GROWTH AND ION EROSION: TWO METHODS FOR PATTERNING SURFACES

摘要

In metal surfaces a build-up of a regular pattern during ion sputtering is produced by two different mechanisms that produce a similar surface instability: the surface curvature dependence of the sputtering yield and the presence of an extra energy barrier whenever diffusing adatoms try to descend step edges. By tuning the competition between erosion- and diffusion-induced surface re-organization, it is possible to investigate new phenomena like the rotation of ripple orientation on an anisotropic fcc(110) substrate and the pattering of a fcc(001) substrate from a mound-like to a ripple structure. Similar phenomena occur in the case of homoepitax-ial growth. In the multilayer regime [Ag on Ag(110)] the rotation of a ripple-like pattern was observed with changing surface temperature. The phenomenon is related to the peculiar hierarchy of inter- and intra-layer diffusion barriers present on the anisotropic Ag(110) substrate. Homoepi-taxial growth on Ag(001) in the multilayer regime is studied with STM. The height, lateral distance, and order of the mound-like structures change with the deposition temperature. The surface morphologies obtained after sputtering and homoepitaxial deposition of Ag(001) have strong similarities. The general approach considers sputtering as the negative of homoepitaxial deposition, i.e. as a deposition of vacancies which can eventually have an asymmetry in their diffusivities. This paper shows that this picture is oversimplified because the dominant effect of ion sputtering is the formation of clusters of adatoms and vacancies.