A self-driven photodetector based on a SnS2/WS2 van der Waals heterojunction with an Al2O3 capping layer

Photodetectors based on two-dimensional (2D) materials have attracted considerable attention because of their unique properties. To further improve the performance of self-driven photodetectors based on van der Waals heterojunctions, a conductive band minimum (CBM) matched self-driven SnS₂/WS₂ van der Waals heterojunction photodetector based on a SiO₂/Si substrate has been designed. The device exhibits a positive current at zero voltage under 365 nm laser illumination. This is attributed to the built-in electric field at the interface of the SnS₂ and WS₂ layer, which will separate and transport the photogenerated carriers, even at zero bias voltage. In addition, the Al₂O₃ layer is covered by the surface of the SnS₂/WS₂ photodetector to further improve the performance, because the Al₂O₃ layer will introduce tensile stress on the surface of the 2D materials leading to a higher electron concentration and smaller effective mass of electrons in the films. This work provides an idea for the research of self-driven photodetectors based on a van der Waals heterogeneous junction.     

基于近红外光谱检测技术的水泥生料成分含量检测研究

近红外光谱检测技术已经成功应用于水泥生料成分的快速检测,但我国水泥企业在生产水泥生料时所用原材料品种不一,使用不同的原材料进行生产时对近红外光谱建模带来一定影响.为了研究不同原料生产的水泥生料近红外光谱建模差异,对不同地区水泥生产线所生产的水泥生料进行建模研究.选取两个不同地区水泥生产线的水泥生料样本各95份和82份,...     

Growth and magnetism of Ni nanoparticles in Ni/Al2O3/Si or Si3N4 multilayers

We report on the fabrication of Ni/Al₂O₃/Si and textured Ni/Al₂O₃/Si₃N₄ multilayers containing Ni nanoparticles that exhibit significantly improved results. The secondary phases arising from thermal reaction between Ni and Si can be remarkably suppressed with increasing layers of Al₂O₃ and deposition of Ni/Al₂O₃ multilayers on Si₃N₄ substrates. Atomic force microscopy shows the formation of large as well as nanoclusters of Ni when grown on Si, whereas textured Ni nanoparticles are formed on Si₃N₄ substrates. The magnetization measurements on Ni/Al₂O₃/Si containing a single buffer layer of Al₂O₃ shows higher coercivity field with magnetic nanowire-like behavior, whereas with several Al₂O₃ alternate layers almost a superparamagnetic-like behavior is observed. However, significantly improved magnetic hysteresis was observed in textured Ni/Al₂O₃/Si₃N₄ multilayers due to preferred alignment of Ni nanocrystallites.     

基于熔融玻璃的预沉积法生长毫米级单晶MoS2及WS2-MoS2异质结

MoS₂是一种具有优异光电性能和奇特物理性质的二维材料,在电子器件领域具有巨大的应用潜力.高效可控生长出大尺寸单晶MoS₂是该材料进入产业应用所必须克服的重大难关,而化学气相沉积技术被认为是工业化生产二维材料的最有效手段.本文介绍了一种利用磁控溅射预沉积钼源至熔融玻璃上,通过快速升温的化学气相沉积技术生长出尺寸达1 mm的单晶MoS₂的方法,并通过引入WO₃粉末生长出了二硫化钼与二硫化钨的横向异质结(WS₂-MoS₂).拉曼和荧光光谱仪测试表明所生长的样品具有较好的晶体质量.利用转移电极技术制备出了背栅器件样品并对其进行了电学测试,在室温常压下开关比可达10~5,迁移率可达4.53 cm~2/(V·s).这种低成本高质量的大尺寸材料生长方法为二维材料电子器件的大规模应用找到了出路.     

Atomic layer deposition of Cr2O3 thin films: Effect of crystallization on growth and properties

Atomic layer deposition of Cr₂O₃ thin films from CrO₂Cl₂ and CH₃OH on amorphous SiO₂ and crystalline Si(1 0 0) and -Al₂O₃() substrates was investigated, and properties of the films were ascertained. Self-limited growth with a rate of 0.05–0.1 nm/cycle was obtained at substrate temperatures of 330–420 °C. In this temperature range epitaxial eskolaite was formed on the -Al₂O₃() substrates. The predominant crystallographic orientation in the epitaxial films depended, however, on the growth temperature and film thickness. Sufficiently thick films grown on the SiO₂ and Si(1 0 0) substrates contained also the eskolaite phase, but thinner films deposited at 330–375 °C on these substrates were amorphous. The growth rate data of films with different phase composition allowed a conclusion that the crystalline phase grew markedly faster than the amorphous phase did. The amorphous, polycrystalline and epitaxial films had densities of 4.9, 5.1 and 5.1–5.3 g/cm³, respectively.     

微通道板离子壁垒膜粒子阻透特性的蒙特卡罗模拟

在三代微光像管中,微通道板(MCP)输入面上覆盖一层超薄离子壁垒膜(IBF),目的是保护光电阴极,延长像管使用寿命.为了深入研究离子壁垒膜的特性,本文对Al2O3和SiO2两种离子壁垒膜的粒子阻透能力进行了蒙特卡罗模拟,结果表明:5 nm厚Al2O3和SiO2离子壁垒膜的死电压分别为230 ～240 V和220～230...     

Enhanced photoluminescence of monolayer MoS2 on stepped gold structure

Different MoS₂/Au heterostructures can play an important role in tuning the photoluminescence (PL) and optoelectrical properties of monolayer MoS₂. Previous studies of PL of MoS₂/Au heterostructures were mainly limited to the PL enhancement by using different Au nanostructures and PL quenching of monolayer MoS₂ on flat Au surfaces. Here, we demonstrate the enhanced excitonic PL emissions of monolayer MoS₂/Au heterostructures on Si/SiO₂ substrates. By transferring the continuous monolayer MoS₂ onto a stepped Au structure consisting of 60-nm and 100-nm Au films, the MoS₂/Au-60 and MoS₂/Au-100 heterostructures exhibit enhanced PL emissions, each with a blue-shifted PL peak in comparison with the MoS₂/SiO₂. Furthermore, the PL intensity of MoS₂/Au-60 is about twice larger than that of MoS₂/Au-100. The different enhanced excitonic PL emissions in MoS₂/Au heterostructures can be attributed to the different charge transfer effects modified by the stepped Au structure. This work may provide an insight into the excitonic PL and charge transfer effect of MoS₂ on Au film and yield novel phenomena in MoS₂/Au heterostructures for further study of PL tuning and optoelectrical properties.     

Pillar effects in MoS2 catalysts supported on Al and Zr pillared clays in a hydrotreatment reaction: A preliminary study

Molybdenum (Mo) supported on aluminum-pillared clay (Al-PILC) and zirconium-pillared clay (Zr-PILC) with contents of 0.6, 1.4 and 2.8 atoms of Mo/nm² were prepared and tested in the hydrogenation (HYD) of naphthalene (NP). It was found that the molybdenum sulfide (MoS₂) catalysts supported on Zr- pillared clays were more active than the samples supported on Al-pillared clays and catalysts supported on alumina. The catalysts were characterized by X-ray diffraction (XRD), thermogravimetric analysis, nitrogen adsorption and transmission electron microscopy (TEM). Characterization analysis clearly pointed out to a close interaction of MoS₂ with ZrO₂ in the pillared clays. Therefore, the highest hydrogenation activities can be related to the presence of an interaction of MoS₂ with ZrO₂, probably with a different electronic interaction between the active phase and the support, than that reported for the MoS₂/Al₂O₃ system.     

太赫兹波段介质微腔光学特性研究

采用匀胶法制备了厚度在微米量级的 Si/[TiO₂/Al₂O₃]²TiO₂和Si/[TiO₂/MgO]²/TiO₂ 多层介质膜反射镜. 采用太赫兹(THz)时域透射光谱系统获得了多层膜的时域透射谱. 用传输矩阵法模拟了Si/[TiO₂/Al₂O₃]²TiO₂ 和Si/[TiO₂/MgO]²/TiO₂两种分布式布拉格反射镜 (DBR)的反射相移和相位穿透深度等光学特性. 设计了两种结构为 DBR/LT-GaAs/DBR的对称THz光学微腔结构并模拟了腔结构的辐射光谱. 结果表明:通过引入谐振腔, 两种DBR组成的微腔器件在谐振波长处的强度分别提高了19和14倍. 其中Si/[TiO₂/Al₂O₃]²TiO₂/LT-GaAs (12 μm)/ [TiO₂/Al₂O₃]²TiO₂腔的辐射光谱存在两个峰, 分别位于208和248 μm, 并分析了出现两个谐振峰的原因. 探讨了通过引入介质谐振腔实现对THz源的辐射特性进行调控的可行性. 关键词： 分布式布拉格反射镜 光子晶体 穿透深度 太赫兹微腔     

测量离子束横向截面的闪烁体屏的热分析

针对基于闪烁屏-CCD(电荷耦合元件)相机的氘离子束横向强度分布测量系统,利用ANSYS软件模拟计算了在直流及脉冲模式下,能量100 keV、束斑直径3 mm氘离子轰击造成的Al₂O₃, SiO₂以及锗酸铋(BGO)三种候选闪烁体材料的表面温度变化。结果表明,在30 μA的直流氘离子束轰击下,闪烁体表面温度随辐照时间急剧地升高。持续时间10 min的氘离子束轰击将使三种材料前表面的温度分别升高131,234和649 ℃。对于峰值流强30 μA、重复频率1 Hz、脉宽5 μs的重复频率脉冲氘离子束,每个脉冲引起的三种闪烁屏表面的温度升高均小于0.05 ℃,且长时间的离子辐照基本不会造成闪烁屏的表面温度有明显的升高。对于脉宽5 μs的单脉冲氘离子束,三种材料的表面温度均随离子流强近似呈线性地增加。在单脉冲模式下,Al₂O₃,SiO₂以及BGO闪烁屏能允许的最高离子流强分别为2.32,1.08和0.72 A,超过此流强其表面温度将达到熔点。     

Dielectrics for passivation of planar InP/InGaAs diodes

We have investigated dielectrics for passivating planar InP or InGaAs photodiodes: thermally evaporated Al₂O₃ and SiO, sputtered Si₃N₄ and SiO₂ and also SiO₂ using chemical vapour deposition. The measured bulk and field-effect properties of all dielectrics excluding sputtered SiO₂ were suitable for this application. In planar InGaAs diodes with Cd diffused or Mg implanted p⁺-region a disordered dielectric/semiconductor surface led to high reverse current densities above 1 mA/cm². In InP diodes with p⁺-diffusion and dielectrics exhibiting positive flatband voltages, e.g. Si₃N₄ and Al₂O₃, reverse current densities of 10 μA/cm² were measured probably caused by a slight inversion of the semiconductor surface. With a SiO or CVD-SiO₂ passivating layer on n-InP lowest leakage current densities (10 nA/cm²) were achieved. Very low dark-current planar photodiodes InP/InGaAsP/InGaAs have been fabricated using SiO passivation (30 nA/cm²).     

沟道层厚度对室温制备的In2O3薄膜晶体管器件性能的影响

在室温下采用直流磁控溅射以SiO₂/Si为衬底制备了不同沟道层厚度的底栅式In₂O₃薄膜晶体管,讨论了沟道层厚度对底栅In₂O₃薄膜晶体管的电学性能的影响。实验结果表明:器件的特性与沟道层厚度有关,最优沟道层厚度的In₂O₃薄膜晶体管为增强型,其阈值电压为2.5 V,开关电流比约为10⁶,场效应迁移率为6.2 cm²·V^-1·s^-1。     

Substrate temperature dependence of the photoluminescence efficiency of co-sputtered Si/SiO2 layers

Si particles embedded in an SiO₂ matrix were obtained by co-sputtering of Si and SiO₂ at various deposition temperatures T_d (200–700°C) and annealing at different temperatures T_a (900–1100°C). The systems were characterized by X-ray photoelectron, Raman scattering, infrared absorption and photoluminescence spectroscopy techniques. The results show that the photoluminescence efficiency is strongly dependent on the degree of phase separation between the Si nanocrystals and the SiO₂ matrix. This is likely connected with the Si/SiO₂ interface characteristics, together with the features indicating the involvement of quantum confinement.     

Stability of silver clusters in mordenites with different SiO2/Al2O3 molar ratio

The stability and decay of silver clusters characterized by absorption bands 320 and 285 nm incorporated in mordenites with different SiO₂/Al₂O₃ molar ratios were studied under ambient conditions. Significantly different rates of disappearance of these two bands were the basis for assigning them to different silver species. Oxidation converts the clusters peaking at 320 and 285 nm into other silver clusters characterized by absorption bands at 310 and 240 nm, respectively. The oxidation of silver clusters peaking at 285 nm is significantly faster than that at 320 nm. The stability of both original clusters decreases with acid site strength that, in its turn, depends on Si0₂/Al₂O₃ molar ratio. The minimum lifetime of clusters peaking at 320 and 285 nm equal to ca. 40 and 20 days, respectively, was observed for mordenite characterized by the strongest acid sites. For mordenites possessing weaker acid sites, the lifetime of these clusters is found to be more than 50 months. The oxidation of silver clusters is reversible, and re-reduced silver clusters were revealed to possess the same electron structure as original ones.     

氢化氧化铝的同位素效应研究

在B3LYP/6-311++G(d,p)水平上预测了Al2O3H3分子的较低能量构型.其基态构型具有C s对称性,电子态为1A′.通过研究Al2O3M3和M2(M=H,D,T)的能量E、定容热容C V和熵S,用电子振动近似讨论了Al2O3+3/2M2→Al2O3M3反应的氢同位素效应,得到了Al2O3氢化的热力学函数?H0,?S0,?G0,及平衡压力与温度的关系.研究表明,氧化物Al2O3吸附氢(氘,氚)反应的同位素排代效应顺序为氚排代氘,氘排代氢,与钛等金属的同位素排代顺序相反.但排代效应都非常弱,且随着温度的增加趋于消失.     

悬浮二维晶体材料反射光谱和光致发光光谱的周期性振荡现象

研究了在二氧化硅/硅衬底上制备的悬浮石墨烯以及二硫化钼的反射光谱以及悬浮二硫化钼的光致发光光谱.研究发现:悬浮多层石墨烯的反射光谱表现出明显的振荡现象,并且该振荡具有一定的周期性;振荡周期的大小不依赖于悬浮多层石墨烯的层数,而是随着衬底上沉孔深度(空气层厚度)的增加而减小.利用多重光学干涉模型可以解释这种振荡现象以及振荡周期随沉孔深度改变的变化趋势.该模型计算结果表明,只有当沉孔深度达到微米量级时这种振荡现象才会显著出现;并且可由振荡周期定量地确定出沉孔深度.对于悬浮的二硫化钼样品,其反射光谱和光致发光光谱也出现了类似的振荡现象.这表明这种振荡现象是在各种衬底上悬浮二维材料反射光谱和光致发光光谱的一种普遍性结果,也预示悬浮二维材料器件的电致发光光谱也会出现类似的振荡现象,对悬浮二维晶体材料的物理性质和器件性能研究具有一定的参考价值.     

Fixed charge and interface traps at heterovalent interfaces between Si(1 0 0) and non-crystalline Al2O3–Ta2O5 alloys

Characterization by Auger electron spectroscopy (AES) and Fourier transformation infrared spectroscopy (FTIR) confirms (Ta₂O₅)_x(Al₂O₃)_1−x alloys are homogeneous pseudo-binary alloys with increased thermal stability with respect to end member oxides, Ta₂O₅ and Al₂O₃. Capacitance–voltage (C–V) and current density–voltage (J–V) data as a function of temperate show that the Ta d-states of the alloys act as localized electron traps, and are at an energy approximately equal to the conduction band offset of Ta₂O₅ with respect to Si.     

Enhanced luminescence from transparent Ni-doped MgO–Al2O3–SiO2 glass ceramics by Ga2O3 addition

Transparent Ni²⁺-doped MgO–Al₂O₃–SiO₂ glass ceramics without and with Ga₂O₃ were synthetized. The precipitation of spinel nanocrystals, which was identified as solid solutions in the glass ceramics, could be favored by Ga₂O₃ addition and their sizes were about 7.6 nm in diameter. The luminescent intensity of the Ni²⁺-doped glass ceramics was largely enhanced by Ga₂O₃ addition which could mainly be caused by increasing of Ni²⁺ in the octahedral sites and the reduction of the mean frequency of phonon density of states in the spinel nanocrystals of solid solutions. The full width at half maximum (FWHM) of emissions for the glass ceramics with different Ga₂O₃ content was all more than 200 nm. The emission lifetime increased with the Ga₂O₃ content and the longest lifetime is about 250 μs. The Ni²⁺-doped transparent glass ceramics with Ga₂O₃ addition have potential application as broadband optical amplifier and laser materials.     

Dramatic reduction in dark current of β-Ga2O3 ultraviolet photodectors via β-(Al0.25Ga0.75)2O3 surface passivation

Solar-blind ultraviolet photodetectors with metal-semiconductor-metal structure were fabricated based on β -(Al_0.25Ga_0.75)₂O₃/β -Ga₂O₃ film grown by metal-organic chemical vapor deposition. It was known that various surface states increase dark current and a large number of defects can hinder the transport of carriers, resulting in low switching ratio and low responsivity of the device. In this work, β -(Al_0.25Ga_0.75)₂O₃ films are used as surface passivation materials. Owning to its wide band gap, we obtain excellent light transmission and high lattice matching with β -Ga₂O₃. We explore the change and mechanism of the detection performance of the β -Ga₂O₃ detector after β -(Al_0.25Ga_0.75)₂O₃ surface passivation. It is found that under the illumination with 254 nm light at bias 5 V, the β -(Al_0.25Ga_0.75)₂O₃/β -Ga₂O₃ photodetectors show dark current of just 18 pA and high current on/off ratio of 2.16×10⁵. The dark current is sharply reduced about 50 times after passivation of the β -Ga₂O₃ surface, and current on/off ratio increases by approximately 2 times. It is obvious that β -Ga₂O₃ detectors with β -(Al_0.25Ga_0.75)₂O₃ surface passivation can offer superior detector performance.     

Acousto-optic light deflection in an Al2O3 optical waveguide structure

The total deflection of an optical guided wave by a surface acoustic wave (SAW) in a silicon-based SiO₂/AL₂O₃/SiO₂ optical waveguide structure is reported. The SAW is generated by an interdigital transducer with piezoelectric ZnO deposited on top of the optical waveguide structure.