Correlation between charge density wave phase transition and hydrogen adsorption in 1T-TaS₂ thin film devices

Abstract 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 gas. Interestingly, the electrical resistance of the 1T-TaS2 thin film in the incommensurate charge–density wave (ICCDW) phase with a metallic state decreases when H2 gas is adsorbed on the 1T-TaS2 film and returns to its initial value upon desorption. In contrast, the electrical resistance of the 1T-TaS2 thin film in the nearly commensurate CDW (NCCDW) phase, which has a slight band overlap or small bandgap, does not change upon H2 gas adsorption/desorption. This difference in H2 gas reactivity is a result of differences in the electronic structures of the two 1T-TaS2 phases, namely, the ICCDW and NCCDW phases. Our experimental results indicate advantages of the use of TaS2 for H2 gas sensing compared to other semiconductor 2D-TMDs such as MoS2 and WS2, as a theoretical prediction that the metallic TaS2 captures gas molecules more easily owing to a stronger positive charge at Ta than those in Mo or W of dichalcogenides. Notably, this study is the first example of H2 gas sensing using 1T-TaS2 thin films and demonstrates the possibility of controlling the reactivity to gas by changing the electronic structure via CDW phase transitions.