Calculation of surface peak intensity in MeV ion scattering. II

Monte Carlo calculations have been performed to evaluate the surface peak from 1 MeV He ions incident on Si(001) and Si(111) crystal surfaces. Detailed angular dependences of the surface peaks were obtained for tilt angles of ?2° and azimuthal angles of ?45° in the vicinity of axial channeling directions. The validity of the triangular background subtraction is discussed for cases of tilted incidence from axial channeling directions. The multiple scattering effect in thin adlayers on the crystal, which is important in application of MeV ion scattering to interfaces studies, is simulated and correlated with evaluation of the interface peak value of the substrate atoms.     

Influence of electric field annealing on atom diffusion in Cu/Ta/Si stacks

In this letter, we present a quantitative analysis of the influences caused by an electric field annealing on interface atom diffusion in a Cu/Ta/Si stack at a range of temperatures 450～650 °C. The results indicate that the external electric field has a remarkably accelerated effect on Cu atom diffusion in the Ta layer and the failure of Ta as the diffusion barrier. The preexponent D ₀ and the activation energy Q for Cu atom diffusion in the Ta layer were both decreased with the application of an external electric field. The activation energy for electric field annealed stacks is 1.22 eV, which is lower than that for annealed stacks (1.58 eV). The accelerating effect is mainly attributed to the perturbation of the electric state of the defects in the interface and grain interior.     

Ni原子倾斜轰击Pt(111)表面低能溅射现象的分子动力学模拟

采用嵌入原子方法的原子间相互作用势,通过分子动力学模拟详细研究了以不同角度入射的低能Ni原子与Pt (111)基体表面相互作用过程中的低能溅射行为.结果表明:随着入射角度从0°增加到80°,溅射产额Y_s和入射原子钉扎系数S的变化均可以根据入射角θ近似地分为以下三个区域:当θ ≤ 20°时,Y_s和S几乎保持不变,其值与垂直入射时接近,溅射原子的发射角分布和能量分布也与垂直入射时的情 关键词： 分子动力学模拟 入射角 低能溅射     

高电荷态离子与Si(110)晶面碰撞的沟道效应研究

不同电荷态低速离子(Ar^q+,Pb^q+)轰击Si(110)晶面,测量不同入射角情况下的次级粒子的产额. 通过比较溅射产额与入射角的关系,证实沟道效应的存在. 高电荷态离子与Si相互作用产生的沟道效应说明溅射产额主要是由动能碰撞引起的. 在小角入射条件下,高电荷态离子能够增大溅射产额. 当高电荷态离子以40°—50°入射时,存在势能越高溅射产额越大的势能效应. 关键词： 高电荷态离子 溅射 沟道效应     

辐照导致钨表面的溅射现象的理论研究

采用基于量子力学的分子动力学方法,模拟了高能粒子辐照导致钨表面的溅射和结构损伤.结果显示,当PKA能量高于200 eV且入射角度大于65°时开始产生溅射原子,当入射角度在45°-65°之间时,钨表面因受辐照而导致的空位数目最少.因此,当PKA入射角度取在45°-65°之间时,可以有效地降低辐照导致的钨表面的结构损伤.还发现钨表面含有间隙原子时会加剧表面原子溅射,而包含空位原子且PKA取在空位附近时则会抑制表面原子的溅射.     

低能单个Cu原子与Cu13团簇沉积到Fe（001）表面的比较

本文利用分子动力学模拟方法对相同初始沉积条件下的单个Cu原子和Cu13团簇与Fe(001)表面的相互作用分别进行了模拟研究, 并将两者的模拟结果进行了比较分析. 单个Cu原子和Cu13团簇的初始入射能量范围均为1eV/atom、3eV/atom、5eV/atom和10eV/atom, 初始入射角度均为0o、10o、30o和45o, 衬底温度分别为100K、300K和800K. 对单个Cu原子和Cu13团簇的原子动能、质心高度、迁移距离和最终沉积形貌进行了分析, 对比研究了相同初始沉积条件下单个Cu原子和Cu13团簇在沉积过程中和沉积效果上的具体差异. 模拟结果表明: 单个Cu原子和Cu13团簇与Fe(001)表面的相互作用机制存在差异, Cu13团簇表现出显著的集体效应. 在特定沉积条件下, 由于Cu13团簇的集体效应, 导致Cu13团簇与Fe(001)表面的结合能力和在Fe(001)表面上的扩散能力均强于单个Cu原子.     

波状结构二维光子晶体负折射现象的研究

结合波状结构二维(2D)光子晶体(PC)与入射介质两者的等频面结构分析了PC内部的负折射现象，采用时域有限差分(FDTD)方法模拟了高斯光束在波状结构2DPC内的负折射，分别得到了折射角/入射角以及折射角/入射波长之间的关系曲线，当入射角为45°，入射波段在1485—1530nm区域时，波状结构2DPC的负折射角与入射波长近似呈线性变化关系，并带有明显的PC超棱镜效应，采用端面投影方法对波状结构2DPC的入射端面和出射端面进行处理，改善了负折射时的透过率. 关键词： 光子晶体 负折射 等频面     

赫兹型微裂纹光场调制增强作用的系统研究

通过改变裂纹的倾角、宽度和深度参数,模拟了赫兹型裂纹在不同参数下对光场调制能力的不同. 模拟发现,倾斜角度为20.9°到45°之间的裂纹危害最大,倾角大于45°小于48.2°的裂纹危害也十分大,而倾斜角度为45°时的裂纹危害最小. 对于30°倾角的赫兹型裂纹,一定范围内,赫兹型裂纹深度的增加会导致其光场调制增强能力呈二次方关系增加,但宽度的增加不会使其光场调制增强作用增加. 裂纹深度和宽度的增加可以用来近似裂纹的演化过程,所以裂纹的扩展导致了其光场调制能力的增加,进而导致损伤增长速率的加快,这和e指数损伤增长规律相符. 关键词： 损伤增长 亚表面缺陷 赫兹型裂纹 光场增强     

Ferromagnetism in Cu-doped silicon carbide

Cu doped silicon carbide is shown to be ferromagnetic based on experiment results and first-principles calculations. The magnetization value of the Cu doped silicon carbide decreased as the Cu concentration increased. When the films were annealed at 800 °C, the ferromagnetic signal was increased. Reduction of the C vacancy concentration will introduce a large total moment in the system. Theoretically, compared with the case of one Cu atom replacing one Si atom, increasing the Cu doping, changing the Cu atom location or including carbon vacancies in the calculations for the system all make the ferromagnetic moment decrease. One Cu atom replacing one Si atom with the addition of one C vacancy makes the energy band gap of the system disappear. Our investigations suggest that the ferromagnetism arises from the hybridization between Cu 3d orbital and C 2p orbital. Ferromagnetic moment is influenced by a symmetry-lowering distortion of the surrounding lattice by the Cu dopant.     

Theoretical studies of fast He atom scattering from a W{100} surface

Theoretical calculations of the scattering of fast neutral He atoms from W{100} are presented which are directly compared to the results from recent experiments of Nielsen and Delchar. The experiments which were performed for He atom energies between 150 and 1000 eV, and for incident polar angles between 0° and 65° as measured from the surface normal, displayed peaks in the polar angle distributions at 72°, 56° and ±10°. The results from classical dynamics calculations are employed here to explain the scattering phenomena that give rise to these peaks in the polar distributions. The calculations indicate that the peak at 72° is primarily due to scattering from the first layer W atoms. The peaks at ± 10° and 56° are unusual in that there are a multitude of different collision paths that result in the He atom being scattered into the same final angle. The peaks at ± 10° result from He atoms scattering mainly from the second, third and fourth layers of W atoms. The He atoms are focused on the outward path into the near normal direction by two first and two second layer W atoms. Subsurface scattering is also responsible for the peak at 56°. In this case the channel of first and second layer W atoms that focuses the outgoing He atoms is oriented at 54.7° with respect to the surface normal. It is proposed that slight variations of the experimental data from the calculated values are due to surface reconstruction of W{100} and that a more thorough analysis could reveal the microscopic nature of this structure.     

载能Ni原子斜入射Pt(111)表面的分子动力学模拟

采用嵌入原子方法的原子间相互作用势,利用分子动力学模拟,详细研究不同角度入射的载能Ni原子在Pt(111)基体表面的沉积过程.结果表明,随着入射角度θ从0°增加到80°,溅射产额、表面吸附原子产额、空位产额的变化情况均可按入射角度近似地分为θ≤20°,20° < θ < 60°和θ≥60°三个区域.当θ≤20°时,载能沉积对基体表面的影响与垂直入射时的情况类似,表面吸附原子的分布较为集中,入射原子容易达到基体表面第二层及以下,对基体内部晶格产生-定的影响;在20° < θ < 60°的范围内,入射原子的注入深度有所下降,对基体内部晶格的影响减小,表面吸附原子的分布较为均匀,有利于薄膜的均匀成核与层状生长;当θ≥60°时,所有入射原子均直接被基体表面反射,表面吸附原子产额、溅射产额、表面空位产额均接近0,载能沉积作用没有体现.     

纳米银增强聚合物太阳能电池光吸收的研究

基于共轭聚合物给体材料P3HT和富勒烯衍生物受体材料PCBM共混的体异质结结构 的聚合物太阳能电池因其空穴载流子迁移率低而限制了P3HT:PCBM功能层厚度, 从而影响了器件对入射光的吸收. 在聚合物功能层内引入金属纳米颗粒可以利用金属表面等离子体效应增强器件内电场并改善器件的光吸收. 本文基于时域有限差分法(finite difference time domain, FDTD)方法模拟得到了聚合物功能层内包含了直径为50 nm纳米银球并且球间距为50 nm的聚合物太阳能 电池器件在波长分别为400 nm和500 nm照射时的二维光电场分布以及入射角分别为15°, 45°, 60°时包覆纳米银聚合物功能层横截面内的光电场强度分布; 计算得到了银纳米颗粒尺寸分别为10 nm, 20 nm和50 nm时以及分布在空穴传输层PEDOT:PSS的纳米银器件的光吸收; 并计算了斜入射时包覆纳米银的聚合物功能层光吸收. 理论分析表明: 聚合物功能层加入纳米银球后, 因为纳米银球的表面等离子体效应使入射光在功能层内散射增强而使器件内的光电场重新分布; 直径较大的纳米银颗粒能产生大角度的光散射, 更有利于聚合物功能层对光的吸收. 这里, 基于有机银盐还原法制备了纳米银颗粒并制备了银等离子体增强的聚合物太阳能电池, 其结构为: glass/ITO (～100 nm)/PEDOT:PSS (40 nm)/P3HT:PCBM (～100 nm)(nano-Ag)/LiF (1 nm)/Al (120 nm). 该器件与平板器件的性能对比实验证实: 通过在聚合物功能层内上引入纳米银颗粒可以有 效增加器件光吸收并改善器件电学性能, 器件外量子效率在520 nm处最大增加了17.9%. 关键词： 纳米银 表面等离子体共振 时域有限差分 聚合物太阳能电池     

Study of combined electroreflectance and double layer effects at lead electrodes

Reflectance changes at lead electrodes have been measured as a function of surface charge at 45° and 70° angles of incidence using solutions of sodium fluoride and quaternary ammonium salts. These solutions were chosen so as to provide quite different composition for the inner layer at the metal/solution interface, and hence different optical contributions there from. Linear reflectance-surface charge relation has been observed for NaF solutions only at a number of wavelengths. The optical effects from the inner layer has been recognized but could not be separated out from the main er effect by comparative measurements at two angles of incidence. This has been rationalized on the basis of similar variation of the er effect and the optical effect from the double-layer as a function of angle of incidence of light.     

Atomic Diffusion in Cu/Si （111） and Cu/SiO2/Si （111） Systems by Neutral Cluster Beam Deposition

The Cu films are deposited on two kinds of p-type Si （111） substrates by ionized duster beam （ICB） technique. The interface reaction and atomic diffusion of Cu/Si （111） and Cu/SiO2/Si （111） systems are studied at different annealing temperatures by x-ray diffraction （XRD） and Rutherford backscattering spectrometry （RBS）. Some significant results are obtained： For the Cu/Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs when annealed at 230℃. The diffusion coefficients of the samples annealed at 230℃ and 500℃ are 8.5 ×10^-15 cm^2.s^-1 and 3.0 ×10^-14 cm^2.s^-1, respectively. The formation of the copper-silicide phase is observed by XRD, and its intensity becomes stronger with the increase of annealing temperature. For the Cu/SiO2//Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs and copper silicides are formed when annealed at 450℃. The diffusion coefficients of Cu in Si are calculated to be 6.0 ×10^-16 cm^2.s^-1 at 450℃, due to the fact that the existence of the SiO2 layer suppresses the interdiffusion of Cu and Si.     

Interface roughness, surface roughness and soft X-ray reflectivity of Mo/Si multilayers with different layer number

A series of Mo/Si multilayers with the same periodic length and different periodic number were prepared by magnetron sputtering, whose top layers were respectively Mo layer and Si layer. Periodic length and interface roughness of Mo/Si multilayers were determined by small angle X-ray diffraction (SAXRD).Surface roughness change curve of Mo/Si multilayer with increasing layer number was studied by atomic force microscope (AFM). Soft X-ray reflectivity of Mo/Si multilayers was measured in National Synchrotron Radiation Laboratory (NSRL). Theoretical and experimental results show that the soft X-ray reflectivity of Mo/Si multilayer is mainly determined by periodic number and interface roughness, surface roughness has little effect on reflectivity.     

Energy and charge distributions of fast hydrogen ions and atoms reflected from Cu in the case of grazing incidence

The energy and charge distributions of protons and hydrogen atoms reflected from the Cu surface in the case of grazing incidence angles are measured at energies of incident particles (H⁺ and H⁰) of 200 and 250 keV. The charged fractions of reflected particles are analyzed. A weak dependence of the neutral fraction of reflected particles on the scattering angle is discovered for incidence angles of 1°–2° and an energy of scattered particles of 60 keV or less. It is shown that the neutral fraction of reflected particles with an energy of 60–80 keV or more is independent of the scattering angle and is determined by the ratio of the cross sections for the electron capture and loss by ions in the material.     

The deposition of Fe or Co clusters on Cu substrate by molecular dynamic simulation

A molecular dynamic method is used to simulate the film growth process of Fe or Co clusters depositing on Cu substrate with low energy. The tight-binding (TB-SMA) many-body potential is used to simulate the interaction between atoms. The effects of different incident energies and/or substrate temperatures on the surface roughness, layer coverage function, radial distribution function (RDF), and residual stress are investigated. From the simulation results, as the substrate temperature and/or incident energy is increased, the surface roughness of the grown film could be reduced, and the interface intermixing is increased. Also, as compared to Co–Cu system, Fe–Cu system has better surface roughness, less interface intermixing, and similar radial distribution function as well as average stresses.     

Angular distribution and differential sputtering yields for low-energy light-ion irradiation of polycrystalline nickel and tungsten

Angular differential and total sputtering yields of polycrystalline nickel and tungsten have been measured for 1 and 4 keV H⁺ and 4 keV He⁺ ion bombardment at incidence angles between 0° and 80°. The differential sputtering yields (dY/dΩ) were determined with the aid of the collector technique, whereas the total yieldY was determined from the weight loss of the target during irradiation. Asymmetric angular distributions are observed at oblique angles of incidence, the emission maximum being shifted in forward direction (with respect to the incident ions). Even more pronounced than the change in shape of the emission distribution is an increase in the differential yield:dY/dΩ rises with increasing incidence angle over the whole range of ejection angles, the increase being most prominent in the direction of primary recoil emission. This effect is therefore ascribed to emission of surface atoms in direct projectile-surface atom collisions. On short term leave from Institut für Plasmaphysik der Kernforschungsanlage Jülich GmbH, D-5170, Jülich, Fed. Rep. Germany.     

Investigation of Brewster anomalies in one-dimensional disordered media having Lévy-type distribution

In this paper, we calculate the localization length of a TM electromagnetic wave in unitof system length versus incident angle in a disordered layered structure where therefractive index of one of its constituents follows a Lévy-type distribution with a powerexponent α.The incident angle at which the localization length takes the maximum value is called thegeneralized Brewster angle as before. However, in contrast to previous works with a weakdisorder, the wave incident at generalized Brewster angle is not always in the extendedregime. For special values of α and the frequency, the system is in a localizedstate at this angle. But, the localization length at this Brewster angle is always largerthan that at other angles. The effects of α variation on the localization length at thisBrewster angle and its position are investigated for different frequencies. Thelocalization at this angle degrades with increasing α for all frequencies. Atsome working frequencies, the generalized Brewster angle is a decreasing function ofα. However,at other frequencies, the dependence of generalized Brewster angle on α is not monotonic. Forincident angles smaller than a specific angle, the localization length increases withincreasing α.However, for incident angles larger than this specific angle, there are incident angles atwhich any increase of α leads to the decrease of localization length. Inother words, for these incident angles, the improvement of Anderson localizationsurprisingly happens with decrease of disorder strength and the refractive index contrast.     

激光入射角度对薄膜热场分布影响的数值分析

在多层介质薄膜中，激光的入射方式是影响薄膜抗损伤能力的关键因素之一.提出了一种模拟锥角高斯光入射多层介质薄膜后电场和热场分布的方法.该方法能够分析薄膜中高斯光各个角谱分量叠加形成的电场分布，进而得到由于薄膜本征吸收产生的热量沉积以及薄膜内部的温度场分布.针对中心波长为4.3 μm的中红外高反膜进行了分析，给出了高反膜系的温升峰值随激光入射角度和偏振态的变化.结果表明：对于s偏振光，斜入射时膜系的最高温升峰值高于垂直入射峰值，而p光的结果则相反.此种模拟方法克服了原有方法对激光入射角度的限制，较好地反映出斜入射情况下激光偏振态对薄膜损伤的影响. 关键词： 多层介质薄膜 高斯光 热过程 数值分析