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

Abstract

The growth of Ge, Sb and Al nanostructures on highly oriented pyrolytic graphite (HOPG)have been studied comparatively using scanning tunnelling microscopy in ultra-highvacuum. Clusters and crystallites of these elements were grown along HOPG steps in theinitial stage. But the nanoparticles of these three elements show quite different sizedistributions and morphological evolution in later growth stages. Using different depositionflux and amount, Ge clusters with self-limiting height, cluster chains and double-layerramified cluster islands were obtained on HOPG at room temperature (RT). Compactcrystalline Ge islands with high-index facets were observed after annealing at 600 Kfollowing RT deposition. Three-dimensional (3D) spherical islands, 2D thin films and 1Dnanorods of Sb have been synthesized using different fluxes on HOPG at RT. With higherflux and a substrate temperature of 375 K, only crystalline 2D and 1D structures of Sb wereobtained. When Al was deposited on HOPG at RT, the growth and coalescence ofclusters formed initially result in flat Al crystallites with (111) top facet. After moredeposition, craters were observed on top of the flattened Al islands resulting from afew smaller islands merging together. The mobile Al islands on HOPG can bepinned by Sb. The morphology difference of observed nanostructures reflectsunique energetic and kinetic properties of atoms and clusters of each element.