BORON-NITRIDE NANOTUBES

Pure boron nitride (BN) nanotubes have been synthesised by are dischar ge between HfB2 electrodes in a nitrogen atmosphere. The high resoluti on electron microscopy (HREM) observations reveal that this route lead s to the formation of highly crystalline tubes with reduced numbers of layers, including tubes with only one or two layers. These nanotubes are found to be chiral or non-chiral, however, a preference towards th e armchair and zig-zag configurations is suggested. Electron energy lo ss spectroscopy yields a B:N ratio of approximately one and a perfect chemical homogeneity. Tubes are empty and closed at their ends by flat layers perpendicular to the tube axis. A tip model consisting of a tr iangular facet based on three 120 degrees disclinations and preserving BN bonds in the honeycomb network accounts for the observations. Fina lly, preliminary electron irradiation experiments on these tubes revea l a specific behaviour. BN tubes transform into aggregates of small ca ges with diameter between 0.5 and 0.8 nm. These diameters suggest that these shells might be B12N12, B16N16 and B28N28 fullerenes which were predicted to be magic clusters. (C) 1998 Published by Elsevier Scienc e Ltd. All rights reserved.