A comparative study of AL, GE and SB self-assembled nanostructures on graphite

In situ scanning tunneling microscopy (STM) investigations of the nucleation, growth,aggregation and coarsening of nanoparticles on an inert substrate, such as graphite, revealmany intrinsic thermodynamic and kinetic properties of nanoparticles important tonanostructural self-assembly and applications. We performed systematic in situ STM studiesof Al, Ge and Sb growth on highly oriented pyrolytic graphite (HOPG). At room temperature(RT), three dimensional (3D) clusters of all three elements nucleate and grow at step edgesand defect sites of HOPG. The clusters of Al and Ge form chains, while Sb islands are mostlyisolated. With increasing deposition at RT, Al clusters grow and coarsen into crystallites with(111) facets on top, which coalesce further into flat islands with craters on the top. In contrast,due to a low sticking probability of Ge atoms on graphite and little coarsening among Geclusters, single- and double-layer cluster chains as well as ramified islands are observed.When deposited or annealed at T ≥ 450 K, Ge forms crystallites but with randomly orientedhigh-index facets. As spherical Sb islands grow beyond certain size, (111) facets appear on thetop. In addition to 3D islands, 2D crystalline Sb films and 1D nanorods are observed. At T ≈ 375 K and a high flux, only 2D and 1D Sb islands are formed, whereas only 3D islands areformed initially when Sb is deposited with a low flux at RT. This selectivity of differentdimensional Sb nano-assembly is explained in terms of Sb4 diffusion and dissociationkinetics. The Sb nanorods start with a simple cubic lattice structure, which is observed underhigh pressure for bulk Sb crystal. These different growth behaviors reflect the unique natureof interaction among the atoms (molecules), clusters and crystallites of each element, as wellas with HOPG substrate.