Uniform-diameter, aligned carbon nanotubes from microwave plasma-enhanced chemical-vapor deposition

Well-aligned multiwalled carbon nanotubes (CNTs) were grown by microwave plasma-enhanced chemical-vapor deposition using N-2 as the carrier gas and CH4 as the carbon source. Thin iron films with different thicknesses (0.5-5 nm) on silicon substrates acted as catalysts. Atomic force microscopy was used to investigate the relationship between the iron film thickness and the size of the iron clusters formed after the plasma treatment. Scanning and transmission electron microscopies were utilized to study the morphology, structure, and diameter of the as-grown CNTs. With the iron film thickness of 0.5 nm, the CNTs showed a remarkable structural uniformity in terms of diameter (standard deviation was 11.4% of the average diameter). Field-emission measurements revealed the turn-on field (at a current density of 10 mu A/cm(2)) and threshold field (at a current density of 10 mA/cm(2)) to be 5-8 and 6-11.5 V/mu m, respectively. (C) 2005 American Institute of Physics.