs-based electrocatalysts with greatly improved electrocatalytic performance and stability that are needed for practical applications.

Syed Asim Ali

University of Barcelona

Ultrafast Hole Trapping in Te-MoTe2-MoSe2/ZnO Quaternary Heterojunctions for Photochemical and Photoelectrochemical Hydrogen Evolution

Te-MoTe2-MoSe2/ZnO quaternary heterostructures were designed to advance their advanced redox ability in sustainable HER process via three different routes. Photo-physical studies have validated the steady state transfer of photo-induced charge carriers whereas the remarkable transfer dynamics was proven by femtosecond transient absorption and irradiated-XPS analysis. 2.5 and 5wt% Te-MoTe2-MoSe2/ZnO photocatalysts (2.5MTMZ and 5MTMZ) exhibited 2.8 and 3.3-fold higher HER performance than pristine ZnO with marvelous apparent quantum efficiency of 35.09 % and 41.42 % at the HER rate of 4.45 and 5.25 mmol/gcat/h respectively. Electrochemical water splitting experiments manifested subdued 384 and 285 mV overpotential values of 2.5MTMZ and 5MTMZ heterostructures to achieve 10 mA/cm2 current density for HER, and 961 and 793 mV for OER respectively. For optimized 5MTMZ photocatalyst, lifetime kinetic decay of interfacial charge transfer step was evaluated to be 138.67 ps as compared to 52.92 ps for bare ZnO.

Sunayana Bora

Indian Institute of Technology (Banaras Hindu University)

Transition Metal Dichalcogenide-Based Sensor for Pharmaceutical Pollutant Detection

The presence of pharmaceutical pollutants such as antibiotic residues in water bodies for a prolonged period has raised significant concerns regarding environmental safety and public health. Transition metal dichalcogenides (TMDs) have arisen as promising materials for ecological monitoring owing to their excellent optical and electronic properties, such as high surface area, superior conductivity, and tunable bandgap, which make them highly suitable candidates for sensing applications. In this study, we synthesized tungsten disulfide quantum dots (WS₂QDs) using a simple and eco-friendly method and worked on developing a composite with another 2D material to enhance its sensing performance. The structural, morphological, optical, and electronic properties of synthesized WS₂QDs and their composite were thoroughly analyzed using various characterization techniques like XRD, UV-vis, TEM, SEM, etc. The fluorescence measurements were explored for the detection of antibiotics in water, where fluorescence quenching was observed upon interaction with the antibiotics. This system demonstrated high selectivity, sensitivity, and anti-interference for antibiotics in water. A portable, paper-based sensor was fabricated for on-site monitoring, enabling rapid, cost-effective, and real-time detection. Our findings highlight the potential of WS₂QDs and their composite system in developing efficient, sustainable, and practical sensor platforms for water quality monitoring.

Yerin Hong

University of Michigan

Electrochemical lithium intercalation cycling-induced phase transition of MoS2 from 2H to 1T and spontaneous reversion to the 2H phase

In this study, we investigated the phase transition behavior of molybdenum disulfide (MoS₂) during and after repeated lithium intercalation and deintercalation cycles, motivated by its potential for energy storage and electronic applications. MoS₂ undergoes a phase transition from the 2H (trigonal prismatic) to the 1T (octahedral) phase upon lithium insertion. After cycling with galvanostatic cycling with potential limitation (GCPL) and using Raman spectroscopy, we confirmed that the 1T phase persisted even after most lithium was removed. Interestingly, a spontaneous reversion of the 1T phase to the 2H phase was observed over time. Raman spectroscopy results showed a significant decrease in 1T phase peaks for cycled MoS2, with the phase converted to 2H after resting periods for several days. Additionally, electrochemical cycling of the cycled MoS₂ flakes revealed lithium potential profiles was comparable to pristine MoS₂, reinforcing the evidence of spontaneous phase reversion. These results demonstrate the metastable nature of the 1T phase and structural evolution of MoS₂ upon and after lithium intercalation cycling. In addition, these findings can provide key insights into the potential strategies of the precise phase control for energy storage and electronic applications, or to synthesize endotaxial structure with distinct quantum states.

Suvigya Kaushik

Indian Institute of Technology Gandhinagar

On the role of surface sites, electronic structures and capillaries of 2D MoS2 for energy harvesting

Molybdenum disulfide (MoS₂) has emerged as a promising candidate for energy harvesting applications due to its unique structural, electronic, and surface properties. In this work, we try to understand the role of surface sites, electronic structures and capillaries of MoS₂ in energy harvesting. We explore novel methods for the exfoliation and stabilization of MoS₂ laminates, as well as their utilization in hydrogen evolution, hydrovoltaic, and osmotic energy harvesting. MoS₂ nanosheets produced via a novel high-pressure liquid-phase exfoliation method achieved an enhanced yield (~7.3%) and nanosheet concentration (~1.5 mg/mL). They exhibit a high hydrogen evolution reaction (HER) rate (~30 mmol/g/h) under ambient conditions. In hydrovoltaic energy generation, metallic 1T’ MoS₂ exhibits three orders higher power output (~2 mW/m2) than semiconducting 2H MoS₂, highlighting the critical role of electronic structure and capillaries in facilitating ion transport. The metallic 1T’ phase is successfully stabilized via acetate functionalization. These nanosheets are also investigated for their osmotic performance. This research advances the understanding of MoS₂ exfoliation techniques, phase-dependent energy harvesting mechanisms, and functionalization strategies for stabilizing metallic phases. The findings offer significant insights into the development of 2D material-based technologies for clean and sustainable energy generation.

Nicholas Wilson

University of Waterloo

MoS2/Metal Hybrids for Enhanced NIR Absorption Photodetectors

Molybdenum disulfide (MoS₂) exhibits inherent limitations in near-infrared-II (NIR-II, 1000–1350 nm) photodetection due to its bandgap constraints. This proposal addresses this challenge through electrochemical intercalation of plasmonic metals (e.g., Cu, Au) into MoS₂ layers, creating hybrids that synergize plasmonic enhancement and tailored charge-transfer dynamics. Electrochemical methods enable precise control over metal intercalation depth and distribution, facilitating the formation of plasmonic “hot spots” while preserving MoS₂’s structural integrity. For instance, cyclic voltammetry-driven copper intercalation induces a distinct mid-infrared plasmonic resonance (~1 eV) within MoS₂ interlayers, broadening absorption beyond 1300 nm and achieving responsivities >10⁴ A/W. Similarly, electrodeposited Au nanoislands on MoS₂ surfaces amplify localized electric fields by 30× via localized surface plasmon resonance (LSPR), enhancing photocarrier generation rates.

The electrochemical approach uniquely optimizes interfacial coupling by tuning metal nucleation sites and defect engineering during intercalation, as shown by X-ray photoelectron spectroscopy confirming sulfur vacancy-mediated Cu diffusion. This method also enables p-type doping through hole transfer from plasmonic metals, reducing dark currents by 2–3 orders of magnitude compared to pristine MoS₂. Advanced configurations, such as vertically aligned MoS₂/Cu carpets synthesized via room-temperature electrochemical deposition, demonstrate broadband NIR-II response (<0.5 s rise time) and detectivity >10¹² Jones. Challenges in scaling are mitigated by electrochemical techniques’ compatibility with flexible substrates, offering a pathway for wearable optoelectronics. By merging plasmonic field confinement with electrochemical precision, this strategy unlocks scalable, high-performance NIR-II photodetectors for biomedical imaging and night-vision systems, while establishing a framework for defect-engineered 2D/plasmonic hybrids.

Shaokai Song

Unversity of Southampton

Graphene Electrodes for In-plane Electrochemical growth of TMDCs

Short-channel effects in field-effect transistors have intensified interest in two-dimensional (2D) materials, particularly transition metal dichalcogenides (TMDCs), due to their potential to mitigate these effects. A significant challenge in TMDC-based transistors is the high contact resistance at metal-semiconductor interfaces, often attributed to van der Waals interactions between layers. Electrodeposition emerges as an industrially compatible technique offering unique advantages for scaling 2D heterostructures. We designed and transferred novel patterns onto graphene substrates, enabling lateral electrodeposition of TMDCs. Through iterative optimization of fabrication processes, including lithography, lift-off, and etching—we overcame challenges related to pattern fidelity and material compatibility. High-quality graphene substrates have been prepared for subsequent TMDC deposition. Our next step involves utilizing these graphene electrodes to deposit various TMDCs and their heterojunctions, aiming to explore diverse applications. Additionally, we have mastered mechanical exfoliation techniques to fabricate comparable transistors, providing benchmarks for evaluating the performance of our electrodeposited structures.

Huanhuan Shi

Karlsruher Institut für Technologie

A general electrochemical approach for high-throughput production of solution-processable van der Waals Heterostructures

Anup Kumar Keshri

Indian Institute of Technology Patna

Simultaneous Exfoliation and Phase Transformation in MoS2

Taoyu Zou

Pohang University of Science and Technology (POSTECH)

Solution-Processed Monolithic 3D Integration of 2D Semiconductors for Flexible and Low-Power Electronics

Monolithic 3D (M3D) integration with 2D semiconductors offers a promising approach for high-density, energy-efficient electronics. However, existing fabrication methods rely on high-temperature processing and complex transfer steps, limiting their scalability and compatibility with flexible substrates. Here, we demonstrate the first solution-processed M3D integration of complementary 2D material-based circuits, achieving high performance, mechanical flexibility, and multifunctionality. By precisely controlling the carrier concentration in n-type MoS₂ and p-type WSe₂ transistors using tailored ionic doping strategies, we fabricate vertically stacked CMOS inverters, NOR and NAND gates, photosensor-in-logic circuits, and ring oscillators (ROs) without the need for high-temperature processing.This work establishes a scalable, low-temperature fabrication platform for M3D electronics, paving the way for next-generation flexible, wearable, and neuromorphic computing systems.

Maria Batuk

University of Antwerp

Transmission electron microscopy for quantitative defects analysis in 2D TMDs

Paulina Lohbeck

Friedrich Schiller University Jena

Control of Photon–Exciton Momentum Transfer in Monolayer MoS2 by Vortex Beams

Hleb Fiadziushkin

RWTH Aachen University

Detailed study of the processing steps and ambient environment impact on the electrical properties of MOCVD-ML-MoS2 FET

Puyan Li

Zhejiang University

Magneto-interactive Cr2Te3-Coated Liquid Metal Droplets for Flexible Memory Arrays and Wearable Sensors

Jinyoung Seo

Yonsei University

In Situ Monitoring of Continuous MoS2 Growth Facilitated by Sodium Catalysis

Atomically thin transition metal chalcogenides (TMCs) possess outstanding optoelectronic properties and compositional tunability, making them key materials for next-generation electronic and photonic applications. Achieving high-quality TMCs requires precise control of growth conditions, with chemical vapor deposition (CVD) being a widely used technique. Previous work by Li et al. (Nanoscale 2019, 11, 16122-16129) demonstrated the successful growth of continuous MoS2 films on sapphire substrates using Na2MoO4 in which sodium and molybdate serve as a catalyst and metal precursor, respectively. However, replicating such growth on SiO2/Si substrates remains challenging, largely due to differences in surface charge that influence precursor adsorption and film continuity. In this study, we report the centimeter-scale, continuous growth of MoS2 films on hydrophilic SiO2/Si substrates by modulating the pH of the metal precursor buffer. Under mildly acidic conditions, Na2MoO4 is formed in situ, uniformly spin-coating the substrate. Upon sulfurization during the CVD process, this coating is converted into a continuous MoS2 film. Real-time monitoring of optical contrast as a function of time and temperature revealed that MoS2 growth initiates at temperatures as low as 500 °C, with grain sizes below one micrometer. This scalable and reproducible method offers a reliable pathway to large-area TMC film fabrication and paves the way for their integration into high-performance optoelectronic devices and other 2D material-based technologies.

Hanbin Cho

Ulsan National Institute of Science and Technology (UNIST)

Bimodal vdW Carrier Injection Layer for Mono-layer CMOS via Ultra-thin Body Effect

The industrialization of chips relies on the integration of field-effect transistors (FETs) on wafer-scale substrates, necessitating high-quality, large-area 2D semiconductors with uniformity and minimal defects. However, chemical vapor deposition (CVD) growth inevitably introduces grain boundaries (GBs), defects, and dislocations that degrade device performance. In particular, grain boundaries formed at the interface of differently oriented grains cause structural discontinuities, increase carrier scattering, introduce additional trap states, and reduce device stability and uniformity, posing a major challenge for high-quality transistor integration. Here, we report a molecular welding strategy for precise grain boundary repair in WS₂. Using a solvent-free post-treatment, 1,4-benzenedithiol (BDT) molecules covalently bridge abundant sulfur vacancies at the grain boundary, forming a conductive “bridge” that enhances carrier transport. This method significantly enhances photoluminescence intensity at the grain boundary, increases the transistor mobility by 200-fold, improves the on-state current by three orders of magnitude, and raises the on/off ratio by 10⁵. Additionally, the carrier concentration in the transistor channel is notably increased, while the trap density at the boundary is reduced to the level of the grain interior, and the repair effect remains stable over time. Beyond precise grain boundary repair, our approach effectively heals sulfur vacancy defects within the grains, improving overall charge transport and device uniformity, providing a reliable technological foundation for 2D semiconductor devices integration.

Satyam Sahu

Czech Academy of Sciences, Charles University

Tuning of MoS2 Photoluminescence in Heterostructures with CrSBr

CrSBr is an air-stable magnetic semiconductor and a van der Waals material with notable intrinsic properties, such as crystalline anisotropy, quasi-1D electronic behavior, and layer-dependent magnetism. In this study, we focus on the emission peak near 1.7 eV observed in its photoluminescence spectrum and the excitation energy-dependent Raman spectroscopy. We also examine the anti-Stokes Raman spectra of CrSBr, revealing an unusually high anti-Stokes to Stokes intensity ratio that changes with laser power and crystal orientation. These findings underscore the unique vibrational and electronic interactions in CrSBr. Finally, we estimate the Raman gain, which surpasses those reported in many three-dimensional systems.

Sudipta Kundu

University of Cambridge

Exchange-mediated Exciton Splitting in Monolayer Transition Metal Dichalcogenide Induced by Ferroelectric Substrate