Electronic Structure Of Single-walled Nanotubes Research Articles

Comparison of electronic and geometric structures of nanotubes with subnanometer diameters: A density functional theory study

All-electron calculations based on density functional theory have been carried out to study the electronic structures of single-walled nanotubes with subnanometer diameters. Present studies suggest the need for performing all-electron calculations, specifically for the nanotubes with very small diameters. Complete geometry optimization is found to be very crucial for predicting the electronic properties. We report here the electronic properties of two of the smallest single-walled carbon nanotubes (SWCNTs)---an armchair (2,2) and a zigzag (4,0) SWCNT---with comparable diameters of about $3\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. It is observed that, both geometrically and electronically, they are quite different. The discussion on the properties of zigzag $(n,0)$ SWCNTs, with diameters in the subnanometer regime, as a function of $n$, involves the elucidation of their geometric and band structures. In the band structures, systematic variations of a nearly-free-electron-like state and a nearly-dispersion-free state are shown as a function of $n$ and their implications have been discussed. The Fermi surfaces calculated for the metallic SWCNTs show signature of a collection of quasi-Fermi-points. This shows the quasi-one-dimensional nature of these nanotubes (NTs). From the present calculations, it is expected that the number of conduction channels is restricted between 2 and 3 for the NTs studied here.

Ab initio studies of elastic properties and electronic structures of C and BN nanotubes

The elastic properties and electronic structures of single-walled nanotubes (SWNTs) are studied using the ab initio package CRYSTAL-03. It is found that the Young modulus correlates strongly with the tube's electronic structure. The study reveals that a semiconductor–metal transition can be induced by uniaxial stress for carbon nanotubes, whereas this transition is not observed for boron nitride nanotubes.

Statistical analysis of the electronic structure of single-wall carbon nanotubes

The electronic structure of single-wall nanotubes in intact, undissolved ``buckypaper'' has been studied using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) at 23 K. STM topography shows, that single-wall carbon nanotubes (SWNT's) form microbundles that in turn aggregate in ropes. STS allows us to distinguish between room temperature metallic and wide-gap SWNT's. We find a distribution ratio of $(49\ifmmode\pm\else\textpm\fi{}7)%:(51\ifmmode\pm\else\textpm\fi{}7)%,$ respectively. A statistical analysis of the observed band gaps and metallic plateaus within these groups is carried out and used to determine the diameter distribution of the SWNT's in the buckypaper.

Electron emission and structural characterization of a rope of single-walled carbon nanotubes

The electron emission and structural properties of an isolated ‘‘rope’’ comprised of ;70 individual singlewalled nanotubes ~SWNT’s! were investigated by measuring the field-emission energy distributions and by using field-ion microscopy~FIM!. Field-emission energy distributions, obtained under ultrahigh-vacuum conditions, revealed that the emitting nanotube has a large density of states near the Fermi energy, with an energy distribution of emitted electrons close to that predicted by the free-electron theory. Two small features located on the trailing edge of the energy distributions are attributed to localized features in the density of states of a SWNT. FIM studies were also performed on the same rope in an attempt to provide structural information about the emitting nanotube. Initial FIM micrographs showed an uneven distribution of atoms. Eventually, rings of atoms were imaged. The atom placement around an individual ring structure is analyzed and found to be consistent with that expected from a single ~19,13! SWNT. I. INTRODUCTION Much work has been done toward an understanding of the structural and electronic properties of carbon nanotubes. Many calculations of the electronic structure of single-walled nanotubes ~SWNT’s! have been reported. 1‐4 SWNT’s of the armchair ~n,n! variety are expected to be metallic; nanotubes of the zigzag ( n,0) family can be either metallic or semiconducting; and nanotubes with an inherent ~n,m! helicity are expected to be either semiconducting or metallic, depending on the exact values of n and m. Calculations illustrating how the density of states ~DOS! varies near the capped end of a nanotube have also been reported. 5‐7 Nanotubes can be imaged in the transmission electron microscope ~TEM! relatively easily which has provided an understanding of the structural properties and the growth mechanisms involved in nanotube formation. 3,8‐10 Scanning

Electronic structure of single-wall carbon nanotubes studied by resonant inelastic X-ray scattering

The electronic structure of single-wall nanotubes in "buckypaper" has been studied by using soft X-ray emission and resonant inelastic soft X-ray scattering. We observe electronic states derived from the K point and located close to E-F in the nanotubes,