Growth Mechanism of Long Aligned Multiwall Carbon Nanotube Arrays by Water-Assisted Chemical Vapor Deposition

Abstract

Highly aligned arrays of multiwalled carbon nanotube (MWCNT) on layered Si substrates have been synthesized by chemical vapor deposition (CVD). The effect of the substrate design and the process parameters on the growth mechanism were studied. Adding water vapor to the reaction gas mixture of hydrogen and ethylene enhanced the growth which led to synthesis of longer CNT arrays with high density. Environmental scanning electron microscopy (ESEM), energy-dispersive spectroscopy (EDS), and atomic force microscopy (AFM) were used to analyze the CNT morphology and composition. Quadrupole mass spectroscopy (QMS) provided in-situ information on the gas spices within the reaction zone. On the basis of results, we verified the top growth mechanism and evaluated the reason of decline and stoppage of the CNT growth after extended period of deposition. Multilayered Si substrates with a top film of Al2O3, having appropriate roughness, provide favorable conditions to form catalyst islands with uniform distribution and size. Using water-assisted CVD process and optimized substrate design, our group succeeded to grow vertically aligned, patterned MWCNT up to 4-mm long. The arrays were of high purity and weak adhesion which allowed to be peeled off easily from the substrate.

Carbon Nanotubes Anchored to Silicon for Device Fabrication

“…''Supergrowth'' of aligned DWCNTs [11,23] and MWCNTs [24] on silicon substrates was first developed by Hata et al [25] and relies on the increased lifetime and activity of the catalyst particles during CVD growth to create longer arrays. The difference in this work is that a weak oxidizer like water is added to selectively remove any amorphous carbon that could stick to the catalyst, while leaving the CNTs intact.…”

Growth and characterization of vertically aligned centimeter long CNT arrays

“…Especially, centimeter long CNT arrays are attractive for environmental sensor to monitor toxic chemicals and gases and for biomedical sensor to detect dopamine due to the excellent electrical, mechanical, electrochemical and thermal properties of CNT [6,[10][11][12][13]. There are variety of methods used to grow long, well-aligned CNT arrays such as oxygen assisted CVD, hot filament CVD, point arc plasma CVD, water assisted CVD, but most of them produce short CNTs (less than a few millimeters) [14][15][16][17][18][19][20][21][22][23]. Nevertheless, vertically aligned, centimeter long CNT arrays have rarely been reported since the window of growth conditions and catalyst composition is very narrow and the substrate design is challenging.…”

Carbon Nanotube Synthesis and Organization

“…The resulting low catalytic activity of CNT synthesis has not only reduced the availability of SWNTs, but the dead catalysts remain in the as-grown material as impurities. Addition of a controlled amount of water vapor in the growth ambient can dramatically enhance the activity and lifetime of the catalysts and address these problems [157][158][159][160][161]. This new CVD approach denoted as "supergrowth", works best on substrates with catalytic nanoparticles.…”