Transition Metal Dichalcogenides: An ab initio investigation*

The control of friction at the nanoscale plays a central role in nanoengineered devices such as nano-electromechanical systems, the latter more and more based on multi-layered Transition Metal Dichalcogenides (TMDs). In the present work, we study the intrinsic friction in MX₂ (M = transition metal, X = chalcogen anion) TMDs in the presence of small molecules of contaminants from the atmosphere.
We perform quantum mechanic calculations on layered MX₂ TMDs-based systems with the hexagonal structure in the presence of contaminants between adjacent layers. We combine outcomes from phonon calculations together with the characterization of the electronic features using non-standard methods like orbital polarization, bond covalency and cophonicity, in order to study how the vibrational frequencies of pristine material are affected by the presence of contaminants. We show how changes in the phonon frequency are related to the nanoscale friction between adjacent layers. We finally present guidelines on how to engineer intrinsic friction in TMDs at the nanoscale.