EFFECT OF SPECIMEN THICKNESS AND CARBON CONTENT ON THE CARBON PEAK REGION IN EEL SPECTRA

Amorphous carbon films of different thicknesses and combinations of carbon films with CaF2 films of different thicknesses were used to create a standard reference library of EEL spectra. The relationship between the size and shape of the carbon peak region and the low-loss part of the spectrum was determined. The steepness of the background of the C-K edge, the size of the carbon peak and the plasmon shoulder on top of the carbon peak were investigated as a function of the thickness of the films and of the relative amount of carbon after normalization of the zero-loss peak. The minimum at the C-K edge and the maximum of the carbon peak were considered as examples for a modelling of the carbon peak region in different specimens. Methodological aspects which affect the accuracy of the measurement (characteristic lines of the detector, calculation of specimen thickness, method of t/lambda measurement, mass loss, gain change correction, normalization of the spectra, energy resolution) were examined. The results indicate that modelling of the whole carbon peak region, considering its dependence on mass thickness and carbon concentration, should be possible from our standard reference spectra without use of the low-loss region. The use of modelled standard reference spectra for background extrapolation in biological specimens with unknown calcium content is proposed.