Abstract Two-dimensional transition metal dichalcogenides (2D-TMDCs) 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 (MoSe2). By precisely probing charge transfer phenomena on the material’s surface, the method allows for the swift detection of MoSe2 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 A series of Mg-doped multilayered hBN films were prepared by atmospheric chemical vapor deposition. Transmission line method measurements were performed using Ti/Ni, Ti/Au, and Ti/Pt ohmic metals. The impact of rapid thermal annealing is investigated at 650, 850, and 1000 ℃, and the measured current increases with each anneal step. The Ti/Pt scheme yields a current of 82 µA, 330 µA, and 1.9 mA after consecutive 650, 850, and 1000 ℃ rapid thermal anneals, respectively. The p-hBN channel current density is 31.6 µA µm -1 for a 10 µm channel spacing at 10 V and is comparable to other p-type two-dimensional semiconductors. For Ti/Ni, Ti/Au, and Ti/Pt, we report a contact resistance of 498.8, 241.7, and 38.3 kΩ µm, respectively, after a 1000 ℃ rapid thermal anneal and a low bulk resistance of 18 mΩ cm. Hall effect analysis confirms that the samples are p-type with an initial sheet carrier density of 5.6×10 11 cm -2 .

Abstract Branch waveguides are essential elements in modern technologies that demand precise manipulation of electrical and optical signals to realize compact, efficient, and high-performance systems. They underpin applications such as passive optical networks and quantum key distribution. Among these, Y-branch junctions, where one input channel divides into multiple output branches, serve as fundamental building blocks for directing and controlling signal flow. The rapid development of two-dimensional (2D) materials has opened new avenues for creating planar electronic waveguides that emulate fiber-optic functionality while enabling miniaturized optoelectronic switching. This review traces the evolution of Y-branch junctions from classical semiconductor architectures to atomically thin platforms, with emphasis on graphene-based implementations. It provides a comparative assessment of representative device concepts, including splitters, interferometers, and logic gates, summarizes theoretical progress and experimental demonstrations, and concludes with a perspective on key challenges and opportunities for future research in nanoscale signal control.

Abstract Accurate prediction of phonon propagation is crucial for modeling temperature-dependent properties in solid-state systems – particularly in two-dimensional (2D) materials and their heterostructures, where interfacial effects strongly influence vibrational and thermal behavior. Here, we employ density functional theory (DFT) to investigate the impact of anharmonicity on thermal expansion and temperature-dependent phonon frequencies in semiconducting monolayers of transition metal dichalcogenides (TMDCs), specifically MoS 2 and WS 2 , and their vertical heterostructures with insulating hexagonal boron nitride (hBN). We specifically examine the often-overlooked rotational invariance condition (RIC) of interatomic force constants (IFCs), a fundamental symmetry requirement. Our results show that thermal expansion significantly affects all geometric parameters in monolayers and heterostructures, including in-plane lattice constants, monolayer thickness, and interlayer separation (with the expansion of the latter reaching ~2.1 × 10 −5 K −1 at 300 K). We also provide first-principles predictions of the temperature dependence of prominent Raman-active E'-like and A' 1 -like phonon modes in TMDC-based systems, highlighting the roles of thermal expansion and phonon-phonon interactions. Notably, we find that anharmonicity alone can alter the frequency difference of a given Raman-active phonon mode between monolayer and heterostructure forms – by ≥ 0.4 cm −1 at 300 K. Furthermore, we demonstrate that neglecting RIC leads to incorrect phonon redshifts, with errors ≥ 0.5 cm −1 in monolayers and ≥ 0.1 cm −1 in heterostructures at 300 K – potentially exceeding Raman spectroscopy resolution. It also distorts thermal expansion coefficients, with deviations of up to ~30%. These discrepancies arise primarily from the mischaracterization of out-of-plane acoustic (ZA) phonons, which may exhibit unphysical imaginary frequencies or erroneous quasi-linear dispersion, instead of the symmetry-preserving quadratic behavior. The framework enables accurate modeling of temperature-dependent vibrational and thermal phenomena in a range of 2D systems.

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 WS2 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, XL, red-shifted by approximately 80 meV from the neutral exciton and exhibiting a linewidth below 200 µeV. Photoluminescence excitation spectroscopy and power-dependent measurements show that XL originates from annealing-induced defects in the WS2 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 The linear absorption spectrum of excitons in TMDC 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 reradation, we find a complex interplay of dark-bright splitting and linewidth difference of both involved spin-bright and spin-dark excitons.

Abstract Ferroelectrics are important in many technological applications, from sensors and actuators to memory and fast switching
devices. The key to their versatility lies in the coupling between their electrical and mechanical properties,
which can be controlled reversibly under different external conditions. Here, we report the effects of hydrostatic pressure
on structural and ferroelectric phase transitions in the van der Waals material indium selenide α-In 2 Se 3 , as probed by Raman spectroscopy and imaging in a high-pressure diamond anvil cell. We demonstrate that 2H-α-In 2 Se 3 has a stronger ferroelectric phase stability than that reported in other polytype phases of polycrystalline In 2 Se 3 . Furthermore, we show that disorder is a key factor in the reversibility of the phase transition from ferroelectric 2H-α-In 2 Se 3 to paraelectric β-In 2 Se 3 .

Abstract Compared to the study of graphene itself, the study of nano-structured graphene is rather limited because it is difficult to prepare atomically ordered edges. In this study, we have fabricated a periodically patterned mesh structure of graphene with atomically precise zigzag edges (zGNM: zigzag graphene nanomesh) and studied its thermal conductivity ( κ ) by opto-thermal Raman measurement. Unintuitively, it is found that the κ of zGNM of 2, 3 monolayers (MLs) thick is weakly inversely proportional to the nanoribbon width ( W ), while that of zGNM of 5∼10 MLs thick is independent of W down to 30 nm. In any cases, their κ is not suppressed by nano-structuring. Since the κ of suspended zigzag graphene nanoribbons (zGNRs) is suppressed by decreasing W , this nonclassical behavior of zGNM is due to the mesh structurκκκe. In addition, zGNRs show a higher κ than GNRs with atomically rough edges. This is probably κdue to the atomically ordered zigzag edges.

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.