| Single-wall carbon nanotubes (SWNTs) are unique molecular conductors that can act as quantum wires or field-effect transistors. Theory gives us detailed understanding about their one-dimensional electronic structure, but very little is known about the internal functioning of real-world devices made of nanotubes. In particular the role of defects and electronic contacts is poorly understood.; Here, we use scanning probe techniques to measure electronic properties of SWNTs on nanometer lengthscales. Atomic resolution scanning tunneling microscopy (STM) shows standing waves that form due to backscattering and interference of electrons. Different patterns are ascribed to scattering with large and small momentum transfer.; Electronic transport through SWNT bundles is analyzed locally by tunneling AFM (T-AFM) and scanning gate microscopy (SGM). We resolve the electrochemical potential of individual nanotubes within bundles and find that electron hopping between nanotubes limits the conductivity in metallic bundles. Semiconducting bottlenecks have a profound influence on transport along thin bundles.; Electronic devices at junctions between two one-dimensional wires are the ultimate goal in miniaturization. We characterize the 1D Schottky barrier at a metal-semiconductor nanotube cross junction by SGM and find a 10 nm depletion width in reverse bias. Nanotube field-effect transistors (FETs) exhibit two back-to-back Schottky barriers at the contacts to Cr/Au leads. They are responsible for the p-type character of the device. Potential modulations due to disorder along the nanotube length determine the turn-off potential for the FET. We are able to characterize defects one by one and find turn-off surface potentials between 250 mV and 800 mV, corresponding to local Fermi levels between 20 meV and 65 meV. Cobalt-contacted nanotube FETs are found to be n-type due to small Schottky barriers for electrons. They behave complementary to the Cr/Au contacted p-type FETs and have experimentally observable conduction band modulations.; Finally, CVD-grown metallic SWNTs have a high contact transparency T ∼ 1/2 and large mean-free path lm ∼ 0.43 μm. At high bias we observe energy dissipation along the nanotube, supporting the theory of optical phonon emission. |
