Potential modulations along carbon nanotubes

True molecular-scale transistors have been realized using semiconducting carbon nanotubes, but no direct measurements of the underlying electronic structure of these have been made. Here we use a new scanning-probe technique to investigate the potential profile of these devices. Surprisingly, we find that the potential does not vary in a smooth, monotonic way, but instead shows marked modulations with a typical period of about 40 nm. Our results have direct relevance for modelling this promising class of molecular devices. (Author)