Interference Phenomena at Transparent Layers in Glow Discharge Optical Emission Spectrometry

At the performance of depth profiling by glow discharge optical emission spectroscopy (GD-OES) the intensities of optical emission lines of sample and sputter gas elements are measured in dependence on the time of sputtering. Radio-frequency (rf) sputtering extended the field of application to nonconducting samples including transparent layers. For transparent coatings in the thickness range up to some micrometers, oscillations of measured intensities were observed. This behavior is explained by a thin-film interference effect and discussed for three different materials, i.e., SiO2, TiO2, and BaTiO3. As a result, a new procedure for the determination of either layer thickness or refractive index from GD-OES depth profiles is presented. This effect has to be considered for quantitative GD-OES analysis as well.