Multiwall Carbon Nanotubes (MWCNTs) were synthesized by Chemical Vapor Deposition (CVD). Two different procedures were used to grow MWCNT films roughly, aligned in the direction normal to the SiO2/Si(111) substrate. Inverse Photoemission Spectroscopy measurements, on these samples, show the existence of resonances which could be traced back to a flat graphene sheet. The unoccupied valence band is fairly similar to that shown by graphite except by an additional intensity in the vicinity of the Fermi level. This resonance could be interpreted both as tubes tips end effects or van Hove singularities in the density of states.
Hevia, S., Ibáñez, W., Segura, R., & Häberle, P. (2006). Inverse photoemission spectroscopy of multiwall carbon nanotubes. 894-897. Paper presented at Brazilian Journal of Physics, . https://doi.org/10.1590/S0103-97332006000600025