X-ray emission spectra and interfacial solid-phase reactions in Hf/(001)Si system

High energy resolved X-ray emission spectroscopy with variable electron beam excitation is applied for the study of solid-phase reactions in the Hf/(001)Si system at different annealing temperatures. It is found that annealing at 700°C is accompanied by formation of HfSi. The HfSi₂ phase is formed at 780°C. The formation of Hf silicides in depth is studied by measurements of Si L_2,3 X-ray emission valence spectra under different accelerating voltages. The data obtained by means of X-ray emission spectroscopy are compared with those obtained by means of Rutherford backscattering and electron-probe microanalysis techniques.     

Interfacial reactions in a Ti-6Al-4V based composite: role of the TiB2 coating

The characterization of TiB₂/C-coated SiC fibres and their interface region in a Ti-6Al-4V based composite has been performed by using scanning electron microscopy (SEM), energy-dispersion X-rays (EDX) and Auger electron spectroscopy (AES). The features of the as-received fibre and the reactivity between fibre and matrix occurring during preparation of the composite have been studied in this paper. The interaction of the TiB₂ external coating of the fibre with both the adjacent carbon layer and the titanium-based matrix is already appreciable in the as-received composite: TiB needles grow from TiB₂ towards the matrix and a new layer containing C, Ti and B appears between TiB₂ and C. The thicknesses of the original carbon and TiB₂ fibre coatings decrease in the composite from 1000 nm to 400 and 800 nm, respectively. The TiB₂ inhibits the reaction between SiC and Ti: there is no evidence of Si _x Ti _y brittle phases.     

Microstructural characterization and ablation mechanism of TiB2/(Cu,Ni) melt-infiltrated ceramic composite

In this study TiB₂/(Cu,Ni) melt-infiltrated composites with the TiB₂ volume content of 81.6% were prepared by mean of pre-sintering of the as-pressed TiB₂ preform and melt-infiltration processing. The thermal ablation behavior of TiB₂/(Cu,Ni) composite was conducted by plasma arc heater. The microstructure, interfacial bonding and ablation behavior were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) pattern. The ablated morphology of cross-section includes three parts: ablated region, transition region and matrix region. The microstructure analysis after ablation experiment reveals a clue of redistribution of infiltrated (Cu,Ni) phase so as to analyze and explain the functioning of transpiration cooling.     

Interfacial reactions in the liquid diffusion couples of Mg/Ni,Al/Ni and Al/(Ni)-Al2O3 systems

The interfacial reactions between various molten metals and solid plates were investigated in this diffusion couple study. The molten metals were pure magnesium, pure aluminium, aluminium-rich Al-Mg alloy, and aluminium-rich Al-Cu alloys, and the solid plates were pure nickel plate, alumina plate, and nickel-plated alumina plate. The interfacial reactions in the diffusion couples were determined by using optical microscopy, scanning electron microscopy and electron probe microanalysis in regard to the formation of intermetallic phases, the dissolution rates of the nickel plates, and the morphology of the interfaces. Mg₂Ni phase was found in the pure Mg/Ni plate diffusion couples, and the Al₃Ni and Al₃Ni₂ phases were observed in the pure Al/Ni plate and Al-alloys/Ni plate diffusion couples. In the Al-Cu alloy/Ni-plated alumina plate diffusion couple, Al₂O₃ formed at the interface, while spinel particles were found in the diffusion couples of Al-7.4wt% Mg alloy/Ni-plated alumina plate. Experimental difficulty was encountered in preparing the diffusion couples with alumina plate, and a gap existing at the interface prohibited reactions between the molten metal with alumina plate.     

重构表面上Si薄膜生长的模拟研究

建立了Si(100)-(2×1)表面上Si薄膜生长的Kinetic Monte Carlo(KMC)模型,并对薄膜生长的初始阶段进行了研究.结果表明:在一定的入射率下存在一最佳成岛温度,该温度随入射率的增大而升高,并满足函数关系T=T0 bln(F c).     

Interfacial solid phase reactions in cobalt/aluminum oxide/silicon(001) system

Auger electron spectroscopy, secondary neutral mass spectrometry and high-resolution transmission electron microscopy were used to assess the chemical, morphological and structural modifications after annealing of cobalt/aluminum oxide/silicon(001) hetero-structure. The results show that the aluminum oxide forms a diffusion barrier for temperatures lower than 200 °C. Beyond this temperature, cobalt atoms diffuse in the silicon region without apparent modification of the barrier. At 340 °C, the asymmetric diffusion could be explained by the formation of an AlCoO complex oxide playing the role of a diffusion barrier for Si atoms.     

Microstructure and Mechanical Properties of TiB2/(Ni+Mo) Composites Fabricated by Hot Pressing

1. IntroductionTitanium diboride is attractive for its high elajsticmodulus, electrical conductivity, hardness, and melting poillt temperature. However the fabrication ofTiBz is difficult. Its sintering temperature is higherthan 1800'C in hot--pressing. Using pressless signeringtechnique, at 2000"C the relative density of sajmplecan not be higher than 95 pci, and mechanical properties will decreajse due to the too big grain size at sucha high temperature. In order to decrease sinteringtemper…     

Temperature variation of the morphology of nanocluster ensembles in the Ge/Si(100) system

The morphological characteristics of hut-cluster ensembles formed in a Ge/Si(100) heteroepitaxial system have been studied as functions of the substrate surface temperature by theoretical methods and by atomic force microscopy. As the temperature increases from 420 to 500°C, the lateral size of nanoclusters with a square base (grown at the same rate of 0.0345 ML/s to a total coverage of 6.2 ML) grows from 12 to 20 nm, while their number density on the substrate surface drops from 5.6×10¹⁰ to 1.5×10¹⁰ cm⁻². Predictions of a kinetic model are in sufficiently good agreement with the experimental data.     

纳米CeO2颗粒的制备及其对硅晶片（100）和（111）的抛光性能

以硝酸铈和六亚甲基四胺为原料,在微波辐射条件下,使用乙醇/水反应体系,通过均相沉淀法制备了纳米CeO2颗粒,利用X射线衍射仪（XRD）、透射电子显微镜（TEM）、傅里叶转换红外光谱仪（FT-IR）和比表面积测定仪（BET-N2）等手段对样品的成分、物相结构、形貌、颗粒大小以及团聚情况进行了表征.将所制备的纳米CeO2颗粒作为磨料用于硅晶片（100）和（111）的化学机械抛光,用原子力显微镜（AFM）观察抛光表面的微观形貌,测量表面粗糙度,并对抛光表面划痕进行了分析.结果表明,微波辐射以及乙醇/水反应体系均有利于制备出粒径更小、分散性更好的纳米CeO2颗粒,而且微波辐射能够显著加快反应速度;经纳米CeO2磨料抛光的硅晶片（100）和（111）表面非常平整,在2μm×2μm范围内的粗糙度Ra值分别为0.275 nm和0.110 nm,获得了具有亚纳米量级粗糙度的抛光表面.     

Si(100)面的STM观察

使用超高真空扫描隧道显微镜(STM)观察了Si(100)面,得到了清洁Si(100)面的STM像。从Chadi模型的形成和表面原子的各向异性扩散分析了STM像的两种类型的台阶棱。Si(100)面的STM像存在许多缺陷,缺陷位置能从在同一区域样品上加正负偏压的STM像来确定。     

硅、锗材料在Si(100)表面的生长研究

利用扫描隧道显微镜和超高真空实验装置系统进行了Si(10 0 )表面生长Si,Ge的实验研究。分析了所生成表面的形貌、结构等物理性质。研究表明 :Si在Si(10 0 )表面的同质生长可以形成纳米结构薄膜。Ge在Si(10 0 )表面生长形成规则的三维小岛。而在Si/Ge/Si(10 0 )多层膜上生长则形成大小二种三维岛。研究表明大岛具有Ge/Si/Ge的壳层结构     

Diffusion in Si(x)Ge(1-x)/Si nanowire heterostructures

Si0.48Ge0.52/Si tip/nanowire heterostructures were grown by pulsed laser vaporization (PLV) at a growth temperature of 1100 degrees C. Ge diffusion in [111]-growth Si nanowires was studied for different post-synthesis annealing temperatures from 200 degrees C to 800 degrees C. Ge composition profiles were quantified by energy-dispersive X-ray spectroscopy in a transmission electron microscope. The compositional profiles were modeled by a limited-source diffusion model to extract temperature-dependent diffusion coefficients. The Ge diffusion coefficients followed an Arrhenius relationship with an activation energy of 0.622 +/- 0.050 eV. This rather low activation energy barrier is similar to the previously reported activation energy barrier of 0.67 eV for Ge surface diffusion on Si, suggesting that surface diffusion may dominate in nanowires at this length scale.     

Boron ions B interaction with Si(100) and Ge(100) surfaces

The goal of this work is simulation of possible structures, formed by boron ions (B⁺) during adsorption on Si(100) and Ge(100) surfaces. Calculations were carried out using a semi-empirical method, known as the Modified Neglect of Differential Overlap method (MNDO). The surface was simulated using of Si₄₉(Ge₄₉) and Si₆₃(Ge₆₃) clusters. Results of quantum-chemical calculations the boron ion (B⁺) interaction with Si(100) − 2 × 1 and Ge(100) − 2 × 1 surfaces are presented and show adsorption barriers for boron ions and migration barriers of adsorbed boron ion (during migration along surface dimer row and along surface dimer).     

Electrochemical properties of Si/(FeSiB) anode materials prepared by high-energy mechanical milling

Nano-structured composite with overall atomic composition Si₆₀/(FeSiB)₄₀ has been synthesized by high-energy mechanical milling (HEMM) for Lithium-ion rechargeable batteries as anode material. Crystal structure, microstructure, electrochemical properties, elastic modulus and Vickers hardness (H_V) have been observed by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), electrochemical test and nano-indentation test. With increasing milling time from 6 to 10 h, we observed a relatively homogeneous structure comprised of nano-crystalline active silicon (Si) embedded in less active FeSiB matrix phase. Electrochemical properties of 10 h milled nano-composite powder offers low capacity fade, high coulombic efficiency from 3rd cycle (540 mAh g⁻¹) to until 102nd cycle (495 mAh g⁻¹). The coulombic efficiencies of both 6 and 10 h milled powders are 98% and 99%, respectively. Coin cell cross sections of 6 and 10 h milled powders showed evidence for the void formation during lithiation and delithiation. Nano-indentation results exhibited that the amorphous FeSiB flakes have 2.96 times higher recoverable energy than Si. Resultant composite powders showed high irreversible capacity and stable lithiation and delithiation due to the reduced particle size, increased surface area and the highly elastic FeSiB matrix phase. Research reveals that the obtained nano-composite can be a promising candidate for lithium-ion rechargeable batteries.     

Crystal chemistry and magnetism in silicides LaFe2−x Rh x Si2 (ThCr2Si2-type)

A complete solid solution has been found for mixed crystals LaFe₂Si₂?LaRh₂Si₂ of the ThCr₂Si₂-type and a statistical distribution of iron-and rhodium atoms on the 4d sites of the space group I4/mmm. Crystal symmetry, atom order and precise atom parameters have been determined from a single crystal study of LaFe_1.6Rh_0.4Si₂ (R=0.015). Magnetic susceptibilities (1.8<T<1100K) are characterized by a temperature independent paramagnetism throughout the solid solution. The iron atoms prove to be in a nonmagnetic state in good agreement with Mössbauer data at 5K and at room temperature, which further confirms a small amount of iron on a second crystallographic site (4e). LaRh₂Si₂ is not superconducting above 1.5K.