Fermi Level Of Carbon Nanotubes Research Articles

Highly Conductive Doped Hybrid Carbon Nanotube-Graphene Wires.

The following paper explores the nature of electronic transport in a hybrid carbon nanotube-graphene conductive network. These networks may have a tremendous impact on the future formation of new electrical conductors, batteries, and supercapacitors, as well as many other electronic and electrical applications. The experiments described show that the deposition of graphene nanoflakes within a carbon nanotube network improves both its electrical conductivity and its current-carrying capacity. They also show that the effectiveness of doping is enhanced. To explain the effects observed in the hybrid carbon nanotube-graphene conductive network, a theoretical model was developed. The theory explains that graphenes are not merely effective conductive fillers of the carbon nanotube networks but also effective bridges that are able to introduce additional states at the Fermi level of carbon nanotubes.

Spin splitting at the Fermi level in carbon nanotubes in the absence of a magnetic field

In this paper, motivated by the possibility of experimental realization, we study the low-energy electronic states of a rotating carbon nanotube within a continuum model. An effective Dirac equation in the rotating reference frame is derived and exact analytical solutions for the eigenfunctions and energy spectrum are obtained. A Zeeman-like splitting results from the coupling of rotation to total angular momentum and the previously known static results are obtained in the no rotation limit.

Investigating the Structural, Electronic, and Chemical Evolution of B-Doped Multi-walled Carbon Nanotubes as a Result of Joule Heating

The evolution of B-doped multiwalled carbon nanotubes in the presence of a passing current has been investigated using the in situ TEM/STM Nanofactory holder. The Joule heating results in the dopant being partially removed as the internal structure of the nanotube is altered, and significant changes in its electrical properties were observed. This is of great importance for electrical applications where doping is used to tune the Fermi level of carbon nanotubes.

Modulating Electronic Transport Properties of Carbon Nanotubes To Improve the Thermoelectric Power FactorviaNanoparticle Decoration

Nanoparticle decoration on carbon nanotubes was employed to modulate their electrical conductance and thermopower and thereby improved the thermoelectric power factor. Nanotubes were made into films by spraying nanotube solutions on glass substrates, and then the films were immersed in different concentrations of CuSO(4) or HAuCl(4) solutions for various time periods. Copper ions in the solutions were reduced on nanotubes by obtaining electrons from zinc electrodes, whose reduction potential is lower than that of copper (galvanic displacement). Gold ions were reduced on nanotubes by both silver counter electrodes and spontaneous reaction due to larger reduction potentials than those of nanotubes. These reactions made electrons donated to (copper incorporation) or withdrawn from (gold incorporation) nanotubes depending on the difference in their work functions and reduction potentials, resulting in considerable changes in electron transport. In this paper, a series of experiments at different ion concentrations and reaction time periods were systematically performed in order to find optimum nanoparticle formation conditions and corresponding electronic transport changes for better thermoelectric power factor. Transport measurement results show that electronic properties can be considerably altered and modulated, resulting in 2-fold improvement in the thermoelectric power factor with 1 mM/30 min reaction. Reactions with solutions of a low metal ion concentration, such as 1 mM, yielded well-distributed small particles over large surface areas, which strongly affected electron transfer between nanoparticles and nanotubes. Successive copper and gold decorations on nanotubes made electrical conductance (or thermopower) serially decreased and increased (or increased and decreased) upon precipitating different metal particles. This transport behavior is believed to be from the changes in the Fermi level as a result of electron exchanges between reduced metals and nanotubes. Thermopower improvement after copper decoration can be attributed to the enlarged gap between the Fermi level and the mean of differential electrical conductivity. Such behaviors often appear when the Fermi level is shifted toward the spike-shape density of states in nanotubes due to anisotropic differential electrical conductivity. Finally, this study demonstrates that the thermoelectric power factor can be considerably increased by properly locating the Fermi level of carbon nanotubes with nanoparticles, providing promising opportunities of developing efficient organic thermoelectric materials as well as various electronic materials of desired properties.

Optical Phonon Tuned by Fermi Level in Carbon Nanotubes

The dependence of the frequency and broadening of optical phonons on carrier concentration is studied in carbon nanotubes within an effective-mass approximation. In metallic nanotubes, the frequency shift exhibits a logarithmic divergence and the broadening vanishes discontinuously when the Fermi level reaches the half of the optical-phonon frequency for the longitudinal mode with displacement in the axis direction, while the transverse mode is not affected. In semiconducting nanotubes, the frequency is raised for both transverse and longitudinal modes, exhibiting a behavior similar to level crossing.

Synthesis, characterization and spectroscopy of carbon based nanoscale materials

We have used chemical vapor deposition (CVD), for the synthesis of carbon nanotubes (CNTs) by the sublimation of iron phthalocyanines (FePcs); by the catalytic decomposition of acetylene over iron nanoparticles, supported on a thermal Si oxide and also by a Pd catalyst supported on alumina. We have explored different means of growing multiple wall CNTs and other carbon materials. Transmission and scanning electron microscopy have been used to characterize the synthesis products. We have also performed inverse photoemission spectroscopy (IPS), to explore the unoccupied electronic states above the Fermi level of CNTs and describe the peculiarities of the nanotubes electronic structure. We have examined by different CNTs samples and determined the origin of the main IPS spectral features.