Electrochemical Impedance Study of Porous Silicon Prepared by Metal-Assisted Chemical Etching

Silicon - Covering with thin metal facilitates the etching of p-type silicon in a solution of HF containing KBrO3, KIO3 or K2S2O8 as an oxidizing agent. Electroless deposition of Ag, Pd or Au was...     

Effect of Etching Duration on the Morphological and Opto-Electrical Properties of Silicon Nanowires Obtained by Ag-Assisted Chemical Etching

Silicon - Silicon nanowires (SiNWs) were obtained on p-Si (100) substrate by Ag-assisted chemical etching method in two-step process. The influence of the etching duration on the morphological,...     

化学腐蚀法制备纳米多孔硅及其表面形貌表征

采用化学腐蚀法制备了纳米多孔硅粉.利用扫描电子显微镜对多孔硅粉的表面形貌进行了表征.结果表明,在HNO3浓度、反应时间和HNO3滴加时间3种因素中,HNO3浓度对硅粉的腐蚀效果影响最大;浓度过高或者较低时,均不能获得良好的硅粉形貌.HNO3质量分数以20％～25％为宜.反应时间对硅粉结构和形貌的影响比硝酸的滴加速率大.在较低HNO3浓度条件下,延长反应时间对硅粉进行腐蚀更为有效.     

Catalytic Activity of Noble Metals for Metal-Assisted Chemical Etching of Silicon

ABSTRACT: Metal-assisted chemical etching of silicon is an electroless method that can produce porous silicon by immersing metal-modified silicon in a hydrofluoric acid solution without electrical bias. We have been studying the metal-assisted hydrofluoric acid etching of silicon using dissolved oxygen as an oxidizing agent. Three major factors control the etching reaction and the porous silicon structure: photoillumination during etching, oxidizing agents, and metal particles. In this study, the influence of noble metal particles, silver, gold, platinum, and rhodium, on this etching is investigated under dark conditions: the absence of photogenerated charges in the silicon. The silicon dissolution is localized under the particles, and nanopores are formed whose diameters resemble the size of the metal nanoparticles. The etching rate of the silicon and the catalytic activity of the metals for the cathodic reduction of oxygen in the hydrofluoric acid solution increase in the order of silver, gold, platinum and rhodium.     

Study of Porous Silicon Prepared Using Metal-Induced Etching (MIE): a Comparison with Laser-Induced Etching (LIE)

Porous silicon (p-Si), prepared by two routes (metal induced etching (MIE) and laser induced etching (LIE)) have been studied by comparing the observed surface morphologies using SEM. A uniformly distributed smaller (submicron sized) pores are formed when MIE technique is used because the pore formation is driven by uniformly distributed metal (silver in present case) nanoparticles, deposited prior to the porosification step. Whereas in p-Si, prepared by LIE technique, wider pores with some variation in pore size as compared to MIE technique is observed because a laser having gaussian profile of intensity is used for porosification. Uniformly distribute well-aligned Si nanowires are observed in samples prepared by MIE method as seen using cross-sectional SEM imaging. A single photoluminescence (PL) peak at 1.96 eV corresponding to red emission at room temperature is observed which reveals that the Si nanowires, present in p-Si prepared by MIE, show quantum confinement effect. The single PL peak confirms the presence of uniform sized nanowires in MIE samples. These vertically aligned Si nanowires can be used for field emission application.     

Photochemical Etching of Silicon

Silicon that was immersed in hydrofluoric acid can be etched photochemically by laser, and it was found to produce long and regular columnar structure, if the laser power density is greater than 10 mW/mm². Another criterion is that the laser wavelength should be at the blue end of visible spectrum. Fine wires with diameter 300–200 nm were also observed at the top of these columns. The dimension of these fine wires is near to quantum confinement dimension, thus can be taken as supporting evidence for quantum confinement. The photoluminescence spectra full width half maximum was narrower than that from porous silicon fabricated from conventional anodisation method. The narrower full width was attributed to the uniformity of the porous silicon structure. A physical model is proposed to explain the observed strong directional etching. The model showed that once the etch sites have randomly initiated, the etching rate becomes directional under the influence of laser. The intensity of laser controls the etching direction such that silicon columns are formed if the intensity of the laser is strong enough.     

化学蚀刻

有一种化学蚀刻法可代替喷砂制作法，该法可做出与表面蚀刻类似的效果，该法的优点在于做法简单，并且也不需要用磨蚀蚀刻所用的一些设备。毫无经验的初学者都可用此法做蚀刻玻璃器皿、小型平板玻璃或镜子等作品。该方法的缺点在于用化学物质做出的蚀刻不像喷砂作品那么坚固、那么亮那么白，也没那么持久耐用，也可能会产生划痕和斑点。     

电化学刻蚀制备宏孔硅研究

半导体硅在含HF电解液阳极氧化体系中可以形成不同的腐蚀形态。当采用背面照明,且反应电流密度小于某个临界值时,可以在N型硅抛光片沿(100)晶向刻蚀产生宏孔结构,控制电化学条件能够调整宏孔的孔径、间距等形貌参数。本文采用相同电阻率N型抛光(100)硅片,考查了恒流条件下不同工作电流、照明强度对刻蚀反应以及刻蚀表面形貌的影响。     

电化学刻蚀制备宏孔硅研究

半导体硅在含HF电解液阳极氧化体系中可以形成不同的腐蚀形态.当采用背面照明,且反应电流密度小于某个临界值时,可以在N型硅抛光片沿(100)晶向刻蚀产生宏孔结构,控制电化学条件能够调整宏孔的孔径、间距等形貌参数.本文采用相同电阻率N型抛光(100)硅片,考查了恒流条件下不同工作电流、照明强度对刻蚀反应以及刻蚀表面形貌的影响.     

电晕法处理超高相对分子质量聚乙烯纤维

用电晕法对超高相对分子质量聚乙烯纤维进行了表面处理。利用DPPH检测纤维表面自由基的产生和变化，并用XPS表面元素分析、SEM等方法探讨了纤维表面性能处理前后的变化。实验发现，通过电晕处理后，纤维复合材料的抗剪切强度从未处理的5．98MPa提高到14．3MPa。     

Ultra-Thin Silicon Wafers Fabrication and Inverted Pyramid Texturing Based on Cu-Catalyzed Chemical Etching

Silicon - The ultra-thin silicon solar devices perform a potential development direction to decrease material usage and thus lowering the expense. The ultra-thin silicon wafer and inverted pyramid...     

HF酸对玻璃浅层蚀刻模型的研究

为控制石英玻璃与HF酸的反应,实现石英玻璃精密元件的化学蚀刻和对石英玻璃工艺品的精确加工,探讨了化学反应机理和腐蚀的动力学过程。重点探究了影响整个蚀刻过程的重要因素,HF酸溶液的浓度c、反应的温度T和反应的时间t与蚀刻深度之间的关系。结合power law幂率模型的原理,建立了适用于石英玻璃浅层蚀刻的数学模型。验证时,选取了10,20℃等温度下,4种不同浓度的HF酸体系,通过模拟曲线和实验数据的对比,得知误差基本维持在5%以内。因此,该模型可以对玻璃的浅层蚀刻进行比较准确的模拟。     

Hydrogen Surface Etching of Molten Silica

Melting experiments with quartz sand were carried out under H₂ atmospheres at temperatures between 1700° and 1850°C. Upon quenching, fine-scale, hemispherical, pitted morphologies were noted at the surface of the melts. The degree of uniformity of the resulting features was observed to depend on the temperature of melting. The results are compared with similar reported observations at lower temperatures that are attributed to impurity-based instabilities in the surface tension and evaporation.     

Visualization of Knoop Indentation Damage of Silicon Nitride by Plasma Etching

A visualizing technique for indentation damage of ceramics was developed. Plasma etching was used to enhance the view of cracks and the subsurface microcracking crush zone following Knoop indentation of hot pressed Si₃N₄. The microcracking zone was readily identified from the surface view of the indented surface as a grain-falling-off region (GFOR), defined as a region in which grains were removed by preferential etching using CF₄ gas, followed by ultrasonic cleaning. A fissure-like opening corresponding to the indentation cracks was also observed. It is inferred that the formation of the GFOR region and the fissure-like opening were caused by the etching/cleaning treatment. Meanwhile, the etching on a section which included diagonals of the impression provided a section view of the microcracking zone.     

Etching processing of Si(111) and Si(100) surfaces in an ammonium fluoride solution investigated by in situ ATR-IR

In situ real-time measurements of etching processes by infrared total reflection spectroscopy were carried out for the first time on Si(100) and Si(100) surfaces in ammonium fluoride solution. The absorption bands became broad by the interaction between terminal hydrides with water molecules. On Si(111), the band at 2083 cm^{− 1} continuously grew and was sharpened by the formation of monohydride on the ideal Si(111) with the decrease of defects. On Si(100), dihydride first appeared, which was subsequently replaced by monohydride on steps produced as a result of etching. The stepped surface was continuously etched, and dihydride on Si(100) again increased with pyramid-like protrusions having (111) facets with many steps. The pyramids kept growing at the expense of dihydride to be the dominant structure on the surface.     

Tent-Shaped Surface Morphologies of Silicon: Texturization by Metal Induced Etching

Silicon - Nano-metal/semiconductor junction dependent porosification of silicon has been studied here. The silicon nanostructures (SiNSs) have been textured on n- and p- type silicon wafers using...     

Suppressing Hydrogen Evolution by Aqueous Silicon Powder Dispersions by Controlled Silicon Surface Oxidation

Aqueous silicon dispersions are used to produce pyrotechnic time delay compositions. The propensity of silicon to react with water and to produce hazardous hydrogen gas must be suppressed. To this end, the effect of air heat treatment temperature on the rate of corrosion of silicon was investigated. It was found that four hour heat treatments at temperatures below 350 °C provided significant passivation. This is attributed to the removal of the hydroxyl groups present on the SiO₂ surface scale layer. It was found that thickening the silica layer, by heat treatment at higher temperatures, causes a further reduction in the amount of hydrogen released. However, differential thermal analysis (DTA) studies showed that excessive silicon surface oxidation increased the ignition temperature and reduced the heat release of a near‐stoichiometric silicon‐lead chromate pyrotechnic composition.     

机械合金法制备(Mg2Ni)100-xAgx粉体及其储氢性质研究

在各种不同氢气储存方式中,用金属氢化物储存氢气具有体积小,压力低,安全性高等优点,其中A2B型的Mg2Ni介金属化合物具有高储氢量,质量轻,价格便宜等优点,而被视为最具潜力储氢系统.本实验采用(Mg2Ni)100-xAgxx(x=0,1.0及5.0)合金系统,进行机械合金法球磨处理,以X光衍射分析(XRD)检测技术观察粉体在球磨过程中结构变化,并将15 h球磨处理后合金粉末进行储氢动力学曲线,压力-成分-温度曲线(P-C-T curve)与热分析等检测,对合金粉末储氢特性进行评估.结果发现15 h球磨处理后,银元素会与Mg2Ni,Mg,Ni形成不同比例纳米晶粒混合物.在储氢特性方面,银元素的添加对Mg2Ni有明显改善,在350 ℃下,添加1.0%银元素与Mg2Ni粉体相比较,最大吸氢量由3.14%(ω)增加至3.83%(ω),可逆吸氢量由2.4%(ω)增加至3.0%(ω).     

Thermal Etching and Grain-Boundary Grooving Silicon Ceramics

Polished polycrystalline specimens of Si, Sic, and Si₃N₄ were heated to high temperatures and the rate of thermal etching was measured. Grain-boundary grooving occurred on silicon by surface diffusion, with a surface-diffusion coefficient given by Silicon carbide surfaces became extremely rough and very little grain-boundary grooving occurred. Silicon nitride decomposed in an N₂-H₂, atmosphere with an activation energy of 757 kJ/mol, which was very near the activation energy calculated from thermochemical data. The surfaces became fairly rough but grain-boundary grooves formed by an evaporation processsimilar to that for decomposition.     

Preparation of Ultrathin-Walled Carbon-Based Nanoporous Structures by Etching Pseudo-Amorphous Silicon Oxycarbide Ceramics

Etching polymer-derived silicon-oxycarbide ceramics with hydrofluoric acid creates nanoporous structures of specific surface areas as high as 600 m²/g. The change in composition upon etching shows the removal of silica, not carbon. The structure remaining after etching is postulated to consist of a scaffolding of graphene networks with their surfaces decorated with mixed bonds of tetrahedral silicon bonded to both oxygen and carbon (SiO _m C_{4− m} , where m =1, 2, or 3). The pores existing within such scaffoldings are presumed to have been filled with SiO₂ tetrahedra, which are removed by etching. The measurement of the average pore size and pore volumes permits us to estimate the width of the graphitic domain walls, δ_W, left behind by the etching process. The smallest value of δ_W, which corresponds to the specimen with the highest surface area, is approximately 1 nm, which is about equal to the total width of one graphene layer and two SiO _m C_{4– m} tetrahedra, one on either side of the graphene sheet. This highest surface area specimen is also believed to have the largest size of the silica domains in the unetched samples. In specimens with smaller domains, the etching is only partially successful in removing the silica, presumably because their small size hinders the access of the etchant to the silica tetrahedra. The above behavior is found for samples with low to moderate carbon content. In one sample with a very high carbon content, the etching process removes some carbon as well as silica.