Laser-induced depletion of ultrathin PFPE lubricants using a quantitative coarse-grained model.

Abstract

Knowledge of laser-pulsed processing of ultrathin liquids on solid surfaces is of great importance in advancing the understanding of synthesis, characterization and applications of functional nanofilms. In this work, we performed molecular dynamics simulations coupled with a novel quantitative coarse-grained model to study laser-induced local heating and depletion behaviors of Fomblin Z2000 lubricants. It was found that the Fomblin lubricant films experience severe evaporation and thermodiffusion-related degradation under laser heating. The ultrathin lubricants inevitably lose their frictional resistance under extremely high temperatures and thermal gradients (i.e., up to 990K and 65.4K/nm) that are required for FePt media in HAMR systems. The factors that influence the local thermal depletion, such as laser power, spot size, and scanning velocity, were investigated as well. The results clearly show that the laser power has the greatest influence on the relative maximum temperature change and subsequently the severe lubricant film depletion during rapid laser heating, while the spot size and scanning velocity play a relatively weaker role in the laser-induced local thermal instability. The findings in this work are thus believed to provide molecular scale insights into laser-induced local heating and depletion of ultrathin lubricant films from a precise quantitative perspective.