Decay Kinetics of Nanoscale Corrugation Gratings on Polymer Surface:  Evidence for Polymer Flow below the Glass Temperature

The near-surface rheology of polystyrene films at temperatures around T g was probed via the decay kinetics of shallow, nanoscale surface corrugation gratings. The gratings were created via hot embossing with a stepped silicon template. The wavelengths are distributed in a range between 25 and 60 nm and have a modulation depth of about 0.8 nm peak-to-peak. Upon heating, one observes a surface tension-driven decay of the surface corrugation at temperatures more than 30 deg below the bulk T g . Such a fast decay is unexpected and indicates a strongly lowered glass temperature near the surface.