Well-aligned multiwalled carbon nanotubes (CNTs) were grown by microwave plasma-enhanced chemical vapor deposition using N-2 and NH3 as the carrier gases and CH4 as the carbon source. Iron films with 1-5 nm thickness on silicon substrates acted as catalysts. Scanning electron microscopy revealed that the CNTs grew via the base growth mechanism at a rate similar to100 nm/s. Transmission electron microscopy showed that multiwalled CNTs had a "bamboo" structure, and the smallest CNTs of similar to6 nm in diameter were acquired on 1 nm Fe film. These "smallest" CNTs were comprised of amorphous structure, due to the formation of sp(3) C-H bonds as proven by Fourier transform infrared spectroscopy and electron energy loss spectroscopy, suggesting hydrogen incorporation during growth of CNTs. Without N-2 gas, no CNTs could be grown, while curly CNTs with poor alignment were grown with no NH3. In both cases, high-purity CNTs with no CNx impurities were obtained. Field electron emission revealed that the lowest turn-on and threshold Fields were obtained from the CNTs grown on the I nm thick iron films on silicon substrate, i.e., 3.5 V/mum and 4.5 V/mum, respectively. Under an applied field of 7.5 V/mum. emission current density of 0.63 A/cm(2) can be obtained.