Symmetry-adapted tight-binding electronic structure analysis of carbon nanotubes with defects, kinks, twist, and stretch

In this paper, a symmetry-adapted method is applied to examine the influence of deformation and defects on the electronic structure and band structure in carbon nanotubes. First, the symmetry-adapted approach is used to develop the analog of Bloch waves. Building on this, the technique of perfectly matched layers is applied to develop a method to truncate the computational domain of electronic structure calculations without spurious size effects. This provides an efficient and accurate numerical approach to compute the electronic structure and electromechanics of defects in nanotubes. The computational method is applied to study the effect of twist, stretch, and bending, with and without various types of defects, on the band structure of nanotubes. Specifically, the effect of stretch and twist on band structure in defect-free conducting and semiconducting nanotubes is examined, and the interaction with vacancy defects is elucidated. Next, the effect of localized bending or kinking on the electronic structure is studied. Finally, the paper examines the effect of 5–8–5 Stone–Wales defects. In all of these settings, the perfectly matched layer method enables the calculation of localized non-propagating defect modes with energies in the bandgap of the defect-free nanotube.

Semi-conducting single-walled carbon nanotubes are detrimental when compared to metallic single-walled carbon nanotubes for electrochemical applications

The performance of as-synthesized SWCNT is superior to that of ultrapure SWCNT towards the detection of different target analytes attributed to the presence of both metallic and semiconducting nanotubes in the former.

A Continuous Flow Device for the Purification of Semiconducting Nanoparticles by AC Dielectrophoresis

ABSTRACTSingle-walled carbon nanotubes (SWCNTs) have attracted significant attention as building blocks for future nanoscale electronics due to their small size and unique electronic properties. However, current SWCNT production techniques generate a mixture of two types of nanotubes with divergent electrical behaviors due to structural variations. Some of the nanotubes act as metallic materials while others display semiconducting properties. This random mixture has prevented the realization of functional carbon nanotube-based nanoelectronics. Here, a method of purifying a continuous flow of semiconducting nanotubes from an initially random mixture of both metallic and semiconducting SWCNTs in suspension is presented. This purification uses A/C dielectrophoresis (DEP), and takes advantage of the large difference of the relative dielectric constants between metallic and semiconducting SWCNTs. Because of a difference in magnitude and opposite directions of a dielectrophoretic force imposed on the random SWCNT solution, metallic SWCNTs deposit onto an electrode while semiconducting SWCNTs remain in suspension [3]. A discussion of these techniques is presented, along with a dielectrophoretic force-utilized microfluidic lab-on-a-chip device that can accomplish purification of semiconducting nanoparticles at high processing rates. The effectiveness of the device is characterized using Raman spectroscopy analysis on separated samples.