INFLUENCE OF HUMIDITY ON FRICTION MEASUREMENTS OF SUPPORTED MOS2 SINGLE LAYERS

We have studied friction of MoS2 single layers on mica and Al2O3 in th e range of 5%-90% relative humidity. Friction coefficients have been d etermined simultaneously for the MoS2 platelets as well as for the sup port. Only a slight influence on the humidity was found for the fricti on coefficient of MoS2 and Al2O3, On the other hand, water adsorption on mica caused a strong increase of the friction coefficient above 40% relative humidity. The change of the friction coefficient was so stro ng that the contrast of the friction images inverted. At very high hum idities (above 60%), the friction coefficient of mica reverted to its initial value, probably because water acted as a boundary lubricant. ( C) 1996 American Vacuum Society.