Supersymmetry in carbon nanotubes in a transverse magnetic field

Electron properties of Carbon nanotubes in a transverse magnetic field are studied using a model of a massless Dirac particle on a cylinder. The problem possesses supersymmetry which protects low energy states and ensures stability of the metallic behavior in arbitrarily large fields. In metallic tubes we find suppression of the Fermi velocity at half-filling and enhancement of the density of states. In semiconducting tubes the energy gap is suppressed. These features qualitatively persist (although to a smaller degree) in the presence of electron interactions. The possibilities of experimental observation of these effects are discussed.Comment: A new section on electron interaction effects added and explanation on roles of supersymmetry expanded. Revtex4, 6 EPS figure file

Reversible Band Gap Engineering in Carbon Nanotubes by Radial Deformation

We present a systematic analysis of the effect of radial deformation on the atomic and electronic structure of zigzag and armchair single wall carbon nanotubes using the first principle plane wave method. The nanotubes were deformed by applying a radial strain, which distorts the circular cross section to an elliptical one. The atomic structure of the nanotubes under this strain are fully optimized, and the electronic structure is calculated self-consistently to determine the response of individual bands to the radial deformation. The band gap of the insulating tube is closed and eventually an insulator-metal transition sets in by the radial strain which is in the elastic range. Using this property a multiple quantum well structure with tunable and reversible electronic structure is formed on an individual nanotube and its band-lineup is determined from first-principles. The elastic energy due to the radial deformation and elastic constants are calculated and compared with classical theories.Comment: To be appear in Phys. Rev. B, Apr 15, 200

Effects of oxygen adsorption on carbon nanotube field emitters

Effects of oxygen adsorption on the field emission of carbon nanotubes are studied through first-principles calculations. Calculated emission currents are significantly enhanced when oxygen is adsorbed at the tip and the underlying physics is explained in terms of the change in the electronic structure by oxidation and the local field increase at the adsorption site. The issue of the current degradation accompanied by the oxidative etching is also addressed. The field-emission-microscopy images on the phosphor screen are simulated, displaying various patterns characteristic of each adsorption configuration.open546

All-perylene-derivative for white light emitting diodes

International audienceAn organic-based bright white light emitting compound, namely Tb(H3PTC)3 [H4PTC = perylene3,4,9,10-tetracarboxylic acid], able to be used as part of a white diode and as a part of a RGB systemthat can withstand high temperatures (B700 K), is developed using perylene-3,4,9,10-tetracarboxylicdianhydride (PTCDA) and terbium(III) nitrate pentahydrate as precursors by hydrothermal synthesis. UsingPTCDA as the red emitter and the new derivative of it, Tb(H3PTC)3, as the blue-green emitter, alongwith a common deep blue LED can form a RGB system for display technologies, around roomtemperature. Temperature-dependent photoluminescence properties of the Tb(H3PTC)3 compound arealso investigated for the involved excitonic-emission processes and the respective recombinationlifetimes. The terbium(III) complex was prepared using a procedure that is reproducible, easily modifiable,inexpensive, and environmentally friendly, opening new pathways for its large-scale applications. UnlikePTCDA, Tb(H3PTC)3 has been shown to be soluble in N-methyl-2-pyrrolidone (NMP) as well as in diluteaqueous solutions of this organic solvent in a straightforward procedure. The light emission propertiesare intimately correlated with the molecular structure and electronic properties of Tb(H3PTC)3elucidated by experimental results of X-ray Absorption Near Edge Spectroscopy (XANES), ExtendedX-ray Absorption Fine Structure (EXAFS) and Density Functional Theory (DFT) calculations. A brightfluorescence yield is attained with a small amount of material either in solution or in solid form showingits potential to be used in state-of-the-art organic optoelectronic device

Electronic structure of boron nitride nanostructures doped with a carbon atom

We have investigated, using first-principles calculations, the role of a substitutional carbon atom on the electronic properties of boron nitride monolayers, nanotubes, and nanocones. It is shown that electron states in the energy-gap are independent of the curvature, being the same for the monolayer, for the cone and for the tube. It is also found, that the presence of carbon in the boron nitride compounds induces a spin polarization, with magnetic moment of 1.0 μB, which does not depend on the curvature