Growth of ultrathin Pt layers and selenization into PtSe₂by molecular beam epitaxy

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.