High energy resolution measurements of the density of states at ferrous grain boundaries by EELS
We have measured the onset of the white lines by using three methods for fitting the L3 edge of the white line. We used a Lorentz function superimposed on an Arctan function (to model the fact that the final state of the electron in the atom is a sharp 3d band superimposed on a free-electron-like continuum) and an empirical function composed of the average of all experimental L3 edges (Figure 2). The onset of the L3 edge was set on the empirical function at 10% of the height of the peak. The empirical function was then scaled through a least squares fitting routine to each of the spectra, and the scaled position of the onset was then measured in each case. Figure 3 shows that the resolution in measuring energy shifts of spectral features depends on the fitting method used. The empirical method is the most accurate in measuring energy shifts because it is the best approximation to the experimental L3 edge. This method fails when the shape of the edge changes (i.e. due to excitonic effects) and as such is a test for our initial assumption that excitonic effects play no role in energy shifts at grain boundaries. The measured stability of the McMullan stabilised spectrometer is 30 meV.