High-current-density electron emissions from nano-carbon films fabricated by high-power microwave-plasma chemical vapour deposition

Nano-structured carbon films were deposited on Si substrates by means of chemical vapour deposition with 3.8-kW microwave plasma. It was found from scanning electron microscope images and Raman spectra that the films were composed of nano-structured graphitic sheets with considerable disorder structures. Field emission (FE) characteristics measured from such films yielded high FE currents, being larger than 20 mA/cm2 at a macroscopic electric field of 10 V/μm. Short-term FE characteristics with standard deviations of ≈ 5% were obtained for FE currents of ≈ 0.3 mA/cm2 at 6 V/μm. A possible mechanism of the observed FEs is discussed in relation to a modified Fowler-Nordheim scheme, which considers field-dependent parameters with statistical distributions. Our proposed scheme allows an adequate description of the measured FE data, suggesting an increasing number of the emission sites with increasing the applied voltages in the nano-structured carbon films.