Formation of ultrananocrystalline diamond films with nitrogen addition

Nitrogen-doped ultrananocrystalline diamond (UNCD) films have been prepared by the microwave plasma jet chemical vapor deposition system (MPJCVD) using a gas mixture of Ar-1%CH4-10%H2 and addition of 0.5–7% nitrogen. This growth process by MPJCVD with 10% hydrogen addition that yields UNCD films compared with those UNCD films produced by MPCVD with a high Ar/CH4 ratio due to the focused microwave plasma jet greatly enhanced the enough dissociation of react gases and formed C2 species with an energetic state at lower argon concentration. The surface morphologies were changed drastically from continuous to rough granular surface with increasing the nitrogen content due to the great rise of CN species in the plasma. The width of grain boundaries composed of sp2-bonded carbon increased with increasing nitrogen content in the films. Moreover, the seldom defects in the UNCD films induced by the addition of nitrogen in the plasma were identified and investigated by using a scanning transmission electron microscope (STEM). The highest nitrogen-doped benefit with a N/C atomic ratio of 3.25% in UNCD films was reached by addition of only 3% N2 in plasma (Ar-1%CH4-10%H2-3%N2), showing the MPJCVD can greatly reduce the used amount of nitrogen in the synthesis of nitrogen-doped UNCD films.