The simultaneous -fitting method is an excellent tool for discriminating overlapping peaks. The method optimally extracts the information contained in a set of spectra obtained at, e.g., different angles. Under this method, various spectra are fitted all together and the algorithm finds a unique set of peak parameters that minimizes the fitting error for all the data. This contrasts with the sequential or traditional method in which a set of parameters is assessed for each spectrum.
More details can be found in the document below or in J. Electron Spectrosc. Relat. Phenom. 184 (2012) 533.
The figure (a) shows the fit to six O 1 s spectra employing simultaneous-fitting. The data corresponds to a silicon wafer with a layer of silicate and a layer of hafnia obtained at six different angles. Each spectrum contains two peaks, one corresponding to oxygen in silicate and the other to oxygen in hafnia. While the center and width of the peaks of each species are the same among the various spectra, the height (area) changes. The latter is indicated in figure (b).
The simultaneous-fitting method allows for a robust deconvolution of these entangled peaks, so the O 1 s peaks associated to hafnia and to silicate can be clearly identified. In turn, this allowed for a meaningful assessment of the electron take-off angle dependence of the area of the peaks. If the traditional method had been employed, the take-off angle dependence would have been much more disperse.