Background subtraction: I. General behaviour of Tougaard-style backgrounds in AES and XPS

An analysis is made of Tougaard-style backgrounds for homogeneous materials to show how parameters interact together and comprise the general inelastic scattering background in electron spectroscopy. It is shown that insight is usefully gained by rewriting the Tougaard universal loss function in terms of two parameters, the characteristic energy, E 1, of the exponential decay observed in multiple self-convolutes of the Tougaard universal single loss function, and the centroid energy Ē of the single loss function. Close fits to the measured background may be made over a wide energy range for only one value of E 1 which defines a unique relation between Tougaard’s B and C values but does not give the unique values themselves. For the single value of E 1, the centroid energy Ē may be varied such that the background subtracted spectra range from those shown by Tougaard, where the intrinsic shake-up and losses may constitute two thirds of the peak intensity, to spectra similar to those of Jo in which all of the intrinsic losses are removed. Studies of Al X-ray excited Sc, Cu, Sm and Au photoelectron spectra, each of which has an extensive range of peaks, show that the relative intensities of the peaks are unaffected by the choice of the value of Ē even though the absolute peak areas may change by a factor of 3.