Annealing of Silicon Nanopatterns

The morphology of surfaces strongly influences optical, electrical, and magnetic properties of thin films. By changing the morphology it is possible to tailor the material properties. Oblique low energy ion beam sputtering produces periodic ripple structures with periodicities in the nanometer range. During sputtering the region near to the surface gets amorphous and some metal is deposited on the surface, i.e. Cu from the sample holder. These ripple patterns can be used as templates. By using amorphous ripples only polycrystalline films can be grown. These films have an morphology induced dipolar anisotropy. In order to grow the films epitaxially the ripples have to be crystalline. Hence, this could induce an additional anisotropy in a magnetic overlayer. One possible route to achieve crystalline ripples is annealing. Therefore, the annealing temperature dependence was studied using STM. With increasing temperature the ripples vanish. They are not removed by a reduction of the amplitude, but by the creation of circular voids. Inside these voids the surface exhibits few steps and is otherwise flat on an atomic scale. In the middle of the voids Cu clusters are found, which appear at steps. Inside the crystalline area of the voids the Si(111) "quasi 5×5" Cu surface is found. For larger temperatures the number and size of these voids increases until the ripples are removed from the whole surface.