SCANNING TUNNELING SPECTROSCOPY OF CARBON NANOTUBES

Calculations predict that carbon nanotubes may exist as either semimet als or semiconductors, depending on diameter and degree of helicity. T his communication presents experimental evidence supporting the calcul ations. Scanning tunneling microscopy and spectroscopy (STM-S) data ta ken in air on nanotubes with outer diameters from 17 to 90 Angstrom, s how evidence of one-dimensional behavior; the current-voltage (I-V) ch aracteristics are consistent with a density of states containing Van H ove type singularities for which the energies vary linearly with inver se nanotube diameter.