Control of Nanofriction Response in Low-Dimensional Materials*

One of the main difficulties in the control of the nanoscale friction is represented by the complexity of non-equilibrium processes occurring in tribological contacts.

To understand the origin of the nanoscale friction and to design new tribological materials, we conduct quantum mechanical studies on Transition Metal Dichalcogenides and TiO2 films, chosen as prototypical materials. We combine structural and dynamic information from group theory and phonon calculations with the electronic density characterization from orbital polarization, bond covalency and cophonicity analyses. We define a phonon-based method to identify and tune possible sliding paths, corresponding energy barriers and dissipation channels. The method allows to extract energy information from atomic force microscopy signals. We identify the electrostatic and electromagnetic fields as possible external knobs which allow the fine tuning of the nanofrictional behaviour, leading to the photocontrol of friction (phototribology). We finally formulate guidelines on how to engineer the intrinsic friction at the nanoscale in order to design novel materials with controlled tribological properties.

The present outcomes can be promptly extended to the design of new materials with diverse applications beyond tribology.