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Abstract:
Films of pure high-quality multiwall carbon nanotubes are grown by laser-assisted thermal chemical vapor deposition in a cold wall reactor. A CO₂ laser is used to locally heat a substrate on which nanotubes are grown, employing the catalytic activity of iron nanoparticles. Two kinds of experiments are reported: In a two-step mode, catalytic iron particles and solid carbon are deposited separately, leading to the formation of homogeneous films of nonaligned pure multiwall nanotubes (MWNTs). The role of gas phase heating was investigated by the addition of a sensitizing molecule that absorbs the laser radiation. It is found that large-volume gas phase heating is not needed for the synthesis of high-quality nanotube films. Focused laser radiation allows growth of locally defined nanotube films. In a second set of experiments, iron and carbon are deposited simultaneously. Films of vertically aligned MWNTs of extremely high packing density were produced in this mode under very lean hydrocarbon supply conditions. (C) 2002 American Vacuum Society.
