Inelastic neutron scattering experiments on the fast dynamics of a glass forming liquid in mesoscopic confinements

In this article we report inelastic neutron scattering experiments on the d ynamics of a confined glass forming liquid. The study was performed by the time-of-flight technique allowing access to an energy range 0.1-40 meV corr esponding Co the fast microscopic dynamics (0.1-20 ps). The most prominent effect was found for the "boson peak" close to 1 meV in the vibrational spe ctrum. A strong reduction of the modes at lowest frequencies could be obser ved. This result can be qualitatively explained by a cut-off of long wavele ngth soundlike modes but yet defies a quantitative description. In contrast to this the "fast process"-a short-time phenomenon of glass forming liquid s at t < 1.5 ps-seems not to depend very strongly on the confinement. This result is in agreement with ideas of the local character of this process.