Chiral Single-walled Carbon Nanotubes Research Articles

Effect of single-wall carbon nanotubes’chiral angle for the phonon frequency

The phonon frequencies at the center of Brillouin zone in a series of chiral single-wall carbon nanotubes were calculated numerically, in which the curvature effect was treated appropriately. According to the numerical results, the classification of the vibration modes for chiral tubes at the center of Brillouin zone were analysed. The relations between frequency-chirality and frequency-tube diameter for 12 non-degenerate vibration modes were illustrated.

Aharonov-Bohm Interference and Beating in Single-Walled Carbon-Nanotube Interferometers

Relatively low magnetic fields applied parallel to the axis of a chiral single-walled carbon nanotube are found causing large modulations to the p channel or valence band conductance of the nanotube in the Fabry-Perot interference regime. Beating in the Aharonov-Bohm type of interference between two field-induced nondegenerate subbands of spiraling electrons is responsible for the observed modulation with a pseudoperiod much smaller than that needed to reach the flux quantum Phi0 = h/e through the nanotube cross section. We show that single-walled nanotubes represent the smallest cylinders exhibiting the Aharonov-Bohm effect with rich interference and beating phenomena arising from well-defined molecular orbitals reflective of the nanotube chirality.

Effects of temperature and vacancy defects on tensile deformation of single-walled carbon nanotubes

This study adopts the Tersoff–Brenner interaction potential function in a series of molecular dynamic (MD) simulations which investigate the mechanical properties under tensile loading of (10,0) zigzag, (8,3) chiral and (6,6) armchair single-walled carbon nanotubes (SWCNTs) of similar radii. The Young's modulus values of the (10,0), (8,3) and (6,6) nanotubes are determined to be approximately 0.92, 0.95, and 1.03 TPa, respectively. Of these nanotubes, the results reveal that the (6,6) nanotube possesses the best tensile strength and toughness properties under tension. Although it is noted that under small tensions, the mechanical properties such as Young's modulus are essentially insensitive to helicity, under larger plastic deformations, they may be influenced by helicity effects. Finally, the simulations demonstrate that the values of the majority of the considered mechanical properties decrease with increasing temperature and increasing vacancy percentage.

Effect of oxygen chemisorption on the energy band gap of a chiral semiconducting single-walled carbon nanotube

We present a detailed investigation of the effect of oxygen chemisorption on the band gap of both a zigzag (10,0) and a chiral (8,4) single-walled carbon nanotube (SWNT) by means of density functional theory (DFT). The chemisorption of an oxygen atom leads to the formation of epoxy or ether structures in several possible sites of the outer wall. In the (10,0) nanotube, oxidation at the two possible sites drastically decreases the energy band gap. In the chiral (8,4) nanotube, the band gap remains almost constant upon oxidation at two of the three available sites and decreases considerably for the third site.

Tuning chirality of single-wall carbon nanotubes by selective etching with carbon dioxide.

CO2 molecule chemisorbs selectively on the zigzag tube edge without an activation barrier, whereas it physisorbs on the armchair edge of nanotubes. In addition, carbon nanotubes can be etched by an adsorbed oxygen atom of CO2 molecule. From our results, we suggest a selective etching mechanism for tuning the chirality of the mass-produced carbon nanotubes.

Nonresonant Raman spectrum in infinite and finite single-wall carbon nanotubes

We use the spectral moments method in the framework of the bond-polarization theory to calculate polarized nonresonant Raman spectra of chiral and achiral single-wall carbon nanotubes as a function of their diameter and length. In a previous approach, an investigation of finite-size effects was limited to a narrow length range (below 50 \AA{}). The present work extends the analysis to a larger range of finite lengths (from 20 to 850 \AA{}) as well as to achiral and chiral tubes of different diameters.

Synthesis of Ultralong and High Percentage of Semiconducting Single-walled Carbon Nanotubes

Two main results are reported here for single-walled carbon nanotubes (SWNTs) synthesized from well-controlled isolated catalytic Fe2O3 nanoparticles. The first is patterned growth of ultralong SWNTs (lengths up to 0.6 millimeters) by using a mixed methane and ethylene carbon source in chemical vapor deposition (CVD). Interesting loop and closed ring structures similar to those of fullerene “crop circles” are observed on these as-grown ultralong tubes. Second, surveying the electronic properties of individual SWNTs by transport measurements reveals that approximately 70% of individual SWNTs grown from isolated nanoparticles are semiconductors exhibiting field effect transistor (FET) characteristics. The distribution of CVD-grown SWNT chirality is elucidated for the first time, and implications to array-based nanotube electronics and sensors are discussed.