Molybdenum and Tungsten Di-sulfides: First Principles Investigation of Adatom Attachment and Diffusion on c-plane Alpha Sapphire and Correlation with Growth

Abstract

Understanding the underlying mechanism to growth of a material greatly assists control over its synthesis. In this investigation, we employ density functional theory to calculate the desorption and diffusion energy barriers to growth of MoS2 and WS2 from a M–C–O–H–S system on c-plane alpha sapphire, a commonly used substrate. We then perform experiments and use these numbers within a nucleation theory framework to explain growth characteristics. Nucleation rates, densities, and step velocities are predicted and analyzed. In particular, differences between MoS2 and WS2 growth─larger nucleation densities and small island sizes in WS2 compared to MoS2─are explained and correlated to the differences between energy barriers to desorption and diffusion of W and Mo.