Nanotribological characteristics of lanthanum-based thin films on phosphorylated 3-aminopropyltriethoxysilane self-assembled monolayers

Lanthanum-based thin films deposited on phosphonate 3-aminopropyltriethoxysilane (APTES) self-assembled monolayers (SAM) were prepared on a hydroxylated silicon substrate by a self-assembling process from a specially formulated solution. Chemical compositions of the films and chemical states of the elements were detected by X-ray photoelectron spectrometry. The thicknesses of the films was determined with an ellipsometer, while their morphologies and nanotribological properties were analyzed by means of atomic force microscopy. It was found that the lanthanum-based thin films showed the lowest friction and adhesion followed by APTES-SAM and phosphorylated APTES-SAM, while silicon substrate showed high friction and adhesion. Microscale scratch/wear studies clearly showed that lanthanum-based thin films were much more scratch/weaf resistant than the other samples. The superior friction reduction and scratch/wear resistance of lanthanum-bascd thin films may be attributed to low work of adhesion of non-polar terminal groups and the strong bonding strength between the films and the substrate.