Probing thermomechanical behavior of polymers at the nanometer scale with single-ion bombardment and scanning force microscopy

Features produced by swift heavy ions on polymer thin films at different te mperatures are used to identify the transition between vitreous and viscoel astic behaviors (the glass transition temperature) and to probe the relaxat ion of nanodeformations in the material. Scanning force microscopy images r eveal nanometer-sized craters and raised regions around the point of ion im pact. The size of such defects is independent of temperature for - 196 degr eesC<T<80 degreesC, but above a critical temperature crater dimensions incr ease steeply and no plastic deformation is observed. This critical temperat ure is sensitive to the cooling rate, and for rapidly cooled targets it is close to the glass transition temperature of the polymer.