Resolution of complex X-ray photoelectron spectra using past discrete Fourier transformation with improved convergence procedure: Assessment of the usability of the procedure

The use of fast discrete Fourier transformation with improved convergence procedure for the resolution of complex X-ray photoelectron spectra is considered. A single spectral line of the test element is used as the kernel of integral equation (unlike the conventional procedure where the kernel is modeled as a superposition of Gaussian and Lorentz functions); the spectral line is input in the numerical form and takes into account the intrinsic line width and the characteristics and actual line broadening obtained on a particular instrument. As a result, separate spectral Lines are extracted from complex spectra containing several peaks; the integral intensities of these lines correspond to the relative amounts of atoms in different chemical environments that occur in the analyzed surface layer. The results are illustrated with a model C1s spectrum of poly(methyl methacrylate) with different noise levels and with experimental C1s spectra of fructose and citric acid. The procedure proposed does not require the input of a priori data on the number of peaks, approximate positions of peaks in the binding energy scale, and peak amplitudes and can also be useful in other methods, e.g., in IR or Auger spectroscopy.