HfS2 and TiS2 Monolayers with Adsorbed C, N, P Atoms: A First Principles Study

First principles density functional theory was used to study the energetic, structural, and electronic properties of HfS2 and TiS2 materials in their bulk, pristine monolayer, as well as in the monolayer structure with the adsorbed C, N, and P atoms. It is shown that the HfS2 monolayer remains a semiconductor while TiS2 changes from semiconductor to metallic behavior after the atomic adsorption. The interaction with the external atoms introduces localized levels inside the band gap of the pristine monolayers, significantly altering their electronic properties, with important consequences on the practical use of these materials in real devices. These results emphasize the importance of considering the interaction of these 2D materials with common external atomic or molecular species.