Study and simulation of the growth of MoSe x -based thin film coatings formed by pulsed laser deposition

Abstract

Physical, chemical and tribological properties of the MoSex and MoSe_xC_y coatings for micromechanical applications grown by pulsed laser deposition in vacuum and in a rarefied inert gas (argon) atmosphere are studied. In a number of experiments a disk-shaped screen was used that is placed on the path of the expansion of laser plume in order to trap the droplet fraction. Upon deposition in a gas at a pressure of ~2 Pa, stoichiometric MoSe₂ coatings with improved antifriction properties as compared vacuum-deposited MoSe_x (x<2) coatings form. However, a too strong increase in the argon pressure (to ~10 Pa) degrades the tribological properties of the coating. Deposition in vacuum or argon at a pressure of 2 Pa leads to formation of rather smooth coatings with a dense amorphous structure containing molybdenum nanoinclusions. Numerical experiments based on the combination of two computer models that describe physical processes on the atomic level using Direct Simulation Monte Carlo and Kinetic Monte Carlo methods are performed to reveal the factors that affect the thickness, chemical composition, and structure of the MoS_x-based coatings. Deposition to a negatively biased substrate is shown to substantially increase the coating density and to smooth the surface relief.