Nanostructure diffusion and aggregation on desorbing rare-gas solids: Slip on an incommensurate lattice
Nanostructure diffusion and aggregation on desorbing rare-gas solids: Slip on an incommensurate lattice
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解吸稀有气体固体时的纳米结构扩散和聚集：不相称晶格上的滑移
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
J. H. Weaver
中科院分区：
文献类型：
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作者：
V. N. Antonov;J. S. Palmer;A. Bhatti;J. H. Weaver
各种物质在稀有气体固体上的物理气相沉积导致了自发性团簇的形成。稀有气体缓冲液的解吸导致团簇聚集，这一过程被称为缓冲层辅助生长。我们研究了金纳米结构的聚集程度和尺寸分布随缓冲液成分(Xe、Kr和Ar)和厚度的变化，并用透射电子显微镜对缓冲液解吸和输送到无定形碳衬底后的Au纳米结构进行了成像。对于细小致密的Au纳米结构(平均半径小于∼5 nm，≤为3×104个原子)，扩散系数随尺寸变化很大，在一定范围内随平均尺寸增大而增大。这种增强的扩散现象归因于合并过程中的自加热。这对小颗粒最为重要，由于界面耦合较弱，在Kr上比在Xe上更明显。在大的分支Au纳米结构(超过∼10 nm平均半径，≥2×105个原子)的极限范围内，扩散系数与接触面积成反比，这与纳米晶体在无公度表面上快速滑移扩散的分子动力学模拟相一致。运动是由团簇和衬底的声子驱动的，并由团簇小面和缓冲面之间的摩擦控制。提出了一个简单的模型来解释观察到的团簇大小与缓冲层厚度的指数依赖关系。在该模型中，生长动力学由团簇扩散速率和缓冲器耗尽速率之间的竞争控制。
Physical vapor deposition of a wide range of materials on rare-gas solids leads to spontaneous cluster formation. Desorption of the rare-gas buffer causes the clusters to aggregate, a process known as buffer-layer-assisted growth. We have studied the extent of aggregation and the size distribution of Au nanostructures as a function of the buffer composition (Xe, Kr, and Ar) and thickness, using transmission electron microscopy to image them after buffer desorption and delivery to amorphous carbon substrates. For small compact Au nanostructures (less than ∼5 nm mean radius, ≤3×10 4 atoms), the diffusivity varies strongly with size and even increases with average size in a limited range. This enhanced diffusion phenomenon is attributed to self-heating during coalescence. It is most important for small particles and is more evident on Kr than on Xe because of weaker interface coupling. In the limit of large ramified Au nanostructures (exceeding ∼10 nm mean radius, ≥2×10 5 atoms), the diffusivity scales as the inverse of the contact area, in agreement with molecular dynamics simulations of fast slip diffusion of nanocrystals on incommensurate surfaces. Motion is driven by phonons of the cluster and substrate, and is controlled by friction between a cluster facet and the buffer surface. A simple model is proposed that explains the observed exponential dependence of cluster size on buffer thickness. In this model, the growth kinetics are controlled by competition between the rate of cluster diffusion and the rate of buffer depletion.