带电液体基底表面银原子的凝聚和扩散行为

研究了沉积在带电液体基底(硅油)表面的银原子的凝聚以及扩散行为.先采用热阴极电子发射方法使液体基底表面均匀带电,然后用蒸发沉积方法将银原子沉积到带电的液体基底表面.实验发现:被沉积的银原子首先凝聚成直径约为12μm的准圆形团簇,然后由于库仑排斥力作用而相互离散,所有团簇均向基底的四周边缘漂移;基底表面的团簇数密度n随时间t指数衰减,衰减时间常量Of≈11×10-4s-1;两团簇相互离散的相对平均速率V与它们之间的相对距离L在统计意义上成正比,即V=HL,其中沉积刚结束时常量H≈29×10-4s-1,然后随扩散时间t而逐渐趋于零.分析表明:由于带电银原子团簇的扩散运动,使基底表面的电荷重新分布,基底表面的电场随时间逐渐趋向于处处均匀 关键词： 薄膜 扩散 凝聚     

金原子在熔融玻璃表面的凝聚特性

研究了沉积在熔融玻璃表面的金原子的扩散、凝聚以及结晶行为.实验结果表明:金原子在胶状的玻璃表面先形成具有特征结构的网状薄膜,其中金原子晶粒直径约为20nm;然后网孔逐渐增大直至薄膜破裂,金原子凝聚成准圆形的团族,其饱和直径约为1.2μm,扩散系数为10^-7—10^-8cm²/s数量级;通过快速且准无规地扩散,准圆形团簇最终凝聚成直径约为50μm的大型分枝状凝聚体 关键词： 薄膜 凝聚 扩散     

具有排斥相互作用的原子团簇非平衡系统研究

在无格点基底表面建立了存在排斥相互作用的原子团簇凝聚及扩散模型，对沉积在均匀带电硅油基底表面的银原子凝聚过程进行了研究.结果表明：当沉积原子凝聚成稳定的原子团簇后，由于带同种电荷，团簇之间存在库仑排斥作用，团簇数密度随时间呈指数形式衰减，衰减时间常数为Oa_a；两团簇相互离散的相对平均速率V与它们之间的相对距离L在 统计意义上成正比，即V=HL.停止沉积后初期,H≈Oa_a，然后随着扩散时间的增 加，H逐渐趋于零；随着液体基底黏滞系数增加，摩擦力增大，H逐渐减小，摩 关键词： 排斥相互作用 团簇 扩散     

封面说明

采用气相沉积方法在液相基底表面成功制备了一种具有近似自由支撑的新型铁薄膜系统．该薄膜的生长机制服从所谓的二阶段生长模型：沉积铁原子在液相基底表面首先成核并凝聚成准圆形原子团簇；然后这些原子团簇在液体表面做无规扩散和旋转运动，从而形成分枝状凝聚体(上图)，并随着薄膜名义厚度的增加，分枝状凝聚体逐渐相互连接成网状薄膜，     

液相基底温度对沉积银原子及其团簇凝聚过程的影响

研究了沉积银原子及其团簇在液相基底(硅油)表面的凝聚过程随基底温度的变化关系.实验结果表明:当硅油基底温度升高时,沉积银原子及其团簇的凝聚过程仍基本符合二阶段生长模型; 样品具有明显的边缘效应,在样品中心区域,凝聚体的覆盖率比边缘的相应值小,样品中心区域的凝聚体覆盖率先随薄膜名义厚度的增加迅速增大,然后逐渐趋于饱和,覆盖率趋于饱和时的膜厚值随基底温度的升高而降低; 对于一定的薄膜名义厚度,硅油基底温度越高,中心区域的凝聚体覆盖率越小.银原子凝聚体的分枝平均长度随基底温度的演化过程也具有类似的规律.对沉积银 关键词： 薄膜 液相基底 分枝状凝聚体 生长模型     

含杂质无格点基底表面分枝状凝聚体的计算机模拟

根据含杂质熔融玻璃表面金原子凝聚的实验规律，在原子团簇具有随机的线扩散步长和刚性 转动角度的特征条件下，建立了含杂质无格点基底表面的各向异性团簇-团簇凝聚模型，对 团簇的无规扩散、刚性转动以及凝聚全过程进行了计算机模拟，系统地研究了基底表面无规 分布的杂质区域对分枝状凝聚体诸多特性的影响，所得结果与实验事实相符合. 关键词： 薄膜生长 Monte Carlo模拟 分形     

准自由支撑铝薄膜中有序表面结构的自组织生长

利用真空热蒸发方法在液体基底表面成功制备出具有自由支撑边界条件的金属铝薄膜系统，研究了薄膜中自发形成的自边界向内部区域逐渐生长而呈带状分布的有序表面结构.该有序结构的形成与薄膜厚度、沉积速率和真空环境中的生长时间等实验参数密切相关，其形成过程可用一个三阶段生长模型来描述.实验证明此类有序结构是在薄膜内应力作用下，铝原子及原子团簇在液体表面自由扩散凝聚所致.进一步的理论研究表明：基于特征的边界条件和固液相互作用，该自由支撑铝薄膜系统中包含了丰富的正弦形内应力分布，各种具有不同振幅和频率的正弦形内应力的合成可形成矩形状畴块和带状有序结构. 关键词： 液体基底 铝薄膜 自组织生长 有序结构     

熔融Cu55团簇在Cu(010)表面上凝固过程的分子动力学模拟

采用基于嵌入原子方法的分子动力学,模拟了熔融Cu₅₅团簇在Cu衬底（010）表面上以两个不同降温速率降温过程中结构的变化.模拟结果表明,降温速率对团簇结构的变化有很大影响.较快的降温速率使得降温过程中团簇原子具有较低的能量;较慢的降温速率有助于高温时位于衬底内的原子向衬底表面扩散,排列形成面心立方结构. 关键词： 团簇 凝固 分子动力学 表面     

硅油基底表面铁薄膜的生长机理及表面有序结构

利用直流溅射方法在液体基底(硅油)表面成功制备出金属铁薄膜系统，研究了其生长机理及特征的表面有序结构.实验发现铁薄膜的生长过程与液相基底表面非磁性金属薄膜的情况类似，基本服从二阶段生长模型.连续铁薄膜中可观测到尺寸巨大的圆盘形有序结构，其生长演化与溅射功率、沉积时间和真空环境中的生长时间等实验条件密切相关.实验证明，此类有序结构是在薄膜内应力作用下，铁原子及原子团簇在液体表面自由扩散迁移，并最终在硅油基底表面某些区域成核凝聚所致.在较大溅射功率和沉积时间条件下，圆盘外部区域的铁薄膜中形成周期分布的波纹褶皱，其波长约为10 μm，波峰基本与圆盘的边界平行.进一步研究表明：在沉积过程中，由于沉积铁原子的局域能量作用，导致硅油的表面层结构发生改变而形成一聚合物层；在随后的冷却过程中，聚合物层的强烈收缩使铁薄膜处于很大的压应力场中，促使薄膜起皱形成波纹结构. 关键词： 液体基底 铁薄膜 生长机理 有序结构     

熔融Cu55团簇在Cu(010)表面上凝固过程的分子动力学模拟

采用基于嵌入原子方法的分子动力学,模拟了熔融Cu55团簇在Cu衬底(010)表面上以两个不同降温速率降温过程中结构的变化.模拟结果表明,降温速率对团簇结构的变化有很大影响.较快的降温速率使得降温过程中团簇原子具有较低的能量;较慢的降温速率有助于高温时位于衬底内的原子向衬底表面扩散,排列形成面心立方结构.     

DIFFUSIVE AGGREGATION ON ION IMPLANTED THIN FILMS

Diffusive aggregation on-ion implanted thin films is studied. It is revealed that aggregation is realized mainly by atoms or clusters in the film matrix. The implanting ions play the role of triggering them into motion and supplying the kinetic energy for their diffusion. The aggregation process is characterized by finite density of aggregating particles, random triggering, and limited diffusion distance. The aggregate observed shows scaling or fractal property.     

Processes involved in the formation of silver clusters on silicon surface

We analyze scanning electron microscopy measurements for structures formed in the deposition of solid silver clusters onto a silicon(100) substrate and consider theoretical models of cluster evolution onto a surface as a result of diffusion and formation of aggregates of merged clusters. Scanning electron microscopy (SEM) data are presented in addition to energy dispersive X-ray spectrometry (EDX) measurements of the these films. Solid silver clusters are produced by a DC magnetron sputtering source with a quadrupole filter for selection of cluster sizes (4.1 and 5.6 nm or 1900 and 5000 atoms per cluster in this experiment); the energy of cluster deposition is 0.7 eV/atom. Rapid thermal annealing of the grown films allows analysis of their behavior at high temperatures. The results exhibit formation of cluster aggregates via the diffusion of deposited solid clusters along the surface; an aggregate consists of up to hundreds of individual clusters. This process is essentially described by the diffusion-limited aggregation (DLA) model, and thus a grown porous film consists of cluster aggregates joined by bridges. Subsequent annealing of this film leads to its melting at temperatures lower than to the melting point of bulk silver. Analysis of evaporation of this film at higher temperatures gives a binding energy in bulk silver of ɛ₀= (2.74 ± 0.03) eV/atom. The text was submitted by the authors in English.     

Three-dimensional growth characteristics of antimony aggregates on graphite

The growth of antimony aggregates on the basal plane of graphite via diffusion and aggregation of Sb₄ clusters has been investigated with scanning electron microscopy, and in 3-dimensions with atomic force microscopy. The aggregate morphologies depend critically on the deposition conditions. It is shown that a transition from compact to branched morphologies with increasing aggregate size, depends on the particle flux. Also, the aggregate heights are strongly influenced by flux, with higher fluxes producing flatter aggregates. The heights of individual island branches are also shown to depend on the local diffusion field.     

金属离子对银溶胶的聚集作用及形成的分数维结构

本文研究了一些离子作用于银溶胶而引起聚集的情况。一价金属离子对银溶胶的聚集作用不明显,第Ⅱ主族的金属离子能够引起银溶胶的聚集而形成分形体(Fractal)态,且随着金属离子半径的增大,其聚集能力增强,对于三价金属离子Al³⁺,它也能引起银溶胶的聚集而形成分形体态。酸根阴离子一般不直接引起银溶胶的聚集,但能影响银溶胶的聚集。 关键词：     

Phase transitions in simple clusters

Formation of the liquid state of clusters with pairwise interactions between atoms is examined within the framework of the void model, in which configurational excitation of atoms results from formation of voids. Void parameters are found from computer simulation by molecular dynamics methods for Lennard-Jones clusters. From that standpoint, phase transitions are analyzed in terms of two aggregate states. This information allows us to divide the entropy jump during a solid-liquid phase transition into two parts: one corresponds to configurational excitation at zero temperature and the other arises from thermal vibrations of atoms. The latter part contributes approximately 40% for Lennard-Jones clusters consisting of 13 and 55 atoms, increasing to 56% for bulk inert gases. These magnitudes explain the validity of melting criteria based on thermal motion of atoms, even though the distinctive mechanism of this phase transition results from configurational excitations. It is shown that the void concept allows analyzing various aspects of the liquid state of clusters including the existence of a limiting freezing temperature below which no metastable liquid state exists, as well as the existence and properties of glassy states that may exist below the freezing limit.     

Plasma resonance — enhanced raman scattering by absorbates on gold colloids: The effects of aggregation

The excitation profile of the 1014 cm^?1 Raman band of pyridine adsorbed on colloidal gold particles, and the extinction and elastic scattering spectra of the colloids, are measured as the colloids slowly aggregate in the presence of pyridine. Transmission electron microscopy shows that the aggregates formed are predominantly strings of particles rather than compact clusters, and the dipolar plasma modes of the aggregates are therefore split into longitudinal and transverse components. It is shown that only for excitation under the longitudinal resonance extinction band is there a large Raman intensity enhancement. The Raman excitation profile maximum corresponding to excitation under this resonance moves progressively to longer wavelengths, increasing substantially in height, as the aggregation proceeds. Thus aggregation is most advantageous for the realization of large Raman signals from these colloids, the Raman intensity at a given excitation wavelength increasing approximately as the square of the absorbance at that wavelength as the aggregation proceeds. These observations are discussed in relation to the electromagnetic field enhancement contribution to the surface Raman effect, with which they are in general agreement, and the large increase in ¦?¦² for gold and silver with increase in wavelength is shown to be a significant factor in accounting for some of these effects of aggregation.     

沉积在硅油表面上的Ag原子分形凝聚体

研究了沉积在硅油表面上的Ag原子团簇,经过随机扩散和转动,最终形成大尺度分形凝聚体的凝聚过程．研究结果表明：Ag原子团簇在这种液体基底上的转动为随机转动,转动角位移的方均值<(Δθ)²>和测量时间间隔Δt满足广义爱因斯坦关系<(Δθ)²>=4D_θΔt．随机转动系数D_θ与凝聚体面积S满足指数关系D_θ∝S^{－γ_θ,其中指数γ_θ＝2.4±0. 关键词：}     

Photoinduced formation and aggregation of silver nanoparticles at the surface of carboxymethylcellulose films

Formation and aggregation of photolytic silver nanoparticles at the surface of silver salt of carboxymethylcellulose films (CMCAg films) have been investigated. Detailed X-ray photoelectron spectroscopy (XPS) study and field emission type scanning electron microscopy (FE-SEM) observation have been carried out to characterize silver nanoparticles at the film surface. When the CMCAg films were irradiated with UV light in wet air at room temperature for 30–60 min, silver nanoparticles of ca. 10 nm size were formed at the irradiated surface. According to the FE-SEM observation, the growth of the particle diameter and aggregation of nanoparticles took place after prolonged irradiation, and finally, the irradiated side of the film surface was densely covered with the silver nanoparticles of ca. 35 nm size. Chemical composition analysis by the XPS measurements has confirmed the increase in the atomic concentration of silver with irradiation time. It is suggested that silver atoms and clusters can move in the film and precipitate at the irradiated surface.