Layer Thickness Measurements on semitransparent Materials
The quality of protective or design coating must be constantly controlled during the coating process, in order to ensure the functionality of the layers and thus to comply with the required properties. The testing of samples from the ongoing production process can be performed as random sampling or as on-line measurement.
By illuminating optically transparent layers with white light, interference spectra are created, which reveal information about the thickness of the layer.
Calculation of Layer Thickness by Interference Pattern Analysis
Different from colors, which produce a spectrum with direct information about their wavelength profile, semi-transparent materials generate a colorful interference pattern, when light is reflected from its top and its bottom boundaries. The interference pattern reveals parameters such as peak maximum, inflection point and intervals, from which the thickness of the semi-transparent layer can be calculated with accuracy in nanometer range.
This procedure is absolute non-destructive and is suitable in particular for shiny metallic surfaces, on which semi-transparent coatings are applied for hardening or corrosion protection. This microscope spectroscopy method can also be applied for glass- and synthetic surfaces, if these materials show enough optical differences in their diffraction properties.
Interference pattern of a semi-transparent diamond like carbon (DLC) layer recorded in NIR range (Blue: fitted curve. Red: measured curve.)
Using a mathematic algorithm (developed by W. Theiss Hard- and Software) the layer thickness is calculated
Further Application Examples:
- Examination of thermal insulation coatings on glass
- Homogeneity evaluation on plasma polymer coatings for hardening of components
- Production of TFT displays