Hidden Role Of Trace Gas Impurities In Chemical Vapor Deposition Growth Of Vertically-Aligned Carbon Nanotube Arrays

Carbon nanotubes (CNTs) grow in a seemingly simple catalytic chemical vapor deposition (CVD) process, yet the detailed mechanism of the process has continued to puzzle researchers. We have examined the role of trace amounts of gas impurities on the kinetics of atmospheric pressure CVD growth of CNTs. Our studies, which used an in situ height monitoring system, revealed that even the nominally ultrapure gases contain enough trace amounts of oxygen-containing species to affect the growth drastically. We were able to obtain the "clean" kinetics of the CNT array growth by passing the feed gases through the high performance gas purifiers. Our data show a remarkable decrease in the catalytic lifetime after the removal of the trace oxygen containing impurities. We suggest that the gas purification is an essential step in obtaining reliable nanotube growth data. (C) 2011 American Institute of Physics. [doi:10.1063/1.3573830]