Hunting the Enhanced Interaction of Donors with Post-Transition and Transition Metal Dichalcogenides: Comparative Study of NO 2 , H 2 S, NH 3 , and Aniline Adsorption on MoS 2 , SnS 2 , and ZrS 2 Monolayers

Two-dimensional transition and post-transition metal dichalcogenides (TMDs and PTMDs) are promising materials for applications in roomtemperature, physisorption-based gas sensing and monitoring. In recent years, the mechanisms behind the adsorption of electron-accepting molecules have been well established, leading to the development of composition-engineering pathways that may be used to enhance the chemiresistive signal, as well as to design and fine-tune selective devices. However, similar trends have yet to be found for the electron-donating species. Consequently, the present study employs density functional theory (DFT) methods to systematically compare the adsorption of three electron donors, hydrogen sulfide (H 2 S), ammonia (NH 3 ), and aniline (C 6 H 5 NH 2 ), and one baseline acceptor, nitrogen dioxide (NO 2 ), on semiconducting 1H-MoS 2 , 1T-SnS 2 , and 1T-ZrS 2 monolayers. The set was selected to provide direct comparison of different substrate symmetries, d-block versus p-block metal centers, and example acceptor-versus donor-molecule behavior under identical theoretical description. It was found that donor analytes can experience substrate-dependent enhancement in charge transfer only when their HOMO lies sufficiently high in energy. Accordingly, at the vdw-DF-cx level of theory, only aniline shows pronounced differences in adsorption, donating on average −0.049, −0.119, and −0.143 e to MoS 2 , SnS 2 , and ZrS 2 , respectively, whereas NH 3 and H 2 S exhibit no comparable trend. This particular substrate order was correlated with the favorable positions of the conduction band edges as well as the spatial availability of the low-lying acceptor states. These results provide a theoretical basis for the mechanisms governing adsorption of donating species on pristine TMDs and PTDMs, and may aid in selecting a suitable material for physisorption-based devices.