Pd doped Janus HfSeS monolayer: Ultrahigh sensitive gas sensing material for reversible detection of NO

Recent studies on two-dimensional (2D) Janus transition metal dichalcogenides (TMDs) show that these materials have excellent electronic property and raised very promising prospects for applying them as gas sensor materials. Here we consider the potential application of replacement doping with Pd on the monolayer HfSeS as well as its pristine structure as gas sensor materials for detecting CO, CO2, NH3 and NO through first principles calculations. The calculated results of Ab initio molecule dynamics (AIMD) simulations as well as phonon spectrum which shows no negative frequencies confirmed the good thermodynamical stability of pristine and doped HfSeS. The formation energies of the doped structures with S and Se atoms substituted by Pd atom are 5.174 and 5.168 eV which further proves the stability of the structures. The pristine HfSeS cannot well distinguish these four gas molecules due to very close adsorption energies (range from-0.142 eV to-0.477 eV). However, after the introduction of Pd, the doped structure could effectively achieve the distinguish of these four gas molecules (with adsorption energy ranges from-0.229 eV to-0.933 eV). Furthermore, the recovery time of these gases is within 500 s, which shows that the adsorption is reversible both in pristine and Pd-doped monolayer HfSeS. Most interestingly, Pd-doped monolayer HfSeS exhibits ultrahigh sensitive to NO, as the systems become metallic after NO adsorption. Due to the change in conductivity, enhanced adsorption energy, and together with a relatively lower recovery time, Pd-doped monolayer HfSeS exhibits promising application as gas sensors for reversible detection of NO.