The study focuses on the optical and electrical properties of Tungsten Ditelluride (WTe2), a type II Weyl semimetal, as well as the influence of its self-limiting oxide (SLO) layer that forms during natural oxidation. WTe2 exhibits promising applications in photodetection and energy harvesting due to its unique gapless linear dispersion and Berry-field-enhanced nonlinear optical effects. However, surface oxidation poses a challenge as it degrades the performance of WTe2. By employing spectroscopic ellipsometry and Raman spectroscopy, the progression of the oxide layer’s thickness and its impact on the optical constants of WTe2 were examined. The results revealed a rapid increase in oxide thickness within the first 24 h, and it reached saturation at ∼10 nm after 45 h of atmospheric exposure. Electrical properties were explored using Kelvin Probe Force Microscopy, uncovering a modification in surface potential and Fermi level following oxidation. Additionally, a SLO/WTe2 heterojunction device exhibited a wide region of positive and negative coexisting photocurrent, highlighting the potential for logical operations in ambient air. Finally, the mechanism of operation of the device is discussed. The electrical and optical properties of the pristine, partially oxidized and fully oxidized WTe2 are analyzed using density functional theory calculations. It shows that the SLO layer has a significant effect on the optical and electronic properties, which is instructive for future wavelength-modulated device optoelectronic logic operations.@en

Van der Waals heterojunctions (vdWHs) have garnered significant attention for their promising applications in optoelectronics, attributed to their exceptional physical attributes. In this study, we present a straightforward approach to fabricating high-performance vdWHs photodetectors. Specifically, we prepared WSO_x/WS₂ vdWH photodetectors through the ozone oxidation of a WS₂ thin films at 100 °C. To characterize the morphology and optical properties of both the WS₂ and WSO_x/WS₂ thin films, we utilized atomic force microscopy (AFM) and Raman spectroscopy. Additionally, X-ray photoelectron spectroscopy (XPS) was employed to delve into the structural evolution by scrutinizing the bonding states of W, O, and S in the WS₂ before and after the ozone oxidation process. The resultant WSO_x/WS₂ vdWH photodetectors exhibited impressive photoelectric performance at wavelengths of 475 nm and 532 nm. It demonstrated a high responsivity of 230.7 A/W, a remarkable specific detectivity of 1.794 × 10¹¹ Jones, and a swift response speed of 60 ms at 475 nm. Furthermore, first-principles calculations based on density functional theory (DFT) were conducted to validate the oxidation kinetics of monolayer WS₂, the type II energy band alignment, and the interlayer charge transfer within the WSO_x/WS₂ vdWH. This research contributes novel insights into the synthesis of two-dimensional transition metal oxides (TMOs)-transition metal dichalcogenides (TMDCs) heterostructures for photodetector applications.

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In the rapidly evolving era of information and intelligence,microelectronic devices are pivotal across various fields, such as mobile devices, big data computing, electric vehicles, and aerospace. However, the electrical performance of these devices often suffers due to residual stress from microelectronic manufacturing. This issue is compounded by the additional thermal stress that accumulates during device operation. Therefore, it is essential to understand, characterize, and control this residual stress to ensure the reliability and efficiency of microelectronic devices. Raman spectroscopy emerges as an invaluable tool for nondestructive, fast, noncontact, and precise testing of micro-scale mechanics, significantly aiding in stress and strain analysis within microelectronic manufacturing. This article aims to provide a thorough overview of the theory and application beyond a mere compilation of recent advances. Theoretically, it critically evaluates existing models that describe the Raman-stress relation. Practically, it explores the application of Raman spectroscopy in researching residual stress in various components, including substrate materials, epitaxial films, and packaging. Through a detailed examination of current applications, it highlights the significance of Raman spectroscopy in understanding micro-scale mechanics. Finally, it offers both theoretical and practical insights into the future developments of Raman-stress detection technology.@en

MAlSiN₃:Eu²⁺ (M = Ca, Sr) is commonly used in high-power phosphor-converted white-light-emitting diodes and laser diodes to promote their color-rendering index. However, the wide application of this phosphor is limited by the degradation of its luminescent properties in high-temperature, high-humidity, and high-sulfur-content environment. Here, the degradation mechanism of the (Sr,Ca)AlSiN₃:Eu²⁺ (SCASN) red phosphor under thermal-moisture-sulfur coupling conditions is investigated. Furthermore, by performing first-principles calculations, the hydrolysis mechanism on an atomic scale is assessed. The adsorption energy (E_ads) and charge transfer (ΔQ) results showed that H₂O chemically adsorbed on the (0 1 0), (3 1 0), and (0 0 1) surfaces of the CaAlSiN₃ (CASN) host lattice. The energy barrier for H₂O dissociation is only 29.73 kJ mol⁻¹ on the CASN (0 1 0) surface, indicating a high dissociation probability. The formation of NH₃, Ca(OH)₂, and CaAl₂Si₂O₈ is confirmed by H⁺ tended to combine with surface N atoms, while OH⁻ combined with the surface Al/Si or Ca atoms. Moreover, ab initio molecular dynamics simulations were performed to further understand the hydrolysis process. This work offers a guidance on the design and applications of luminescent materials in LED packages with higher reliability and stability requirements in harsh environment.

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This work addresses a novel technique for selecting the best process parameters for the 4H–SiC epitaxial layer in a horizontal hot-wall chemical vapor reactor using a transient multi-physical (thermal-fluid-chemical) simulation model and combined with a machine-learning model. An experiment was performed to validate the feasibility of the numerical model. Secondly, a single-factor analysis was conducted to investigate the effects of process parameters, including the deposition temperature, inlet-flow volume, rotational speed of the susceptor, and cavity pressure, on the quality of the 4H–SiC epitaxial layer. Finally, a machine learning algorithm, the ant colony optimization-back propagation neural network (ACO–BPNN), was employed to develop the input/output model and optimize process parameters for obtaining a high-quality epitaxial layer and reducing the optimization cycle and costs. Notably, the optimized process was validated by real experiments, where the error between calculation and experiment is 4.03 % for deposition rate and 0.49 % for coefficient of variation, respectively. The results highlight the model as reliable and lay the foundation for the CVD growth of the 4H–SiC epitaxial layer.

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Tungsten disulfide (WS2) has recently attracted considerable attention owing to its excellent physical, chemical, electronic, and optical properties, leading to increased research into its applications in electronic and optoelectronic devices. However, the oxidation of 2D material affects significantly its optical and electronic properties during storage or processing. This study employs density functional theory (DFT) to analyze the effects of natural and thermal oxidation on the optical and electronic properties of WS2 monolayer. First, the climbing-image nudged elastic band (cNEB) method is applied to analyze transitional states and the potential barriers of WS2 oxidation. It reveals that primarily involves the bonding of oxygen atoms with sulfur atoms, whereas thermal oxidation introduces both oxygen substitutions and generates oxygen vacancies. Second, the electron band structures after natural and thermal oxidation are comparably analyzed, which reveals that natural and thermal oxidation both can narrow the bandgap. Lastly, we investigate the optical properties of WS2 monolayer under different oxidation conditions. The results demonstrate that natural oxidation results in weakened light absorption and a blue shift relative to the pristine WS2, whereas thermal oxidation enhances absorption and induces a red shift. These findings underscore the importance of carefully managing oxidation conditions to effectively modulate the optoelectronic properties of WS2.@en