The electron emission properties and field enhancement effects of carbon nanotubes (CNTs) have been extensively studied. However, all of these studies focus only on the field emission aspect of the materials and its application in cold cathode electron emitters. So far, we have not seen any studies in the literature that link CNTs with thermionic cathodes, which are an equally important cathode type because of their many applications. We present a study of field enhanced electron emissions from a new type of cathode: the CNT-based field enhanced thermionic cathode. This new cathode consists of a metal substrate with CNTs grown on top of its surface. The CNTs are coated with thermionic emission materials (BaO, SrO, and CaO). This unique cathode structure takes advantage of both the field enhancement effect from CNTs and the high electron emission capability of thermionic materials. The electron emission properties of this new cathode, particularly the field enhancement factor and effective work function, are compared with the conventional thermionic cathodes that are made of same oxide coating.

The radial breathing mode (RBM) region of the resonance Raman spectra of HiPco single walled carbon nanotubes (SWNTs) was investigated as a function of aggregation. This was modeled using an energetic deviation term (ΔE), imparted to the optical transitions (Eii(n, m)) by bundling effect. Eii(n, m) values obtained from photoluminescence (PL) measurements were used to reconstruct these RBM profiles. The simulation revealed that the PL-determined Eii(n, m) set provided a good fit in terms of peak position. Providing an accurate set of Eii(n, m) values becomes available, the RBM profile reconstruction methodology discussed herein could greatly enhance our ability to model a range of physicochemical changes to the immediate environment of SWNTs.

Charged particles in suspension tend to move when an electric field is applied. This simple phenomenon of migration of charged particles in a liquid medium and their subsequent deposition onto an oppositely charged electrode is called electrophoretic deposition (EPD), and is used in assembly of nanoparticles into microfabricated devices. This work reports the application of the EPD process for deposition of commercially available purified single-walled carbon nanotubes (CNT) onto microfabricated device structures. A direct current EPD in aqueous medium was used to position CNTs into two different microfabricated device structures: gold electrodes of 100nm thickness and gold microcantilevers. Control of the mass of CNTs deposited using EPD process is addressed in this work.

Single walled carbon nanotubes (SWNT) were synthesized by methane CVD on a supported mixed transition metal (Fe/Mo) catalyst. Gas feed composition and reaction temperature were varied to identify the threshold conditions for the growth of SWNT. These reaction conditions closely approximate pseudo-equilibrium conditions with some active reaction intermediate (likely chemisorbed carbon atoms) that proceeds to nucleate and grow SWNT. This value also serves as an estimated upper limit of the free energy of formation ΔG*(T)SWNT since the active intermediate proceeds to form SWNT through a process that is thought to be essentially irreversible. The difference relative to graphite is in good agreement with literature values predicted from simulations for SWNT nuclei containing approximately 80 atoms, while considerably larger than that predicted for bulk 5, 5 SWNT. Our estimate over the range 700 to 1000 °C of 16.1 to 13.9 kJ/mol is considerably greater than the free energy of formation for diamond (between 5.8 and 6.9 kJ/mol from 700 to 925 °C).

Dodecanethiol-stabilized-Au nanoparticles are successfully attached to the sidewall of as-grown single walled carbon nanotubes (SWCNTs) via a simple approach. This provides a straightforward method to functionalize and dissolve SWCNTs of full length in organic solvents. The modified nanotubes exhibit dramatic increase in tube resistance and strong gate dependence with a memory effect, which is explained in terms of nanotube structure deformation induced by surface thiolation. The mechanism for Au particle attachment is shown to be via dodecanethiol groups.

We find that functionalized SWCNT and DWCNT's (mainly double wall carbon nanotubes) in composites, DWCNTs under hydrostatic pressure and blue illuminated DWCNTs in methanol show the same up shift of the Raman G band and the appearance of a new band at 1455cm−1. This is attributed to the interaction of the CH3 group of the amphiphilic molecule in composites or the CH3 group of alcohol with the outer tube of DWCNT's and indicates that laser heating of DWCNT's in methanol can induce the chemical adsorption of CH3 onto the CNT (carbon nanotube) surface.

Carbon nanotubes and nanofibres are typically synthesised under substrate temperatures above 600°C. Here we investigate the influence of the substrate temperature and the plasma conditions on the growth of vertically aligned carbon nanostructures using Direct Current plasma Chemical Vapour Deposition, at temperatures below 550°C. These nanostructures are produced using a C2H2 based plasma and nickel thin film as the catalyst. We found that preferential deposition of amorphous carbon takes place as the synthesis temperature is lowered below 500°C. However, lowering the carbon concentration in the gas feedstock (<2% conc.) allows for the nucleation of nanofibre-like structures, whilst balancing the buildup of amorphous carbon. This method allows for the synthesis of vertically aligned structures at low temperatures (around 230°C) without intentional heating, while still achieving reasonable average growth rates up to 27 nm/min. The only heating was provided by the plasma, which typically consumes ∼ 4 W/cm2. It was found that by varying the applied plasma bias during high temperature synthesis, we increased the growth rate up to 165 nm/min. Based on the observations of experimental process variations and the morphology of the synthesised structures, we propose a growth mechanism for such low temperature growth and examine the resulting morphology changes.

We present a detailed photoluminescence study of a (6, 5) enriched DNA-wrapped single wall carbon nanotube (DNA-CNT) solid sample and an as-produced DNA-CNT solution. Multiple strong PL peaks were observed at excitation energies that do not correspond to the interband electronic transitions that are strongly enhanced by electronic van Hove singularities. These strong PL peaks are assigned to different mechanisms of excitation and relaxation, including one phonon, two phonon, hot luminescence processes, as well as radiative and non-radiative energy transferring mechanisms between neighboring nanotubes. These processes are assigned to different channels of phonon-assisted electron relaxation. The study shows that the electronic relaxation processes observed in PL can be used as a means to probe different physical interactions between photons, electrons, and phonons that are not separately identified in bulk semiconducting materials.

In this paper we describe a single wall carbon nanotube (SWNT) based biological sensor for the detection of biomolecules using streptavidin and IgG. Two types of sensing mechanisms have been used to demonstrate the ability of carbon nanotubes to form nanoscale biosensors. The first sensing mechanism involves a CNT based conduction sensor in which the decrease in the current was observed when the specific biomolecule was bound. In the second mechanism Quartz Crystal Microbalance (QCM) was used to quantify the mass of the biomolecule bound on the sidewalls of the carbon nanotube. Both sensing mechanisms proved to be efficient and consistent. Immobilization of the biomolecules on the carbon nanotube surface was confirmed by Atomic Force Microscopy.

The wetting properties and surface characteristics of individual carbon nanotubes are elucidated by immersing the nanotube into various organic liquid. The resultant force acting on the nanotube can be used to evaluate a liquid contact angle at the nanotube surface from classical methods. This technique was shown to be accurate enough to discern differences in wetting behavior due to both structural and chemical changes in the nanotube structure.

High-quality electron sources can be made from individual multi-walled carbon nanotubes. A process was developed allowing the control over 1) the length of the fraction of the nanotube protruding from the support tip, 2) the contact length of the nanotube with the support tip, 3) the diameter of the nanotube. In addition, the cap of the nanotube was closed and the nanotube was cleaned thoroughly. The field emission model successfully describes the electron emission process of these electron sources and the work function is 5.1 eV. The emitters show a highly stable emission, as expected on account of the extremely stable structure of the carbon nanotube.

We report anisotropic optical absorption and saturable absorption (SA) properties of aligned single wall carbon nanotubes (SWNT) embedded in the mechanically stretched polyvinyl alcohol (PVA) film. Polarized absorption spectra of the film showed a strong anisotropy for the near-infrared band gap transition of semiconductor SWNT with a dichroic ratio of 7.4, indicating the good alignment of the embedded SWNT. The SA property of the band gap transition measured using a polarized femtosecond fiber laser showed a strong polarization angle dependence for the stretched film. When the polarization of light is parallel to the stretching direction, the absorption saturation of the stretched film became more efficient than that of the unstretched film because of the apparently stronger transition moment.

We use diblock copolymers as nanotemplates to produce various catalyst nanoclusters or catalyst-containing inorganic nanostructures with controlled size and spacing for carbon nanotube growth. We are able to generate periodically ordered catalytic nanostructures by spin coating polymer-based catalyst systems. As a result, uniformly distributed, low defect density single walled nanotubes(CNTs) have been obtained. CNTs with diameters of 1nm or less have been produced from iron-containing inorganic nanostructures using conventional chemical vapor deposition. The superior film forming ability of polymer-based catalyst systems enables selective growth of carbon nanotubes on lithographically predefined catalyst islands over a large surface area. The ability to control the density and location of CNTs offers great potential for practical applications. The initial MALDI-MS (Matrix Assisted Laser Desorption Ionization-Mass Spectrometry) results indicate that we can positively identify bovine serum albumin (BSA) at 500 attomoles using CNT surfaces produced by this method.

Carbon nanotubes nanocomposites with unique opto-mechanical properties have been developed as smart coatings. Remote polarized Raman spectroscopy has been used to monitor optical strain sensitivity of deformed coatings and determine local strains on the micron scale directly from stress/strain induced Raman band shifts.

Chemically engineered carbon nanotubes and polymer matrices have been developed in order to overcome the limitations highlighted in previous reports. They have proved to be of significance importance in the optimization of the stress transfer between the nanotubes and the polyurethane matrix.

Wavelength-resolved femtosecond transient absorption spectroscopy is used to follow the electronic dynamics of single-walled carbon nanotubes in polymers following visible and near IR photoexcitation. Electron-hole (e-h) pairs give rise to sharp features in the transient spectra that decay in amplitude and exhibit rapid spectral shifts. The decay reflects (e-h) recombination on both short (1.3 ps) and long (35 ps) time scales. Transient spectra also exhibit a broad photobleach at early times that arises from the cooling of a hot electron gas created via excitation at the red edge of a π-plasmon band.

Raman spectroscopy is used to probe the structure and electronic properties of nanotubes dispersed in a liquid phase. We show that the radial breathing modes are upshifted in suspensions due to the molecular pressure of the solvent. On the other hand, we directly probe charge transfer in solutions of nanotube polyelectrolytes and its reversibility after oxydation in air.

Single-walled carbon nanotubes (SWCNTs) have been grown for the first time by microwave plasma-enhanced chemical vapor deposition (PECVD) at 800°C using methane as the precursor and bimetallic Mo/Co catalyst supported on MgO dispersed on a silicon wafer. The nanotubes grown consist of bundles, each composed of individual tubes of a single diameter associated with either metallic or semiconducting SWCNTs, based on characterization by Raman spectroscopy. Field-emission scanning electron microscopy and atomic force microscopy show that the bundles are relatively thin – 5 to 10 nm in diameter – and up to a few micrometers in length. The results are compared with those obtained on recently reported SWCNTs grown by radio frequency PECVD.

The formation mechanisms of carbon deposits and silicon carbide whiskers on metal surface catalysts have some common steps. The most important are: (1) the formation of metal particle alloys oversaturated with carbon or silicon and carbon atoms and (2) the nucleation of corresponding deposits on the metal catalyst surface. A thermodynamic analysis of the carbon and/or silicon carbide nucleation on the metal surface was performed. The master equations for the dependence of critical radius of carbon or SiC nucleus on reaction parameters, such as reaction temperature, supersaturation degree of catalyst particles with C (or Si and C), work of adhesion of metal to carbon (or metal to SiC), were obtained. These equations combined with the phase diagram approach can be used for the description of different scenarios of carbon and/or SiC deposits formation and for the development of the main principles of catalyst and promoters design.

Isolated single wall carbon nanotubes (SWNTs) were prepared on bare quartz and SiO2/ Si substrates using chemical vapor deposition (CVD) in which a liquid precursor, such as xylene, was used as the carbon source. The coverage of isolated SWNTs on the substrates was controlled by adjusting the concentration of iron (III) nitrate nonahydrate/2-propanol solution which provided the Fe seed catalyst particles. Micro-Raman spectra were obtained using the 514.5 nm excitation which showed the typical tangential band around 1590 cm−1 for semiconducting nanotubes. The radial breathing mode (RBM) frequencies ranged between 150 to 240 cm−1 and the estimated tube diameters are in good agreement with those obtained from atomic force microscope (AFM) images. In our synthesis approach controlled doping of isolated SWNTs with nitrogen was achieved by mixing appropriate amount of acetonitrile with xylene. As the nitrogen concentration in the feed was increased from 0 – 33 at. %, the RBM intensity decreased dramatically while the intensity of the D-band increased gradually relative to that of the G-band. Interestingly, the D' band was observed for the first time in the Raman spectrum of carbon nanotubes when the nitrogen concentration reached ∼2–3 at. %.

Structural, electrical and thermal methods are applied to characterize single-walled carbon nanotube (SWNT) fibers with post-extrusion stretching as the independent variable. HiPco SWNTs are dispersed in water using sodium dodecyl sulfate (SDS), and then co-extruded with polyvinyl alcohol (PVA)/water through a long syringe into a rotating water/PVA coagulation bath. Partial axial alignment is thereby achieved, and further enhanced by applying tension to the flexible green fibers in the coagulation bath. Our findings include: (1) X-ray diffraction shows that the full width at half maximum (FWHM) of the Bragg peaks decreases from 55 (as-extruded) to less than 30 degrees by 80% elongation. That is, SWNT alignment increases linearly with stretch (up to 80%). (2) In resistivity at room temperature vs. stretch ratio, result shows an initial rapid decrease followed by saturation; essentially all the improvement in electronic transport is obtained once alignment reached 40° FWHM. (3) Annealing in hydrogen at 1000°C is performed to drive out PVA, to improve inter-tube and inter-bundle contacts, and to heal damage on the tube walls. Such annealing is found to increase conductivity by at least 4 orders of magnitude. (4) Below 25 K, resistivity vs. temperature of the annealed fiber is well-represented by Coulomb gap variable range hopping (CG-VRH). It is rationalized that the Coulomb interactions in disordered systems open a gap at the Fermi energy. Above 25 K, the thermal energy is greater than the Coulomb gap, so thermal activation is more probable than correlated electron hops. (5) Finally, a measurable thermal conductivity is observed as stretch alignment increases.