Abstract Submitted to the    NANOTUBE'04 Conference:

The electronic structure of carbon nanotubes has been investigated in situ with UV-photoemission spectroscopy (photon energies of 21.2 and 40.8 eV). The investigated samples correspond to CNTs with different diameters grown by CVD either onto bare Si substrates or onto Si covered with buffer layers of Al₂O₃, TiN or TiO₂. Since there was no exposure to air, no cleaning procedure was necessary before the measurement. Although the diameter distributions of the CNTs are broad the samples analyzed belong to clearly separated CNT families: nanotubes around 7 nm diameter onto Si and Al₂O₃, and nanotubes around 20-30 nm diameter onto TiN and TiO₂ layers. Since the diameter distributions were not overlapping, we could identify features in the spectra that were clearly dependent of CNT curvature, like for example a progressive decrease in the intensity of p-states around 3 eV binding energy, in dicative of higher degree of s-p hybridization with decreasing radius. Surprisingly, a curvature dependence was also observed in other spectral features, which to our knowledge have not been reported before. The observed effects will be discussed and compared with structural information obtained from high-resolution TEM and micro-Raman measurements of the nanotubes.