Study of Si and C adatoms and SiC clusters on the silicon surface by the molecular dynamics method

Individual Si and C adatoms, as well as SiC clusters, on a Si surface are simulated by the molecular dynamics method in the course of investigation of the initial stages of formation of a SiC layer on silicon with the help of molecular beam epitaxy. The potential energy surfaces for Si and C adatoms on the (2 × 1) reconstructed Si(001) surface and on the nonreconstructed Si(111) surface, as well as on the Si(111) surface with a SiC cluster, are calculated and analyzed. The values of migration barriers for adatoms on these surfaces are calculated. The effect of the SiC cluster on deformation of the surface region of Si(111) and on the migration of adatoms is investigated. The deep minima observed on the potential energy surfaces immediately above a cluster and at its boundaries can trap diffusing adatoms. The distributions of stresses and strains in the silicon lattice under a cluster on the surface are studied and described.     

小液滴撞击壁面传热特性数值分析

小液滴撞击壁面现象在喷雾冷却等领域都有广泛应用.为研究小液滴(微米)撞击热壁面(非沸腾区)传热过程,建立了二维液滴撞壁瞬态模型,并采用相场方法对小液滴换热过程中对流热通量和导热热通量的大小进行了对比.研究结果表明:液滴撞击壁面初期形成“冷斑”,有利于小液滴与壁面的传热;小液滴撞击壁面过程中热通量峰值存在于三相接触点附近,数量级在105—106 W/m²;小液滴撞击壁面过程中受壁面浸润性和液滴尺寸对传导热通量的影响较为显著,而速度和液滴尺寸对对流热通量的影响较为显著;大多数情况下,小液滴撞击壁面传导热通量数量级在103—105 W/m²,对流热通量数量级在104—106 W/m²,对流热通量大于传导热通量,在整个换热过程中占据主导地位.     

Polarization and extra-atomic relaxation on the surface and in the bulk of solids: influence of the molecular shape, polarizability and complex nature of the adsorbate

The influence of the molecular cavity shape and of the angular dependence of the dielectric constants in a low symmetry crystal on the polarization energy E_pol, induced by electron holes in the bulk and on the surface of the molecular solids, is investigated. The analytical expressions are obtained and evaluated for SF₆, SO₂, CS₂ and seven aromatic organic compounds. The theory is in good agreement with the experimental data. The deviation of the molecular cavity shape from a sphere has a marked influence on the calculated extra-atomic relaxation energy in large molecules. The E_pol value depends on the hole position. In SF₆ this value is larger for F atom photoionization than for S atom photoionization. The angular dependence of the dielectric constants has a smaller effect on the E_pol value than does that of the cavity shape. The E_pol value on the surface of a single crystal depends on the crystallographic plane. The polarization energy for CO molecules on the top of Xe layers on Al(111) is calculated in dependence on the number of Xe layers. The calculated extra-atomic relaxation energy is in good agreement with experiment.     

Ge薄膜特性及其在光子计数成像系统中的应用

利用电子束真空蒸镀方法制作了Ge薄膜,用作感应读出方式光子计数成像系统的电荷感应层,研究了石英玻璃衬底和陶瓷衬底上Ge薄膜的结构特征、表面形态以及各种工艺参数对薄膜电阻的影响.X射线衍射(XRD)测试表明,两种衬底上沉积的Ge薄膜均为立方相非晶态.场发射扫描电子显微镜(FESEM)图像表明石英玻璃衬底上的薄膜致密平整,陶瓷衬底上的薄膜比较粗糙,厚度较薄时,陶瓷晶界处薄膜不连续导致电阻较大.通过改变沉积速率、薄膜厚度及采用退火的方法可以控制薄膜电阻.对比了采用不同阻值电荷感应层时系统的性能,发现阻值对探测器的分辨率影响小,对计数率影响较大.     

Adsorption and dissociation of ammonia on Au(1 1 1) surface: A density functional theory study

Periodic density functional theory (DFT) calculations using plane waves had been performed to systematically investigate the stable adsorption amine and its dehydrogenated reaction on Au(1 1 1) surface. The equilibrium configuration including on top, bridge, and hollow (fcc and hcp) sites had been determined by relaxation of the system. The adsorption both NH₃ on top site and NH₂ on bridge site is favorable on Au(1 1 1) surface, while the adsorption of NH on hollow (fcc) site is preferred. The adsorbates are adsorbed on the gold surface with the interaction between p orbital of adsorbate and the d orbital of gold atoms. The interaction between adsorbate and gold slab is more evident on the first layer than on any others. Furthermore, the dissociation reaction of NH₃ on clean gold surface, as well as on the pre-covered oxygen atom and pre-covered hydroxyl group surface had been investigated. The results show that the dehydrogenated reaction energy barrier on the pre-covered oxygen gold surface is lower. The adsorbed O can promote the dehydrogenation of amine. Additionally, OH as the product of the NH₃ dissociation reaction participates in continuous dehydrogenation reaction, and the reaction energy barrier is the lowest (22.77 kJ/mol). The results indicated that OH_ads play a key role in the dehydrogenated reaction on Au(1 1 1) surface.     

单液滴正碰球面动态行为特性实验研究

在考虑空气阻力影响,确定液滴撞击球面速度的基础上,对较高韦伯数液滴撞击干燥球面动态行为过程进行了实验研究,分析了球面曲率与韦伯数对液滴撞击行为和铺展因子的影响,并与前人撞击平面结果进行了对比.实验表明,靠近撞击球面时,液滴降落速度出现明显波动;球面曲率对液滴撞击后行为影响明显,曲率较大时,液滴撞击后铺展液膜会超出球面直径并滑落,曲率较小时,液滴撞击后在球面上呈现明显的铺展、回缩、震荡、着附动态变化行为,此时最大铺展因子受曲率影响小,随曲率减小,逐渐趋向于撞击平面时的最大铺展因子;韦伯数对液膜铺展速率影响较小,但对液膜回缩时间影响明显,最大铺展因子随韦伯数增加逐渐增大,获得的关联式呈指数变化.     

Adsorption and molecular dynamics of low-molecular substances on modified montmorillonite nanoparticles

The effect of the structure of stable nitroxyl radicals on their adsorption from organic solvents on montmorillonite modified with cationic surfactants is examined. The influence of the nature and content of the modifier and solvent, as well as additional modification with cationic dyes, on the adsorption is considered. The kinetic parameters of the adsorption of decane, toluene, and ethanol from the gas phase are determined. The spin probe method is used to determine the phase state and distribution of adsorbed additives, as well as the influence of an additional adsorption of hydrocarbons on the molecular dynamics at the surface of nanoparticles of montmorillonite and nanopigments based on cationic dyes.     

航电设备通用检测维护台的设计

为了适应机载武器装备系统的多样化以及通用性要求,搭建了基于PXI总线的航电设备通用检测维护台,在系统架构、硬件设计以及软件开发等各方面进行了通用性设计。该航电设备通用检测维护台基于PXI构架,挂装不同种类的适配器,操作通用平台上的人机接口,可满足多种设备的检测、测试任务。航电设备通用检测维护台在一个机柜内实现了人机交互操作,大功率、高精度、多种类通用电源及PXI智能测试平台等的高度集成。该通用平台具有良好的通用性和扩展性,适用多种机型、多种航电设备。通用平台已在某型航电设备的检测维护中完成了工程验证,系统性能稳定,适用性强,可实现多种航电设备的检测维护工作,也可推广至海军舰艇、兵器车载装备等。     

Formation of Ti1–x Si x and Ti1–x Si x N films by magnetron co-sputtering

The paper reports on surface morphology, structure and microhardness of TiSi–N films formed by cosputtering from two target-facing unbalanced magnetrons, equipped with pure Ti and Si targets, on an unheated substrate rotating in front of both targets. The ratio Si/Ti in the TiSi–N film was achieved by modifying the magnitude of currents in the individual magnetrons and by the addition of nitrogen to the film. The rotation of the substrate has a strong effect on the film deposition rate and its morphology. The deposition rate is 3 times lower than that of the film deposited on a stationary substrate. The surface roughness of a polycrystalline Ti film deposited on the rotating substrate is considerably higher than that on a stationary substrate. On the contrary, the surface of an amorphous Si film is smooth and there is no difference between the roughness of Si films sputtered on stationary and on rotating substrates. The hardness of the film increases with increasing Si content and with the addition of nitrogen to the TiSi film. The Ti(26 at.%)Si(8.5 at.%)N(65 at.%)-film sputtered on an unheated rotating steel substrate, held at a floating potential, exhibited the best result with a hardness of 29 GPa.     

Selective oxidation of dual phase steel after annealing at different dew points

Hot galvanized steels have been extensively used in the automotive industry. Selective oxidation on the steel surface affects the wettability of zinc on steel and the grain orientation of inhibition layer (Fe-Al-Zn alloy) and reduces the iron diffusion to the zinc layer. The aim of this work is to identify and quantify selective oxidation on the surface of a dual phase steel, and an experimental steel with a lower content of manganese, annealed at different dew points. The techniques employed were atomic force microscopy, X-ray photoelectron spectroscopy, and glow discharge optical emission spectroscopy. External selective oxidation was observed for phosphorus on steel surface annealed at 0 °C dp, and for manganese, silicon, and aluminum at a lower dew point. The concentration of manganese was higher on the dual phase steel surface than on the surface of the experimental steel. The concentration of molybdenum on the surface of both steels increased as the depth increased.     

Nucleon-nucleon potential for isotopic triplet state

The nucleon-nucleon potential for the isotopic triplet state is computed as a superposition of Yukawa-type potentials. It contains the central, spin, spin-orbit, quadratic spin-orbit and tensor term and is dependent on the total angular momentumJ. The parameters of the individual terms are fitted to the experimental data.The computing was performed on the Elliot 4130 computer in Prague. The authors are indebted to Z. Janout for valuable discussions on phase shift analysis.The authors would like to express their gratitude to Prof. G. Alaga and Prof. M. K. Pal for arranging a special seminar on this topic at the International Course on Nuclear Theory (Trieste 1969).Dedicated to Professor V. Votruba on his sixtieth birthday.     

Experiments on Sprouting Inhibition in Onions

The effect of irradiation on sprouting depends on the irradiation dose, on the irradiation time after harvest and on the physiological development stage of onions. The best conditions of an effective irradiation were found out. Experiments were carried out in order to study the physiological causes of sprout inhibition. The effect of the irradiation on cell elongation and cell division was investigated.     

High-speed optical signal processing using semiconductor optical amplifiers

The authors report on all-optical switching devices based on semiconductor optical amplifiers (SOA) in applications for optical time division multiplexing (OTDM) transmission technology. The report includes a discussion on the basic properties of an SOA, on the nonlinear processes of cross-phase modulation and four-wave mixing in the SOA used for all-optical switching, and on the application of the SOA as demultiplexer, add-drop multiplexer, clock recovery and wavelength converter. The devices considered here operate at data rates in excess of \Gb80, where electrical signal processing is not available today.     

FTIR-ATR技术考察TiO2膜对油酸的光催化氧化性能

采用Sol-Gel和PVD法在玻璃、陶瓷、铝片表面制备出TiO2膜,直接将食用油中的主成分油酸用溶剂稀释后均匀涂在膜表面,采用FTIR-ATR技术实现了对膜样品光催化自清洁性能的快速准确评价,并通过测量水的接触角评价了膜的亲水性。结果表明,Sol-Gel法和PVD法制备的TiO2/玻璃膜都具有较好的光致亲水性和光催化降解油酸性能,两者的亲水性没有明显差别,但前者的光催化活性稍优于后者。比较Sol-Gel法制备的TiO2/玻璃、TiO2/陶瓷和TiO2/铝片膜对油酸的光催化降解性能发现,光照3·5h后3个样品的降解率分别为92%,85%和46%,表明基底材料性质对TiO2膜的光催化活性有明显影响,镀在非导电性玻璃和陶瓷表面的TiO2膜比镀在导电性金属铝表面的TiO2膜对油酸有更高的光催化降解能力。     

富勒烯C32分子器件结构和传导特性的理论研究

利用基于第一性原理的密度泛函理论(DFT)和非平衡格林函数(NEGF)方法对富勒烯C32分子及在C32的距离最远的两个碳原子处外接Li电极的C32分子器件进行了电子结构、电子传输性质的研究。设计了C32笼内嵌入Mg原子,外接Li电极的分子器件。通过计算,得出了两个分子器件的电子传输谱,分析了他们的电子结构和电子输运特性。说明了C32分子器件的电子传输主要集中于C32分子的壳表上,并且分子球的内侧和外侧的电子传输相近似。在C32分子内部嵌入Mg原子后,分子器件的电子传输仍主要集中在分子表面上,但在系统Mg@C32中,表面内侧的电子传输要比表面外侧的电子传输强。通过比较,结果表明两种富勒烯分子的电子传输性能顺序为Mg@C32>C32。     

Collagen immobilization on 316L stainless steel surface with cathodic deposition of calcium phosphate

Collagen fibril/(calcium phosphate and carbonate) composite coatings on 316L stainless steel were developed with a cathodic deposition technique. The response of SaOS-2 osteoblast-like cells to the collagen/calcium salt-coated 316L steel was investigated. The collagen fibrils were self-assembled on the 316L steel surface and immobilized by their partial incorporation into a calcium salt layer electrodeposited cathodically in Hanks’ solution. The amount of calcium salt depended on the applied cathodic potential. The mineralization of collagen fibrils was observed. The collagen coverage localized and the composition of calcium salts varied on the same specimen. Such non-uniform surfaces affected the cell response. The observed outlines of cell bodies and nuclei on the thin collagen coating were clearer than those on the thick collagen coating in most cases. The collagen coating did not significantly influence the mean viability of cells on the whole specimen surface. Interestingly, the alkaline phosphatase activity per cell on the collagen/calcium salt-coated specimens was higher than that on the as-received specimen. It was revealed that cathodic deposition is an effective technique to immobilize collagen fibrils on a 316L steel surface.     

Still Few-Nucleon Systems��After So Many Years

Three- and four-nucleon reactions are discussed. The focus is on the notion of nuclear potentials, on conceptual and technical issues of calculations and on unresolved problems between existing theoretical predictions and experimental data. The special focus is on some historic aspects of the evolution of the field. The views presented have a strong personal bias.     

Coupled flow and heat transfer of power-law nanofluids on non-isothermal rough rotary disk subjected to magnetic field

We study the coupled flow and heat transfer of power-law nanofluids on a non-isothermal rough rotating disk subjected to a magnetic field. The problem is formulated in terms of specified curvilinear orthogonal coordinate system. An improved BVP4C algorithm is proposed, and numerical solutions are obtained. The influence of volume fraction, types and shapes of nanoparticles, magnetic field and power-law index on the flow, and heat transfer behavior are discussed. The obtained results show that the power-law exponents (PLE), nanoparticle volume fraction (NVF), and magnetic field inclination angle (MFIA) have almost no effects on velocities in the wave surface direction, but have small or significant effects on the azimuth direction. The NVF has remarkable influences on local Nusselt number (LNN) and friction coefficients (FC) in the radial direction and the azimuth direction (AD). The LNN increases with NVF increasing while FC in AD decreases. The types of nanoparticles, magnetic field strength, and inclination have small effects on LNN, but they have remarkable influences on the friction coefficients with positively correlated heat transfer rate, while the inclination is negatively correlated with heat transfer rate. The size of the nanoparticle shape factor is positively correlated with LNN.     

Polarizabilities and Hyperpolarizabilities for Lithium Atoms in Debye Plasmas

The effects of plasma environments on energies, oscillator strengths, polarizabilities and hyperpolarizabilities for lithium atom have been calculated by combining the l-dependent model potential of free lithium atom and linear variation method based on B-spline basis functions. The influence of plasma on lithium atom is represented by the Debye screened potential, which describes effectively the averaged effect of the plasma environment on atomic spectra. The results are in agreement with other reported ones.     

激光触发能量对横向结构4H-SiC光导开关导通电阻的影响

采用钒掺杂半绝缘4H-SiC衬底,利用磁控溅射在硅衬底上制备了Ni/Au金属电极,并封装加工成同面型横向电极结构SiC光导开关,研究了不同激光触发能量对光导开关光电响应及导通电阻的影响。用波长532nm的激光作为触发源,当激光触发能量从26.7mJ增加到43.9mJ时,光导开关的导通电阻从295Ω降低到197Ω。利用复合理论推导出激光触发时导带中载流子浓度随时间的变化规律,并利用MATLAB模拟计算了不同触发能量下开关的导通电阻,得到了与实验较一致的结果。在此基础上,提出了降低开关导通电阻的两种途径。