Synthesis of 2D WSe2 Using an Intermediate UV–Ozone Treatment of Tungsten Precursor

Two-dimensional transition metal dichalcogenides (TMDCs) require highly controllable and scalable synthesis methods for successful integration into next-generation optoelectronic technologies. This study presents a modified two-step thermally assisted conversion approach for synthesizing 2D tungsten diselenide (WSe2) by introducing an intermediate UV–ozone treatment. Magnetron-sputtered tungsten films are exposed to UV–ozone, converting the precursor into a uniform, dense layer of amorphous tungsten trioxide (WO3) prior to the selenization process via chemical vapor deposition. X-ray photoelectron spectroscopy and Raman spectroscopy confirm the complete phase transition from the oxidized precursor to the 2H-WSe2 crystal lattice. Morphological evaluations utilizing transmission electron microscopy and atomic force microscopy demonstrate that the ozonated precursors yield highly uniform, triangular flakes exceeding 5 µm in lateral size, effectively eliminating the unreacted WO3 phases observed in untreated samples. Furthermore, the intermediate oxidation step finetunes the electronic band structure; the resulting WSe2 exhibits an enhanced p-type character with a valence band maximum shift to 0.35 eV, a tuning attributed to residual oxygen doping. Optical characterizations reveal significantly improved transmittance in the visible spectrum, accompanied by excitonic absorption shifts indicative of reduced layer dimensionality. This intermediate ozonation strategy provides a highly effective pathway for producing high-quality WSe2 nanosheets with tailored structural and optoelectronic properties.