Growth of Single-Walled Carbon Nanotubes by Microwave Plasma Enhanced Chemical Vapor Deposition
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Growth of Single-Walled Carbon Nanotubes by Microwave Plasma Enhanced Chemical Vapor Deposition
Matthew R. Maschmann+, Amit Goyal*, Zafar Iqbal*, Timothy S. Fisher+, Roy Gat#
+
Purdue University, School of Mechanical Engineering and Birck Nanotechnology Center, West Lafayette, Indiana 47904
*
New Jersey Institute of Technology, Department of Chemistry, Newark, New Jersey 07102 #
Sekitechnotron USA, 1153 Bordeaux Dr #102, Sunnyvale, California 94089
ABSTRACT Single-walled carbon nanotubes (SWCNTs) have been grown for the first time by microwave plasma-enhanced chemical vapor deposition (PECVD) at 800oC using methane as the precursor and bimetallic Mo/Co catalyst supported on MgO dispersed on a silicon wafer. The nanotubes grown consist of bundles, each composed of individual tubes of a single diameter associated with either metallic or semiconducting SWCNTs,
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based on characterization by Raman spectroscopy. Field-emission scanning electron microscopy and atomic force microscopy show that the bundles are relatively thin – 5 to 10 nm in diameter – and up to a few micrometers in length. The results are compared with those obtained on recently reported SWCNTs grown by radio frequency PECVD.
Introduction.
Single walled carbon nanotubes (SWCNTs) possess unparalleled
mechanical strength and transport characteristics and show great promise for use in a variety of applications. The ultimate impact of functionalized SWCNTs in engineering applications will depend on precise control of the physical properties of SWCNTs and thus the environment in which they grow. Plasma-enhanced chemical vapor deposition (PECVD) enables independent control of synthesis variables such as substrate temperature, substrate bias, operating pressure and, perhaps most importantly, local gas chemistry. The dissociation of hydrocarbons in plasma permits synthesis of CNTs and carbon nanofibers (CNFs) to proceed at temperatures much lower1,2 than those encountered in other techniques and allows for controllable gas chemistry near the growth substrate. In addition, vertical alignment of CNTs grown by PECVD has been well documented3-5 and could aid in development of devices requiring high spatial density of individual components, such as ultra dense digital memory. Until two very recent reports on SWCNT growth by radio-frequency PECVD 6,7, however, synthesis of carbon nanotubes by PECVD had been limited to multi-walled CNTs (MWCNTs).
The
production of SWCNTs by microwave PECVD, as described in this note, represents a breakthrough that could significantly advance the control of SWCNT-based device manufacturing.
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In previous work on SWCNT synthesis, Kanzow and Ding8 suggested that an overabundance of carbon may inhibit the growth of SWCNTs, and Meyyappan et al.4 speculated that the abundance of carbon produced by hydrocarbon dissociation in the plasma probably hinders growth of SWCNTs in PECVD. Indeed, attempts to synthesize SWCNTs in PECVD using catalysts known to produce SWCNTs by thermal CVD produced only MWCNTs in P
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