| Abstrakt: |
Ag thin films on an Re(0001) surface prepared by vapor deposition at 300, 400 and 600 K were studied by means of low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). At T= 300K, Ag atoms nucleate heterogeneously at every monoatomic Re step edge and diffusion-limited aggregation leads to dendritic Ag islands, which coalesce to a porous film near the monolayer. Still larger coverages result in more densified Ag layers, due to enhanced interlayer mass transport facilitated by low Schwoebel barriers for second-layer Ag islands. At T> 400K Ag atoms nucleate only at every secondmonoatomic step, indicating a preference for the formation of (111) microfacets and a pronounced mobility of Ag atoms perpendicular to the step edges. Compared to the 300 K situation, even more compact and better ordered layers are formed, resulting in a clear layer-by-layer growth (of Frank-van-der-Merwe type), but with a strongly layer-dependent morphology. Ag grows pseudomorphically in the first layer as indicated by misfit dislocation domains, uniaxially expanded lines of Ag atoms form in the second layer and STM moiréstructures (paralled by appropriate LEED superstructures) appear for the third and fourth layer (at T≥ 400K). In the fifth layer the 4.7% AgRe lattice misfit is practically accommodated and clear epitaxial growth of Ag(111) crystallites occurs. |
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