Atomic scattering as a probe of polymer surface and thin film dynamics

Collisional energy transfer at the surface of poly(methyl methacrylate) thin films on Si Ox Si was investigated using low-energy neutral helium atom scattering. Analysis of spectra in two scattering regimes yields results consistent with the hypothesis that thinner films are stiffer, suggesting that for highly nanoconfined films, polymer-substrate interactions influence vibrational dynamics at the polymer-vacuum interface. Specifically, thinner films are found to have lower mean-square displacements and decreased annihilation events as compared to thicker films. The scattering spectra are fit well by a semiclassical scattering model, though deviations arise at sample temperatures near the bulk glass transition. We have found helium atom scattering to be a sensitive probe of the vibrational dynamics of the polymer thin film surface. This technique holds promise for the exploration of glassy dynamics of polymer thin films.