Study of Growth Kinetics of Ultra-Long Carbon Nanotube Arrays through Wall Number Statistical Investigation
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1204-K05-01
Study of Growth Kinetics of Ultra-Long Carbon Nanotube Arrays through Wall Number Statistical Investigation Xinwei Cui1, Weifeng Wei2 and Weixing Chen1 1
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada, T6G 2G6 2 Department of Materials Science and Engineering, Massachusetts Institute of Technology, 4229, 77 Massachusetts Ave, Cambridge, MA 02139, U.S.A.
ABSTRACT The unique properties of carbon nanotubes (CNTs) strongly depend on their structures. In this study, the growth kinetics of ultra-long multi-walled CNT (MWCNT) arrays by waterassisted chemical vapor deposition (WACVD) has been investigated based on the statistical studies of CNT wall number. It was found that the kinetics of MWCNT arrays in WACVD demonstrated a lengthening and thickening growth. In the linear lengthening stage, CNT wall number remains constant and catalysts preserve the activity; while in the thickening stage, CNTs thicken substantially through the gas phase-induced thickening process and catalysts start to deactivate. The effects of ethylene and hydrogen flow rates on the MWCNT array growth have also been studied. It was found that by changing ethylene flow rate, different linear lengthening stages corresponding to different CNT wall numbers could be obtained. These findings provide experimental solutions to fabrication MWCNT arrays with both selective heights and controllable wall numbers by WACVD. INTRODUCTION The unique electrical, thermal and mechanical properties of carbon nanotubes (CNTs) strongly depend on their structures [1, 2]; however, to produce CNTs with desirable structures remains challenging, although some efforts have been undertaken to control CNT structures, such as CNT length [3], diameter [4, 5], wall number [6, 7], chirality [8] and purity [9]. To some extent, CNT array height can be controlled by the growth time, temperature and catalyst activity [10], while CNT wall number can be affected by catalyst particle size [5] and reaction gas flow rate [11]. However, the fabrication of MWCNT arrays with both selective heights and controlled wall numbers hasn’t been achieved. A clear understanding of the growth mechanism and growth kinetics of CNT arrays would serve as a guide to the manipulation of CNT structures; however, so far, the explicit growth mechanism and growth kinetics of MWCNT arrays haven’t been clearly elucidated. This study was initiated to investigate and understand the growth kinetics of MWCNT arrays in WACVD based on the statistical observation of CNT wall number. It was found that the kinetics demonstrates a lengthening and thickening growth. Here, the lengthening is defined as the increase of CNT array height, while the thickening is referred to as the increase of CNT wall number. The detailed analyses of the kinetics in the lengthening stage and thickening stage are presented, and the effects of ethylene and hydrogen have also been elucidated.
EXPERIMENT Catalyst film preparation, pretreatment and MWCNT array growth were presented in de
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