Enhancement in Electron Field Emission of Microcrystalline Diamond Films upon Iron Coating and Annealing Processes

Abstract

The electron field emission (EFE) properties of diamond films were markedly improved by Fe-coating and postannealing processes. Transmission electron microscopy examination indicated that the possible mechanism of enhancing the EFE behavior is the reaction of the Fe layer with diamond and the reprecipitation of the dissolved carbon species to form nanographite. Scanning electron micrographs showed that the Fe coating first formed Fe particles at 700 °C and then reacted with diamond, forming iron carbide (Fe3C) at 800 °C. The dissolution and reprecipitation processes occurred simultaneously during the postannealing process at higher temperatures (800–950 °C), which leads to the formation of amorphous carbon when the postannealing temperature is low (800–850 °C) and to that of nanographite when the postannealing temperature is high (900–950 °C). The 900 °C-postannealed diamond films exhibit the best EFE properties, which can be turned on at a field of E0=2.8 V/µm, and attain an EFE current density of Je=21.4 µA/cm2 at 8 V/µm.