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 varoius 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 an 10mA/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

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Field electron emission of nanocrystalline diamond films with controllable grain size and graphite content, grown by microwave plasma-assisted chemical vapor deposition using N2/CH4/H2 as precursors, is studied. A bistable current–voltage characteristic is found. Current jumps (“steps”) are observed when a point probe of Mo is used as the anode. However, when the point probe is replaced by a large quartz plate coated with indium–tin–oxide (ITO), emission domains, which consist of many lighting spots, appear on the ITO plate. Bistable behavior may be understood in terms of the negative differential conductance induced instability. Current jumps can be attributed to the generation and elimination of conducting channels. It is suggested that the electron emission from individual diamond nanocrystallites is a switching process. It is noticed that, when the microstructure of the films is uniform enough, the micro-scale switching behavior can even be amplified to macroscale.