Pasha Nikolaev

Catalytic growth of single-walled nanotubes by laser vaporization

Direct laser vaporization of transition-metal/graphite composite rods produced single-walled carbon nanotubes (SWT) in the condensing vapor in a heated flow tube. A much higher yield of nanotubes was found, with little of the amorphous overcoating on those produced by the metal-catalyzed arc-discharge method. A mixture of Co with Ni catalyzed about 50% of all the carbon vaporized to SWT. A model for SWT growth is presented for both the present case and the arc in which the metal particle size is limited due to the concurrent carbon condensation.

Single-wall nanotubes produced by metal-catalyzed disproportionation of carbon monoxide

Abstract Isolated single-wall carbon nanotubes (SWNT) were grown by disproportionation of carbon monoxide at 1200°C, catalyzed by molybdenum particles a few nanometers in size. The tube diameters, ranging from 1 to 5 nm, closely correlated with the size of the catalytic particle found attached to the tube end. This result represents the first experimental evidence of SWNT produced by pre-formed catalytic particles. A mechanism for nucleation that is quite distinct from our recently proposed mechanism of SWNT produced by laser vaporization is advanced for formation of SWNT in the present case.

Fine structure of the low-frequency Raman phonon bands of single-wall carbon nanotubes

Abstract The Raman spectra of single-wall carbon nanotubes produced by a laser and arc process were studied between 5 and 500 K. The linewidth versus temperature dependence of the low-frequency Raman bands between 150 and 200 cm −1 deviates from that expected for phonon decay through a phonon–phonon scattering mechanism. The experimental results and their analysis provide convincing evidence that each of the low-frequency Raman bands is a superposition of several narrower Raman lines corresponding to tubes of nearly the same diameter. At low temperatures the width Δ ( T )= γ + Γ ( T ) of these components is determined mainly by the temperature-independent part γ ≈2 cm −1 .

Fast characterization of magnetic impurities in single-walled carbon nanotubes

We have demonstrated that the magnetic susceptibility measurement is a nondestructive, fast, and accurate method to determine the residual metal catalysts in a few microgram single-walled carbon nanotube (SWCNT) sample. We have studied magnetic impurities in raw and purified SWCNTs by magnetic susceptibility measurements, transmission electron microscopy, and thermogravimetry. The data suggest that the saturation magnetic moment and the effective field, which are caused by the interparticle interactions, decrease and increase, respectively, with the decrease of the particle size. Methods are suggested to overcome the uncertainty associated.

Calibrating the single-wall carbon nanotube resonance Raman intensity by high resolution transmission electron microscopy for a spectroscopy-based diameter distribution determination

We study a single-wall carbon nanotube (SWNT) sample grown by water-assisted chemical vapor deposition with both resonance Raman scattering (RRS) and high resolution transmission electron microscopy. High resolution transmission electron microscopy measurements of 395 SWNTs determined the diameter distribution of the sample, allowing us to calibrate an RRS radial breathing mode (RBM) map obtained with 51 laser excitation energies from 1.26 to 1.73 eV. Thus, we determined the diameter dependence of the RRS RBM cross-section, which in turn allows the determination of the diameter distribution of any SWNT sample by measuring the RBM Raman signal.

Advanced life support for space exploration: Air revitalization using amine coated single wall carbon nanotubes.

The challenges posed by long duration human space flight have made regenerable air revitalization a critical technology. Current systems using disposable lithium hydroxide do not address the difficulties presented by long duration missions. Solid amine systems offer the capability to regeneratively adsorb CO 2 using an amine—impregnated porous substrate. Desorption of CO 2 is then achieved by exposing the system to vacuum or by increasing temperature. However, thermal inefficiencies and system size constraints prevent adoption of regenerable systems on current and future space vehicles. A key challenge is the thermal management of the adsorbing bed. The adsorbing surface increases in temperature which reduces adsorbing efficiency. The removal of CO 2 reduces temperature, which in turn produces a loss in regeneration efficiency. These thermal inefficiencies necessitate prohibitively large volumes of traditional solid-amine materials, which do not have optimized surface areas and pore distributions. Single-wall carbon nanotubes (SWCNTs) may provide a means to increase surface area of the amine support and thermal efficiency. Recent work by Cinke et. al. provided a method of functionalizing SWCNTs and increasing the surface area to the order of 1500 m 2 /g [1]. We will report on the production of free standing, high surface area carbon nanotube structures currently being impregnated with amines. This novel SWCNT/amine approach will be compared with the current state of the art polymer structure-based system and characterized using SEM, TEM, surface area analysis through Brunauer-Emmett-Teller (BET), and also thermogravimetric equilibrium absorption. Results of SWCNT material improvements from processing modifications will also be presented.

Spin relaxation times of single-wall carbon nanotubes

We have measured temperature (

Growth mechanisms for single-wall carbon nanotubes in a laser-ablation process

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A model for nucleation and growth of single wall carbon nanotubes via the HiPcO process: a catalyst concentration study.

)- and power-dependent electron spin resonance in bulk single-wall carbon nanotubes to determine both the spin-lattice and spin-spin relaxation times,

PEM fuel cell electrodes using Single Wall Carbon Nanotubes

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