Strain-Modulated CO and HCHO Sensing Property of Pd-Doped HfSSe Monolayer Using First-Principles Simulations.

In this paper, the adsorption behaviors of pristine and Pd-doped Janus HfSSe (Pd-HfSSe) monolayers toward CO and HCHO were systematically investigated using first-principles calculations. Pd preferentially substitutes the Se site of the HfSSe monolayer, and the Pd-HfSSe monolayer exhibits significantly enhanced adsorption performance toward CO and HCHO, with adsorption energies of -0.747 and -0.663 eV, respectively, which are approximately 5.3 and 2.9 times higher than those of the pristine monolayer. The significant bandgap variations of 6.64% and 1.09% for the CO- and HCHO-adsorbed systems, respectively, demonstrate the strong potential of the Pd-HfSSe monolayer as a chemiresistive gas sensor, while the moderate recovery times enable repeated sensing cycles. Moreover, the Pd-HfSSe monolayer exhibits excellent strain-tunable sensing characteristics, particularly under compressive strain, where both the bandgap and charge transfer can be effectively regulated by biaxial strain. These findings provide valuable insights into the development of Janus HfSSe-based gas sensors and pave the way for their potential applications in toxic gas detection and environmental monitoring.