Diz 76 en
The role of structural dynamics in energy dissipation and layer exfoliation in transition metal dichalcogenides
Author: Florian Belviso
In materials science, understanding friction between surfaces is challenging, as it calls for a multiscale approach. Yet, finding ways to control the friction at the nanoscale is a growing necessity for the fabrication and operation of optimal nano-engineered devices. Throughout this thesis, the author demonstrates how the use of external electric fields and contaminant molecules can influence the frictional behaviour of MX 2 Transition Metal Dichalcogenides. The study is based on Density Functional Theory calculations and phonon spectrum analysis of the considered materials. Electronic descriptors allow us to describe the changes in the electronic structures, while we quantify the dynamical response in terms of atomic participations to the vibrational behavior. We present the theoretical tools and the methodology used, along with the computational details. Three distinct investigations are described in the Results part. The first study examines the effect of an electrostatic field on the frictional properties of the material. The analysis shows that a specific charge accumulation within the material favors the relative layer sliding, hence reduces the nanoscale friction. A second study discusses the effect of the intercalation of N 2 and CO 2 contaminants on the same materials, and how the valence band is correlated to the layer-layer frictional response. Finally, the third study shows how the insertion of an N 2 contaminant molecule in the interlayer region of the systems can stabilise the frictional response of the materials exposed to an electrostatic field. The obtained results constitute guidelines on how to select proper fields and contaminants to design new tribological materials with a customized frictional response.