Synthesis of single-walled carbon nanotubes produced using a three layer Al/Fe/Mo metal catalyst and their field emission properties

Single-walled carbon nanotubes (SWCNTs) were synthesized on SiO2/Si substrates by thermal chemical vapor deposition using an Al/Fe/Mo triple layer catalyst, methane (CH4) as the carbon source, and a mixture of Ar/H-2 (10% H-2) as the carrier gas. The effects of volume ratio of CH4 to Ar/H-2 (10% H-2), pretreatment time, growth temperature, and Al underlayer thickness on SWCNT growth were studied. The pretreatment time in Ar/H-2 and Al underlayer thickness were found to be crucial for a high-yield of high-purity SWCNTs, since they both governed the size of the catalyst nanoparticles. The optimum growth conditions were found to be a pretreatment time of 20 min, growth time of 10 min, growth temperature of 900 degrees C, and CH4/Ar/H-2 flow rates of 50/900/100 seem, with a catalyst composed of Al (2 nm)/Fe (1 nm)/Mo (0.5 nm). The SWCNTs grown under these conditions have excellent field emission characteristics with low turn-on and threshold fields of 2.4 and 4.3 V/mu m, respectively, and a current density of 38.5 mA/cm(2) at 5 V/mu m. (C) 2007 Elsevier Ltd. All rights reserved.