1,480 research outputs found
Pseudo-spin-dependent scattering in carbon nanotubes
The breaking of symmetry is the ground on which many physical phenomena are
explained. This is important in particular for bipartite lattice structure as
graphene and carbon nanotubes, where particle-hole and pseudo-spin are relevant
symmetries. Here we investigate the role played by the defect-induced breaking
of these symmetries in the electronic scattering properties of armchair
single-walled carbon nanotubes. From Fourier transform of the local density of
states we show that the active electron scattering channels depend on the
conservation of the pseudo-spin. Further, we show that the lack of
particle-hole symmetry is responsible for the pseudo-spin selection rules
observed in several experiments. This symmetry breaking arises from the lattice
reconstruction appearing at defect sites. Our analysis gives an intuitive way
to understand the scattering properties of carbon nanotubes, and can be
employed for newly interpret several experiments on this subject. Further, it
can be used to design devices such as pseudo-spin filter by opportune defect
engineering
Tunable Resonant Raman Scattering from Singly Resonant Single Wall Carbon Nanotubes
We perform tunable resonant Raman scattering on 17 semiconducting and 7
metallic singly resonant single wall carbon nanotubes. The measured scattering
cross-section as a function laser energy provides information about a tube's
electronic structure, the lifetime of intermediate states involved in the
scattering process and also energies of zone center optical phonons. Recording
the scattered Raman signal as a function of tube location in the microscope
focal plane allows us to construct two-dimensional spatial maps of singly
resonant tubes. We also describe a spectral nanoscale artifact we have coined
the "nano-slit effect"
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Single-Molecule Carbon Nanotube Field-Effect Transistors for Genomic Applications
Single-molecule carbon nanotube-based field-effect transistors are promising all-electronic devices for probing interactions of various biological and chemical molecules at the single- molecule level. Such devices consist of point-functionalized carbon nanotubes which are charge sensitive in the vicinity of a generated defect on the nanotube sidewall. Of particular interest is the characterization of the kinetic rates and thermodynamics of DNA duplex formation through repeated association (hybridization) and dissociation (melting) events on timescales unmatched by conventional single-molecule methods. In this work, we study the kinetics and thermodynamics of DNA duplex formation with two types of single-walled nanotubes: CVD-grown and solution-processed. In both assessments, we are able to extract kinetic and thermodynamic parameters governing the hybridization and melting of DNA oligonucleotides. In the latter case, devices are spun onto a wafer surface from an organic suspension, revealing consistent electrical characteristics. Significant effort is made to expand this work to wafer-level, in an effort to make the fabrication manufacturable
Atomic Configuration of Nitrogen Doped Single-Walled Carbon Nanotubes
Having access to the chemical environment at the atomic level of a dopant in
a nanostructure is crucial for the understanding of its properties. We have
performed atomically-resolved electron energy-loss spectroscopy to detect
individual nitrogen dopants in single-walled carbon nanotubes and compared with
first principles calculations. We demonstrate that nitrogen doping occurs as
single atoms in different bonding configurations: graphitic-like and
pyrrolic-like substitutional nitrogen neighbouring local lattice distortion
such as Stone-Thrower-Wales defects. The stability under the electron beam of
these nanotubes has been studied in two extreme cases of nitrogen incorporation
content and configuration. These findings provide key information for the
applications of these nanostructures.Comment: 25 pages, 13 figure
Towards a fullerene-based quantum computer
Molecular structures appear to be natural candidates for a quantum
technology: individual atoms can support quantum superpositions for long
periods, and such atoms can in principle be embedded in a permanent molecular
scaffolding to form an array. This would be true nanotechnology, with
dimensions of order of a nanometre. However, the challenges of realising such a
vision are immense. One must identify a suitable elementary unit and
demonstrate its merits for qubit storage and manipulation, including input /
output. These units must then be formed into large arrays corresponding to an
functional quantum architecture, including a mechanism for gate operations.
Here we report our efforts, both experimental and theoretical, to create such a
technology based on endohedral fullerenes or 'buckyballs'. We describe our
successes with respect to these criteria, along with the obstacles we are
currently facing and the questions that remain to be addressed.Comment: 20 pages, 13 figs, single column forma
CARBON NANOTUBES AND NANOCOMPOSITES FOR THERMAL AND ELECTRICAL APPLICATIONS
The known electrical and thermal properties of carbon nanotubes have prompted many predictions on their extraordinary potentials for ultimately performing polymeric nanocomposites. In this dissertation, chemical modification and functionalization of carbon nanotubes have been demonstrated as being effective for high-quality polymeric carbon nanotube composites, especially with our approach of using polymers that are structurally identical or maximally similar to the matrix polymers in the nanotube functionalization. For example, a poly(N-vinyl carbazole) (PVK) copolymer containing pendant hydroxyl groups was synthesized for the functionalization of single-walled carbon nanotubes (SWNTs). The shared solubility of the functionalized nanotube samples with PVK matrix polymer enabled the wet-casting of high-quality PVK-SWNT nanocomposite thin films for an evaluation of their enhanced charge dissipation under photo illumination. For desired electrical properties, not only the dispersion of carbon nanotubes in the polymer matrix is important to the performance, but also the use of only metallic nanotubes may offer solutions in some of the more demanding applications. Here demonstrated is that the bulk-separated metallic SWNTs offer superior performance (consistently and substantially better than the as-produced nanotube sample) not only in conductive composites with both poly(3-hexylthiophene) and PEDOT:PSS matrixes, but also in transparent conductive coatings of neat SWNTs
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