Photoacoustic infrared spectroscopy of nanoclustersAl2O3clusters and cluster-assembled solids

Abstract

Stoichiometric nanometer-sized ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ clusters were generated by direct rf magnetron sputtering from an α-${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ target in an inert atmosphere. Nanostructured compacts were derived by compacting the clusters in situ under ultrahigh vacuum. Photoacoustic infrared spectroscopy was applied in the vibrational study of the ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ nanoclusters and nanostructured compacts. The two samples were associated with considerable spectral broadening of the phonon band, compared to conventional α- and γ-${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ polycrystals. These were attributed to the finite-crystal effects of the nanometer-sized grains and to the disorder in the grain boundaries which made up a significant volume fraction of the samples, particularly in the nanostructured compacts.