Quasielastic nuclear forward scattering as a background-free probe of slow glass 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, has been investigated in a temperature range between 70 and 200 K by nuclear resonant scattering of synchrotron radiation. The decay of the coherently forward scattered signal is enhanced owing to the diffusive motion of resonant nuclei on the timescale of the nuclear resonance lifetime. This enhancement contains information about the self-correlation function for a fixed wave 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.