Energy loss of the electron system in individual single-walled carbon nanotubes.

We characterize the energy loss of the nonequilibrium electron system in individual metallic single-walled carbon nanotubes at low temperature. Using Johnson noise thermometry, we demonstrate that, for a nanotube with Ohmic contacts, the dc resistance at finite bias current directly reflects the average electron temperature. This enables a straightforward determination of the thermal conductance associated with cooling of the nanotube electron system. In analyzing the temperature- and length-dependence of the thermal conductance, we consider contributions from acoustic phonon emission, optical phonon emission, and hot electron outdiffusion.

Molecular-scale quantum dots from carbon nanotube heterojunctions.

Carbon nanotube heterojunctions (HJs), which seamlessly connect nanotubes of different chiral structure using a small number of atomic-scale defects, represent the ultimate scaling of electronic interfaces. Here we report the first electrical transport measurements on a HJ formed between semiconducting and metallic nanotubes of known chiralities. These measurements reveal asymmetric IV-characteristics and the presence of a quantum dot (QD) with approximately 60 meV charging energy and approximately 75 meV level spacing. A detailed atomistic and electronic model of the HJ enables the identification of specific defect arrangements that lead to the QD behavior consistent with the experiment.

Scaling of resistance and electron mean free path of single-walled carbon nanotubes.

We present an experimental investigation on the scaling of resistance in individual single-walled carbon nanotube devices with channel lengths that vary 4 orders of magnitude on the same sample. The electron mean free path is obtained from the linear scaling of resistance with length at various temperatures. The low temperature mean free path is determined by impurity scattering, while at high temperature, the mean free path decreases with increasing temperature, indicating that it is limited by electron-phonon scattering. An unusually long mean free path at room temperature has been experimentally confirmed. Exponentially increasing resistance with length at extremely long length scales suggests anomalous localization effects.

Covalently bridging gaps in single-walled carbon nanotubes with conducting molecules.

Molecular electronics is often limited by the poorly defined nature of the contact between the molecules and the metal surface. We describe a method to wire molecules into gaps in single-walled carbon nanotubes (SWNTs). Precise oxidative cutting of a SWNT produces carboxylic acid-terminated electrodes separated by gaps of

Extracting subnanometer single shells from ultralong multiwalled carbon nanotubes.

We report a simple but powerful method for engineering multi-walled carbon nanotubes (MWNTs) by using manipulation by an atomic-force microscope. The successive shell-by-shell extraction process of ultralong MWNTs allows the exposure of the innermost single-walled carbon nanotubes (SWNTs), which have diameters as small as approximately 0.4 nm. The inner-shell extraction process changes the electrical characteristics of the MWNTs. Whereas the outer hollowed-out nanotubes show either metallic or semiconducting character, the innermost SWNTs of small diameter exhibit predominantly metallic transport properties.