Single-walled carbon nanotubes: from fundamental studies to new device concepts.
Single-walled carbon nanotubes (SWNTs) are ideal systems for investigating fundamental properties in one-dimensional electronic systems and have the potential to revolutionize many aspects of nano/molecular electronics. Scanning tunneling microscopy (STM) has been used to characterize the atomic structure and tunneling density of states of individual SWNTs. Detailed spectroscopic measurements showed one-dimensional singularities in the SWNT density of states for both metallic and semiconducting nanotubes. The results obtained were compared to and agree well with theoretical predictions and tight-binding calculations. SWNTs were also shortened using the STM to explore the role of finite size, which might be exploited for device applications. Segments less than 10 nm exhibited discrete peaks in their tunneling spectra, which correspond to quantized energy levels, and whose spacing scales inversely with length. Finally, the interaction between magnetic impurities and electrons confined to one dimension was studied by spatially resolving the local electronic density of states of small cobalt clusters on metallic SWNTs. Spectroscopic measurements performed on and near these clusters exhibited a narrow peak near the Fermi level that has been identified as a Kondo resonance. In addition, spectroscopic studies of ultrasmall magnetic nanostructures, consisting of small cobalt clusters on short nanotube pieces, exhibited features characteristic of the bulk Kondo resonance, but also new features due to their finite size.