Temperature gradient chemical vapor deposition of vertically aligned carbon nanotubes

We present temperature gradient chemical vapor deposition (TG CVD) for producing vertically aligned (VA-) carbon nanotubes (CNTs). Independent heaters on the gas inlet and catalyst substrate sides of a cold-wall, vertical CVD reactor can modulate the gas temperature gradient to lead to controlled thermal histories of acetylene precursor. Our growth results reveal that such a precursor thermal history can play a significant role in the growth and structural features of the resultant VA-CNTs. We find several gas thermal zones particularly important to the VA-CNT growth by evaluating the precursor dwell time in different zones. Thermal treatment of the acetylene precursor at 600-700 degrees C is found crucial for the synthesis of VA-CNTs. When this thermal zone is conjoined in particular with a zone >700 degrees C, efficient growths of single-walled and double-walled VA-CNTs can be achieved. These gas thermal zones can contribute to VA-CNT growths by mixing various secondary hydrocarbons with acetylene, corroborated by the results of our reacting flow simulation. Our findings emphasize the influence of gas-phase reactions on the VA-CNT growth and suggest that our TG CVD approach can be practically utilized to modulate complex gas-phase phenomena for the controlled growth of VA-CNTs. (c) 2012 Elsevier Ltd. All rights reserved.