QUANTITATIVE-ANALYSIS OF THE FRICTIONAL-PROPERTIES OF SOLID MATERIALSAT LOW LOADS .2. MICA AND GERMANIUM SULFIDE

Load-dependent studies of the frictional properties of mica and german ium sulfide were performed by friction force spectroscopy in air and i n argon atmosphere. Well-defined spherical tips made from amorphous ca rbon were used to profile the surface at low loads. In air, the fricti onal force F-f as a function of the normal force F-n for GeS follows a n F-f similar to F-n(2/3) behavior with good agreement, as is predicte d by contact mechanical theories for a Hertz-type contact with small t ip radius, with not too soft tip and sample materials, and with low su rface energies involved. The friction of mica, however, deviates signi ficantly in many cases from the F-f similar to F-n(2/3) law due to its higher surface energy. In argon, chemical reactions between clean sam ple and tip material prevent the observation of wearless friction on i n situ prepared samples. These effects were partially suppressed by an ex situ cleavage of the mica or germanium sulfide samples.