Determination of the thickness of metal coatings on granular diamond materials by spatially resolved optical methods

The embedding of surface-modified granulates into metallic matrices is a promising way to optimize the interface matrix/granulate in respect to mechanical and thermal properties. In the case of surface modification by coating, a reliable determination of the coating thickness on granulates is desirable, since the interface properties may depend on it to a critical extent. This paper proposes a simple method to determine the thickness of transparent metal coatings on diamond substrates. Diamond granulates with grain sizes between 100 and 120 μm were coated with molybdenum in an intermixing device which allows reasonable film uniformity on granulates. The deposition method was single source DC magnetron sputtering with argon as working gas. By comparing the transmission of the uncoated and coated diamonds with an optical scanner, the coating thickness could be determined from the known extinction coefficient. A good correlation between the measured film thicknesses and the deposition time was achieved. It can be concluded therefore, that the presented method is a viable and cost-efficient way for the determination of the average thickness of transparent metallic coatings on a sample of transparent granular substrates, with an estimated minimum and maximum measurable thickness of 2.5 nm and 15 nm respectively for molybdenum.