硫离子注入纳米金刚石薄膜的微结构和电化学性能

Microstructural and electrochemical properties of sulfur ion implanted nanocrystalline diamond films

采用热丝化学气相沉积法制备纳米金刚石薄膜,并对薄膜进行硫离子注入和真空退火处理.系统研究了退火温度对薄膜微结构和电化学性能的影响.结果表明,硫离子注入有利于提升薄膜的电化学可逆性.在800°C及以下温度退火时,薄膜中晶界处的非晶碳相逐渐向反式聚乙炔相转变,致使电化学性能逐渐变差.当退火温度上升到900°C时, Raman光谱和TEM结果显示此时薄膜中金刚石相含量较多且晶格质量较好,晶界中的反式聚乙炔发生裂解;X射线光电子能谱结果表明,此时C-O键、C=O键、p-p*含量显著增多;Hall效应测试显示此时薄膜迁移率与载流子浓度较未退火时明显升高;在铁氰化钾电解液中氧化还原峰高度对称,峰电位差减小至0.20 V,电化学活性面积增加到0.64 mC/cm^2,电化学可逆性远好于600, 700, 800°C退火时的样品.

Nanocrystalline diamond(NCD) films have a composite structure composed of diamond grains and amorphous carbon grain boundaries. Compared with microcrystalline diamond(MCD) films, the NCD film grain boundaries are rich in a large number of p bonds, thus providing conductive channels. Its conductivity is 3-7 orders of magnitude higher than that of MCD, and the surface of NCD film is uniform and dense, and the roughness is lower, so the NCD film is a promising electrode material. In our previous study, microwave plasma chemical vapor deposition was successfully used to prepare n-type sulfur-doped diamond films with good electrical properties. However, the electrochemical properties of sulfur-doped nanocrystalline diamond films have not been studied till now. In the present work, the nanocrystalline diamond films are prepared by the hot-wire chemical vapor deposition. The films are subjected to ion implantation and vacuum annealing. The effects of annealing temperature on the microstructure and electrochemical properties of the films are investigated. The results show that the sulfur ion implantation is beneficial to the improvement of the electrochemical reversibility of the film. When annealed at 800 °C and below, the amorphous carbon phase at the grain boundary in the film gradually changes into the trans-acetylene phase, resulting in a gradual deterioration of electrochemical performance. When the annealing temperature rises to 900 °C, Raman spectrum and TEM results show that the film has more diamond phase content and better lattice quality, and the transpolyacetylene in the grain boundary is cracked;XPS results indicate that the CO bond at this time, C=O bond, and p—p* content increase significantly;Hall test shows that the film mobility and carrier concentration are significantly higher than those of unannealed film. The redox peak in the electrolyte is highly symmetrical,the peak potential difference is reduced to 0.20 V, the electrochemical active area is increased to 0.64 mC/cm^2,and the electrochemical reversibility is much better thanthose of samples annealed at 600 °C, 700 °C, and 800 °C,respectively.