Modelling of Glow Discharge Optical Emission Spectroscopy depth profiles of metal (Cr,Ti) multilayer coatings

The broadening effects found in the depth profiles of abrupt periodic multilayers obtained by Glow Discharge Optical Emission Spectroscopy (GDOES) have been modelled by assuming that the resulting absolute concentration profiles can be described by Gaussian functions of constant area (equal to that of the cross section of the individual layers) and decreasing amplitude. The full width at half maximum (FWHM) of these functions has been assumed to increase with depth z according to a power law of the type: FWHM (z) = a + bzc, using for a and c, values estimated from previous works. In this model, the parameter b, defining the broadening and degradation of the layer interfaces, is obtained by fitting the experimental profiles with the theoretical spectra. We have found a correlation between b and the erosion rate of the material layers. In general, the model properly describes the depth profiles of multilayer structures made of alternating Ti and Cr layers in the nanometre range, and can be an useful tool to explain the profiles of more complex systems.