Abstract Vitrimers are a new class of polymers that contain a covalent adaptable network where molecular bonds can be exchanged and reformed when heated above its Tv, providing them with stress relaxation, self-healing and reshaping abilities, which traditional thermosets lack. Herein, MoS2 and WS2 were used as nanofillers to fabricate nanocomposites based on a disulphide exchange based vitrimer. Their microstructure, Tg and thermomechanical properties were evaluated and compared to those observed for their epoxy-based analogues, and the vitrimer materials dynamic bonding exchange behaviour was investigated. The vitrimer exhibited a lower Tg than the neat epoxy due to its dynamic covalent network, with both matrices showing further Tg reductions upon filler addition as particles hindered cross linking. Only the WS₂/vitrimer nanocomposite displayed mechanical reinforcement, attributed to stronger vitrimer/WS₂ interactions enabled by thicker, flatter WS₂ platelets providing more accessible surfaces for H···S bonding, which was relevant for their dynamic bonding exchange behaviour. The stress relaxation of the vitrimer was found to accelerate with increasing temperature due to a promotion of the chain mobility and thermal bond-exchange activation, with the addition of the fillers further promoting such acceleration at T > 75 °C and leading to slower stress relaxation at lower T, due to them increasing the vitrimer’s activation energy (Ea),. The Tv of the polymer and the nanocomposites were determined and related to their Tg in order to establish their optimal processing windows. These results suggest that by strategically choosing a filler, the disulfide bond exchange process can be modified through tuning the filler-polymer interactions, hence changing Ea and Tv, and thus the range of temperatures for providing structural integrity or, alternatively, promoting their reprocessing, reshaping or recycling abilities can be tuned, opening the door to a wide range of new applications.
Abstract The technological impact of III-nitrides in lighting and power electronics is well established. However, heteroepitaxy on rigid foreign substrates often results in high defect densities and limited mechanical compliance. This poses hurdles for the exploitation of electronic and photonic integrated circuits. Graphene interlayers offer an appealing alternative: by weakening interfacial adhesion while maintaining crystalline alignment under specific epitaxy conditions, they facilitate the lift-off of freestanding nitride membranes, allowing for substrate reuse. This review maps the experimental landscape with the theoretical background of graphene-assisted III-nitride growth, connecting macroscopic outcomes to competing interfacial regimes of van der Waals (vdW) epitaxy, quasi-vdW epitaxy, thru-hole growth, and remote epitaxy. Each process has a specific operational window under metal-organic chemical vapor deposition (MOCVD) conditions. Central challenges associated with the selection of a regime are traced to the exact root causes: suppressed nucleation on pristine graphene, uncontrolled defect formation and contamination during graphene preparation, and graphene degradation or interfacial reactions under the aggressive MOCVD environment, each of which can shift the dominant regime. Recent advances in direct graphene synthesis, controlled functionalization, buffers, and flow-modulation schemes have been assessed as practical routes to coalesced, transferable GaN- and AlN-based membranes, which constitute the main focus of this review. Future priorities for field advancement include standardized metrics for distinguishing growth modes, robust interface engineering, and considerations for novel device creation.
Abstract Nearly dispersionless energy bands are realized in armchair graphene nanoribbons by a periodic repetition of segments characterized by two different widths. The quasi-flat bands are created when interfacial junction states emerge due to the topological dissimilarity between the nanoribbon segments. With the elongation of the period of the nanoribbon superlattice, the band energies approach the Dirac point of graphene with increasing the flatness of the dispersion. The topological winding number is utilized in designing the junctions to control the presence and the number of the topological junction states (TJSs). The existence of the TJSs and the exclusive localization of their wavefunctions in the sublattices of graphene are shown to be maintained when the second-nearest-neighbour hopping in the honeycomb lattice is taken into account with the hopping strength expected for graphene.
Abstract Two-dimensional (2D) materials and their van der Waals (vdW) heterostructures have emerged as a powerful platform for engineering multifunctional thin-film systems with tunable electronic, optical, magnetic, and thermal properties. By vertically or laterally integrating atomically thin layers such as graphene, transition metal dichalcogenides, hexagonal boron nitride, black phosphorus, MXenes, intrinsic 2D magnets, transition metal monochalcogenides, and Janus materials, these vdW heterostructures enable the combination of complementary physical properties that are difficult to achieve in individual materials. This review provides a comprehensive overview of recent progress in the classification, synthesis, and fabrication of 2D heterostructured thin-films, with particular emphasis on interface physics and interlayer coupling mechanisms. Key phenomena including band alignment, ultrafast charge transfer, interlayer excitons, moiré superlattices, spin-orbit coupling, and magnetic proximity effects are discussed in relation to their role in determining structure-property relationships. The review further summarizes emerging device architectures based on 2D heterostructures, including optoelectronic devices, spintronic systems, neuromorphic computing platforms, sensors, and flexible electronic technologies. Finally, critical challenges associated with scalable synthesis, interface quality, environmental stability, and integration with existing semiconductor technologies are examined. A particular emphasis is placed on industrially relevant strategies, such as scalable chemical vapor deposition, direct heterostructure growth, vdW contact engineering, and machine-learning-assisted process optimization. By bridging the gap between fundamental physics and manufacturing requirements, this review provides a forward-looking roadmap for the development of reliable, scalable, and high-performance 2D heterostructure-based technologies.
In this paper, we report on the growth of sp2-BN films by chemical vapor deposition on nickel (111). More precisely, we propose to explore a new parameter variation, which to our knowledge has never been studied in the literature, namely the thickness of the nickel substrate. The structure, the quality and the homogeneity of the resulting BN film are characterized from the atomic to the millimeter scale with a set of spectroscopic and imaging techniques. We show that by reducing the nickel thickness without changing all the other growth parameters, BN films pass from a thickness of 4-6 layers (1.2-1.6 nm) to 2-3 layers (0.6-0.9 nm). We discuss this result in relation to the literature on the growth mechanism. We propose that the growth occurs essentially during the cooling phase by precipitation on the Ni(111) substrate involving a bulk diffusion-segregation process of boron and nitrogen.
Abstract Reconfigurable logic-in-memory devices are attracting increasing attention for compact and energy-efficient computing architectures, yet most existing approaches rely on complex device structures or additional control circuitry to achieve logic reconfiguration. Here, we demonstrate an ambipolar MoTe 2 split-gate field-effect transistor incorporating a charge-trap gate stack that enables logic polarity reconfiguration solely through the selection of the read voltage, without any modification of the device structure or gate configuration. The split-gate electrodes provide local electrostatic control of the channel polarity, while charge trapping induces a programmable threshold-voltage shift, leading to butterfly-shaped hysteresis in the transfer characteristics. By exploiting this behavior, AND and NOR logic operations are realized within a single device through read-voltage-controlled polarity switching. The device exhibits a large threshold-voltage window of approximately 3 V. and stable retention of the stored logic states for up to 1000 s. These results highlight a compact and hardware-efficient route toward reconfigurable logic-in-memory platforms based on ambipolar two-dimensional semiconductors.
Two-dimensional (2D) semiconductor materials are considered as promising candidates for next generation field-effect transistors (FETs). However, the dielectric properties and the interface quality between the 2D semiconductors and dielectric hinder the realization of the full potential of 2D FETs. In this work, we demonstrate the van der Waals integrable high-kappa HfOx dielectric by chemically converting 2D semiconducting HfS2 via ultraviolet ozone treatment. By measuring the dielectric properties of the Au/HfOx/Au capacitor, an electric breakdown field of similar to 8.9 MV cm-1, dielectric constant of similar to 9.6 and ultralow leakage current of similar to 10-5 A cm-2 can be achieved. Back-gate MoS2 transistors with HfOx as the gate dielectric show a current on/off ratio of similar to 109 and electron mobility of similar to 35.3 cm2 & centerdot;V-1 & centerdot;s-1. Top-gate MoS2 transistors with HfOx as the gate dielectric exhibit a subthreshold swing of similar to 80.2 mV dec-1, indicating the efficient gate control and minimal interface trap states in the MoS2 channel between the 2D MoS2 channel and the high-kappa HfOx dielectric. When using HfOx as the tunneling layer in floating-gate transistors, the devices show a large memory window of up to 14 V, a current on/off ratio of similar to 108, data retention time of exceeding 8000 s, and endurance over 350 cycles. These results demonstrate that the van der Waals integrable high-kappa HfOx facilitate the construction of high-quality dielectrics on 2D materials to enhance overall device performance.
Abstract Twisted two-dimensional (2D) materials, formed by stacking two monolayers with specific angles, exhibit a series of strongly correlated quantum phenomena, such as unconventional superconductivity, Wigner crystal and Mott-like insulating behavior owing to the electron flat band structure. This provides a new and controllable research platform for studying novel coupled electronic states by constructing artificial moiré superlattices. Utilizing moiré superlattices to modulate the band structure and introduce electron correlation facilitates the understanding of strongly correlated phenomena. Large-scale fabrication of twisted 2D materials is the essential prerequisite for the application of these unique properties. Direct growth by chemical vapor deposition (CVD) is a promising approach for scalable fabrication of twisted 2D materials. However, it remains in its nascent stage as there are still challenges in achieving large size and precise twist angle in the CVD growth. In this review, we systematically summarize recent advances in CVD growth of twisted 2D materials. We offer a comprehensive overview of growth mechanism, modulation of growth conditions, technical advantages and limitations of the CVD synthetic strategy. This review further investigates the prospects for the development of twisted multilayer 2D materials, as well as the new changes brought about by artificial intelligence in this field. This work will offer novel perspectives and inspiration for advanced research on twisted 2D materials, especially in the field of the fundamental research and device applications.
Abstract We report that ultrathin sp²-hybridized amorphous carbon (aC) can act as a non-epitaxial template promoting nucleation of two-dimensional MoS₂. The aC surface, structurally disordered yet electronically uniform, reduces interfacial energy and limits adatom diffusion, preventing dewetting and enabling uniform film growth at low, back-end-of-line (BEOL) compatible temperatures (~250–400 °C), where nucleation on bare SiO₂ is suppressed. Low temperature deposition yields continuous, sulfur-rich amorphous MoS₂₊ₓ films with short-range Mo–S order and no long-range crystallinity, as confirmed by Raman scattering, X-ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy. Subsequent high-temperature annealing drives transformation into polycrystalline 2D MoS₂ with well-defined grain boundaries, while preserving the aC template. This observation demonstrates that aC decouples nucleation from crystallization, stabilizing metastable amorphous phases and directing phase evolution. The amorphous templating strategy extends beyond conventional epitaxy, offering a scalable platform for phase-engineered 2D materials, with potential applications in electronics, memory devices, and energy technologies.
Two-dimensional vanadium diselenide (VSe2) has demonstrated potential ferromagnetic ordering at the few-layer limit under ambient conditions; however, the fundamental origin of this room-temperature ferromagnetism remains unclear. While some studies attribute the observed magnetism to extrinsic factors such as selenium vacancies or strain, others suggest it arises intrinsically from spin-spin interactions involving the 2d1 electron of the V3+ ion. Here, we report the observation of room-temperature ferromagnetism in similar to 300 nm-thick VSe2 flakes, which is 30x thicker than any previous report measured by SQUID magnetometry. Our results show a clear in-plane hysteresis loop at 300 K. To understand the underlying origin of this ferromagnetism, we performed density-functional theory calculations and toy-model simulations correlating selenium vacancy concentration with local lattice strain. By introducing 1%-10% Se vacancies in a 2 & times; 2 supercell, we observe a local in-plane tensile distortion that nearly doubles the magnetic moment (peak Delta M approximate to 2 & times; at 10% vacancy). Additionally, strain-only calculations show that tensile in-plane strain enhances the magnetic moment, indicating that both homogeneous strain and vacancy-induced local distortions provide tunable routes to engineer magnetism in VSe2.
Janus WSSe transition metal dichalcogenides monolayer dissimilar top and bottom layer breaks the mirror symmetry, instigating an out-of-plane electric field. This work shows how the out-of-plane electric field impacts the valley physics of the neutral exciton, its complex, and its excited states. Laser excitation energy sweeping reveals the position of the excited 2s exciton and the B-exciton. The exciton binding energy difference between 1s exciton and 2s exciton in Janus WSSe is larger than both parents WSe2 and WS2. When in resonance with the B-exciton, excitons are predominantly generated in the opposite valley indicating enhanced Dexter coupling. These results constitute a comprehensive polarization-resolved photoluminescence study of Janus WSSe at resonant excitation, confirming the expected presence of valley polarization and valley coherence of the exciton, its complex, and its excited states; unveiling stronger Dexter coupling in conjunction with a larger exciton binding energy attributed to reduced screening.
Abstract The linear absorption spectrum of excitons in transition metal dichalcogenides monolayers under the influence of an in-plane magnetic field is theoretically studied. We demonstrate that in-plane magnetic fields induce a hybridization between spin-bright and spin-dark exciton transitions, resulting in a brightening of spin-dark excitons. We analytically investigate spectral features including resonance energy shifts, broadening and amplitudes ratios. In particular, for a MoSe 2 monolayer with linewidths dominated by reradiation, we find a complex interplay of dark-bright splitting and linewidth difference of both involved spin-bright and spin-dark excitons.
Abstract Controlled activation of defect-bound excitonic states in two-dimensional semiconductors provides a route to isolated quantum emitters and a sensitive probe of defect physics. Here we demonstrate that in situ high-temperature annealing of hBN-encapsulated monolayer WS 2 on a suspended microheater leads to the emergence of spectrally isolated single-photon emitters at cryogenic temperatures. Annealing at temperatures around 1100 K produces a sharp emission line, X L , red-shifted by approximately 80 meV from the neutral exciton and exhibiting a linewidth below 200 µ eV. Photoluminescence excitation spectroscopy and power-dependent measurements show that X L originates from annealing-induced defects in the WS 2 monolayer, while second-order photon correlation measurements reveal clear antibunching with g ( 2 ) ( 0 ) < 0.5 . These results establish high-temperature in situ annealing as a controlled means to access defect-bound excitonic states and single-photon emission in van der Waals materials.
Abstract Organic thin-film transistors (OTFTs) represent foundational components of flexible electronics, holding immense promises in flexible displays, wearable sensing, and low-cost optoelectronic detection. Nevertheless, their widespread implementation is currently constrained by the inherent environmental sensitivity of organic semiconductor active materials, leading to performance degradation, and the inability of conventional dielectric layers to meet high integration and thermal stability. Covalent organic frameworks (COFs), a novel class of crystalline porous polymers formed by robust covalent bonds, emerge as a compelling solution. Leveraging unique attributes—including precise pore tunability, high specific surface area, and long-range ordered π -conjugated systems—COFs offer a versatile materials platform to tackle key challenges in OTFTs. This review systematically summarizes the structure-property relationships and interface synthesis strategies of COFs, with a primary focus on their pivotal role as semiconductor active layers and dielectric materials in OTFTs. We delineate key design strategies and recent progress across diverse aspects, including molecular building blocks, linkage chemistry, topological structures, molecular symmetry, and thin-film integration. Finally, we provide an outlook on future directions of COF synthesis engineering, post-functionalization strategies, and physical-chemical mechanism studies to further advance this field.
Abstract This work presents a detailed investigation of the pyrolysis and sintering processes of hydridopolycarbosilane (HPCS) polymers, focusing on the formation of β -silicon carbide ( β -SiC) and the influence of Ti 3 C 2 –O x in this process. Due to the computational limitations of density functional theory (DFT), molecular dynamics methods with appropriate potentials are necessary for simulating large-scale systems, however, the available potentials are limited when the modeling process evolves relatively more element types or complex chemical-mechanical processes are studied. In this work, a machine learning based MACE (Multi-body ACE) model is adopted and trained to accurately capture the polymer’s transformation into crystal SiC structures. Comparisons showed that the energy deviations between trained MACE and DFT remained below 0.4% across pyrolysis products, validating the accuracy of the model. Based on this trained model, the interface between Ti 3 C 2 –O x and both the amorphous polymer and SiC crystal structures were studied. The influence of the Ti 3 C 2 –O x layer on SiC formation was explored. It was found that stable bonds, particularly between Ti and C atoms, formed first at the interface. These bonds significantly contribute to the stabilization of the structure and promote an increased fraction of crystalline SiC in the final system.
Abstract Two-dimensional van der Waals (vdW) materials constitute a unique class of layered crystals in which adjacent layers are bonded through weak vdW interactions. Their orientation, stacking sequence, and twist angle can be precisely engineered, enabling atomic-level modulation of electronic structures and interfacial properties. This structural tunability has led to the discovery of diverse emergent phenomena in stacking, twisting, and heterointegration. Yet most of these findings rely on atomically defined local configurations, and extending such deterministic arrangements to wafer-scale level remains a central challenge for practical implementation. Recent years have witnessed major progress in the wafer-scale growth of single-crystalline vdW materials. Advances in symmetry-guided epitaxy, step-edge mediation, and interfacial engineering have elucidated how orientational selection, nucleation barriers, and seamless coalescence arise from substrate–film coupling. Meanwhile, stacking and twisting technologies have made notable progress in scalability and interfacial cleanliness, now enabling the assembly of large-area, deterministic vdW architectures. This Review provides a unified overview of the growth and stacking strategies that enable scalable deterministic atomic arrangements in vdW materials. Emphasis is placed on the correlations between structural configuration, interfacial characteristics, and functional performance in both homostructure stacking and lateral or vertical heterostructure fabrication. Finally, we highlight emerging directions—low-temperature epitaxy on non-epitaxial substrates, deterministic twist control for wafer-scale uniformity, and metrology connecting atomic order to device performance—toward rationally engineered, large-area vdW architectures.
Abstract Two-dimensional transition metal dichalcogenides (2D) hold tremendous potential for applications in electronics, optics, and catalysis, where controlling and characterizing defects are critical to optimizing material performance. This paper presents a novel defect detection method that enables rapid and non-destructive analysis of 2D materials such as molybdenum selenide (MoSe 2 ). By precisely probing charge transfer phenomena on the material’s surface, the method allows for the swift detection of MoSe 2 with varying defect concentrations, providing an efficient and non-invasive approach to defect evaluation. Previous studies have demonstrated that surface charge transfer doping can induce p–n doping conversion in materials. This process not only alters their electrical properties but also enhances the overall performance of 2D materials by regulating carrier types. Compared with conventional detection techniques, this method offers notable advantages in simplicity, non-destructiveness, and high sensitivity, making it broadly applicable for large-scale defect screening. The proposed approach provides a promising pathway for defect assessment, quality control, and performance optimization in 2D materials, with significant potential for future applications in semiconductor devices and optoelectronic systems.
Abstract Thin inorganic films, such as metal oxides, are frequently employed as functional materials for decoupling or optimization of the interaction between molecular magnetic layers and metallic surfaces. In the case of single-molecule magnet (SMM) deposits, an effective decoupling layer can reduce the hybridization with the metallic substrate, which would otherwise suppress their intrinsic magnetic bistability. In this work, we investigate the potential of an ultra-thin Fe oxide layer as a substrate for the Tb(III) bis-phthalocyaninato (TbPc 2 ) SMM in technological platforms. A multi-technique approach was employed to evaluate the integrity of a TbPc 2 sub-monolayer (ML) deposit and to determine the molecular adsorption geometry at the surface. Furthermore, large-scale facilities experiments were performed, and x-ray magnetic circular dichroism was used to probe the magnetic properties of the TbPc 2 sub-ML. The central finding is that while the magnetic moments and electronic configuration of the molecule are preserved, the characteristic slow magnetic relaxation is suppressed. This highlights the critical role of substrate phonon stiffness and tunnel barrier thickness in stabilizing the SMM behaviour.
