X-ray microanalysis of multi-elements coatings using Auger formalism: application to biomaterials

For the thickness determination of thin coatings on substrate in scanning electron microscopy using x-ray energy dispersive spectrometry, a method called Auger formalism has been established in our laboratory. It consists of applying a formalism derived from that in the Auger spectroscopy which assumes a linear relationship between the signal intensity emitted by the coating and its thickness. In this paper, a development of the Auger formalism in the case of heterogeneous coatings is presented. Using x-ray energy dispersive spectrometry, this method allows one to determine the atomic concentrations of the elements which composed the coating. The capability of the proposed method is illustrated by two different applications: a Ni-Cu film on titanium alloy substrate (academic specimen) and calcium phosphate film on titanium alloy substrate (prosthetic coating). An iterative procedure established for the proposed method is also presented. The results show that the Auger formalism may now be applied not only to simple coatings for thickness determination but also to the complex ones for concentration determination. And its use does not require the local knowledge of the substrate composition which is not accessible in the Auger spectroscopy.