Preparation and lithium storage performance of silicon and carbon microrods by chemical vapor co-deposition

Silicon/carbon microrods are co-deposited on copper substrate and graphite spheres surface using dimethyl dichlorosilance as carbon and silicon precursor. The obtained composites are characterized by X-ray diffraction and scanning electron microscopy. The experimental results show that silicon/carbon microrods deposited on the copper substrate, whose diameter is about 500 nm, are accumulated into sisallike morphology, those deposited on the graphite spheres surface form hedgehog-like feature, whose diameter is about 200 nm and whose top is like cauliflower. When current density of 50 mA/g is applied, charge capacity of silicon/carbon microrods is 1492 mA h/g (deposited on copper substrate) and 693 mA h/g (deposited on the graphite spheres surface). Moreover, silicon/carbon microrods deposited on the graphite spehres and copper substrate respectively deliver the capacity of 592, 985 mA h/g, and display no capacity decay at all after the 20 cycles, when cycled under current density of 500 mA/g.     

Ta2O5在Si(100)表面原子层沉积反应机理的密度泛函研究

采用密度泛函方法研究了以TaCl5和H2O作为前驱体在硅表面原子层沉积(ALD) Ta2O5的初始反应机理. Ta2O5的原子层沉积过程包括两个连续的“半反应”, 即TaCl5和H2O“半反应”. 两个“半反应”都经历了一个相似的吸附中间体反应路径. 通过H钝化和羟基预处理硅表面反应能量的比较发现, TaCl5在羟基预处理硅的表面反应是热力学和动力学都更加有利的反应. 另外, 从能量上看, H2O的“半反应”不容易向生成产物的方向进行.     

Fabrication of crystalline silicon spheres by selective laser heating in liquid medium

Micrometer and submicrometer crystalline silicon spheres were fabricated by selective laser heating of irregular silicon particles in liquid medium. TEM, SEM, XRD, and XPS characterized the structure and morphology of the prepared silicon spheres. The results suggested that they were spherical with a single crystalline structure. In this study, the formation mechanism of the spheres is analyzed, and the process parameters are optimized to obtain high-quality silicon spheres. A theoretical deduction regarding the relationship between critical laser energy density and particle size is also discussed, by which we can predict that larger spheres can be obtained at higher laser energy densities.     

Friction coefficients of spheres having sticky or hairy surfaces

The theoretical equations for friction coefficients of spheres having sticky or hairy surfaces are presented. In the present treatment, the sticky surface is represented by a higher viscosity of fluid in the surface layer and the hairy surface is assumed to have a porous structure. The friction coefficients are given as functions of the thickness of the surface layer, the fluid viscosity in the surface layer and the segmental density of hairy chains.     

Controlled free radical polymerization of styrene initiated from the alkoxyamine-functionalized silicon surface

Manipulation of surface properties of wafer is im- portant in technologies of biotechnology and advanced microelectronics[1,2]. A number of methods have been developed to modify the surface properties[3]. Among them, polymer brush is a well recognized met…     

Density profile of spin cast polymethylmethacrylate thin films

The density profiles of polymethylmethacrylate (PMMA) thin films on silicon (111) single crystal wafers were investigated via neutron reflectivity measurements. Films were prepared by spin casting PMMA onto silicon wafers from o-xylene solution followed by annealing under vacuum at 90°C for 5 h. A ～45 Å thick layer at the free polymer surface was observed in the as-prepared samples that has a density about half the value of bulk PMMA. After heating above 110°C, this diffuse layer disappeared and the thin film density profile was transformed to one with a sharp free polymer surface. This transition was found to be irreversible. © 1994 John Wiley & Sons, Inc.     

Facile preparation of silicon hollow spheres and their use in electrochemical capacitive energy storage

Nanostructured silicon hollow spheres with a thin shell have been synthesized by magnesium reduction of silica spheres, which possess a high BET surface area and are electrochemically active in capacitive energy storage with a maximum specific capacitance of 193 F g(-1) in the neutral Na(2)SO(4) aqueous solution.     

纳米结构TiO2/SiO2的逐层自组装

采用逐层自组装方法在二氧化硅球表面交替组装了十二烷基硫酸钠单分子膜和二氧化钛纳米粒子膜 ,该复合多层膜经高温煅烧后得到了核壳型纳米结构二氧化钛 /二氧化硅复合颗粒 .利用XRD ,SEM ,X射线能谱等对复合颗粒进行了表征 .结果表明 :二氧化钛在复合颗粒表面排列紧密、均匀 ,粒径在 5 0nm左右 ,为锐钛矿型结构 .复合颗粒中二氧化钛的含量随组装层数的增加而均匀增加     

Quantum-chemical modeling of lithiation of a silicon–silicon carbide composite

With the aim of searching for promising anode materials for lithium-ion batteries, quantum-chemical modeling of the introduction of lithium into a silicon layer supported by nitrogen-doped silicon carbide at Li: Si ratios of 1: 1, 2: 1, and 3: 1 has been performed by the density functional theory method with inclusion of gradient correction and periodic boundary conditions. It has been demonstrated that the absorption of lithium by silicon is energetically more favorable than the formation of a metal layer on the silicon surface. As the lithium concentration increases, the energy difference decreases; i.e., the introduction of lithium into silicon becomes increasingly less favorable, the network of silicon atoms is broken down into smaller and smaller pieces, while the layer thickness increases threefold.     

Fabrication of superhydrophobic surfaces from binary colloidal assembly

In this work, superhydrophobic surfaces were derived from binary colloidal assemblies. CaCO(3)-loaded hydrogel spheres and silica or polystyrene ones were consecutively dip-coated on silicon wafers. The former assemblies were recruited as templates for the latter self-assembly. Due to the hydrophilicity difference between silicon wafers and CaCO(3)-loaded hydrogel spheres, the region selective localization of silica or polystyrene spheres leads to irregular binary structures with a hierarchical roughness. The subsequent modification with low surface energy molecules yields a superhydrophobic surface. The heating treatment may largely enhance the mechanical stability of the resulting binary structures, which allows regeneration of the surface superhydrophobicity, providing a good durability in practice.     

CALCULATION OF THE YOUNG''''S MODULUS OF AN ADSORBED POLYMER LAYER

Polymer layers adsorbed to a surface or in a confined environment often change their mechanical properties. There is even the possibility of solidification of the confined layer. To judge the stiffness of such a layer, we used the Hertz model to calculate the Young's modulus of the polymer layer in the confinement of AFM experiments with silicon nitride tip with a radius of curvature of R≈50 nm and a glass sphere attached to the cantilever R = 5μm. Since there is no visible indentation of the layer in the AFM experiments, the layer is either penetrated very easily, or the indentation is too small to be seen in a force curve. The latter would be the case for a polymer layer with a Young's modulus above 4×108 Pa in case of an experiment with a silicon nitride tip and 4×105 Pa in case of a glass sphere.     

Quantum chemical calculations of silicon clusters in silicon dioxide and point defects in β-cristobalite

A local electronic-state density in β-cristobalite in the empirical tight-binding approximation has been calculated by the recursion method. In particular, silicon clusters have been considered in β-cristobalite containing up to three coordination spheres of silicon atoms.     

Curvature effect on nanometer-scale surface properties of phospholipid layers

Phospholipid bilayers were formed through liposome fusion on surfaces with different curvatures that were defined with silica spheres deposited on silicon water. Prior to the fusion, the surfaces became hydrophobic with octadecyltrimethoxysilane solution. Using atomic force microscope, surface forces were measured on dipalmitoylphosphatidylcholine (DPPC) layers and dioleoylphosphatidylcholine (DOPC) layers upon the curvature at 25°C. The short-range repulsions were higher at 20 and 100 nm curvatures than other curvatures for the DPPC layer, while they were lower for the DOPC layer. Since it was known that the forces are related to its low mechanical stability of the lipid layer, this opposite behavior was analyzed in terms of stability upon the curvature, which appears to be eventually determined by the correlation between the lipid molecule geometry and the surface curvature.     

Quantitative Analyse von Schichtsystemen mit der Methode der Rutherford-Weitwinkelstreuung

The use of Rutherford backscattering for the investigation of monocrystals overlaid with thin amorphous layers is briefly described. Using silicon crystals covered with silicon nitride and aluminium layers, methods are exhibited, which provide special informations about surface layers (mass and area concentration of the layer atoms, composition of the layers and density and thickness, respectively).      

Hollow spheres of aromatic polyamide prepared by reaction‐induced phase separation

Hollow spheres of aromatic polyamide are obtained by the reaction‐induced phase separation during polymerization of 5‐hydroxyisophthalic acid and 1,4‐phenylene diamine in an aromatic solvent at a concentration of 1–2% at 320 °C without stirring. The hollow sphere has a dimple hole and the diameters of the hollow spheres are 3–4 μm. The droplets are initially generated via liquid–liquid phase separation and then rigid cross‐linked network structure formed the rigid skin layer on the surface of the droplets. The solidification of the droplets occurred owing to the further polymerization in them with maintaining the morphology to form the hollow spheres. The hollow spheres exhibit outstanding thermal stability. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

SIMS-characterization of ultra shallow boron-profiles after BF 2 + -and B+-low-energy-implantation in silicon

It has been shown using SIMS profiling that, by means of low energy ion implantation into crystalline and amorphous silicon, doping profiles with depths around 30 nm can be reproducibly produced. The deposition of a cap layer onto the silicon surface considerably improves the depth resolution of the SIMS apparatus in the case of extremely shallow doping layers. Fifty nanometre thick Au/Ge cap layers were applied successfully for the accurate measurement of the trailing course of the boron distribution. For future measurements of the course of reaction, a silicon cap layer is necessary to avoid or minimize the change of the sputter rate and the secondary ion yield in the interface region to the boron implanted silicon. A comparison with the measured boron distributions showed good agreement with simulations in the case of implantation into amorphous material.     

SIMS-characterization of ultra shallow boron-profiles after BF2+-and B+-low-energy-implantation in silicon

It has been shown using SIMS profiling that, by means of low energy ion implantation into crystalline and amorphous silicon, doping profiles with depths around 30 nm can be reproducibly produced. The deposition of a cap layer onto the silicon surface considerably improves the depth resolution of the SIMS apparatus in the case of extremely shallow doping layers. Fifty nanometre thick Au/Ge cap layers were applied successfully for the accurate measurement of the trailing course of the boron distribution. For future measurements of the course of reaction, a silicon cap layer is necessary to avoid or minimize the change of the sputter rate and the secondary ion yield in the interface region to the boron implanted silicon. A comparison with the measured boron distributions showed good agreement with simulations in the case of implantation into amorphous material.     

Structural and nanomechanical properties of porous silicon: Cheap substrate for CMOS process industry

The surface topology of porous silicon (PSi) is a relevant parameter that decides the compatibility of such substrate with CMOS process. Using standard resistivity (1–10 Ω·cm) of Si substrate to fabricate PSi-S is a low cost solution for the industry. In this paper, through an atomic force microscopy (AFM) analysis, the root mean square (RMS) roughness, the power spectral density and the correlation length were determined for different PSi layers. Furthermore, the measured hardness, Young's modulus, and stress have been made for different thicknesses of PSi: 5, 10, 50, and 200 μm. The obtained results demonstrated that very interesting properties have been achieved with the 50 μm-thick PSi-S layer with a maximum porosity around 65%, a surface roughness less than 1 nm and a hardness value of (~1 GPa). The realized results encourage the utilization the PSi-based substrate into the industry process and thus the development of a Systems-on-Chip (SoC).     

DNA adsorption at functionalized Si/buffer interfaces studied by x-ray reflectivity

The adsorption of DNA on chemically homogeneous, functionalized, oxide-free single-crystal silicon surfaces is studied by x-ray reflectivity. The adsorption of monodisperse, 294 base-pair double-stranded DNA on a positively charged surface is detected through the deformation of the molecular monolayer of aminated alkyl-chain molecules covalently bonded to the surface. The adsorption of single-stranded DNA does not lead to the same deformation. A detailed quantitative characterization of the density profiles yield surface densities of the covalently grafted, molecular monolayers that are in excellent agreement with infrared spectroscopic measurements. The additional mass density that is measured following the adsorption of DNA corresponds either to the partial embedding of a densely-packed adsorbed layer or to a deeper penetration into the soft surface layer at a lower surface density of the adsorbed double-stranded DNA molecules. The adsorption is found to be irreversible under high added salt concentrations, suggesting a partial dehydration of the double-stranded DNA.     

Enhancement and stabilization of the photoluminescence from porous silicon prepared by Ag‐assisted electrochemical etching

In this paper, we present the results of studies on the photoluminescence (PL) of porous silicon (PSi) samples obtained by etching with the assistance of silver metal in different ways. If the Si sample, after being coated with a layer of silver nanoparticles, is electrochemically etched, its PL intensity becomes hundreds of times stronger than the PL intensity when it is chemically etched in the similar conditions. The difference in the PL intensities is explained partly by the anodic oxidation of silicon which occurs during the electrochemical etching process. The most obvious evidence that silicon had been oxidized anodically in the electrochemical etching process is the disappearance of the PSi layer and the appearance of the silicon oxide layer with mosaic structure when the anodization current density is large enough. The anodic oxidation has the effect of PSi surface passivation. Because of that, the PL of obtained PSi becomes stronger and more stable with time. Copyright © 2012 John Wiley & Sons, Ltd.