First-principles calculations of small silicon clusters adsorbed on a graphite surface

The structural and electronic properties of small Si-clusters adsorbed on the graphite (0001) surface are studied by density functional theory (DFT) within periodic boundary conditions. A 5-layer graphite slab is used to represent the graphite substrate. Maximum stability is encountered for particle site adsorption of the Si-clusters on the surface. This finding is attributed to the formation of covalent carbon-silicon bonds. As a consequence of the interaction between the substrate and the adsorbate, a distinct narrowing of the Si cluster energy gap is observed, in accordance with experimental results. Density of states (DOS) distributions are used for detailed band structure analysis of the system combined of Si-n clusters and a graphite substrate. Comparison is made with the analogous situation of the Na-n cluster adsorption on graphite.