Transport spectroscopy of chemical nanostructures: the case of metallic single-walled carbon nanotubes

Transport spectroscopy, a technique based on current-voltage measurements of individual nanostructures in a three-terminal transistor geometry, has emerged as a powerful new tool to investigate the electronic properties of chemically derived nanostructures. In this review, we discuss the utility of this approach using the recent studies of single-nanotube transistors as an example. Specifically, we discuss how transport measurements can be used to gain detailed insight into the electronic motion in metallic single-walled carbon nanotubes in several distinct regimes, depending on the coupling strength of the contacts to the nanotubes. Measurements of nanotube devices in these different conductance regimes have enabled a detailed analysis of the transport properties, including the experimental determination of all Hartree-Fock parameters that govern the electronic structure of metallic nanotubes and the demonstration of Fabry-Perot resonators based on the interference of electron waves

Novel nano-biosensors for life science systems and their applications in early, accurate, and non-invasive melanoma and other types of cancer detection

Melanoma (the 5th and 6th most common cancer in Caucasian males and females, respectively), is the most severe form of skin cancer, which is often fatal if recognized in its advanced stage. Melanoma is the tumor that originates from melanocytes (the cells that make the pigment melanin), and may develop from a nevus (commonly named "mole"). Clinically, it is very difficult to correctly differentiate nevi with atypical features or dysplastic nevi, and nevi of special sites from melanoma. Clearly, new, more powerful, less invasive, time consuming and expensive tools are needed for an early and accurate detection of melanoma. In order to address this need, we propose a development of a new set of tools, namely, carbon-nanotube-based biosensors for the early and accurate detection of melanoma. Once successful, we will modify and apply this new technology to early and accurately detect other types of cancer

Shell Filling and Exchange Coupling in Metallic Single-Walled Carbon Nanotubes

We report the characterization of electronic shell filling in metallic single-walled carbon nanotubes by low-temperature transport measurements. Nanotube quantum dots with average conductance ∼(1–2)e^2/h exhibit a distinct four-electron periodicity for electron addition as well as signatures of Kondo and inelastic cotunneling. The Hartree-Fock parameters that govern the electronic structure of metallic nanotubes are determined from the analysis of transport data using a shell-filling model that incorporates the nanotube band structure and Coulomb and exchange interactions

Thermal resistance of the nanoscale constrictions between carbon nanotubes and solid substrates

We have determined the thermal resistance for transferring heat between individual single-walled carbon nanotube devices and solid substrates. Using sapphire and comparing our results to previous results obtained from SiO2, we find that the resistance is dominated by interfacial resistance rather than the spreading resistance of heat for diffusing into the substrate. Our results are in agreement to a recent model for the thermal resistance of nanoscale constrictions. Our results suggest that relatively short contact lengths (~10–30 nm) to a typical solid should be sufficient to transfer heat efficiently into carbon nanotubes, underscoring the potential of carbon nanotubes for nanoscale thermal management

One-dimensional transport in bundles of single-walled carbon nanotubes

We report measurements of the temperature and gate voltage dependence for individual bundles (ropes) of single-walled nanotubes. When the conductance is less than about e^2/h at room temperature, it is found to decrease as an approximate power law of temperature down to the region where Coulomb blockade sets in. The power-law exponents are consistent with those expected for electron tunneling into a Luttinger liquid. When the conductance is greater than e^2/h at room temperature, it changes much more slowly at high temperatures, but eventually develops very large fluctuations as a function of gate voltage when sufficiently cold. We discuss the interpretation of these results in terms of transport through a Luttinger liquid.Comment: 5 pages latex including 3 figures, for proceedings of IWEPNM 99 (Kirchberg

Sagnac interference in Carbon nanotube loops

In this paper we study electron interference in nanotube loops. The conductance as a function of the applied voltage is shown to oscillate due to interference between electron beams traversing the loop in two opposite directions, with slightly different velocities. The period of these oscillations with respect to the gate voltage, as well as the temperatures required for the effect to appear, are shown to be much larger than those of the related Fabry-Perot interference. This effect is analogous to the Sagnac effect in light interferometers. We calculate the effect of interactions on the period of the oscillations, and show that even though interactions destroy much of the near-degeneracy of velocities in the symmetric spin channel, the slow interference effects survive.Comment: 5 pages, 4 figure

Sagnac interference in Carbon nanotubes

The Sagnac interference mode arises when two interfering counterpropogating beams traverse a loop, but with their velocities detuned by a small amount $2u$, with $v_{R/L}=v_F\pm u$. In this paper we perform a perturbative non-equilibrium calculation of Sagnac interference in single channel wires as well as armchair nanotube loops. We study the dependence of the Sagnac conductance oscillations on temperature and interactions. We find that the Sagnac interference is not destroyed by strong interactions, but becomes weakly dependent on the velocity detuning $u$. In armchairs nanotubes with typical interaction strength, $0.25 \leq g \leq 0.5$, we find that the necessary temperature for observing the interference effect, $T_{SAG}$ is also only weakly dependent on the interaction, and is enhanced by a factor of 8 relative to the temperature necessary for observing Fabry-Perot interference in the same system, $T_{FP}$.Comment: 12 pages, 8 figure

Gate Voltage Controllable Non-Equilibrium and Non-Ohmic Behavior in Suspended Carbon Nanotubes

In this work, we measure the electrical conductance and temperature of individual, suspended quasi-metallic single-walled carbon nanotubes under high voltage biases using Raman spectroscopy, while varying the doping conditions with an applied gate voltage. By applying a gate voltage, the high-bias conductance can be switched dramatically between linear (Ohmic) behavior and nonlinear behavior exhibiting negative differential conductance (NDC). Phonon populations are observed to be in thermal equilibrium under Ohmic conditions but switch to nonequilibrium under NDC conditions. A typical Landauer transport model assuming zero bandgap is found to be inadequate to describe the experimental data. A more detailed model is presented, which incorporates the doping dependence in order to fit this data

Chemical doping of individual semiconducting carbon-nanotube ropes

We report the effects of potassium doping on the conductance of individual semiconducting single-walled carbon nanotube ropes. We are able to control the level of doping by reversibly intercalating and de-intercalating potassium. Potassium doping changes the carriers in the ropes from holes to electrons. Typical values for the carrier density are found to be ∼100–1000 electrons/μm. The effective mobility for the electrons is μeff∼20–60 cm2 V-1 s-1, a value similar to that reported for the hole effective mobility in nanotubes [R. Martel et al., Appl. Phys. Lett. 73, 2447 (1998)]