Novel two-step synthesis and characterization of oxide-free vanadium diselenide thin films

Vanadium diselenide (VSe₂) has attracted a significant attention for spintronic and memory devices, catalytic reactions, and sensors because of its superior magnetic and electrical properties. However, the high oxidation tendency of vanadium (V) makes the synthesis of VSe₂ challenging, making it one of the least studied two-dimensional (2D) materials. In the present study, a novel two-step method was developed to synthesize oxide-free VSe₂ thin films. In the first step, V metallic film was deposited on SiO₂/Si substrates using radio frequency (RF) sputter method. X-ray diffraction (XRD) measurements showed that the V thin film oxidized in the form of VO_0.532 crystal structure. After VO_0.532 film was thermally selenized in a chemical vapor deposition (CVD) reaction tube, both V_xO_y and VSe₂ structures were observed. The oxidation was successfully suppressed by pre-hydrogenation before thermal selenization. Subsequently, the thermal selenization was carried for varying durations, and different phases of V and Se were obtained depending on the selenization time. It was also found the thickness values of the films were strongly dependent on the selenization time. The electrical measurements were conducted on the V_xSe_y films, and their electrical properties were compared based on selenization time.