Abstract
Diamond-like carbon (DLC) films are extensively used in various industries due to their superior protective and lubrication properties. However, DLC films including sp2 and sp3 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 sp2-to-sp3 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.
Highlights
Diamond-like carbon (DLC) films are widely used as a surface protective coating for many engineering and scientific devices due to the superior properties including enhanced mechanical strength, chemical inertness, self-lubricity, bio-compatibility, and low fabrication temperature
This study focused mainly on the development of new Raman spectroscopy technique to evaluate and compare the thermal stability of DLC film
It was observed that the type-A DLC film showed a sudden increase of G peak position at the laser power of 1W, which indicates that its sp2 -to-sp3 bond ratio significantly increased between the temperatures of 386.1 and 752.1 ◦ C, while the G peak width of the type-A DLC film experienced a sudden drop at the laser power of 400 mW, which indicated that its sp2 clusters became significantly larger between the temperatures 239.6 and 312.8 ◦ C
Summary
DLC films are widely used as a surface protective coating for many engineering and scientific devices due to the superior properties including enhanced mechanical strength, chemical inertness, self-lubricity, bio-compatibility, and low fabrication temperature. With these excellent properties, DLC films have been applied to the surface of cutting tools, razors, artificial joints, and components of internal combustion (IC) engine, solar panels, aircrafts, spacecrafts, and hard disk drives (HDD) [1,2,3,4,5]. Researchers found that a lubricated DLC film with ester containing oilcan decrease the coefficient of friction to ~0.006 [1].
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