随机吸附、无序致密岛和分形亚单层的He散射：表面无序的强度表现
He Scattering from Random Adsorbates, Disordered Compact Islands and Fractal Submonolayers: Intensity Manifestations of Surface Disorder
摘要：
本文从理论上研究了He在三种基本的无序吸附层（a）平移随机吸附物，（b）无序致密岛和（c）分形亚单层上的散射。讨论了这些结果对He在无序表面上散射的实验研究的意义，并对Pt（111）表面上Ag亚单层进行了实验和理论相结合的研究。一些主要的理论发现是：（1）结构方面的计算强度从随机集群被发现是强烈相关的与那些个别集群。(2)低强度的布拉格干涉峰出现，即使从非常小的广告岛散射，并包含广告岛的局部电子结构的信息。(3)对于分形岛，就像具有不同结构的岛一样，离镜强度取决于He/Ag相互作用的参数，并且不遵循文献中先前提出的普适幂律。在Ag在Pt（111）上的实验-理论研究中，我们使用来自低覆盖度（单吸附质）系统的第一个实验He散射数据来确定良好质量的经验He/Ag-Pt势。然后，我们进行了高覆盖率的He散射计算，并与实验进行了比较。结论是，实际的实验相对应的小紧凑的银团簇的尺寸分布窄，表面上的无序。
英文摘要：
A theoretical study is made on He scattering from three fundamental classes of disordered ad-layers: (a) Translationally random adsorbates, (b) disordered compact islands and (c) fractal submonolayers. The implications of the results to experimental studies of He scattering from disordered surfaces are discussed, and a combined experimental-theoretical study is made for Ag submonolayers on Pt(111). Some of the main theoretical findings are: (1) Structural aspects of the calculated intensities from translationally random clusters were found to be strongly correlated with those of individual clusters. (2) Low intensity Bragg interference peaks appear even for scattering from very small ad-islands, and contain information on the ad-island local electron structure. (3) For fractal islands, just as for islands with a different structure, the off-specular intensity depends on the parameters of the He/Ag interaction, and does not follow a universal power law as previously proposed in the literature. In the experimental-theoretical study of Ag on Pt(111), we use first experimental He scattering data from low-coverage (single adsorbate) systems to determine an empirical He/Ag-Pt potential of good quality. Then, we carry out He scattering calculations for high coverage and compare with experiments. The conclusions are that the actual experimental phase corresponds to small compact Ag clusters of narrow size distribution, translationally disordered on the surface.
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