The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
Zhe Chuan Feng - One of the best experts on this subject based on the ideXlab platform.
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revealing the surface electronic structures of algan deep ultraviolet multiple quantum wells with lateral polarity domains
Photonics Research, 2020Co-Authors: Wei Guo, Li Chen, Yingda Qian, Moheb Sheikhi, Jason Hoo, Shiping Guo, Jianzhe Liu, Feras Alqatari, Zhe Chuan FengAbstract:We report on the carrier dynamic and electronic structure investigations on AlGaN-based deep-ultraviolet multiple quantum wells (MQWs) with lateral polarity domains. The localized potential maximum is predicted near the domain boundaries by first-principle calculation, suggesting carrier localization and efficient radiative recombination. More importantly, lateral Band diagrams of the MQWs are proposed based on electron affinities and Valance Band levels calculated from ultraviolet (UV) photoelectron spectroscopy. The proposed lateral Band diagram is further demonstrated by surface potential distribution collected by Kelvin probe microscopy and the density-of-state calculation of energy Bands. This work illustrates that lateral polarity structures are playing essential roles in the electronic properties of III-nitride photonic devices and may provide novel perspective in the realization of high-efficiency UV emitters.
Hrvoje Petek - One of the best experts on this subject based on the ideXlab platform.
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theoretical study of the molecular and electronic structure of methanol on a tio 2 110 surface
Physical Review B, 2009Co-Authors: Jin Zhao, Jinlong Yang, Hrvoje PetekAbstract:We present density-functional-theory calculations of the molecular and electronic structure of methanol adsorption on stoichiometric TiO2(110) surface. We have investigated 11 different molecular and dissociated adsorption structures of CH3OH at 1 monolayer coverage. The relative stabilities of different structures depend on the chemisorption-induced charge transfer, the relative strengths of different types of hydrogen bonds, the steric hindrance between methyl groups and the surface stress. We found the intermolecular hydrogen bonding to play an important role in stabilizing the overlayer. We also investigated the occupied and unoccupied surface electronic structure, and the adsorbate-induced surface dipole moment and work-function changes. The electronic structures show that the highest-occupied molecular orbital of CH3OH is near the Valance-Band maximum, which reflects the character of CH3OH as a hole scavenger on TiO2 surfaces. The unoccupied partially solvated or “wet” electron states for CH3OH on TiO2 are primarily distributed on H atoms of methyl groups. Despite many different structural motifs, the wet-electron-state energy primarily correlates with the surface dipole moment.
Alaa A Akl - One of the best experts on this subject based on the ideXlab platform.
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effect of se addition on optical and electrical properties of chalcogenide cdsse thin films
Superlattices and Microstructures, 2016Co-Authors: Ahmed Saeed Hassanien, Alaa A AklAbstract:Abstract Compositional dependence of optical and electrical properties of chalcogenide CdSxSe1−x (0.4 ≥ x ≥ 0.0 at. %) thin films was studied. Cadmium sulphoselenide films were deposited by thermal evaporation technique at vacuum (8.2 × 10−4 Pa) onto preheated glass substrates (523 K). The evaporation rate and film thickness were kept constant at 2.50 nm/s and 375 ± 5 nm, respectively. X-ray diffractograms showed that, the deposited films have the low crystalline nature. Energy dispersive analysis by X-ray (EDAX) was used to check the compositional elements of deposited films. The absorption coefficient was determined from transmission and reflection measurements at room temperature in the wavelength range 300–2500 nm. Optical density, skin depth, optical energy gap and Urbach's parameters of CdSSe thin films have also been estimated. The direct optical energy gap decreased from 2.248 eV to 1.749 eV when the ratio of Se-content was increased from 0.60 to 1.00 . Conduction Band and Valance Band positions were evaluated. The temperature dependence of dc-electrical resistivity in the temperature range (293–450 K) has been reported. Three conduction regions due to different conduction mechanisms were detected. Electrical sheet resistance, activation energy and pre-exponential parameters were discussed. The estimated values of optical and electrical parameters were strongly dependent upon the Se-content in CdSSe matrix.
Yanhui Lv - One of the best experts on this subject based on the ideXlab platform.
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the surface oxygen vacancy induced visible activity and enhanced uv activity of a zno1 x photocatalyst
Catalysis Science & Technology, 2013Co-Authors: Yanhui Lv, Xinguo G, Ruilong L ZongAbstract:A ZnO1−x photocatalyst with surface oxygen vacancies was fabricated by the controllable reduction of H2. After surface oxygen vacancies were introduced into the ZnO photocatalyst, a high visible-light-driven activity and photocurrent was produced. The UV activity for the degradation of MB and the photocurrent was enhanced about 2.2 times and 2.5 times, respectively. The visible-light activity resulted from the narrowed Band gap due to the overlap of the Valance Band (VB) of the surface oxygen vacancy with O2p. The main active species are photoinduced holes and MB can be mineralized completely under visible-light irradiation. The overlap of the VB of the surface oxygen vacancy with O2p also extended the width of the VB and resulted in the increase of the separation efficiency of the photoinduced electron–hole pairs and the enhancement of the UV photoactivity greatly. The surface oxygen vacancy only increased the separation efficiency and did not change the photocatalytic degradation process, and the main oxidative species was still the photoinduced holes. The bulk oxygen vacancy can be formed via depth reduction at 700 °C for 5 h and resulted in the loss of photoactivity due to bulk defects.
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production of visible activity and uv performance enhancement of zno photocatalyst via vacuum deoxidation
Applied Catalysis B-environmental, 2013Co-Authors: Yanhui Lv, Ruilong ZongAbstract:Abstract ZnO photocatalyst with surface oxygen vacancies was obtained via vacuum deoxidation method. The concentration of surface oxygen vacancies could be controlled by tuning the temperature and time in vacuum, which governs the production of visible activity and the enhanced level of photocatalytic activity. The optimum UV photocatalytic activity and photocurrent of vacuum ZnO are almost 1.7 and 2.4 times as high as that of pure ZnO, respectively. Interestingly, the dramatic visible photocatalytic activity and distinct photocurrent both are generated due to the introducing of oxygen vacancies on ZnO surface. The enhancement in performance is attributed to the high separation efficiency of photogeneration electron–hole pairs due to the broadening of the Valance Band (VB) induced by surface oxygen-vacancies states. The production of visible photoactivity is demonstrated to be the narrow of energy Band gap resulting from the rising of VB.
Hyun Jae Kim - One of the best experts on this subject based on the ideXlab platform.
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defect reduction in photon accelerated negative bias instability of ingazno thin film transistors by high pressure water vapor annealing
Applied Physics Letters, 2013Co-Authors: You Seung Rim, Wooho Jeong, Byung Du Ahn, Hyun Jae KimAbstract:We investigated the effects of high-pressure water vapor annealing (WHPA) under negative bias temperature illumination stress and light incidence on amorphous InGaZnO thin-film transistors. WHPA could improve device reliability and reduce the hump occurrence. It was attributed to the effective reduction and passivation in oxygen vacancies under WHPA. By comparing the experimental and technology computer-aided design simulation, we could confirm that the low-density of deep-donor-like oxygen vacancy (Vo) states near the Valance Band maximum contributed to the reduction of photo-excited single ionized oxygen vacancies (Vo+) and double ionized oxygen vacancies (Vo2+) as shallow-donor states near the conduction Band minimum.
