The effect of interface electrostatic interaction based on acid-base theory on friction behavior

Fluorine-containing amorphous carbon films [fluoring-containing diamond-like carbon (F-DLC)] were fabricated on Si wafer by direct current plasma enhanced chemical vapor deposition (dc-PECVD) technique using CF4 and Ar as gas sources, confirmed by XPS and Raman analyses. The friction tests were carried out on a rotating ball-on-disk apparatus in high vacuum atmosphere (<= 5.0 x 10(-4) Pa) at the load of 0.5 N selecting glass (mainly containing silicon-oxygen tetrahedron structure) and Al2O3 with the same hardness and surface roughness as the counterpart balls. The results indicate that glass/F-DLC results in lower friction coefficient of 0.14 than that of the Al2O3/F-DLC (0.20). At the same time, no wear was occurred, and the transfer layer was not formed on the counterpart ball for glass/F-DLC, while the wear of Al2O3/F-DLC is slightly larger than that of glass/F-DLC. However, just like the glass ball, there is no formation of transfer layer on the Al2O3 ball surface. Furthermore, the chemical state of fluorine in the film after friction, which mainly existed in the form of the C-CF and C-F bonds, did not change compared with the F-DLC film, while the fluorine content has changed significantly. As a result, it is assumed that interface electrostatic interaction based on acid-base theory plays an extremely important role in the process of friction. Copyright (C) 2017 John Wiley & Sons, Ltd.