Improved field emission characteristics of nano-structured carbon films deposited on polycrystalline CVD diamond

Nano-structured carbon films were deposited on polycrystalline diamond films grown on Si wafers by means of high-power microwave-plasma chemical-vapour-deposition (MWPCVD) method. Scanning electron microscope images show that the deposited carbon films were composed of wrinkled graphitic nano-sheets with considerably disordered structures and carbon needles on the CVD diamond grains. Field emission (FE) characteristics obtained from such films yielded very high FE currents, being larger than 100 mA/cm2 at a macroscopic electric field of 9.5 V/μm. A possible mechanism of the observed strong FEs is discussed in relation to a modified Fowler–Nordheim (F–N) equation considering field-dependent parameters. Rugged CVD diamond grains played an important role in enhancing the FE current density. These experimental results suggest that some field-dependent effect should be taken into account as well as the surface geometry effect to quantitatively explain the increases in the FE current density observed in the region where no saturation behaviour of the FE current occurred.