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Using a tight-binding model and the Landauer–Büttiker formalism, we have calculated the current–voltage characteristics of a semiconducting single-walled carbon nanotube and that of a fullerene (C[sub 60])-doped carbon nanotube (peapod) structure. Our calculation shows that fullerene encapsulation in a semiconducting nanotube enhances the electrical conductivity of the nanotube, which is consistent with recent experimental measurements. We explain the increased electronic conduction in the semiconducting nanopeapod structure by analyzing the density of states of both pristine and C[sub 60]-doped nanotubes. A first-principles density functional calculation shows a significant amount of charge transfer (0.62e[sup -]) from the nanotube to C[sub 60], suggesting that holes are the primary charge carriers in the peapod. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Capillary forces arising during the evaporation of liquids from dense carbon nanotube arrays are used to reassemble the nanotubes into two-dimensional contiguous cellular foams. The stable nanotube foams can be elastically deformed, transferred to other substrates, or floated out to produce free-standing macroscopic fabrics. The lightweight cellular foams made of condensed nanotubes could have applications as shock-absorbent structural reinforcements and elastic membranes. The ability to control the length scale, orientation, and shape of the cellular structures and the simplicity of the assembly process make this a particularly attractive system for studying pattern formation in ordered media. [ABSTRACT FROM AUTHOR]

Controlled introduction of defects into aligned multiwalled carbon nanotubes (MWCNTs) was achieved by time-dependent plasma etching. The subsequent morphological changes in MWCNTs have been fingerprinted using Raman and x-ray photoelectron spectroscopy, by which induction of defects by functionalization was confirmed. We found that the introduction of defects along the nanotube body affects all Raman vibrational modes. A systematic analysis of the relationship between D, D′, D*, and G modes leads us to believe that no one peak can be used as an accurate standard for estimation of defects in nanotubes. [ABSTRACT FROM AUTHOR]

Gate modulated transport in semiconducting single-wall carbon nanotubes shows significant hysteresis in their transfer characteristics. The origin of this hysteresis is generally attributed to the screening of the gate voltage due to the movement of mobile charges/ions in the inherent presence of a trapping/detrapping mechanism in the adjacent dielectric, as in conventional silicon metal-oxide-semiconductor field-effect transistors. However, recent works have conjectured that the screening charges may originate from the nanotube itself. From an extensive study of the temperature dependence of the hysteresis behavior in nanotube field-effect transistors the authors experimentally establish this alternative mechanism, in which the screening charges are injected from the nanotube itself into the surrounding dielectric. Any detailed trapping/detrapping mechanism does not appear to play a significant role, and all experimental results can be simply explained in terms of a capacitive charging of the surrounding dielectric due to the charge injection. [ABSTRACT FROM AUTHOR]

The authors demonstrate the fabrication of different architectures of carbon nanotubes on conducting substrates via contact transfer of nanotubes using low temperature solders. Lithographically patterned multiwalled carbon nanotube arrays grown on silica substrates by chemical vapor deposition methods are transferred onto solder coated substrates. Both negative and positive patterns can be obtained by changing the printing parameters. Good wetting and electrical contacts are confirmed by measuring their field emission properties. This method can be used to construct nanotube structures of different shapes and dimensions over large areas on substrates of choice and could be a feasible process to integrate nanotubes into various devices. [ABSTRACT FROM AUTHOR]

Optical absorption of thin-film single-walled carbon nanotubes was investigated. The excitation energies were tailored by controlling the film thickness and the average nanotube diameter. The lowest absorption band (S1, peaked at ∼0.68 eV) moves toward higher energy with increasing nanotube film thickness linearly at 5.5 meV/μm, due to the band-gap increase of stretched nanotubes stacked in the film. A subsequent heating of nanotube films at 400°C in air could further shift the S1 band upward for over 35 meV. We created a tandem structure by combining multiple nanotube layers with different diameter distributions in order to define a particular excitation energy. Our nanotube thin films are macrodevices with tunable optical properties in optoelectronic and photonic applications. [ABSTRACT FROM AUTHOR]

Electrical transport through high-density arrays of carbon nanotubes grown within vertical pores of anodized alumina was measured. Individual nanotubes were studied using conductive tip atomic force microscopy, with bias applied between the tip and platinum back electrode. Multiwalled nanotubes of diameter about 50 nm, with 5 nm thick walls were found to have a resistivity lower than 1.4×10-5 Ω m. A potential barrier was found to exist between the sensing tip and nanotube, resulting in nonlinear current–voltage characteristics. Low-resistance contact was formed by breaking down this barrier, once the circuit was stressed beyond 1.5 V. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have studied the adsorption of H[sub 2]O molecules on a single-wall carbon nanotube (NT) using first-principles gradient-corrected density-functional theory. Subsequently, Green's function-based Landauer-Büttiker multichannel formalism within a tight-binding model is used to calculate the electron transport, and our results suggest that H[sub 2]O molecules adsorbed on the NT surface reduce the electronic conduction in the tube in agreement with recent experimental measurements. The decrease of conductance with water adsorption is explained on the basis of charge transfer between the adsorbate and the NT. [ABSTRACT FROM AUTHOR]

Using the large maximal current density and the small diameter of carbon nanotubes, a flash memory arrangement is proposed. It makes use of the spin sensitive transport through hybrid conductor junctions. This memory contains no moving mechanical part and a single layer’s theoretical information density can reach beyond 40 Gbit/cm2. It is easy to build a three-dimensional memory structure. Then, the theoretical capacity can reach beyond 1015 bit/cm3 (1000 Terrabit/cm3), which means that a memory with 1 cm area and 1 mm thickness could have about 10 TerraByte capacity. [ABSTRACT FROM AUTHOR]

Multiwalled carbon nanotube thin films were fabricated using catalytic chemical vapor deposition of xylene–ferrocene mixture precursor. The nanotube films were employed as inter-layers within composite systems to reinforce the interfaces between composite plies, enhancing laminate stiffness as well as structural damping. Experiments conducted using a piezo-silica composite beam with an embedded nano-film sub-layer indicated up to 200% increase in the inherent damping level and 30% increase in the baseline bending stiffness with minimal increase in structural weight. Scanning Electron Microscopy (SEM) characterization of the nano-film was also conducted to investigate the mechanics of stiffness and damping augmentation. The study revealed a fascinating network of densely packed, highly interlinked multiwalled nanotubes (MWNTs). This inter-tube connectivity resulted in strong interactions between adjacent nanotube clusters as they shear relative to each other causing energy dissipation within the nano-film. The cross-links between nanotubes also served to improve load transfer within the network resulting in improved stiffness properties. [Copyright &y& Elsevier]

Abstract: We report a simple way to produce fully densified aligned carbon nanotube (ACNT) films. The simultaneous growth of nanotubes and densification of the ACNT films by carbon infiltration in the interstitial spaces between nanotubes are accomplished in a single step by the combination of the chemical vapor deposition and chemical vapor infiltration processes. Scanning electron microscope analysis and microbalance measurements showed that after infiltration, the diameters of nanotubes and bulk density of the ACNT films are increased by an order of magnitude (and hence the porosity of the ACNT films is decreased). Transmission electron microscope and Raman scattering analysis showed that after densification, the nanotubes are conformally coated by partially graphitized pyrolytic carbon. The compressive modulus of the densified ACNT films could be increased by three orders of magnitude compared to the pristine ACNT films. Electrical properties are also measured for the densified films showing marked differences with the ACNT films. The property enhanced densified ACNT films constitute a new form of carbon–carbon nanocomposites and could find applications as multifunctional nanocomposites. [Copyright &y& Elsevier]

Abstract: Carbon nanotubes (CNT), despite their diverse application potential, have demonstrated adverse impacts in vitro and in vivo. Previous studies have focused on the combined in vitro cytotoxic impact of CNT aggregates and associated nanoparticulate impurities. However, the isolated effect of CNT aggregates and associated non-aggregated nanoparticulates have not been addressed in detail. In this work, the impact of single-walled nanotubes (SWNT) on rat aortic smooth muscle cells (SMC) was examined for SWNT (0.0–0.1mg/ml) over a 3.5-day time-course. Cell culture medium was filtered to remove the aggregate material and both nanomaterial (un-filtered) and filtered SWNT media were used to examine cell growth. In general, the removal of SWNT aggregates from cell culture test medium by filtration increased the SMC number in comparison to unfiltered medium at pre-filtered SWNT dosages below 0.1mg/ml. However, at 0.1mg/ml, both filtered and unfiltered media exhibited a similar decrease in cell number relative to the control medium. The filtered medium was characterized and contained both suspended nanoparticles as well as a small quantity of SWNT, which may have contributed to the observed cell growth inhibition. As a comparison to the SWNT, activated carbon (0.1mg/ml), a nanoporous, microparticulate carbon material, was found to be less inhibitory to SMC growth than the SWNT at the same dosage, implying an inverse proportionality between carbon nanomaterial size regimes and cell growth inhibition. [Copyright &y& Elsevier]

We report that freestanding films of vertically aligned carbon nanotubes exhibit super-compressible foamlike behavior. Under compression, the nanotubes collectively form zigzag buckles that can fully unfold to their original length upon load release. Compared with conventional low-density flexible foams, the nanotube films show much higher compressive strength, recovery rate, and sag factor, and the open-cell nature of the nanotube arrays gives excellent breathability. The nanotube films present a class of open-cell foam structures, consisting of well-arranged one-dimensional units (nanotube struts). The lightweight, highly resilient nanotube films may be useful as compliant and energy-absorbing coatings. [ABSTRACT FROM AUTHOR]

Discusses the development of a novel approach to in situ composite synthesis by attachment of polystyrene chains to full-length pristine single-wall carbon nanotubes without disrupting the original structure. Anionic polymerization scheme; Homogeneous dispersion of nanotubes; Electrostatic repulsion between individual tubes.