Tribocharging phenomena in hard disk amorphous carbon coatings with and without perfluoropolyether lubricants

Scanning polarization force microscopy was used to study changes in surface potential (tribocharging) caused by the contact between a tungsten carbide tip and the amorphous carbon coating of a hard disk, both when bare and when covered with Zdol-TX lubricant. The surface potential change produced by tip contact decays with time at a rate that is strongly dependent on lubricant coverage and on the presence of oxygen and water vapor in the environment. Two different charging mechanisms are proposed. One involves chemical modification of the surface by removal of oxygen bound to the surface. This gives rise to a potential change that decays with time. Another mechanism involves trapping of charge in states within the energy gap of the insulating carbon film. The potential change due to this trapped charge does not decay over periods much greater than 1 h. (C) 2001 American Institute of Physics.