二氧化硅气凝胶微球制备技术

 采用悬浊液成球技术制备低密度二氧化硅气凝胶微球，介绍了TEOS的水解、缩聚过程，主要论述了悬浊液成球技术、密度匹配技术、老化时间对微球性能，特别是收缩对微球密度的影响。实验制备了密度分别为70,100,150,200mg/cm³四种小球，结果表明：熟化时间取6d，制得的微球直径为0.1~2mm,密度为50~500mg/cm³,非球形参数为1.8%。     

二氧化硅气凝胶微球制备技术

采用悬浊液成球技术制备低密度二氧化硅气凝胶微球,介绍了TEOS的水解、缩聚过程,主要论述了悬浊液成球技术、密度匹配技术、老化时间对微球性能,特别是收缩对微球密度的影响。实验制备了密度分别为70,100,150,200mg/cm3四种小球,结果表明：熟化时间取6d,制得的微球直径为0.1~2mm,密度为50~500mg/cm3,非球形参数为1.8%。     

The microstructure of SiO thin films: from nanoclusters to nanocrystals

The microstructure and electronic structure of silicon-rich oxide (SRO) films were investigated using transmission electron microscopy and electron energy loss spectroscopy as the main analytical techniques. The as-deposited SRO film was found to be a single phase SiO_1.0, as suggested by its electronic structure characteristics determined by the valence electron energy loss spectrum. This single phase undergoes a continuous but incomplete phase decomposition to Si and SiO₂ for films annealed between 300 and 1100°C. The resulting Si phase first appears as ～2?nm-diameter amorphous clusters which grow to larger sizes at higher annealing temperatures, but only crystallize at a critical temperature between 800 and 900°C. This cluster/matrix configuration of the SRO films is consistent with the appearance of the interface plasmon and its oscillator strength as a function of the nanoparticle size. Three separate stages were identified in the sequence of annealed films that were characterized by the presence of single-phase SiO, amorphous silicon nanoclusters, and silicon nanocrystals, respectively. The presence of amorphous silicon nanoclusters in the intermediate stage, the mean size of which can be controlled via annealing, may offer an alternative to silicon nanocrystal composites for optical applications.     

Mössbauer studies on ultraporous Fe-Oxide/SiO2 aerogel

Magnetic aerogels with very low volume density of ～0.2 g/cm³ were prepared by sol-gel method and supercritical drying. The resulting materials were monolithic and displayed high surface area. By X-ray diffraction and Mössbauer spectroscopy the crystalline phase formed inside the mesopores of the SiO₂ matrix was identified as a spinel iron oxide. Comparison of the magnetic measurements with Mössbauer spectra at various temperatures contributed to the elucidation of the magnetic state of this nanocomposite system with restricted magnetic interactions, in particular its transition to a superparamagnetic state.     

Wet and dry etching of Sc2O3

Wet chemical and plasma etch processes were developed for pattering of Sc₂O₃ films on GaN. Chlorine-based plasma chemistries produced a significant chemical enhancement of removal rate over pure Ar sputtering. The etching was anisotropic and did not significantly alter the surface composition of the Sc₂O₃ films. Reaction-limited wet etching in the HNO₃/HCl/HF system was investigated as a function of solution formulation and temperature. The activation energy for the wet etching ranged from 8 to 14 kcal/mol and the etch rates were independent of solution agitation.     

触发电压对±100 kV多级多通道开关性能的影响

研制了一种用于快脉冲直线型脉冲变压器的±100 kV多级多通道火花开关,研究了触发电压极性、幅值对多级多通道火花开关触发性能的影响,分析了不同触发电压下开关各部分延时及抖动。研究结果表明:触发电压的极性对双极性多级多通道火花开关触发性能影响较小;开关的触发放电延时和抖动随着触发电压的增大而减小。进一步分析了多级多通道火花开关的触发击穿模式以及影响开关击穿延时和抖动的主要因素,提出了减小开关触发击穿延时及抖动的技术途径。     

Thin SiO2 films on GaAs substrates

The formation of thin dielectric SiO₂ films on n-type GaAs substrates and obtained results on the investigation of their physical and chemical parameters are described. The SiO₂ films are produced by low-temperature deposition of tetraethoxisilane in the continuous flow system with argon as a carrier gas. Some of the technological aspects of this preparation (as the growth conditions and proper apparatus) are discussed in great detail. For improvement of some typical parameters (infrared spectra, etch rate and permitivity) a suitable thermal treatment is recommended. From the results we have achieved, the potential possibilities for construction of various types of electronic devices are also proposed.The authors wish to thank Ing. I.Srb for infrared spectra measurements. The technical assistance of Mrs. O.Janouková is also greatly appreciated.     

Annealing and oxidation effects after CF4/H2 dry etching for damage recovery

When a Si substrate, just after SiO₂ etching, is exposed to an additional etch using CF₄ + H₂ reactive sputter etching, carbon and fluorine atoms penetrate into the Si substrate to a depth of ≈ 100–150 Å. The effects of an annealing and oxidation atmosphere for this damage recovery and impurity redistribution in the Si substrate are investigated using IMA and Secco etching. Annealing in N₂ gas is only effective for removing fluorine atoms. After dry O₂ oxidation, though the carbon atoms are removed, the fluorine atoms are still confined in the oxidized layer. Under wet oxidation, carbon and fluorine atoms are removed as soon as the damaged layer is oxidized. Moreover, after 300 Å wet oxidation, no impurity atoms or defects are observed. Wet oxidation may serve as a pretreatment for Si selective epitaxial growth on a dry etched Si substrate.     

二氧化硅气凝胶的防爆震性能及机理研究

利用聚偏二氟乙烯压电传感器研究了爆炸加载下冲击波在二氧化硅气凝胶中的传播特性,并对冲击波在二氧化硅气凝胶和泡沫铝中的传播特性进行了比较.结果表明:在二氧化硅气凝胶中冲击波的强度随传播距离的增加呈现指数衰减的趋势.冲击波在二氧化硅气凝胶中衰减比在泡沫铝中衰减明显.由于二氧化硅气凝胶内部特殊的纳米多孔网状结构,导致冲击波在二氧化硅气凝胶中的衰减效果较好.冲击波在二氧化硅气凝胶中的传播速度极低,因此冲击波在二氧化硅气凝胶中传播时卸载波的追赶卸载效应非常明显,这又进一步促进了冲击波的衰减.     

Growth of Nb thin films on SiO2

Nb thin films have been prepared by electron beam evaporation under ultrahigh vacuum conditions on fused silica substrates at various temperatures, and their structural and morphological evolutions have been investigated using X-ray diffraction and atomic force microscopy. The crystallographic texture of the Nb films is found to depend on the growth temperature. At room temperature, the [1 1 0] texture is dominant. However, at 200°C, the [3 1 0] oriented growth is favored, co-existing with [1 1 0] and [2 0 0] oriented grains. At 400–600°C, a completely [1 1 0] textured film is formed. At even higher temperature (800°C), a complex texture of [1 1 0] (dominant), [2 0 0] and [3 1 0] is observed again. It is also found that the single [1 1 0] textured Nb films have smooth surfaces, and the complex textured Nb films have rough surfaces.     

ZrO2/SiO2溶胶-凝胶薄膜膜层间的渗透行为

 分别以丙醇锆和正硅酸乙酯为原料，采用溶胶-凝胶工艺制备了性能稳定的ZrO₂和SiO₂溶胶。用旋转镀膜法在K9玻璃上分别制备了单层SiO₂薄膜、单层ZrO₂薄膜、ZrO₂/ SiO₂双层膜和SiO₂/ZrO₂双层膜。采用原子力显微镜观察了薄膜的表面形貌，用椭偏仪测量薄膜的厚度与折射率，用紫外-可见光分光光度计测量了薄膜的透射率。对薄膜的透射光谱和椭偏仪模拟的数据进行分析，发现SiO₂/ZrO₂双层膜之间的渗透十分明显，而ZrO₂/SiO₂双层膜之间几乎不发生渗透。利用TFCalc模系设计软件,采用三层膜模型对薄膜的透射率进行模拟，得出的透射曲线与用紫外-可见光分光光度计测量的透射曲线十分符合。     

ZrO2/SiO2溶胶-凝胶薄膜膜层间的渗透行为

分别以丙醇锆和正硅酸乙酯为原料,采用溶胶-凝胶工艺制备了性能稳定的ZrO2和SiO2溶胶。用旋转镀膜法在K9玻璃上分别制备了单层SiO2薄膜、单层ZrO2薄膜、ZrO2/ SiO2双层膜和SiO2/ZrO2双层膜。采用原子力显微镜观察了薄膜的表面形貌,用椭偏仪测量薄膜的厚度与折射率,用紫外-可见光分光光度计测量了薄膜的透射率。对薄膜的透射光谱和椭偏仪模拟的数据进行分析,发现SiO2/ZrO2双层膜之间的渗透十分明显,而ZrO2/SiO2双层膜之间几乎不发生渗透。利用TFCalc模系设计软件,采用三层膜模型对薄膜的透射率进行模拟,得出的透射曲线与用紫外-可见光分光光度计测量的透射曲线十分符合。     

Dielectric properties of pyroactivated SiO2 films

The physical properties of SiO₂ films obtained by pyrolytic decomposition of tetraethoxysilane vapor in an inert medium using activating ultraviolet radiation are analyzed. The mechanisms of current flow in Me-SiO₂-Me systems are discussed on the basis of qualitative ideas concerning the nature of the conductivity in amorphous dielectrics, when there is a complex trap spectrum and reversible temperature changes present in the film structure.     

Substrate effects on the microstructure of hydrogenated amorphous carbon films

In this work, plasma enhanced chemical vapour deposition was used to prepare hydrogenated amorphous carbon films (a-C:H) on different substrates over a wide range of thickness. In order to observe clear substrate effect the films were produced under identical growth conditions. Raman and near edge X-ray absorption fine structure (NEXAFS) spectroscopies were employed to probe the chemical bonding of the films. For the films deposited on silicon substrates, the Raman I_D/I_G ratio and G-peak positions were constant for most thickness. For metallic and polymeric substrates, these parameters increased with film thickness, suggesting a change from a sp³-bonded hydrogenated structure to a more sp² network, NEXAFS results also indicate a higher sp² content of a-C:H films grown on metals than silicon. The metals, which are poor carbide precursors, gave carbon films with low adhesion, easily delaminated from the substrate. The delamination can be decreased/eliminated by deposition of a thin (∼10 nm) silicon layer on stainless steel substrates prior to a-C:H coatings. Additionally we noted the electrical resistivity decreased with thickness and higher dielectric breakdown strength for a-C:H on silicon substrate.     

Annealing effects on the microstructure of amorphous carbon nitride films

Amorphous carbon nitride films, prepared using a dc facing-target reactive sputtering system, were annealed at temperatures up to 650 °C for 1 h in vacuum. The effects of heat treatment on the films, i.e. changes in the composition and structure, were investigated. It was found that annealing at temperatures ranging from 300 to 650 °C, results in the N content decreasing from ∼33 at.% in the as-deposited films to ∼5 at.%. The loss of N, especially those bonded to sp³C, causes the rearrangement of the film's microstructure, and the dual effects of the thermal annealing are quite noticeable: (1) annealing destroys most graphite-like structures, and more non-aromatic sp²C components and C≡N terminal structures are formed at higher annealing temperatures, contributing to a looser film's structure. (2) Annealing makes the remaining aromatic sp²C structure become more order. The results also reveal that N atoms bonded to sp³C are easily removed with the increasing temperature compared to those bonded to sp²C, which indicates that Nsp²C bonds had a higher thermal stability than Nsp³C.     

Plasma transformation of SiO films in SiO2 at room temperature

Oxygen plasma has been used to transform thin SiO deposited films into SiO₂ layers. Nuclear microanalysis, Rutherford backscattering and infrared spectroscopy have confirmed the formation of stoichiometric silicon dioxide by room temperature plasma anodization. Isotopic tracing experiments were carried out to study the ionic movements under high electric field [(1–2)X10⁷ V/cm] during oxide growth. This process differs strongly from the pure Si plasma anodization, and leads to the formation of a few tens nm thick SiO₂ films in sequential steps: low temperature deposition of SiO and low temperature plasma treatment.     

Comparison of plasma chemistries for the dry etching of bulk single-crystal zinc-oxide and rf-sputtered indium-zinc-oxide films

The dry etching characteristics of bulk, single-crystal zinc-oxide (ZnO) and rf-sputtered indium-zinc-oxide (IZO) films have been investigated using an inductively coupled high-density plasma with different plasma chemistries. The introduction of interhalogens such as ICl, IBr, BI₃, and BBr₃ to the Ar plasma produced no enhancement of the ZnO and IZO etch rates with respect to physical sputtering in a pure argon atmosphere under the same experimental conditions. In these plasma chemistries, the etch rate of both materials increased with source power and ion energy, indicating that ion bombardment plays an important role in enhancing desorption of etch products. Except in Ar/CH₄/H₂ discharges, the ZnO etch rate was very similar to that of IZO, which indicates that zinc and indium atoms are driven by a similar plasma etching dynamic. CH₄/H₂-containing plasmas produced higher etch rates for IZO than for ZnO due to the preferential desorption of the group III etch products. Application of the CH₄/H₂/Ar plasma to the etching of deep features in bulk, single-crystal ZnO produced highly anisotropic profiles although some trenches were observed near the sidewalls.     

Effect of the surface state on pulsed laser etching of ultrananocrystalline nitrogen-doped diamond films

It is shown that the rate of laser oxidation of ultrananocrystalline films in the nanoablation mode is limited by the presence of physically and chemically adsorbed hydrogen-containing molecules on the surface and can be increased by preliminary thermal annealing. It is proposed to explain the observed saturation of the laser etching rate with the number of pulses by water molecule dissociation on the surface and film saturation with hydride and hydroxyl groups.