Jeudi 7 décembre 2000
Carbon nanotubes are long cylindrical all-carbon molecules with unprecedented electrical and mechanical properties. I will review our recent electron-transport and STM results obtained on individual carbon nanotube molecules. STM imaging and spectroscopy data on single-wall nanotubes allow to make the correlation between the atomic and electronic structure of nanotubes. The central theoretical prediction that chiral nanotubes are either semiconducting or metallic is confirmed experimentally. Standing electron waves can be observed by STM spectroscopy in nanotubes of finite length. Electrical transport has been studied through individual nanotube molecules deposited onto nanofabricated metal contacts. Measurements at mK temperatures show mesoscopic signatures of coherent transport. We can build a single-molecule field-effect transistor that operates at room temperature. I will also present measurements on kinked nanotubes, which act as an ontube junctions. Manipulation of the lateral position of nanotubes by the tip of an AFM can be used to create local tunnel junctions within nanotubes.
Biopolymers such as DNA have been proposed to act as conducting wires as well. We have carried out transport experiments on single short (30 base pairs) polyG-polyC DNA molecules between very closely spaced (10nm) metallic contacts. Nonlinear current-voltage curves demonstrate that DNA is a semiconductor that can be tuned to conduct carriers at large bias voltages. At longer length scales (100 nm) however the transport currents through DNA are immeasurably small. DNA also allow the construction of molecular-precise circuits by self assembly. Upon coating DNA with metal ions, metallic wires can be realized. First experimental steps towards realizing such DNA-based wires may be discussed.