High graphene permeability for silicon atoms during deposition at room temperature: the role of defects
Résumé
Graphene (Gr) is known to be an excellent barrier preventing atoms and molecules to diffuse through it. This is due to the carbon atom arrangement in a two-dimensional (2D) honeycomb structure with a very small lattice parameter thus forming an electron cloud that prevents atoms and molecules crossing. Nonetheless at high temperature of annealing, intercalation of atoms through graphene occurs, opening the path for formation of vertical heterojunctions formed of two-dimensional layers. In this paper, we report on the ability of silicon atoms to penetrate the graphene network, fully epitaxially grown on a Ni(111) surface, even at room temperature. Our scanning tunneling microscopy (STM) shows that defects like vacancies and dislocations of the graphene lattice favor the Si intercalation below the Gr layer forming two-dimensional, flat and disordered islands. Ab-initio molecular dynamics calculations confirm that Gr defects are necessary for Si intercalation at room temperature and show that a hypothetical intercalated silicene layer cannot be stable for more than 8 ps and that the corresponding Si atoms completely lose their in-plane order resulting in a random planar distribution and form strong covalent bonds with Ni atoms.
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