Self-assembled Ge, Sb and Al nanostructures on graphite: Comparative STM studies

The growth of Ge, Sb and Al nanostructures on highly oriented pyrolytic graphite (HOPG) have been studied comparatively using scanning tunnelling microscopy in ultra-high vacuum. Clusters and crystallites of these elements were grown along HOPG steps in the initial stage. But the nanoparticles of these three elements show quite different size distributions and morphological evolution in later growth stages. Using different deposition flux and amount, Ge clusters with self-limiting height, cluster chains and double-layer ramified cluster islands were obtained on HOPG at room temperature (RT). Compact crystalline Ge islands with high-index facets were observed after annealing at 600 K following RT deposition. Three-dimensional (3D) spherical islands, 2D thin films and 1D nanorods of Sb have been synthesized using different fluxes on HOPG at RT. With higher flux and a substrate temperature of 375 K, only crystalline 2D and 1D structures of Sb were obtained. When Al was deposited on HOPG at RT, the growth and coalescence of clusters formed initially result in flat Al crystallites with (111) top facet. After more deposition, craters were observed on top of the flattened Al islands resulting from a few smaller islands merging together. The mobile Al islands on HOPG can be pinned by Sb. The morphology difference of observed nanostructures reflects unique energetic and kinetic properties of atoms and clusters of each element.