Abstract
The angular intensity distribution of He beams scattered from compact clusters and from diffusion limited aggregates, epitaxially grown on metal surfaces, is investigated theoretically. The purpose is two-fold: to distinguish compact cluster structures from diffusion limited aggregates, and to find observable signatures that can characterize the compact clusters at the atomic level of detail. To simplify the collision dynamics, the study is carried out in the framework of the sudden approximation, which assumes that momentum changes perpendicular to the surface are large compared with momentum transfer due to surface corrugation. The diffusion limited aggregates on which the scattering calculations were done, were generated by kinetic Monte Carlo simulations. It is demonstrated, by focusing on the example of compact Pt heptamers, that signatures of structure of compact clusters may indeed be extracted from the scattering distribution. These signatures enable both an experimental distinction between diffusion limited aggregates and compact clusters, and a determination of the cluster structure. The characteristics comprising the signatures are, to varying degrees, the rainbow, Fraunhofer, specular and constructive interference peaks, all seen in the intensity distribution. It is also shown, how the distribution of adsorbate heights above the metal surface can be obtained by an analysis of the specular peak attenuation. The results contribute to establishing He scattering as a powerful tool in the investigation of surface disorder and epitaxial growth on surfaces, alongside with STM.
Highlights
The process of epitaxial growth of metal or semiconductor films on a surface presents some major theoretical, experimental and technological challenges
In this study we focused on the utility of TEAS as a tool for learning about surface disorder
This determination is based on the identification of Rainbow and Fraunhofer peaks in the angular intensity distribution, and an analysis of cross-section oscillations dependence on incidence energy
Summary
The process of epitaxial growth of metal or semiconductor films on a surface presents some major theoretical, experimental and technological challenges. Clusters in particular play an important role in the epitaxial-growth kinetics, as it is the continual process of their formation, restructuring and dissociation, through which growth takes place Issues such as the structure, stability and surface diffusion of metal clusters have been addressed experimentally by Wang and Ehrlich. The purpose of the present article is to address the questions of whether “signatures” of the various shapes assumed by the clusters and DLA are present in the spectra obtained with He-scattering experiments, and to find how they may be extracted with the proper analysis The answers to these questions are crucial to the understanding of epitaxial-growth induced surface disorder, and to enhance the usefulness of TEAS as an indispensable tool in the study of such surface phenomena.
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