Investigation of the structure of fluoroalkylsilanes deposited on alumina surface

This paper presents investigation of the structure of fluoroalkylsilanes on alumina surface by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), Fourier transform infrared (FT-IR) spectroscopy and atomic force microscopy (AFM). The fluoroalkylsilanes were prepared on alumina surface using the vapor phase deposition (VPD) method. XPS and ToF-SIMS measurements confirm the presence of fluoroalkylsilanes on the alumina surface. AFM was used to compare the frictional behavior of samples after modifying the alumina surface by fluoroalkylsilanes. Nanotribological studies of fluoroalkylsilanes films with different head groups on the alumina surface include, besides frictional studies, also adhesive forces investigations. It is shown that surface modification of alumina by fluoroalkylsilanes decreases coefficient of friction and adhesive forces values by more than 50% compared to unmodified alumina. In comparison to a non-modified alumina surface all tested silanes, particularly compounds with three reactive atoms in the head group, cause a decrease in the friction coefficients in nanofriction tests. The same effect was also observed for adhesion measurements. It was found that the alumina modified by trifunctional fluoroalkylsilanes have a higher degree of hydrophobicity, lower adhesion, and lower coefficient of friction than the monofunctional fluoroalkylsilanes covered alumina surface.