Microstructures, mechanical properties and surface wettability of La-doped diamond-like carbon films deposited by magnetron co-sputtering

Abstract

In this study, La-doped diamond-like carbon (DLC) films were prepared by magnetron co-sputtering of individual graphite and La targets. The mechanical properties and surface wettability of the DLC films were investigated in terms of the evolutions of microstructures and chemical compositions with La content. The results revealed that the doped La dissolved into the DLC films working as a catalyst made them smoother and locally graphitized. Moreover, a different dependency of residual stress upon sp3-C fraction to that of hardness and elastic modulus was found in the DLC films. Further, the air-exposed DLC films suffered from a series of surface physical/chemical reactions with air molecules and ubiquitous volatile organic compounds (VOCs), accompanied by brilliant and quick color evolutions over initial time, which dominated the time-dependent surface wettability. Finally, the doping-induced enhancements of both VOCs adsorption and sp2-C fraction contributed to the surface wettability transition from the intrinsic hydrophilicity to desired hydrophobicity of the DLC film. This study demonstrated here aims to expose the complex microstructures and related properties of DLC films with La doping, and offer a feasible method of preparing high-performance DLC films with low residual stress and adjustable surface wettability.