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

Thin films of tantalum disulfide in the 1T-polytype structural phase (1T-TaS), a type of metallic two-dimensional (2D) transition metal dichalcogenides (TMDs), are reactive to H. Interestingly, in the incommensurate charge-density wave (ICCDW) phase with a metallic state, the electrical resistance of the 1T-TaSthin film decreases when His 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 Hadsorption/desorption. This difference in Hreactivity is a result of differences in the electronic structure of the two 1T-TaSphases, namely, the ICCDW and NCCDW phases. Compared to other semiconductor 2D-TMDs such as MoSand WS, the metallic TaShas 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 Hsensing using 1T-TaSthin films and demonstrates the possibility of controlling the reactivity of the sensors to the gas by changing the electronic structure via CDW phase transitions.