Evolution, Activity, and Lifetime of Alumina-Supported Fe Catalyst during Super Growth of Single-Walled Carbon Nanotube
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1258-R03-02
Evolution, Activity, and Lifetime of Alumina-Supported Fe Catalyst during Super Growth of Single-Walled Carbon Nanotube Carpets: Influence of the Type of Alumina
Placidus B. Amama,1,2 Cary L. Pint,3 Seung Min Kim,4 Kurt G. Eyink,1 Eric A. Stach,4 Robert H. Hauge,3 Benji Maruyama1 1
Air Force Research Laboratory, Materials and Manufacturing Directorate, WPAFB, OH 45433. 2University of Dayton Research Institute (UDRI), University of Dayton, Dayton, OH 45469. 3 Smalley Institute for Nanoscale Science and Technology, Rice University, Houston, TX 77251. 4 Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907.
ABSTRACT
The influence of the type of alumina used as catalyst support on the evolution, activity, and lifetime of the catalyst during water-assisted CVD growth (or ‘supergrowth’) of single-walled carbon nanotube (SWNT) carpets has been studied. The catalyst consisted of a thin Fe film supported on alumina films deposited by different methods: atomic layer deposition (ALD), ebeam, and magnetron sputtering. In order to fully understand the influence of the type of alumina on SWNT carpet growth, crystalline alumina (c-cut sapphire) and annealed alumina deposited by e-beam were also used as catalyst supports. The activity and lifetime of Fe catalyst during SWNT carpet growth showed a strong dependence on the type of alumina used as support. Fe supported on sputtered alumina (sputtered/Fe) showed the highest catalytic activity and lifetime, which was closely followed by e-beam/Fe while Fe supported on sapphire (sapphire/Fe) showed the least catalytic activity and lifetime. AFM, XPS depth profile, variable angle spectroscopic ellipsometry (VASE) studies revealed that the catalyst evolution and the porosity of the different alumina supports correlate with the lifetime and activity of the catalysts. INTRODUCTION Due to the unique properties of single-walled carbon nanotubes (SWNTs) [1], “carpets” composed of vertically aligned SWNTs have been receiving growing attention in the nanotube community. SWNT carpets have shown promise in a number of important applications such as membranes, Li ion batteries, supercapacitors, super hydrophobic surfaces, polymer-nanotube composites and “gecko” tapes [2]. For these applications and many others, the collective properties and the uniformity of the SWNT carpet are extremely critical thereby placing higher requirements on the growth process. The preferred method for SWNT carpet growth is catalytic chemical vapor deposition (CCVD) using a thin Fe film ( 3.5 nm for annealed/Fe, and > 6 nm for sapphire/Fe). Based on the increase in the mean height of the particles, the Ostwald ripening rate decreases in the following order: sapphire/Fe < annealed/Fe < ALD/Fe < e-beam/Fe ≈ sputtered/Fe.
70
Roughness ratio Carpet height
12
60
10
50
4 2 0
sapphire
30 ALD
6
e-beam
40 sputtered
8
20 10 0 -10
1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80
Carpet height after 15 min (µm)
Roughness ratio (5 min / 0 min)
Second, the number density of catalyst particles
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