Mechanically robust hydrophobic fluorine-doped diamond-like carbon film on glass substrate

Abstract

Development of hydrophobic surfaces with a low friction coefficient is an impressive strategy for improving performance of self-cleaning glasses and photovoltaic cells. To this end, diamond-like carbon (DLC) films have been fabricated by plasma-enhanced chemical vapor deposition (PECVD) by varying the fluorine concentration of the film. As fluorine is introduced to the DLC film, some fluorocarbon compounds, including CF and CF2 and also CF3, are formed as confirmed by X-ray photoelectron spectroscopy (XPS). Additionally, the Raman spectroscopy analysis revealed a decrease in the sp3/sp2 hybridization ratio of carbon atoms as the fluorine concentration increased in the DLC films. It is believed that the presence of fluorocarbon compounds on the surface and high surface roughness are the key factors responsible for the high hydrophobicity of the fluorine-doped DLC films. Nano-scratch and nanoindentation tests indicated a significant relationship between fluorine content and mechanical properties of the DLC films. The hardness and elastic modulus of the film were decreased by increasing the fluorine content of the film. With incorporation of fluorine (19.2 at.%) into the DLC film, the friction coefficient of 0.2 was obtained. The potential of the fluorine-doped DLC films with a moderate concentration of fluorine (19.2 at.%) was confirmed as a robust interface with adequate hydrophobicity for surface engineering of self-cleaning glasses.