Quality Control of DLC Layers

Significance of the Topic

Diamond-Like Carbon (DLC) coatings deliver exceptional hardness, wear resistance and low friction, making them essential for applications in tooling, engine components, medical implants and high-precision devices.

Objectives and Study Overview

This application note presents a rapid, non-destructive method for measuring DLC layer thickness and homogeneity using infrared microscopy. It contrasts traditional ball grinding with interferometric FT-IR analysis and outlines a streamlined workflow for quality control and failure analysis.

Methodology and Instrumentation

Infrared microscopy in reflection mode captures interference patterns generated by multiple internal reflections within the DLC film. The spacing between maxima in the sinusoidal spectral baseline is used to calculate coating thickness. No sample preparation is required, and complex or uneven surfaces can be analyzed directly.

Used Instrumentation

• LUMOS II FT-IR Microscope (Bruker) featuring a motorized stage and large working distance for easy positioning of bulky samples.
• OPUS Spectroscopic Software with integrated layer thickness function for automated evaluation.

Main Results and Discussion

• Interferometric IR measurements provide precise thickness values on flat and curved surfaces, outperforming destructive ball grinding in speed and reliability.
• Automated mapping generates chemical images that visualize thickness distribution and reveal local variations (e.g., from 1.70 µm to 1.76 µm).
• Accurate evaluation requires entering the refractive index of DLC (n = 2.41), a well-established value from literature.

Benefits and Practical Applications

• Non-destructive, contact-free analysis reduces sample damage and operator errors.
• Versatile measurements on complex geometries without extensive preparation.
• Rapid data acquisition and guided workflows support routine quality control and research and development labs.
• Detailed thickness mapping enhances failure analysis and ensures coating consistency.

Future Trends and Possibilities

• Integration of advanced imaging algorithms to improve spatial resolution of thickness maps.
• Development of real-time, in-line monitoring systems for deposition processes.
• Extension of IR-microscopy techniques to other transparent or semi-transparent coatings.
• Combination with complementary methods such as Raman microscopy for comprehensive film characterization.

Conclusion

Infrared microscopy using the LUMOS II and OPUS software offers a robust, efficient solution for DLC layer quality control. Its non-destructive nature, applicability to intricate geometries and rapid mapping capabilities make it a superior alternative to conventional thickness determination methods.

References

No formal literature references were provided in the source document.