退火时间对硼掺杂纳米金刚石薄膜微结构和电化学性能的影响

采用高分辨透射电镜、紫外和可见光Raman光谱及循环伏安法研究了1000 ℃下退火不同时间的硼掺杂纳米金刚石薄膜的微结构和电化学性能. 结果表明,随退火时间的延长,薄膜中纳米金刚石晶粒尺寸逐渐减小.当退火时间为0.5 h时, 金刚石晶粒尺寸由未退火样品的约15 nm减小为约8 nm, 金刚石相含量增加;当退火时间为2.0 h时,金刚石晶粒减小为2—3 nm, 此时晶界增多,金刚石相含量减少;退火时间为2.5 h时纳米金刚石晶粒尺寸和金刚石相含量又略有上升.晶粒尺寸和金刚石相含量的变化表明薄膜在退火过程中发生了金刚石和非晶碳相的相互转变.可见光Raman光谱测试结果表明,不同退火时间下, G峰位置变化趋势与I_D/I_G值变化一致,说明薄膜内sp²碳团簇较大时, 非晶石墨相的有序化程度较高.退火0.5, 1.0, 1.5和2.0 h时, 电极表面进行准可逆电化学反应,而未退火和退火时间为2.5 h时电极表面进行不可逆电化学反应.退火有利于提高薄膜电极的传质效率, 退火0.5 h时薄膜电极的传质效率最高,催化氧化性能最好.较小的晶粒尺寸、 较高的金刚石相含量以及纳米金刚石晶粒的均匀分布有利于提高电极表面反应的可逆性和催化氧化性能.

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 I_d/I_g 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.