Nucleation and growth of aluminum on an inert substrate of graphite

We have investigated the nucleation, growth and structure of Al on an inert graphite surface at room temperature (RT) using insitu scanning tunneling microscopy. It was observed that Al initially nucleates at step edges and defect sites of graphite surfaces, due to the inertness of the substrate and weak interfacial interaction. From a diffusion and capture model, the mean adatom diffusion length before desorption was derived to be 170 ± 80 nm, correspondingly giving a lower bound of the adatom-substrate binding energy of 0.39 ± 0.03 eV. With successive Al deposition of ∼0.5 nm, the growth and coarsening of small clusters results in flat-top crystalline islands with (111)-oriented facets located at step edges as well as on defect-free terraces. The crystalline islands have essential translational and rotational mobility, which leads to the formation of craters on islands after Al deposition of ∼6 nm. A simple island-coalescence model based on fast edge diffusion and suppressed detachment from step edges was proposed for rationalizing the crater formation. It was also observed that isolated islands of Al can be stabilized by two-dimensional structures of Sb surrounding Al islands after Sb deposition at RT.