Effects of annealing time on the microstructural and electrochemical properties of B-doped nanocrystalline diamond films

The effects of annealing time under 1000 ℃ on the microstructural and the electrochemical properties of boron-doped nanocrystalline diamond (BDND) films are investigated by HRTEM, UV and visible Raman spectroscopy, and cyclic voltammetry measurements. The results show that the size of nano-diamond grain in the film decreases with annealing time increasing. When the annealing time is 0.5 h, the grain size decreases from about 15 nm in the unannealed sample to about 8 nm and the content of diamond phase increases. When the annealing time increases to 2.0 h, the diamond grain size decreases to 2-3 nm, and the content of diamond phase decreases with the grain boundary increasing. In the case of annealing time of 2.5 h, the grain size of nano-diamond and the content of diamond phase increase slightly. The variations of nano-diamond grain size and the content of diamond phase indicate that the transformation between the diamond phase and the amorphous carbon occurs under the annealing with different times. The visible Raman spectra show that the G-peak position and the ID/IG value exhibit similar variations with annealing time increasing, revealing that the ordering of the amorphous graphite phase is improved when sp2 carbon cluster increases in number or size. The reactions on the electrode surface are quasi-reversible when the annealing times are 0.5, 1.0, 1.5 and 2.0 h. On the contrary, the reactions are irreversible when the sample is unannealed or annealed for 2.5 h. It is observed that the annealing treatment is beneficial to the improvement of the electrode mass transfer efficiency of BDND film. When the annealing time is 0.5 h, the electrode mass transfer efficiency as well as the ability of catalytic oxidation of BDND film is best. The results suggest that the smaller size of nano-diamond grain, the higher content of diamond phase and the uniform distribution of the nanocrystalline diamond grains are conducible to the improvement of the reaction reversibility on the electrode surface and the ability of catalytic oxidation of BDND films.