Correlation between charge density wave phase transition and hydrogen adsorption in 1T-TaS₂thin film devices

Thin films of tantalum disulfide in the 1T-polytype structural phase (1T-TaS₂), a type of metallic two-dimensional (2D) transition metal dichalcogenides (TMDs), are reactive to H₂. Interestingly, in the incommensurate charge-density wave (ICCDW) phase with a metallic state, the electrical resistance of the 1T-TaS₂thin film decreases when H₂is adsorbed on it and returns to its initial value upon desorption. In contrast, the electrical resistance of the film in the nearly commensurate CDW (NCCDW) phase, which has a subtle band overlap or a small bandgap, does not change upon H₂adsorption/desorption. This difference in H₂reactivity is a result of differences in the electronic structure of the two 1T-TaS₂phases, namely, the ICCDW and NCCDW phases. Compared to other semiconductor 2D-TMDs such as MoS₂and WS₂, the metallic TaS₂has been theoretically proven to capture gas molecules more easily because Ta has a stronger positive charge than Mo or W. Our experimental results provide evidence of this. Notably, this study is the first example of H₂sensing using 1T-TaS₂thin films and demonstrates the possibility of controlling the reactivity of the sensors to the gas by changing the electronic structure via CDW phase transitions.