Diffusion and intercalation of alkali atoms in transition metal dichalcogenides

Alkali metal atoms deposited on transition metal dichalcogenides (TMDCs) ca n either diffuse on the surface or intercalate into the van der Waals gaps of the substrate. In order to understand the interplay between adsorption a nd intercalation of alkali atoms at these layered crystals, we performed a detailed study of the migration and energetics of Li adatorn on TiSe2(0 0 0 1) surface. employing total-energy density-functional theory calculations. To get insight into stable and metastable states. diffusion paths and diff usion barriers for the Li adatom, we calculated the adatoms potential energ y surface, to find e.g. the hcp site energetically slightly preferred over the fcc site. Results are also given for other alkali atoms. To obtain info rmation about the adsorbate-substrate bond, the change in the valence elect ron density and orbital distribution was studied. The paths of direct inter calation for the alkali atom from the surface through the three layered TiS e2 sandwich into the van der Waals gap were investigated. It was found that the alkali atom has to overcome an energy barrier of at least 3.81 eV to m ake the direct intercalation possible. (C) 2001 Elsevier Science B.V. All r ights reserved.