The dissipation mechanism of nanoscale kinetic friction between an atomic force microscopy tip and a surface of amorphous glassy polystyrene has been studied as a function of two parameters: the scanning velocity and the temperature. Superposition of the friction results using the method of reduced variables revealed the dissipative behavior as an activated relaxation process with a potential barrier height of $7.0\mathrm{k}\mathrm{c}\mathrm{a}\mathrm{l}/\mathrm{m}\mathrm{o}\mathrm{l}$, corresponding to the hindered rotation of phenyl groups around the C-C bond with the backbone. The velocity relationship with friction $F(v)$ was found to satisfy simple fluctuation surface potential models with $F\propto \mathrm{c}\mathrm{o}\mathrm{n}\mathrm{s}\mathrm{t}-\ln (v)$ and $F\propto \mathrm{c}\mathrm{o}\mathrm{n}\mathrm{s}\mathrm{t}-\ln (v{)}^{2/3}$.

• Received 15 April 2003

DOI:https://doi.org/10.1103/PhysRevLett.91.095501