ULTRATHIN IONIC FILMS EPITAXIALLY GROWN ON 111-V SEMICONDUCTORS STUDIED WITH ATOMIC RESOLUTION M. SZYMONSKI, J. J. KOLODZIEJ, B. SUCH, P. CZUBA AND P. PIATKOWSKI Institute of Physics, Jagiellonian University, ul. Reymonta 4, 30-059 Krakow, Poland AND F. KROK Regional Laboratory for Physicochemical Analysis and Structural Research, ul. Ingardena 3, 30-060 Krakow, Poland Abstract. Ultrathin films (> 0.3 ML) of NaCI and KBr have been grown epitaxially on GaAs (001) and InSb (001) surfaces, respectively. Scanning tunnelling (STM) and non-contact atomic force (NC-AFM) microscopies in ultrahigh vacuum were used to study surface structureS generated by growth. It was found that initially islands of monatomic thickness are formed. These islands are often cut along (110) crystallographic directions and the distribution of these islands on the substrate surface is anisotropic, which reflects the anisotropic diffusion of KBr molecules during growth. We argue that the KBr flnSb interface is stabilized by a bond between the halide ion and AlII atoms arranged in chains on (4x1) InSb. At 1-1.5 ML, a wetting single-atomic KBr film is formed and material in excess of 1 ML forms rectangular islands with edges oriented along (lOO) and (OlO) crystal- lographic directions. For multilayer KBr coverages, the growth is basically a layer-by-Iayer type, but due to slow diffusion of KBr molecules down across steps, the (n + 1)th layer starts to grow before the completion of the nth one. As a 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 (> 0.1 J.Lm) atomically flat (001) terraces. Ex- periments on nanoscale modification of such terraces by electron excitation are also described. 499 M. Kotrla et aL (eds.). Atomistic Aspects of EpitQJCial Growth, 499--509. e 2002 Kluwer Academic Publishers.