Lengthening and thickening of multi-walled carbon nanotube arrays grown by chemical vapor deposition in the presence and absence of water

Multi-walled carbon nanotube (MWCNT) array growth demonstrates lengthening and thickening stages by chemical vapor deposition (CVD) in the presence (water-assisted CVD (WACVD)) and absence (conventional CVD (CCVD)) of water. In the lengthening stage of WACVD, CNT wall number remains constant and catalysts preserve the activity; while in the thickening stage of WACVD, MWCNTs thicken substantially and catalysts deactivate following the previously proposed radioactive decay model. In CCVD, however, the lengthening and thickening were found to be competitive. Mechanisms of thickening in WACVD and CCVD were comparatively analyzed, from which the effect of water was elucidated. These findings provide experimental solutions to the fabrication of MWCNT arrays with controlled wall numbers by WACVD and CCVD.