Field emission characteristics of nano-sheet carbon films deposited by quartz-tube microwave plasma chemical vapour deposition

Nano-sheet carbon films are prepared on Si wafers by means of quartz-tube microwave plasma chemical vapour deposition (MPCVD) in a gas mixture of hydrogen and methane. The structure of the fabricated films is investigated by using field emission scanning electron microscope (FESEM) and Raman spectroscopy. These nano-carbon films are possessed of good field emission (FE) characteristics with a low threshold field of 2.6\,V/$\mu $m and a high current density of 12.6\,mA/cm$^{2}$ at an electric field of 9\,V/$\mu $m. As the FE currents tend to be saturated in a high $E$ region, no simple Fowler--Nordheim (F--N) model is applicable. A modified F--N model considering statistic effects of FE tip structures and a space-charge-limited-current (SCLC) effect is applied successfully to explaining the FE data observed at low and high electric fields, respectively.