1,288 research outputs found
Ab initio study of semiconducting carbon nanotubes adsorbed on the Si(100) surface: diameter- and registration-dependent atomic configurations and electronic properties
We present a first-principles study of semiconducting carbon nanotubes
adsorbed on the unpassivated Si(100) surface. We have found metallicity for the
combined system caused by n-doping of the silicon slab representing the surface
by the SWNT. We confirm this metallicity for nanotubes of different diameters
and chiral angles, and find the effect to be independent of the orientation of
the nanotubes on the surface. We also present adsorption energetics and
configurations which show semiconducting SWNTs farther apart from the surface
and transferring less charge, in comparison with metallic SWNTs of similar
diameter.Comment: Replaces old (Jan 2006) version; more supporting material. 11 pages,
8 figures, 7 table
Bromophenyl functionalization of carbon nanotubes : an ab initio study
We study the thermodynamics of bromophenyl functionalization of carbon
nanotubes with respect to diameter and metallic/insulating character using
density-functional theory (DFT). On one hand, we show that the activation
energy for the grafting of a bromophenyl molecule onto a semiconducting zigzag
nanotube ranges from 0.73 eV to 0.76 eV without any clear trend with respect to
diameter within numerical accuracy. On the other hand, the binding energy of a
single bromophenyl molecule shows a clear diameter dependence and ranges from
1.51 eV for a (8,0) zigzag nanotube to 0.83 eV for a (20,0) zigzag nanotube.
This is in part explained by the transition from sp2 to sp3 bonding occurring
to a carbon atom of a nanotube when a phenyl is grafted to it and the fact that
smaller nanotubes are closer to a sp3 hybridization than larger ones due to
increased curvature. Since a second bromophenyl unit can attach without energy
barrier next to an isolated grafted unit, they are assumed to exist in pairs.
The para configuration is found to be favored for the pairs and their binding
energy decreases with increasing diameter, ranging from 4.34 eV for a (7,0)
nanotube to 2.27 eV for a (29,0) nanotube. An analytic form for this radius
dependence is derived using a tight binding hamiltonian and first order
perturbation theory. The 1/R^2 dependance obtained (where R is the nanotube
radius) is verified by our DFT results within numerical accuracy. Finally,
metallic nanotubes are found to be more reactive than semiconducting nanotubes,
a feature that can be explained by a non-zero density of states at the Fermi
level for metallic nanotubes.Comment: 7 pages, 5 figures and 3 table
Large Magnetic Susceptibility Anisotropy of Metallic Carbon Nanotubes
Through magnetic linear dichroism spectroscopy, the magnetic susceptibility
anisotropy of metallic single-walled carbon nanotubes has been extracted and
found to be 2-4 times greater than values for semiconducting single-walled
carbon nanotubes. This large anisotropy is consistent with our calculations and
can be understood in terms of large orbital paramagnetism of electrons in
metallic nanotubes arising from the Aharonov-Bohm-phase-induced gap opening in
a parallel field. We also compare our values with previous work for
semiconducting nanotubes, which confirm a break from the prediction that the
magnetic susceptibility anisotropy increases linearly with the diameter.Comment: 4 pages, 4 figure
Exciton Energy Transfer in Pairs of Single-Walled Carbon Nanotubes
We studied the exciton energy transfer in pairs of semiconducting nanotubes using high-resolution optical microscopy and spectroscopy on the nanoscale. Photoluminescence from large band gap nanotubes within bundles is observed with spatially varying intensities due to distance-dependent internanotube transfer. The range of efficient energy transfer is found to be limited to a few nanometers because of competing fast nonradiative relaxation responsible for low photoluminescence quantum yield
Process for separating metallic from semiconducting single-walled carbon nanotubes
A method for separating semiconducting single-walled carbon nanotubes from metallic single-walled carbon nanotubes is disclosed. The method utilizes separation agents that preferentially associate with semiconducting nanotubes due to the electrical nature of the nanotubes. The separation agents are those that have a planar orientation, .pi.-electrons available for association with the surface of the nanotubes, and also include a soluble portion of the molecule. Following preferential association of the separation agent with the semiconducting nanotubes, the agent/nanotubes complex is soluble and can be solubilized with the solution enriched in semiconducting nanotubes while the residual solid is enriched in metallic nanotubes
Chemical doping of individual semiconducting carbon-nanotube ropes
We report the effects of potassium doping on the conductance of individual semiconducting single-walled carbon nanotube ropes. We are able to control the level of doping by reversibly intercalating and de-intercalating potassium. Potassium doping changes the carriers in the ropes from holes to electrons. Typical values for the carrier density are found to be ∼100–1000 electrons/μm. The effective mobility for the electrons is μeff∼20–60 cm2 V-1 s-1, a value similar to that reported for the hole effective mobility in nanotubes [R. Martel et al., Appl. Phys. Lett. 73, 2447 (1998)]
Electronic Devices Based on Purified Carbon Nanotubes Grown By High Pressure Decomposition of Carbon Monoxide
The excellent properties of transistors, wires, and sensors made from
single-walled carbon nanotubes (SWNTs) make them promising candidates for use
in advanced nanoelectronic systems. Gas-phase growth procedures such as the
high pressure decomposition of carbon monoxide (HiPCO) method yield large
quantities of small diameter semiconducting SWNTs, which are ideal for use in
nanoelectronic circuits. As-grown HiPCO material, however, commonly contains a
large fraction of carbonaceous impurities that degrade properties of SWNT
devices. Here we demonstrate a purification, deposition, and fabrication
process that yields devices consisting of metallic and semiconducting nanotubes
with electronic characteristics vastly superior to those of circuits made from
raw HiPCO. Source-drain current measurements on the circuits as a function of
temperature and backgate voltage are used to quantify the energy gap of
semiconducting nanotubes in a field effect transistor geometry. This work
demonstrates significant progress towards the goal of producing complex
integrated circuits from bulk-grown SWNT material.Comment: 6 pages, 4 figures, to appear in Nature Material
Orbital and spin magnetic moments of transforming 1D iron inside metallic and semiconducting carbon nanotubes
The orbital and spin magnetic properties of iron inside transforming metallic
and semiconducting 1D carbon nanotube hybrids are studied by means of local
x-ray magnetic circular dichroism (XMCD) and bulk superconducting quantum
interference device (SQUID) measurements. Nanotube hybrids are initially
ferrocene filled single-walled carbon nanotubes (SWCNT) of different
metallicities. After a high temperature nanochemical reaction ferrocene
molecules react with each other to form iron nano clusters. We show that the
ferrocenes molecular orbitals interact differently with the SWCNT of different
metallicities without significant XMCD response. This XMCD at various
temperatures and magnetic fields reveals that the orbital and/or spin magnetic
moments of the encapsulated iron are altered drastically as the transformation
to 1D Fe nanoclusters takes place. The orbital and spin magnetic moments are
both found to be larger in filled semiconducting nanotubes than in the metallic
sample. This could mean that the magnetic polarizations of the encapsulated
material is dependent on the metallicity of the tubes. From a comparison
between the iron 3d magnetic moments and the bulk magnetism measured by SQUID,
we conclude that the delocalized magnetisms dictate the magnetic properties of
these 1D hybrid nanostructures
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