Nanometer Scale Dielectric Fluctuations at the Glass Transition

Using noncontact scanning probe microscopy techniques, dielectric properties were studied on 50 nm length scales in polyvinyl-acetate films in the vicinity of the glass transition. Low frequency $(1/f)$ noise observed in the measurements was shown to arise from thermal fluctuations of the electric polarization. Anomalous variations observed in the noise spectrum provide direct evidence for cooperative nanoregions with heterogeneous kinetics. The cooperative length scale was determined. Heterogeneity was long lived only well below the glass transition for faster than average processes.