Diss-adsopt-APL2004

Dissociative adsorption has been widely simplified as part of the vapor–liquid–solid (VLS) growth

model. We found that the addition of specific carrier gases can critically modify the growth rate and

growth density of multiwall carbon nanotubes (MWNTs). These results were explained by

dissociative adsorption of C2H2 molecules and a solid-core VLS growth model. Based on these

integrated mechanisms, vertically aligned MWNTs were grown with an initial growth rate as high

as ,800 mm/h. This efficient growth process results at temperature and C2H2 partial pressures at

which the decomposition and segregation rates of carbon are balanced. Appropriate use of carrier

gas is one of the factors that could facilitate efficient and continuous growth of carbon nanotubes in

the future.

DEP-Carbon2010

The effects of AC field strength and AC frequency on the density of dielectrophoretically deposited multi-walled carbon nanotubes (MWCNTs) were investigated and explained in terms of existing theory. We show that while both parameters can be used to control deposition density, the experimentally observed frequency trend can not be explained by the theoretical Clausius–Mossotti factors. We demonstrate the ability to make surfactant-free dispersions of long, difficult to disperse MWCNTs and use them with dielectrophoresis to make clean, single and few connections between electrodes.

DEP_CNT_MRS2008

Controlled deposition of carbon nanotubes (CNTs) across desired electrodes is important

for the fabrication of nanoelectronic devices. Dieletrophoresis (DEP) has been recognized as a

convenient and affordable technique for the deposition of nanotubes and nanowires on

electrodes. Although DEP has been quite well studied for dielectric particles, the application for

depositing nanotubes is still at the early stage of development. Here, we show that multi-walled

CNTs can be deposited by DEP with controllable density and degree of alignment.

CNT_Syn_MRS2004

We attempt to understand the fundamental factors that determine the growth rate

of carbon nanotubes. In a series of experiments on growing multiwall carbon nanotubes

(MWNTs) by thermal chemical vapor deposition, we found that the addition of carrier

gas and the type of carrier gas can change the growth rate, growth density, and structures

of MWNTs. We explain these results based on the dissociative adsorption of C2H2 on Fe

nanoparticles and the vapor-liquid-solid (VLS) growth model. Finally, high-density,

vertically aligned MWNTs were grown when decomposition and segregation rates of

carbon were balanced.

CNT_SpacePropulsionMRS2004

Are carbon nanotubes more resistant than diamonds against ion erosion?

Here, we report an evaluation of multiwall carbon nanotubes (MWNTs) as the protective

coating against plasma erosion in advanced space propulsion systems. We have compared

polycrystalline diamond films with MWNTs, amorphous carbon (a-C) and boron nitride

(BN) films. Two types of MWNTs were investigated including vertically aligned (VA)

MWNTs, and those horizontally laid on the substrate surfaces. Only diamond films and

VA-MWNTs survived erosion by 250 eV krypton ions of a flight-quality Hall-effect

thruster. VA-MWNTs are found to bundle at their tips after ion erosion.

CNT_MRS2005

Plasma enhanced chemical vapor deposition (PECVD) is a unique technique for growing

vertically-aligned multiwall carbon nanotubes (VA-MWNTs) at controllable tube densities. This

technique is of considerable importance for low temperature growth of VA-MWNTs at desired

locations. However, the graphitic order of these MWNTs is inferior to those grown by laser

ablation, arc discharge, and thermal CVD techniques. Previously, these VA-MWNTs were

grown by a one-plasma approach (DC, microwave etc), either for gas decomposition or substrate

biasing. Here, we describe a dual-RF plasma enhanced CVD (dual-RF-PECVD) technique that

offers unique capability for controlling the graphitic order and diameters of VA-MWNTs.