Self-assembled monolayers on ta-C surfaces:: Effect of sp3/sp2 ratio on adsorption rate and friction

Self-assembled monolayers of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS), CF3(CF2)(7)(CH2)(2)SiCl3 were deposited on tetrahedral amorphous carbon (ta-C) surfaces by immersion process. The ta-C films were deposited on silicon substrates by using a filtered cathodic arc system and the sp(3)/sp(2) ratios of the ta-C films were controlled by changing the sample bias voltage. In results of the x-ray photoelectron spectroscopy measurements, it was found that the adsorption rate of silane molecules on sample A (whose sp(3) content is about 85%) was higher than that of on sample B (whose sp(3) content is about 65%). This trend was qualitatively the same as that found for water contact angle measurement. The friction forces of FDTS/sample A and FDTS/sample B measured by lateral force microscope show FDTS/sample A has lower friction value than that of FDTS/sample B. We conclude the following: the density of dangling bonds, which are effective adsorption sites for silane molecules, increases with sp(3) content. Consequently, the adsorption rate of silane molecules increases with increasing sp(3) content. The friction force decreases with increasing sp(3) content of the ta-C film since more of a close-packed self-assembled monolayer can be formed. (C) 2003 American Institute of Physics.