Preparation and tribological studies of C60 thin film chemisorbed on a functional polymer surface

A novel self-assembled C-60 film was prepared by chemical adsorption of C-60 molecules onto an amino-group-containing polyethyleneimine-coated silicon substrate surface. The contact angle of distilled water on the C-60 film was measured, the thickness was determined by means of ellipsometric analysis, and the morphology was observed with an atomic force microscope. The tribological properties of the films were investigated as well. It was found that the C-60 thin film had a contact angle of about 72degrees and thickness of 1.8 nm and exhibited a surface domain microstructure composed of fullerene clusters. Due to the hydrophobicity and low surface energy, the C-60 film possessed good adhesive resistance and had an adhesive force of about 7.1 nN, which was about an order of magnitude lower than that of the silicon substrate surface. Moreover, the C-60 film showed good friction reduction, load-carrying capacity, and antiwear ability, which were attributed to the higher mechanical stiffness and elastic modulus of C-60 molecules. Besides, the friction coefficient decreased with increasing sliding velocity and normal loads, due to the rolling effect of the physisorbed C-60 molecules.