Structure and Dynamics of Co and Ru Adatoms and Nanoclusters on Tungsten Dichalcogenide Monolayers

Abstract

Tungsten dichalcogenide monolayers have unique properties that make them promising as channel materials in next-generation semiconductor devices, atomically thin diffusion barriers in interconnects, and low-dimensional supports for catalysis. These applications require interfacing the monolayer with a metal, whose morphology typically determines which applications are viable. An atomistic understanding of how metals interact and grow on these monolayers is therefore essential. Theoretical work has largely addressed single-atom adsorption and doping, or pristine metal–monolayer interfaces, leaving the early stages of metal growth unexplored. Using density functional theory, we study the relaxations and dynamics of Co and Ru adatoms, dimers, and 4-atom nanoclusters on WS2, WSe2, and WTe2. This allows us to develop a comprehensive understanding of the fundamental interactions between adsorbed metal atoms and monolayers, revealing the role different metal–substrate and metal–metal interactions have in affecting preferred adsorption sites, nanocluster structure, and potential morphology. We find both metals interact strongly with all three monolayers and may also induce structural changes that affect thin-film growth. The larger lattice parameters of WSe2 and WTe2 drive a strong preference for interstitial adsorption. Interstitial adsorption can cause displacement of W atoms in WTe2 and trigger a local hexagonal-to-orthorhombic phase change in the monolayer. Co and Ru can also promote the formation of chalcogen vacancies by displacing the chalcogen atom and occupying the resulting vacant site. Overall, Ru favors vertical growth, with stability driven by metal–metal interaction, whereas Co is most stable at interstitial sites.