Synthesis and field-emission testing of carbon nanoflake edge emitters

Abstract
A nanometer-edged carbon structure [carbon nanoflake (CNF)] has been synthesized on 50–150-nm-diameter nickel arrays. The Ni dot arrays are patterned using a polystyrene nanosphere lithography technique capable of creating arrays of regularly spaced nanometer-diameter structures of Ni. The flake-like morphology was formed by an inductively coupled rf plasma-enhanced chemical vapor deposition system, with H2 as the carrier gas and CH4 as the carbon source. Typical deposition conditions are: substrate temperature of 680 °C, chamber pressure of 70–90 mTorr, overall gas flow rate of 10 sccm, and CH4 concentration in the range of 10%–40%. Scanning electron microscopy (SEM) shows CNF preferentially growing on the Ni dots, with the irregular carbon flakes standing vertically on the substrate. The flake edge widths are ∼10 nm and the interflake spacing on a given Ni dot is on the order of 15–100 nm. Experiments show that the density, height, and interspacing of the flakes are controllable by varying patterning and deposition parameters. The structures show no degradation or vibration under small-spot SEM imaging, indicating good thermal stability. Raman spectra show a typical carbon feature with D and G peaks at 1350 and 1580 cm−1, respectively. Intensity ratio of these two peaks, I(D)/I(G), increases with CH4 concentration. The work function of this structure determined by Kelvin probe measurement is about 4.3 eV, which is near that of graphitic carbon. Preliminary results of I–V curve testing indicate that this structure could act as a conductive, robust, edge emitter.