Substrate effects on the growth of multiwalled carbon nanotubes by thermal chemical vapor deposition

Different shapes and sizes of multiwalled carbon nanotubes (MWCNTs) were prepared by the thermal chemical vapor deposition (CVD) process using ferrocene and toluene on conducting (cobalt/silicon), semiconducting (silicon) and insulating (quartz) substrates to investigate the change in surface morphology, microstructure and electron field emission properties. The lengths and diameters of the MWCNTs were estimated from the scanning and transmission electron microscopy, revealing that although the lengths were not identical, changing within the range 150-350 μm, there was no significant change in diameter. The I _D/I _G and I _D/I _G' ratios were obtained from Raman spectra and found to be higher at the tip rather than the sidewalls of MWCNTs grown on different substrates. Electron field emission was also higher for the CNTs grown on the conducting substrate, rather than the semiconducting substrate. Turn-on electric fields obtained from the F-N plot were measured as 0.4 V/μm and 0.7 V/μm for CNTs grown on cobalt/silicon and silicon substrate respectively.