The high-frequency frictional properties of thin lubricating layers of perfluoropolyethers coated onto the surface of quartz-crystal resonators were probed by measuring the increase in resonance bandwidth when the quartz surface comes into contact with a ceramic sphere. For a lubricant thickness of up to 11 A. a maximum in bandwidth is observed. The width and the height of the maximum decrease with increasing lubricant thickness. This is attributed to dissipation occurring during intermittent contact between the substrate and the sphere. With a 25 A lubricant film the sphere discontinuously jumps into contact, after which the movements of the sphere and the quartz are locked.
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