Curvature-induced bonding changes in carbon nanotubes investigated by electron energy-loss spectrometry

Effect of curvature-induced strain on the covalent bonding in isolated and selected single-shell and multi- shell carbon nanotubes is explored, using electron energy-loss spectroscopy (EELS) on the core K level, which probes the distribution of available unoccupied states in the conduction band. Results show that the curvature and mostly the layer stacking affect the σ* conduction states. On the contratry, no influence is detected concerning the π* band, even with corrugation angles up to 7° in a 1-nm-wide single-walled tube. First-principle local-density calculations are used to relate the features in the EELS spectra to the different atomic interactions in nanotubes. Finally, the covalent character of the bonding in existing nanotubes is discussed. © 1996 The American Physical Society.