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.

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.