Growth of ultrathin Pt layers and selenization into PtSe2 by molecular beam epitaxy

Abstract

This work investigates the growth of Pt layers down to the monolayer (ML) limit and the subsequent conversion process into PtSe2 by direct selenization in a molecular beam epitaxy (MBE) environment. The optimum deposition temperature for smooth (111)-oriented, single crystal Pt layers was found to be 300 to 600 °C. A minimal nominal film thickness for full Pt film coverage was determined to be about 3 ML. Optimization of the subsequent reaction with selenium using 3-nm-thick Pt layers to form PtSe2 was found most efficient at 200 °C. Crystalline PtSe2 layers with smooth surfaces were formed, but temperature was too low to completely convert the entire 3-nm-thick Pt film. Thinner, uncoalesced Pt films were nearly fully converted into PtSe2 at 200 °C, but revealed a reduced degree of crystallinity, which was significantly improved by a post-selenization anneal at 400 °C under a Se flux, providing a bottom-up synthesis strategy for PtSe2 fabrication in the monolayer limit.