X-ray diffraction phase analyses of thin layers using an electroluminescence detector with different evaluation procedures

The use of an electroluminescence detector (ELD) with high energetic resolution can lead to several times higher X-ray diffraction intensities and to a better peak to background ratio in comparison with a secondary graphite monochromator and a scintillation counter. However the use of ELD in simple operation mode with a single channel analyser showed some disadvantages: For Cu-radiation the K-beta to K-alpha ratio can be reduced only just to 1 - 2 percent, so that K-beta reflections of main phases or strong reflecting lattice planes can disturb the diagram evaluation. Additionally we got a K-alpha reduction to 75 - 80 percent the background was considerably higher compared to the graphite monochromator. For solving this problem a multichannel software version for the ELD system was realised within the APX63 software package, which deals with the superimposing K-alpha and K-beta peaks of the characteristic lines of the X-ray tube. For accurate separation of these peaks an asymmetric Gau ssian profile is used for modelling the peak shape. Start values for the iteration (peak position, peak width) are gained from a pulse height analysis. During measurement a non-linear least square fit is perforated to predict the actual intensity values. This fit consumes no additional computing time because of the multitasking operation between measurement and evaluation processes. The fitting algorithm is insensitive to small drufts of the detector pulse height. Applying the MCA version of the ELD to thin surface layers dense silicon nitride, implanted with Ti, 0, N, were analysed in grazing incidence geometry.