Effect of N2 addition in Ar plasma on the development of microstructure of ultra-nanocrystalline diamond films

The effect of the N-2 and H-2 addition in Ar plasma on the characteristics of the UNCD films was systematically investigated. It is found that, while the N-2/Ar plasma results in UNCD films with ultra-small grains (similar to 5 nm), incorporation of H-2 into the N-2/Ar plasma increased monotonously the size of the grains. Moreover, the diamond grains synthesized in H-2 free plasma are of equi-axed geometry and those grown in H-2-containing plasma are of plate-like one. The optical emission spectroscopic investigation indicated that the increase in electron temperature due to the addition of H-2 into Ar plasma is the main cause, altering the microstructure of the UNCD films. As the H-2 content increases, the spherical diamond grains first agglomerated to form elongated grains, which coalesce to form dendrite clusters. The proportion of grain boundaries is thus decreased that increased the turn-on field necessary for inducing the electron field emission process. (C) 2009 Elsevier B.V. All rights reserved.