Microstructural modification of diamond-graphite nanohybrid films via adjusting deposition temperatures for enhanced electron field emission

Abstract

To achieve enhanced electron field emission, diamond-graphite nanohybrid films are deposited on Si substrates by means of a microwave plasma chemical vapor deposition (MPCVD) reactor. Liquid diethylamine is used as a sole reactive source. An increase of deposition temperature from 730 °C to 830 °C leads to remarkable changes of morphology and microstructure of diamond-graphite nanohybrid films, namely from a typical planar ultrananocrystalline diamond (UNCD) film at 730 °C to a novel nanocrystalline diamond/graphene nanowall (ND/GNW) film at 830 °C. The electrical conductivity of a ND/GNW film is measured to be 762.4 Ω−1·cm−1, while for a UNCD film it is 18.0 Ω−1·cm−1. Moreover, the electron field emission is significantly enhanced on a ND/GNW film. With an applied electrical field of 9.9 V μm−1 its emission current density is 1.6 mA cm−2, 8-time larger than that for a UNCD film. The possible electron emission mechanism is then discussed based on the Fowler-Nordheim theory. This work offers a simple way to alter effectively the microstructures of sp2/sp3 nanohybrid films that benefit greatly to develop carbon-based field emission cold cathodes featuring high performance.