Scanning-tunneling/atomic-force microscopy study of the growth of KBr films on InSb(0 0 1)

Thin epitaxial films of KBr have been grown on InSb(0 0 1) substrate. Scanning tunneling microscopy and non-contact atomic-force microscopy in ultra-high vacuum have been used to study the film surfaces for coverages ranging from 0.3 to 120 ML. It has been found that initially islands of monatomic thickness are formed. These islands are often cut along 〈1 1 0〉 crystallographic direction and the distribution of these islands on the substrate surface is anisotropic which reflects the anisotropic diffusion of KBr molecules during growth. At 1–1.5 ML coverage a wetting single-atomic KBr film is formed and the deposited material in excess of 1 ML forms rectangular islands with edges oriented along 〈1 0 0〉 and 〈0 1 0〉 crystallographic directions. The KBr/InSb interface is likely stabilized by a bond between the halide ion and AIII atoms arranged in chains on c(8×2) InSb. For high (multilayer) KBr coverages the growth is basically a layer-by-layer type but, due to slow diffusion of KBr molecules down across steps, the (n+1)th layer starts to grow before the completion of nth layer. In result, pyramidal structures of rectangular bases are formed on the surface. These rough films can be, with thermal annealing, converted to flat films exposing large (0 0 1) terraces.