Tunable Dipole Moment in Janus Single-Layer MoSSe via Transition-Metal Atom Adsorption

Intrinsic dipole moment is an important characteristic of Janus single-layer MoSSe. Tuning the dipole moment would broaden the potential applications of Janus MoSSe in the field of piezoelectricity and molecular sensing. In this study, the dipole moments of Janus single-layer MoSSe with 3d transition-metal (TM) adatoms (Sc–Ni) are explored by using first-principles calculations. Our results demonstrate that the dipole moments of Janus MoSSe change with TM atom adsorption. For the adsorption of TM atoms on the Se surface, the dipole moments are enhanced when compared to the case of pristine MoSSe, regardless of at the M adsorption site or at the H adsorption site. However, in the case of S surface adsorption, the dipole moments are weakened or even reversed for some TM atoms. Among all the 3d TMs considered, the effect of Sc atom adsorption is the largest, while it is the smallest for Ni atom adsorption. By means of a simplified model, the total dipole moments can be regarded as the superposition of the dipole moments from the Janus MoSSe and the ionic TM atoms. Strengthening and weakening of the dipole moments depend on the direction of dipole moments from the ionic TM atoms. Thus, we could utilize TM atom adsorption to tune the dipole moments with both magnitude and direction.