Performance of thin film carbon materials and carbon nanotubes as cold cathodes

The field emissions from three different types of carbon films are studied using a Kiethly voltage-current source-measure unit under computer control. The three types of carbon films are : 1) a-C:H:N deposited using an inductively coupled rf PECVD process, where the N content in the films can be as high as 30 at %; 2) cathodic arc deposited tetrahedral amorphous carbon with embedded regions of carbon nanotube and anion structures and 3) unoriented carbon nanotube films on a porous substrate. The films are formed by filtering a solution of nanotubes dispersed in alcohol through the pores and drying.

Microwave characterization of multi-walled carbon nanotube arrays

A vertically aligned multi-walled carbon nanotube (VACNT) film has been characterized by rectangular waveguide measurements. The complex scattering parameters (S-parameters) are measured by a vector network analyzer at X-band frequencies. The effective complex permittivity and permeability of the VACNT film have been extracted using the Nicolson-Ross-Weir (NWR) approach. The extracted parameters are verified by full wave simulations (CST Microwave Studio) and very good agreement has been obtained. A systematic error analysis is presented and the errors are within the acceptable range. The performance of VACNT films as an absorber is examined, and comparison with the conventional carbon loaded materials shows that a 90% size reduction is possible whilst maintaining the same absorption level. © 2011 EUROPEAN MICROWAVE ASSOC.

Optical trapping of carbon nanotubes and graphene

We study optical trapping of nanotubes and graphene. We extract the distribution of both centre-of-mass and angular fuctuations from three-dimensional tracking of these optically trapped carbon nanostructures. The optical force and torque constants are measured from auto and cross-correlation of the tracking signals. We demonstrate that nanotubes enable nanometer spatial, and femto-Newton force resolution in photonic force microscopy by accurately measuring the radiation pressure in a double frequency optical tweezers. Finally, we integrate optical trapping with Raman and photoluminescence spectroscopy demonstrating the use of a Raman and photoluminescence tweezers by investigating the spectroscopy of nanotubes and graphene fakes in solution. Experimental results are compared with calculations based on electromagnetic scattering theory. © 2011 by the Author(s); licensee Accademia Peloritana dei Pericolanti, Messina, Italy.

Growth window and possible mechanism of millimeter-thick single-walled carbon nanotube forests.

Our group recently reproduced the water-assisted growth method, so-called "SuperGrowth", of millimeter-thick single-walled carbon nanotube (SWNT) forests by using C2H4/H2/H2O/Ar reactant gas and Fe/Al2O3, catalyst. In this current work, a parametric study was carried out on both reaction and catalyst conditions. Results revealed that a thin Fe catalyst layer (about 0.5 nm) yielded rapid growth of SWNTs only when supported on Al2O3, and that Al2O3 support enhanced the activity of Fe, Co, and Ni catalysts. The growth window for the rapid SWNT growth was narrow, however. Optimum amount of added H2O increased the SWNT growth rate but further addition of H2O degraded both the SWNT growth rate and quality. Addition of H2 was also essential for rapid SWNT growth, but again, further addition decreased both the SWNT growth rate and quality. Because Al2O3 catalyzes hydrocarbon reforming, Al2O3 support possibly enhances the SWNT growth rate by supplying the carbon source to the catalyst nanoparticles. The origin of the narrow window for rapid SWNT growth is also discussed.