Non-vacuum Preparation of wse2 Thin Films via the Selenization of Hydrated Tungsten Oxide Prepared using Chemical Solution Methods

It is known that tungsten oxide may be reacted with selenium sources to form WSe2 but literature reports include processing steps that involve high temperatures, reducing atmospheres, and/or oxidative pre-treatments of tungsten oxide. In this work, we report a non-vacuum process for the fabrication of compositionally high quality WSe2 thin films via the selenization of tungsten oxide under milder conditions. Tungsten source materials were various hydrated WO3 and WO2.9 compounds that were prepared using chemical solution techniques. Resulting films were selenized using a two-stage heating profile (250 oC for 15 minutes and 550 oC for 30 minutes) under a static argon atmosphere. Effects of the starting tungsten oxide phase on WSe2 formation after single and double selenization cycles were investigated using Raman spectroscopy and X-ray diffraction (XRD). After two selenization cycles, hydrated WO3 was converted to (002)-oriented WSe2 that exhibits well-resolved peaks for E12g and A1g phonon modes. Only a single selenization cycle was required to convert amorphous WO2.9 to WSe2. All selenizations in this work were achieved in non-reducing atmospheres and at lower temperatures and shorter times than any non-laser-assisted processes reported for WO3-to-WSe2 conversions.