Photoacoustic infrared spectroscopy of nanoclusters Al2O3 clusters and cluster-assembled solids

Stoichiometric nanometer-sized Al2O3 clusters were generated by direct rf magnetron sputtering from an -Al2O3 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 Al2O3 nanoclusters and nanostructured compacts. The two samples were associated with considerable spectral broadening of the phonon band, compared to conventional - and -Al2O3 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.