This talk will review some of the work on electrical transport through single molecules, as carried out in our group at Delft. I will start my talk with a brief introduction to molecular electronics and our work on carbon nanotubes and then discuss the possible use of DNA wires for molecular electronics.
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. Nanotubes appear to be semiconducting or metallic. The atomic structure and molecular orbitals can be studied by STM spectroscopy in nanotubes of finite length. Electrical transport has been studied through individual nanotube molecules between nanofabricated metal contacts. Nanotubes appear to be excellent coherent conductors. We have realized a variety of single-molecule devices that operate at room temperature.
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 indicate that DNA is a large-gap semiconductor that can be tuned to conduct carriers at very large bias voltages. At long length scales (100 nm) however, the transport currents through DNA are immeasurably small. I will show a number of experimental results from our lab and others. The prospects of using the intrinsic conductance properties of DNA for electronics are very very weak. However, DNA does allow the construction of molecular-precise circuits by self assembly.
Finally I will discuss our first attempts to couple nanotubes with DNA ends.