Influence of alumina type on the evolution and activity of alumina-supported Fe catalysts in single-walled carbon nanotube carpet growth.
We have studied the lifetime, activity, and evolution of Fe catalysts supported on different types of alumina: (a) sputter deposited alumina films (sputtered/Fe), (b) electron-beam deposited alumina films (e-beam/Fe), (c) annealed e-beam deposited alumina films (annealed e-beam/Fe), (d) alumina films deposited by atomic layer deposition (ALD/Fe), and (e) c-cut sapphire (sapphire/Fe). We show that the catalytic behavior, Ostwald ripening, and subsurface diffusion rates of Fe catalyst supported on alumina during water-assisted growth or "supergrowth" of single-walled carbon nanotube (SWNT) carpets are strongly influenced by the porosity of the alumina support. The catalytic activity increases in the following order: sapphire/Fe < annealed e-beam/Fe < ALD/Fe < e-beam/Fe < sputtered/Fe. With a combination of microscopic and spectroscopic characterization, we further show that the Ostwald ripening rates of the catalysts and the porosity of the alumina support correlate with the lifetime and activity of the catalysts. Specifically, our results reveal that SWNT carpet growth is maximized by very low Ostwald ripening rates, mild subsurface diffusion rates, and high porosity, which is best achieved in the sputtered/Fe catalyst. These results not only emphasize the connection between catalytic activity and particle stability during growth, but guide current efforts aimed at rational design of catalysts for enhanced and controlled SWNT carpet growth.
Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433, USA. Placidus.Amama@wpafb.af.mil
Placidus B
PB
Amama
Cary L
CL
Pint
Seung Min
SM
Kim
Laura
L
McJilton
Kurt G
KG
Eyink
Eric A
EA
Stach
Robert H
RH
Hauge
Benji
B
Maruyama