Abstract ：

Single-crystalline hexagonal tantalum pentoxide (delta-Ta2O5) films were grown on LaAlO3 (010) substrates by MOCVD. A high substrate temperature of 840 degrees C was required to achieve the best crystalline quality and the rootmean-square surface roughness of the optimum film was 0.26 nm. The films grew along the delta-Ta2O5 [100] direction and the heteroepitaxial relationship between the film and the substrate was confirmed as delta-Ta2O5 (100) & Vert;LaAlO3 (010) with delta-Ta2O5 [0001] & Vert;LaAlO3 <001>. The film showed a stoichiometric ratio of Ta2O5 and a pentavalent state of Ta element. The optical band gap of the single-crystalline delta-Ta2O5 film was determined as 4.19 eV.

Keyword ：

delta-Ta2O5 Wide bandgap Heteroepitaxial growth Single-crystalline

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Inorganic-organic hybrid halide perovskites exhibit outstanding optoelectronic characteristics, rendering them promising materials for photovoltaic applications. Despite achieving an impressive power conversion efficiency of up to 26.1%, their extensive use is hampered by the inherent instability of organic constituents and the toxicity associated with lead. With the motivation of searching for stable and non-toxic perovskite photovoltaic materials, we turned our attention to inorganic chalcogenide perovskites and performed extensive material screening excluding toxic elements. We found a stable and flexible chalcogenide perovskite Ba3Te2S7 with the distorted phase. This material boasts partial covalent bonds between Te4+ and S2- ions, enhancing both its structural stability and charge transfer capabilities. Furthermore, we observed a direct-to-indirect bandgap transition in Ba3Te2S7 with values of 0.39 eV and 0.37 eV from the monolayer to bulk, respectively. Notably, the electron mobility of Ba3Te2S7 can reach 10(4) cm(2) V-1 s(-1), surpassing hole mobility by two orders of magnitude. Moreover, the high optical absorption coefficient (10(5)-10(6) cm(-1)) of bulk Ba3Te2S7 in the visible-light region, owing to the allowed band-edge optical transitions, combined with favorable conduction-band offsets for efficient electron injection from the absorber to the electron transporting layer (TiO2), positions Ba3Te2S7 as a promising material for photovoltaic applications.

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Advanced composites with superior wave attenuation or vibration isolation capacity are in high demand in engineering practice. In this study, we develop the hybrid dynamic shear -lag model with Bloch's theorem to investigate the hybrid effect of reinforcement on wave attenuation in bioinspired staggered composites. We present for the first time the relationship between macroscopic wave filtering and hybridization of building blocks in staggered composites. Viscoelasticity was taken into account for both reinforcement and matrix to reflect the damping effect on wave transmission. Our findings indicate that reinforcement hybridization significantly enhances wave attenuation performance through two critical parameters: the linear stiffness and linear density of reinforcements. For purely elastic constituents, reinforcement hybridization consistently improves wave attenuation by reducing the initial frequency of the first bandgap and broadening it. For viscoelastic constituents, increasing the heterogeneity of reinforcements can benefit wave attenuation, particularly in ultralow frequency regimes, due to the strengthening of the damping effect. Our case study demonstrates that controlling the difference in linear density can result in up to a 59 % reduction in energy transmission. Our analysis suggests that hybridizing reinforcements could provide a new approach to designing and synthesizing advanced composites with exceptional wave attenuation performance.

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Phononic crystal Hybrid effect Bioinspired composites Viscoelastic wave Wave attenuation

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Carrier-selective passivating contacts in crystalline silicon (c-Si) solar cells have expanded from doped silicon films to non-silicon wide-bandgap materials to reduce parasitic absorption and production costs. Titanium oxide (TiOx) has emerged as one of the most promising materials and has achieved high performance in c-Si solar cells. In this work, TiOx is explored as a passivation interlayer in hole-selective contacts rather than conventional electron-selective contacts. Theoretical calculations and experimental results demonstrate that negative charges and shallow states in TiOx, derived from oxygen vacancies (VO), enhance surface passivation and assist hole tunneling, respectively. As a strategy to modulate VO, forming gas annealing is performed to further improve hole selectivity. By incorporating the TiOx passivation interlayer into MoOx-based c-Si solar cells, we achieve an improved efficiency and stability of the device, with the highest efficiency of 21.28%. This work advances the understanding of TiOx as a promising material to enhance hole selectivity for c-Si solar cells.

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The second-order nonlinear-polarization originated from the interaction between thin-film materials with second-order nonlinear susceptibility (chi((2))) and high-power laser is essential for integrated optics and photonics. In this work, strong second-order nonlinear-polarization was found in a-axis oriented Zn1-xMgxO (ZnMgO) epitaxial thin-films with Li incorporation, which were deposited by radio-frequency magnetron sputtering. Mg incorporation (x > 0.3) causes a sharp fall in the matrix element chi(33) of chi((2)) tensor, although it widens optical bandgap (E-opt). In contrast, moderate Li incorporation significantly improves chi(33) and resistance to high-power laser pulses with a little influence on E-opt. In particular, a Zn0.67Mg0.33O:Li [Li/(Zn + Mg + Li) = 0.07] thin-film shows a |chi(33)| of 36.1 pm V-1 under a peak power density (E-p) of 81.2 GW cm(-2), a resistance to laser pulses with E-p of up to 124.9 GW cm(-2), and an E-opt of 3.95 eV. Compared to that of ZnO, these parameters increase by 37.8%, 53.4%, and 18.6%, respectively. Specially, the Zn0.67Mg0.33O:Li shows higher radiation resistance than a Mg-doped LiNbO3 crystal with a comparable E-opt. First-principle calculations reveal the Li occupation at octahedral interstitial sites of wurtzite ZnO enhances radiation resistance by improving structural stability. X-ray photoelectron spectroscopy characterizations suggest moderate Li incorporation increases chi(33) via enhancing electronic polarization. These findings uncover the close relationship between the octahedra interstitial defects in wurtzite ZnMgO and its nonlinear-polarization behavior under the optical frequency electric field of high-power laser.

Keyword ：

high-power laser Li incorporation second-order nonlinear susceptibility ZnMgO thin-films interstitial defects resistance

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In order to investigate the propagation and isolation mechanisms of elastic waves, we propose a programmable curved beam periodic structure (PCBPS). The PCBPS is assembled by a unit cell containing bistable curved beams, which is equivalent to a spring oscillator system, and is used to analyze the principle of bandgap formation. We employ the finite element method (FEM) and theoretical analysis to validate the proposed equivalent model. By equating the spring oscillator system, we compute closed-form solutions to demonstrate the accuracy and predictability of the dispersion relation. Our results show that the spring-oscillator model can accurately predict the structural bandgap of PCBPS while obtaining the effect of the geometrical parameters of the unit cell on the structural bandgap. The ideas presented and the results obtained have significant potential for designing functional structures and facilitating the practical application of periodic structures for wave insulation and propagation control in different frequency ranges. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.

Keyword ：

Elastic waves Energy gap Curved beams and girders Geometry Periodic structures

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2D materials hold potential for developing low-cost, high-performance broadband polarized infrared photodetectors. However, the development of 2D broadband polarized infrared photodetectors is largely constrained by the fixed bandgap spectral (cutoff wavelength) limitations of available semiconductors. Here, an approach is presented that leverages anisotropic interlayer excitons (IEXs) within a type-II van der Waals heterojunction, achieving polarization photoresponse beyond the intrinsic bandgap spectral limits of its constituent semiconductors. By constructing heterojunctions using CrPS4 and ReS2, a unique type-II band alignment, enabling strong anisotropic optical excitation is achieved through the interlayer sub-bandgap, which is lower than the intrinsic bandgaps of both CrPS4 and ReS2. The heterojunction exhibits a responsivity of 0.3 A W-1 and a polarization ratio of 1.3 at an incident photon energy of 0.8 eV, comparable to naturally anisotropic materials with intrinsic bandgaps. Additionally, the potential of anisotropic IEXs is demonstrated for dual-band polarization detection by introducing a ReS2/CrPS4/MoS2 heterojunctions with distinct inte rlayer sub-bandgaps. This flexible design of IEXs offers a new platform for multi-dimensional optical sensing and on-chip optoelectronic applications.

Keyword ：

polarization detection Interlayer excitons van der waals heterojunction band alignment

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Suppression of noise and vibration suppression is important in various fields, such as the living environment, industrial development, and national defense and security. The bandgap properties of phononic crystal metamaterials provide an approach for controlling and eliminating harmful vibrations in equipment and noise in the environment. In this study, we used two types of two-dimensional honeycomb gyroscopic metamaterials: free and constrained. The dynamic equations of the two systems were established using angular momentum and Lagrange theorems. The dispersion relations of the two systems were obtained based on the Bloch theorem, and the influence of the gyroscope angular momentum or gyroscope speed on the dispersion relations was analyzed. Numerical simulations were conducted to analyze the wave propagation characteristics and polarization under different excitation conditions in a limited space for both types of metamaterial structures. The constrained -type and free -type metamaterials were compared, and the regularities of the dispersion relations and wave propagation characteristics by the gyroscope effect were summarized. This study provided a comprehensive and in-depth understanding of the bandgap and wave propagation properties of gyroscopic metamaterials and provided ideas for the design of bandgap modulation in metamaterials.

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Planar feedback micro-nanoscale cavities, shaped by advances in nanofabrication, have revolutionized laser technology, giving rise to chip-scale, low-threshold lasers with wide-ranging applications, spanning from atmospheric investigation to incorporation into central devices such as smartphones and computer chips. The complicated designs of these cavities, shaped by the physics of periodic and quasiperiodic structures, empower efficient manipulation of light-matter interaction and coherent light coupling, minimizing losses. This review thoroughly explores the underlying concepts and crucial parameters of planar feedback microcavities, shedding light on the photophysical behavior of recent gain materials pivotal for realizing optimal lasing properties. The examination extends to photonic crystal bandgap (PhC BG) microcavity lasers, specifically with periodic and quasiperiodic architectures. In-depth assessments probe into the principles and designs of each architecture, exploring features such as wavelength selectivity, tuneability, lasing patterns, and the narrow linewidth characteristics inherent in distributed feedback (DFB) microcavity lasers. The review highlights the intriguing characteristics of non-radiative bound states in the continuum (BIC) within periodic architectures, emphasizing trends toward high-quality factors, low thresholds, and directional and vortex beam lasing. It also explores the nascent field of Quasiperiodic (QP) microcavity lasers, addressing challenges related to disorder in traditional periodic structures. Comparative inquiries offer insights into the strengths and limitations of each architecture, while discussions on challenges and future directions aim to inspire innovation and collaboration in this dynamic field. © 2024, Electromagnetics Academy. All rights reserved.

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Microcavities Nanotechnology

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Violet-emitting perovskite quantum dots (QDs) are of great significance for theoretical and experimental research aimed at promoting the development of environmentally friendly violet light-emitting diodes (LEDs). Nevertheless, the synthesis of violet perovskite QDs via ligand-assisted reprecipitation is challenging due to the significant bandgap. A simple and economical cryo-bonding ligand-assisted reprecipitation (Cb-LARP) method is proposed as a means of synthesizing deep violet lead-free organic-inorganic hybrid perovskite (OIHP) QDs, with the objective of increasing the bandgap in the material. The MA(3)Bi(2)Br(9) QDs synthesized by the Cb-LARP method exhibit bright violet luminescence at 400 nm, with a PLQY of 50.1%. Moreover, the photoluminescence peak of the QDs can be adjusted from 402 to 393 nm by modifying the final reaction time. It is noteworthy that the MA(3)Bi(2)Br(6)Cl(3) QDs exhibited ultraviolet emission at 379 nm, corresponding to a PLQY of 35.4%. Similarly, the emission peak of the QDs can be tuned from 379 to 376 nm by changing the final reaction time. The results demonstrate that the deep violet emitting OIHP QDs have been successfully synthesized. This study provides a theoretical reference for short-wavelength perovskite materials and an experimental reference for the study of violet and UV quantum-dot light-emitting diode devices.

Keyword ：

ultraviolet light Cb-LARP perovskite structure quantum dots

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