Neutron inelastic scattering from fumed silica

Neutron inelastic scattering measurement have been performed on samples of fumed silica ('Cab-O-Sil') as a function of energy, momentum-transfer vector Q, and temperature T, and compared with analogous results for amorphous quartz. No evidence seen for a sharp crossover in the vibrational density of states of Cab-O-Sil between phonon and fracton regimes, but the inelastic scattering shows anomalous behavior in several respects. Neither the T dependence nor the Q dependence nor the absolute intensity of the scattering from Cab-O-Sil is in accord with simple phonon models. (author)