Evaluation of Thermal Degradation of DLC Film Using a Novel Raman Spectroscopy Technique

Diamond-like carbon (DLC) films are extensively used in various industries due to their superior protective and lubrication properties. However, DLC films including sp(2) and sp(3) carbon bonding are metastable materials, which can be thermally degraded (or graphitized) at elevated temperature. In this study, a novel Raman spectroscopy technique was developed to evaluate the in-situ thermal stability of DLC films. When a laser beam is applied onto a DLC film, the surface temperature can increase depending on the laser power, laser duration time, and surface reflectivity. Based on this laser heating concept, the Raman spectrum data of DLC films (i.e., G peak position and width) were obtained at the controlled Raman laser power, which enabled to determine the critical temperature to initiate the thermal degradation of DLC films. Two different designs of DLC film (i.e., types A and B with different initial sp(2)-to-sp(3) ratio) were prepared and their thermal stability was evaluated using the proposed Raman spectroscopy technique. From the systematic data analysis and comparison, it could be observed that the type-A DLC film showed the significant change of Raman parameters (i.e., G peak position and width) at lower laser power value (=lower temperature) than the type-B DLC film, which indicated that the type-B DLC film had better thermal stability.