  A non-contact scanning-probe-microscopy method was used to probe local
near-surface dielectric susceptibility and dielectric relaxation in
poly-vinyl-acetate (PVAc) near the glass transition. Dielectric spectra were
measured from 10-4 Hz to 102 Hz as a function of temperature. The measurements
probed a 20 nm thick layer below the free-surface of a bulk film. A small (4 K)
reduction in glass transition temperature and moderate narrowing of the
distribution of relaxation times was found. In contrast to results for
ultra-thin-films confined on or between metallic electrodes, no reduction in
the dielectric strength was found, inconsistent with the immobilization of
slower modes.
