Quasielastic nuclear forward scattering as a background-free probe of slowglass dynamics in confined geometries

The microscopic dynamics of dibutylphthalate/ferrocene in nanoporous silica matrices with pore sizes of 25, 50, 75, and 200 Angstrom, respectively, ha s been investigated in a temperature range between 70 and 200 K by nuclear resonant scattering of synchrotron radiation. The decay of the coherently f orward scattered signal is enhanced owing to the diffusive motion of resona nt nuclei on the timescale of the nuclear resonance lifetime. This enhancem ent contains information about the self-correlation function for a fixed wa ve vector k = 7.3 Angstrom (-1). In the viscous regime and for 25 Angstrom pores the diffusional dynamics is clearly slowed down when compared to the bulk material.