Particle Dynamics in Polymer/Metal Nanocomposite Thin Films on Nanometer Length Scales*

X-ray photon correlation spectroscopy was used in conjunction with resonance-enhanced grazing-incidence small-angle x-ray scattering to probe the particle dynamics and kinetics in gold/polystyrene nanocomposite thin films. Such enhanced coherent scattering enables, for the first time, to measure the particle dynamics at wavevectors up to 1 \textit{nm}$^{-1}$ (or a few nm spatially), well in the regime where entanglement, confinement and particle interaction dominate the dynamics and kinetics. The dynamics at such length scales has been difficult, if not impossible to study, by any other probes. Measurements of the intermediate structure factor f(q,t) indicate a mechanism of particle motion very different from Brownian diffusion (governed by Stokes-Einstein equation). The measured dynamics is explained in terms of inter-particle and hydrodynamic interactions.