Microstructure and its effect on field electron emission of grain-size-controlled nanocrystalline diamond films

Nanocrystalline diamond films were grown by microwave plasma assisted chemical vapor deposition using N2 and CH4 as precursors. The microstructure of the films such as the diamond grain size, graphite content, and N incorporation, was controlled by introducing a small amount of hydrogen gas (0–10 sccm) in the growth. Effects of the growth parameters on the film microstructure were investigated using transmission electron microscopy, x-ray diffraction, Raman spectroscopy, and secondary ion mass spectroscopy. A surface stabilizing model is suggested to explain the formation mechanism of the uniformly grain size-controlled nanocrystalline diamond. A systematic investigation on the film microstructure and their field electron emission (FEE) property is presented for various films of different diamond grain sizes and graphite contents. It was found that the FEE property highly depended on the diamond/graphite mixed phase structure. Novel field emission properties (1 V/mum emission threshold and 10 mA/cm2 emission current) are obtained by optimizing the growth parameters. A transport-tunneling mechanism is applied to explain the experimental observations. Our results showed that nanocrystalline diamond film can be a very promising cold cathode material for field emission applications.