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Abstract The growth of wafer‐scale van der Waals (vdW) thin films and heterostructures by molecular beam epitaxy (MBE) is important for future applications in quantum technologies, next‐generation optoelectronic devices, and fundamental physics investigations. When grown using co‐deposition methods that are typically used for compound semiconductor MBE, vdW materials typically show a high density of structural defects, including twin or antiphase domains, spiral growth, and pyramidal growth. These defects are caused by the relatively weak film/substrate interaction and/or the poor wettability of typical substrates by many vdW materials. These difficulties can be mitigated using a multi‐step growth procedure in which growth stages, including nucleation and coalescence, can be rigorously controlled, resulting in high‐quality deposition of vdW thin films. This article will describe a general recipe for the growth of highly‐crystalline wafer‐scale vdW thin films by MBE. 

Abstract We report the growth of InSe films on semi-insulating GaAs(111)B substrates by molecular beam epitaxy (MBE). Excellent nucleation behavior resulted in the growth of smooth, single-phase InSe films. The dominant polytype was the targeted γ-InSe. Transmission electron microscopy revealed the presence of three bulk polytypes β, γ, and ε-InSe arranged in nanosized domains, which can be interpreted as sequences of stacking faults and rotational twin boundaries of γ-InSe. Additionally, a centrosymmetric Se-In-In-Se layer polymorph with$$P\bar{3}m$$ $P\bar{3}m$ symmetry was identified as typically not present in bulk. Sizeable differences in their electronic properties were found, which resulted in sizeable electronic disorder arising from the nanoscale polytype arrangement that dominated the electronic transport properties. While MBE is a viable synthesis route towards stabilization of InSe polytypes not present in the bulk, an improved understanding to form the targeted polymorph is required to ultimately inscribe a layer sequence on demand utilizing bottom-up synthesis approaches. 

Abstract Memristive crossbar architectures are promising as efficient, low-power inference engines for edge AI applications. However, inputs with minor differences often yield similar outputs, requiring additional processing methods such as confidence scoring, feedback mechanisms, crossbar redundancy, or hybrid analog-digital approaches to resolve. These methods can be impractical for resource-limited edge devices. In contrast, three-terminal memtransistors can dynamically tune conductance via gate control, effectively resolving similar outputs and enhancing separability without retraining. Here, we present dense, large-scale crossbar array architectures incorporating up to 2048 MoS₂memtransistors per array, achieving >92% yield across multiple arrays while individual memtransistors exhibit write energies as low as ~0.2 fJ, maintain read margins up to 10⁵, and offer a projected retention exceeding three years. These architectures demonstrate the ability to resolve inference ambiguities through gate modulation without the need for costly retraining or reprogramming. We also validate their performance by successfully classifying handwritten digits from the MNIST database. Finally, we benchmark the performance of MoS₂memtransistors against other 2D material-based architectures and project their potential compared to state-of-the-art AI accelerators. We believe that this work furthers the ongoing development of in-memory processors for decentralized edge applications and that future studies aimed at reducing device-to-device variation and improving long-term non-volatile memory would only enhance inference capabilities. 

Abstract Epitaxial growth of transition metal dichalcogenides (TMDs) by metalorganic chemical vapor deposition is a promising method for wafer-scale synthesis of monolayer films. This study focuses on a comparison of the epitaxial growth of MoS₂, WS₂, and WSe₂monolayers on 2 inch c-plane sapphire substrates using a cold-wall reactor with metal hexacarbonyl and hydride chalcogen sources. Uniform thermofluidic conditions enabled a comparative analysis of nucleation density, domain size, and lateral growth rate across TMD compounds, shedding light on the impact of TMD chemistry on epitaxial growth. Despite the use of chemically analogous precursors such as Mo(CO)₆or W(CO)₆and H₂S or H₂Se, significant differences in growth behavior are observed. Comprehensive structural, optical, and transport characterizations provide insights into sulfur versus selenium-based TMDs, advancing the understanding of optimized growth conditions for these emerging materials. 

Abstract A detailed understanding of the composition and polymerization mechanism of elemental sulfur remains a decades long unresolved question for modern chemistry. However, the dynamic nature of molten sulfur significantly complicates its accurate characterization. To overcome this challenge, we performed the first comprehensive molecular dynamics (MD) simulations using a ReaxFF reactive force field specifically parameterized to capture the complex ring‐opening polymerization dynamics of elemental sulfur. Rigorous development of the force field parameters, trained against extensive quantum mechanical datasets, was key to enabling these large‐scale (>10 000 atoms) reactive MD simulations at polymerization‐relevant temperatures. This study provides the first detailed atomic‐level description of liquid sulfur, elucidating temperature‐dependent molecular composition and offering unprecedented insights into sulfur polymerization mechanisms. These are the first simulations to reveal the formation of remarkably large macrocyclic sulfur rings at the onset of polymerization—a discovery that challenges longstanding mechanistic misconceptions, thus reshaping our understanding of sulfur polymerization. Our findings highlight the power of molecular dynamics in exploring complex polymerization processes, with broad impact in dynamic covalent chemistry and covalent adaptable polymers. 

Abstract The nonlinear Hall effect (NLHE) with time‐reversal symmetry has emerged as a transformative phenomenon within the Hall effect family, attracting significant interest due to its profound implications for both fundamental physics and technological applications. While prior studies have predominantly focused on NLHE in 2D materials, advancements in practical applications have been constrained by low operating temperatures and limited responsivity, typically below 10⁻⁴m/V. Achieving significant responsivity at room temperature (RT) in 3D systems has proven challenging, particularly for scattering‐induced NLHE. Here, the discovery of disorder scattering‐induced NLHE in chalcopyrite‐type CdGeAs₂bulk single crystals is reported, demonstrating a remarkable responsivity of up to 10⁻³m/V at RT. The studies reveal that NLHE not only facilitates ac‐driven second harmonic and rectification Hall responses but also induces an exceptionally large anomalous Hall angle. Through band structure measurements by ARPES, DFT calculations, as well as symmetry and nonlinear Hall conductivity scaling analyses, disorder scattering is identified as the dominant mechanism for the NLHE in CdGeAs₂. Leveraging the observed strong responsivity of NLHE at RT, its broadband electronic frequency mixing capability in the MHz range is further demonstrated. This work sets the foundation for integrating scattering‐induced NLHE in 3D materials into very high‐frequency mixing technologies. 

Abstract In this study, we explore the operation and performance of electrolyte-gated junctionless III-V nanowire (NW) transistors featuring compositionally graded In_xGa_1-xAs channels. These devices leverage the electric double-layer (EDL) gating mechanism at the electrolyte/semiconductor interface to achieve ultra-high charge carrier densities, surpassing those possible with conventional oxide dielectrics. Fermi–Dirac statistics are introduced by a numerical method to reproduce associated charge densities of EDL transistors. A 1 nm interfacial HfO₂layer is introduced to capture the electrostatics of the EDL, prevent charge transfer between the electrolyte and the semiconductor, and mimic the Stern layer. Device simulations are conducted to optimize the heterostructured NW composition and doping profile, followed by benchmarking against traditional HfO₂-gated structures. The EDL-gated device achieves anI_ON/I_OFFratio of 10⁶, with a subthreshold slope of 60 mV/dec and a threshold voltage of 0.31 V at a low drain voltage of 0.3 V, indicating a two-order magnitude improvement over conventional junctionless oxide-gated NW transistors. Computational methodologies include finite element modeling in COMSOL to extract voltage-dependent ion densities and subsequent device simulations using Silvaco's Atlas software. The results indicate that the optimized EDL-gated device exhibits superior electrostatic integrity and performance metrics compared to conventional gating methods. The findings underscore the potential of EDL gating in III-V NW configurations for advanced electronic applications, demonstrating significant improvements in switching characteristics and power efficiency. Further optimization and exploration of bias-dependent ionic concentrations and configurable device geometries highlight the robustness and scalability of this approach for next-generation low-power electronics. 

Abstract Magnetic topological materials have recently emerged as a promising platform for studying quantum geometry by the nonlinear transport in thin film devices. In this work, an antiferromagnetic (AFM) semiconductor EuSc₂Te₄ as the first bulk crystal that exhibits quantum geometry‐driven nonlinear transport is reported. This material crystallizes into an orthorhombic lattice with AFM order below 5.2 K and a bandgap of less than 50 meV. The calculated band structure aligns with the angle‐resolved photoemission spectroscopy spectrum. The AFM order preserves combined space‐time inversion symmetry but breaks both spatial inversion and time‐reversal symmetry, leading to the nonlinear Hall effect (NLHE). Nonlinear Hall voltage measured in bulk crystals appears at zero field, peaks near the spin‐flop transition as the field increases, and then diminishes as the spin moments align into a ferromagnetic order. This field dependence, along with the scaling analysis of the nonlinear Hall conductivity, suggests that the NLHE of EuSc₂Te₄ involves contributions from quantum metric, in addition to extrinsic contributions, such as spin scattering and junction effects. Furthermore, this NLHE is found to have the functionality of broadband frequency mixing, indicating its potential applications in electronics. This work reveals a new avenue for studying magnetism‐induced nonlinear transport in magnetic materials. 

Abstract Altermagnets are a newly identified family of collinear antiferromagnets with a momentum‐dependent spin‐split band structure of non‐relativistic origin, derived from spin‐group symmetry‐protected crystal structures. Among candidate altermagnets, CrSb is attractive for potential applications because of a large spin‐splitting near the Fermi level and a high Néel transition temperature of around 700 K. Molecular beam epitaxy is used to synthesize CrSb (0001) thin films with thicknesses ranging from 10 to 100 nm. Structural characterization, using reflection high energy electron diffraction, scanning transmission electron microscopy, and X‐ray diffraction, demonstrates the growth of epitaxial films with good crystallinity. Polarized neutron reflectometry shows the absence of any net magnetization, consistent with antiferromagnetic order.In vacuoangle resolved photoemission spectroscopy (ARPES) measurements probe the band structure in a previously unexplored regime of film thickness, down to 10 nm. These ARPES measurements show a bulk‐type, 3D momentum‐dependent band splitting of up to 0.7 eV with g‐wave symmetry, consistent with that seen in prior studies of bulk single crystals. The distinct altermagnetic band structure required for potential spin‐transport applications survives down to the ∼10 nm thin film limit at room temperature. 

Abstract C–H bond activation enables the facile synthesis of new chemicals. While C–H activation in short-chain alkanes has been widely investigated, it remains largely unexplored for long-chain organic molecules. Here, we report light-driven C–H activation in complex organic materials mediated by 2D transition metal dichalcogenides (TMDCs) and the resultant solid-state synthesis of luminescent carbon dots in a spatially-resolved fashion. We unravel the efficient H adsorption and a lowered energy barrier of C–C coupling mediated by 2D TMDCs to promote C–H activation and carbon dots synthesis. Our results shed light on 2D materials for C–H activation in organic compounds for applications in organic chemistry, environmental remediation, and photonic materials.