Observation of a tribo-induced transition from solid to liquidlike behavior is reported for a scanning tunneling microscope tip in sliding contact with an indium electrode of a quartz crystal microbalance (QCM). In particular, at a sufficiently high asperity sliding speed (about $1\mathrm{m}/\mathrm{s}$) and/or sample temperature, a change in the contact mechanics is observed that is consistent with melting in terms of both the QCM response and an energy analysis. The results confirm that the surface, rather than bulk, melting point temperature is the more relevant quantity for tribological considerations.

• Received 22 June 2009

DOI:https://doi.org/10.1103/PhysRevLett.103.205502