Relaxation times of nanoscale deformations on the surface of a polymer thin film near and below the glass transition

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(T) many orders of magnitude smaller than bulk values at the same T. The local T-g was around 86 degrees C, roughly 30 degrees C below the conventional bulk T-g. At the vicinity of the local T-g, tau(T) follows the Vogel-Fulcher type of T dependence, but at lower T a transition towards a less steep behavior is seen.