基于X射线光电子能谱定量分析金刚石自支撑膜高温石墨化

Quantitative Analysis on Graphitization of CVD Free-standing Diamond Films at High Temperatures Based on X-ray Photoelectron Spectroscopy

目的针对金刚石红外窗口在高温环境下的石墨化失效问题进行研究。方法使用等离子体电弧发生器对CVD金刚石自支撑膜进行1500～1800℃热冲击实验,双面抛光后,采用光学显微镜、X射线衍射仪(XRD)、拉曼光谱仪、傅里叶变换红外光谱仪(FTIR)对热冲击后的金刚石膜进行表征,着重通过X射线光电子能谱仪(XPS)对键合特征的演变与热冲击温度之间的关系进行分析。结果热冲击后金刚石膜中的石墨主要存在于晶界处,晶界石墨化过程随温度升高而加快,并致使红外透过率损失。在C1s结合能谱峰解析中,对比了一般的双峰拟合与改进的三峰拟合两种方法,通过引入AC成分,解决了双峰拟合中sp^3与sp^2两峰位的结合能差ΔEB不固定的问题。AC成分的出现是由于碳原子没有形成完美的等性sp^3电子轨道杂化方式引起的,主要存在于金刚石膜重构表面以及原子排列紊乱的晶界处,通过对比AC成分与sp^3成分含量之间的固定关系,论证三峰拟合的合理性。根据键合特征演变与红外吸收变化获得的金刚石膜石墨化活化能分别为227 kJ/mol和250 kJ/mol,结果一致性较好。结论晶界石墨化是导致热冲击后金刚石膜红外透过性能损失的主要原因,建立了热冲击温度与红外透过率及sp^2碳含量之间的关系。

The work aims to investigate the failure of the diamond infrared windows at high temperatures due to graphitization. The 1500~1800 ℃ thermal shock test was carried out to CVD free-standing diamond films by plasma arc generator. After double-sides polishing, optical microscopy, X-ray diffraction(XRD), Raman spectroscopy and Fourier transform infrared spectroscopy(FTIR) were used to characterize the diamond films treated by thermal shock. X-ray photoelectron spectroscopy(XPS)was applied to analyze the relationship between the evolution of the carbon bonds and the shock temperatures. After thermal shock, the graphite of the diamond film mainly existed in the boundaries and the graphitization process accelerated as the treating temperature increased and then resulted in the loss of IR transmittance. General two-peak fitting and improved three-peak fitting methods were compared in the deconvolution of C1 s core level. By introducing the AC component, the problem that ΔEB(the difference between the sp^3 and sp^2 peak positions) was not fixed has been solved. The appearance of the AC component, which mainly existed in the diamond film reconstitution surfaces and the grain boundaries where the atomic arrangement was disorder, was caused by the fact that the carbon atoms did not form a perfect equivalent sp^3 electron orbital hybridization. The rationality of the three-peak fitting was demonstrated by comparing the relationship between the percentage of AC and sp^3 component. According to the evolution of bonding characteristics and IR absorption, the estimated activation energies of diamond graphitization were consistent, which were 227 kJ/mol and 250 kJ/mol, respectively. Graphitization along grain boundaries is the main cause for the loss of IR transmittance of CVD diamond films after thermal shock. The relationship between shock temperature and IR transmittance as well as sp^2 carbon content is established.