Plasma Post-Treatment Process-Induced Grain Coalescence to Improve the Electron Field-Emission Properties of Ultrananocrystalline Diamond Films

Plasma post-treatment (PPT) process is an effective way to improve the electron field-emission (EFE) properties of microwave plasma chemical vapor deposited ultrananocrystalline diamond (MP-UNCD) films, while its effects on hot-filament chemical vapor deposited UNCD (HF-UNCD) films were not confirmed. Due to monodispersed Ta atoms existing in HF-UNCD films, PPT process shows different effects on the structure evolution and EFE properties of HF-UNCD films and MP-UNCD films. CH4/N-2 PPT process make diamond grains change from small spherical particles to large plate-like aggregates with lots of stacking faults in HF-UNCD films. This is ascribed to both the CN species in CH4/N-2 plasma, which induces anisotropic growth of diamond and the monodispersed Ta atoms resulted in transition of graphite to diamond, which connect the neighboring nanosized diamond grains to a larger one and produce lots of stacking faults. The charges are easier to accumulate and emitted in the edges of the plate-like diamond and stacking faults have lower negative electron affinity. These lower the turn-on field from 26.3 to 12.7 V mu m(-1). It is different from that of MP-UNCD films, in which only anisotropic growth occurs and forms needle-like diamond due to CN species.

Automated summary

The PPT process has different effects on the structure evolution and EFE properties of HF-UNCD films and MP-UNCD films. In HF-UNCD films, CH4/N-2 PPT process can lead to the enlargement of diamond grains and the generation of stacking faults, resulting in a lower turn-on field. However, in MP-UNCD films, only isotropic growth occurs.