We report on measurements of relaxation times of nanometer-sized deformations resulting from the impact of individual energetic ions on poly(methyl methacrylate) surfaces at temperatures close to and below the glass transition $T_g$. The temporal evolution of the dimensions of the deformations is well described by a stretched exponential function, but with relaxation times $\tau \left(T\right)$ many orders of magnitude smaller than bulk values at the same $T$. The local $T_g$ was around $86°\mathrm{C}$, roughly $30°\mathrm{C}$ below the conventional bulk $T_g$. At the vicinity of the local $T_g$, $\tau \left(T\right)$ follows the Vogel-Fulcher type of $T$ dependence, but at lower $T$ a transition towards a less steep behavior is seen.

• Received 2 May 2006

DOI:https://doi.org/10.1103/PhysRevB.74.094203