Field emission properties of nano-structured carbon films with carbon needles deposited on Si using high-power-density microwave-plasma CVD method

Nano-structured carbon films (NCFs) were fabricated on Si wafer chips with hydrogen–methane gas mixture by creating high-power-density microwave (MW) plasma in a quartz tube with a low-output MW power source. Carbon sheets with many nano-protuberances were complicatedly twisted each other in the center region of the NCF while carbon needles were additionally formed in the fringe region of the NCF. These NCFs yielded field emission (FE) characteristics with the FE current density of 68 mA/cm2 at a macroscopic electric field, E, of 10 V/μm. Since the FE currents tended to be saturated even in a medium E region, no simple Fowler–Nordheim (F–N) model was applicable. A model considering the F–N mechanism, statistic effects of FE tip structures and a space-charge-limited-current effect has been applied successfully to explain all the FE data observed for E < 10 V/μm. It turned out that E-dependent parameters such as the effective total emission area and the effective field enhancement factor should be employed to obtain sufficient quantitative agreements between the model and the experiments.