Catalyst and catalyst support morphology evolution in single-walled carbon nanotube supergrowth: Growth deceleration and
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Cary L. Pinta) Department of Physics and Astronomy, and Richard E. Smalley Institute for Nanoscale Science and Technology, Rice University, Houston, Texas 77005
Placidus B. Amama Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433; and University of Dayton Research Institute (UDRI), University of Dayton, Dayton, Ohio 45469
Robert H. Hauge Department of Chemistry and Richard E. Smalley Institute for Nanoscale Science and Technology, Rice University, Houston, Texas 77005
Benji Maruyama Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433
Eric A. Stachb) School of Materials Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (Received 1 June 2010; accepted 1 July 2010)
Detailed understanding of growth termination in vertically aligned single-walled carbon nanotubes (SWNTs) made via supergrowth, or water-assisted growth, remains critical to achieving the ultralong SWNTs necessary for next-generation applications. We describe the irreversible catalyst morphology evolution that occurs during growth, and which limits the lifetime of surface supported catalysts. Growth termination is strongly dependent on growth temperature, but not sensitive to C2H2:H2O ratio. In addition to both planar Ostwald ripening of small (sub-5 nm) Fe catalyst particles and diffusion of metal atoms into the alumina support, other features that contribute to growth termination or deceleration are described, including center-of-mass particle motions and coalescence of smaller species of surface supported Fe nanoparticles. Additionally, a temperatureinduced structural transition in the alumina catalyst support is found to be coincident with abrupt growth termination at temperatures of 800 C and higher. In situ electron microscopy observations are used to directly support these observations. I. INTRODUCTION
Single-walled carbon nanotubes (SWNTs) are a class of all-carbon molecules with incredible single-molecule properties, including strengths 100 times greater than steel at only 1/6 the weight1,2 and current carrying capacities three orders of magnitude higher than conventional metals.2,3 However, both the mechanical and particularly the electrical properties of SWNT materials can be reduced to levels that are worse than conventional materials a)
These authors contributed equally to this work. Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/JMR.2010.0264
b)
J. Mater. Res., Vol. 25, No. 10, Oct 2010
when these molecules are arranged into macroscopic scaffolds having length scales much larger than that of the SWNT.4–6 Therefore, even though many exciting applications have been demonstrated with SWNTs, the promise for using SWNT in many next-generation applications is based on the growth of meter or longer SWNTs in hierarchical assemblies, such as fibers7 or thin conducting films,8 which
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