CH₄/(Ar-H₂) plasma post-treatments produce nano-diamond aggregation and improvement in field emission properties of ultrananocrystalline diamond films

We performed the CH4/(Ar-H-2) plasma post-treatments on ultrananocrystalline diamond films prepared by hot filament chemical vapor deposition. The results show that during the CH4/(Ar-H-2) plasma treatment, 3-5 nm diamond grains agglomerate and regrow, and the graphite between the grains transformed into diamond due to the combined action of hydrogen and tantalum atoms in the samples. This produces bigger diamond grains in size of 200 nm with a large number of stacking faults formed during the grain aggregation, and the graphite phase is greatly reduced. Moreover, the electron field emission (EFE) performance of the films is significantly improved after the CH4/(Ar-H-2) plasma treatment. This suggests that the improved EFE performance is not caused by the graphite phase, but by the diamond grains with lots of stacking faults that provide transport channels for electrons. This provides a method for enhancing the EFE properties of diamond films.