Synthesis of horizontally aligned single-walled carbon nanotubes without external force and their growth characteristics

Horizontally aligned single-walled carbon nanotubes (SWNTs) were synthesized on diverse substrates by thermal chemical vapor deposition using two different kinds of catalyst sources. Different from the methods to synthesis horizontally aligned SWNTs reported by other groups, our method does not need any external force such as electrical field and special substrates. Instead of using a high speed gas flow, a low speed gas flow was adopted in our strategy to synthesis horizontally aligned SWNTs. It was found that the growth of such SWNTs is independent on the catalysts and substrates, but sensitive to the speed of the gas flow, indicating that SWNTs were not aligned by substrate surfaces but by gas flow. Calculations of the Reynolds numbers of different gas flows shows that a laminar flow was crucial for the growth of horizontally aligned SWNTs. The catalyst of SWNT and part SWNT were considered to be kept floating during the growth of SWNT. The laminar flow was suggested to stably direct the SWNTs to grow along the gas flow direction.