Interface chemistry and thermoelectric characterization of Ti and TiOx contacts to MBE-grown WSe2

Abstract

WSe2 has demonstrated potential for applications in thermoelectric energy conversion. Optimization of such devices requires control over interfacial thermal and electrical transport properties. Ti, TiOx, and Ti/TiOx contacts to the MBE-grown WSe2 are characterized by XPS and transport measurements. The deposition of Ti is found to result in W-Se bond scission yielding metallic W and Ti-Se chemical states. The deposition of Ti on WSe2 in the presence of a partial pressure of O2, which yields a TiOx overlayer, results in the formation of substoichiometric WSex (x<2) as well as WOx. The thermal boundary conductance at Ti/WSe2 contacts is found to be reduced for greater WSe2 film thickness or when Au/TiOx interface is present at the contact. Electrical resistance of Au/Ti contacts is found to be higher than that of Au/TiOx contacts with no significant difference in the Seebeck coefficient between the two types of contact structures. This report documents the first experimental study of Ti/WSe2 interface chemistry and thermoelectric properties.