Neutron characterization of aluminium nitride nanotubes

The results of experiments carried out at the ILL neutron facilities in Grenoble on nanotubes of aluminum nitride synthesized through a DC arc plasma process are presented. We discuss the phonon generalized density of states G(omega) of the nanotubes in comparison with bulk AlN. G(omega) for the bulk features two main bands at low (about 30 meV) and high (about 80 meV) frequencies. Both bands are completely smeared out in the nanomaterial indicating a broad distribution of force constants induced by structural disorder. Apart from the smearing out of the vibrational bands, we observe enhanced intensities at low frequencies (omega < 10 meV) as usually found in disordered systems. Two additional bands at 12 and 17 meV hint at pure aluminium regions within the nanomaterial. The observed changes in the microscopic dynamics must lead to appreciable differences in the thermal and transport properties of the nanotubes with respect to the bulk material. Powder diffraction experiments show sharp lines from crystalline regions superimposed on a high and rather unstructured background.