Different desorption rates prompting an indirect isotopic effect on nanoscale friction

Abstract

Friction behavior at the nanoscale may be split into different contributions, including phononic dissipation. Despite the isotopic effect in the phononic component being previously explored, experimental and theoretical approaches determined contradictory conclusions. Here, a desorption-based model is proposed, and it is found to be consistent with previously published experimental data on hydrogenated and/or deuterated amorphous carbon films. Moreover, molecular dynamics simulations showed that a surface coverage difference as low as 5% might promote an effect on friction even greater than that observed experimentally. This happens when reactive defects are created after desorption (prompting carbon dangling bonds), reinforcing the assumption that minor surface differences may be sufficient for the effects observed, meeting both experimental and theoretical approaches in the same overall trend. Therefore, the phononic dissipation occurs, but the isotopic effect may be indirect, where the desorption rate of hydrogen and deuterium plays a role by exposing carbon dangling bonds, changing the interface of interaction and the nanoscale friction ultimately.

Keywords

• Friction
• Isotopic effect
• Phononic dissipation
• Hydrogen
• Deuterium
• Carbon