SiOx precipitate composition in Si,revisited: Discussion closed?

The composition SiO_x of oxide precipitates in Si has been discussed for the past thirty years with experimentally estimated x ‐values ranging between 1 and 2. It is shown that this spread of x ‐values can be explained by calculating the average composition taking into account temperature and anneal time dependent size and shape of the precipitates and the limitations and probing volumes of the various characterization techniques. Hereby it is assumed that the oxygen‐rich (SiO₂?) core of the precipitates is surrounded by a 2 nm thin SiO layer as revealed by recent electron energy loss spectroscopy analyses. For plate‐like precipitates thinner than and for octahedral precipitates smaller than 6 nm, x ≈ 1. For larger precipitates, the central part of the precipitate consists of SiO_x with x close to 2 and the precipitate has an average x between 1 and 1.3 for plate‐like and up to 1.9 for octahedral precipitates. The predicted x ‐values for different precipitate sizes and morphologies, are compared with published experimental data. SiO_x precipitate nucleation and initial growth should be simulated assuming x = 1 and Fourier transform infrared spectra of precipitates assuming a mixture of SiO₂ and amorphous Si. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

SiOx纳米管的制备及其发光特性

Amorphous SiOx nanotubes with homogeneous diameters were fabricated in large-scale on silicon substrate by thermal evaporation method, with liquid gallium as medium. The average diameter of tubes is about 80 nm and the length is more than 10 1m, with small ratio between the inner and outer diameter of the tube. The silicon element in the substrate and the residual oxygen element in reaction chamber were first dissolved into liquid Ga. Then the SiOx precipitated from the surface of gallium droplet, forming the nanotube structure with Ga droplet being the center. The room temperature photoluminescence measurements under excitation at 260 nm show that the SiOx nanotubes has a strong blue emission at 453 nm with two shoulders at 410 and 480 nm respectively, which may be related to oxygen defects. The preparation method improved the traditional complicated method and also provided a new way to fabricate SiOx nanotubes in large quantity.     

新奇纳米结构SiO_x的自组织生长及其发光

采用化学气相沉积法,以纳米Mg2Si和SiO2的混合粉体作为硅源,在较低温度自组织生长了大量绳状SiOx新奇纳米结构。利用扫描电子显微镜、透射电子显微镜等手段对纳米结构进行了系统表征,并在室温观测到了光致发光,其发光峰峰位在560nm附近,在此基础上对该纳米结构的生长机理进行了深入的讨论。     

Ultrathin Silicon Oxide Film-Induced Enhancement of Charge Separation and Transport of Nanostructured Titanium(IV) Oxide Photoelectrode

The development of nanostructured semiconductor electrodes represented by a mesoporous TiO₂ nanocrystalline (mp-TiO₂) film is currently bringing great progresses in photoelectrochemical (PEC) devices for solar-to-electricity and solar-to-chemical conversion. Two serious losses can occur in PEC devices: 1) recombination between the conduction band (CB) electrons and valence band (VB) holes in the bulk and at the surface and 2) back reaction or electron trapping by oxidant in the electrolyte solution during transport to the electron-collecting electrode. Thus, the major challenge in common with the nanostructured semiconductor photoanodes is to achieve efficient charge separation and electron transport. In this study, an ultrathin SiO_x layer was formed on both the external and the internal surface of mp-TiO₂ using an original chemisorption-calcination technique employing 1,3,5,7-tetramethyltetrasiloxane as a starting material. The SiO_x surface modification of the mp-TiO₂ photoanode drastically prolongs the mean lifetime of CB-electrons in TiO₂ because of enhanced charge separation and electron transport by the negative charge applied in aqueous electrolyte solution. We have demonstrated that the performance of a one-compartment H₂O₂-photofuel cell using mp-TiO₂ as the photoanode is greatly boosted by the surface modification with the SiO_x layer. We anticipate that this methodology is widely applicable to nanostructured metal oxide semiconductor electrodes, contributing to the improvement in the performance of PEC devices.     

基于Cu/SiO_x/Al结构的阻变存储器多值特性及机理的研究

采用氧化硅材料构建了Cu/SiOx/Al的三明治结构阻变存储器件.用半导体参数分析仪对其阻变特性进行测量,结果表明其具有明显的阻变特性,并且通过调节限制电流,得到了四个稳定的阻态,各相邻阻态的电阻比大于10,并且具有良好的数据保持能力.在不同温度条件下对各个阻态进行电学测试及拟合,明确了不同阻态的电子传输机理不尽相同:阻态1和阻态2为欧姆传导机制,阻态3为P-F(Pool-Frenkel)发射机制,阻态4为肖特基发射机制.根据电子传输机制,建立了铜细丝导电模型并对Cu/SiOx/Al阻变存储器件各个阻态的电致阻变机制进行解释.     

ZnO纳米电缆的制备、结构和生长机理

以混合的锌粉和锡粉作为原料, 通过热蒸发的方法在沉积有金膜的硅基片上制备出具有“芯线-壳层”同轴结构的ZnO/SiO_x纳米电缆. 扫描和透射电镜的研究表明, 这种纳米电缆的产量很高, 长度达到数个微米, 并且确认了其“芯线-壳层”的独特结构. 不同于以往ZnO一维纳米材料的三个快速生长方向〈0001〉、〈0110〉及〈2110〉, 其ZnO芯线的生长方向为[2021]. 本实验中锡粉和金膜分别作为抑制剂和催化剂, 通过控制锌粉的蒸发速率以及金硅共熔反应使ZnO纳米电缆在硅基片上得到一维生长. 这种纳米电缆可望在纳米尺度的电路、电器以及力学和光学信号的耦合和转换方面得到应用.     

Influence of substrate morphology on the cohesion and adhesion of thin PECVD oxide films on semi‐crystalline polymers

The influence of the surface morphology of semi‐crystalline poly(ethylene terephthalate) (PET) and polyamide 12 (PA12) films on the adhesion and cohesion of thin oxide coatings is analysed, with attention paid to the role of spherulites and processing additives. The failure mechanisms of the coating are determined by means of fragmentation tests and the results are modelled using a constant interfacial strength approach with a Weibull‐type probability of fracture. Coating failure is shown to be initiated at defect sites such as pinholes and, in the case of PET, the presence of additives in the superficial layers of the polymer leads to a decrease of the crack onset strain by a factor of 20%. Large spherulitic structures found at the surface of PA12 films are shown to lead to preferential delamination at spherulites boundaries. For the two types of semi‐crystalline polymers, the interfacial shear strength is found to be comparable to the bulk shear strength of the polymer. Copyright © 2003 John Wiley & Sons, Ltd.     

飞秒脉冲激光辐照对硅发光性能的影响

利用飞秒脉冲激光对单晶硅进行辐照,研究了在不同环境(纯水和空气)和能量密度条件下激光刻蚀过后硅片的光致荧光特性.对于辐照后的硅片,利用了场发射扫描电子显微镜(FESEM)、能谱仪(EDS)、傅里叶红外光谱仪(FT-IR)、光致荧光光谱仪(PL)进行表征.结果显示:在空气中样品表面形成了条纹状微结构,纯水中硅片表面生成了尺寸更小的珊瑚状微结构;激光刻蚀后在硅片表面的生成物主要是SiOx(x2),在纯水中处理后硅片氧元素的含量接近是空气中的4倍;傅里叶变换红外透射谱中主要为Si—Si键(610 cm-1)和Si—O—Si键(1105 cm-1)的振动;在空气和纯水中激发出的荧光均为蓝光(420—470 nm),在各自最佳激发波长下,纯水中荧光强度比空气中强2到3倍,但是在可见光范围内荧光峰的位置和形状都基本没有发生变化.研究表明:氧元素在光致发光增强上起着重要作用,光致发光最主要是由形成的氧缺陷SiOx(x2)导致的,生成低值氧化物SiOx的多少决定了发光的强弱.     

Fabrication of polycrystalline silicon films by Al‐induced crystallization of silicon‐rich oxide films

Polycrystalline silicon (poly‐Si) films were fabricated by aluminum (Al)‐induced crystallization of Si‐rich oxide (SiO_x) films. The fabrication was achieved by thermal annealing of SiO_x /Al bilayers below the eutectic temperature of the Al–Si alloy. The poly‐Si film resulting from SiO_1.45 exhibited good crystallinity with highly preferential (111) orientation, as deduced from Raman scattering, X‐ray diffraction, and transmission electron microscopy measurements. The poly‐Si film is probably formed by the Al‐induced layer exchange mechanism, which is mediated by Al oxide.     

A Titanium‐Doped SiOx Passivation Layer for Greatly Enhanced Performance of a Hematite‐Based Photoelectrochemical System

This study introduces an in situ fabrication of nanoporous hematite with a Ti‐doped SiO_x passivation layer for a high‐performance water‐splitting system. The nanoporous hematite with a Ti‐doped SiO_x layer (Ti‐(SiO_x/np‐Fe₂O₃)) has a photocurrent density of 2.44 mA cm^?2 at 1.23 V_RHE and 3.70 mA cm^?2 at 1.50 V_RHE. When a cobalt phosphate co‐catalyst was applied to Ti‐(SiO_x/np‐Fe₂O₃), the photocurrent density reached 3.19 mA cm^?2 at 1.23 V_RHE with stability, which shows great potential of the use of the Ti‐doped SiO_x layer with a synergistic effect of decreased charge recombination, the increased number of active sites, and the reduced hole‐diffusion pathway from the hematite to the electrolyte.