P. Jiricek

On line shape analysis in X-ray photoelectron spectroscopy

Abstract Any solid state X-ray photoelectron spectrum (XPS) contains contributions due to multiple inelastic scattering in the bulk, surface excitations, energy losses originating from the screening of the final state hole (intrinsic losses), and, for non-monochromatized incident radiation, ghost lines originating from the X-ray satellites. In the present paper it is shown how all these contributions can be consecutively removed from an experimental spectrum employing a single general deconvolution procedure. Application of this method is possible whenever the contributions mentioned above are uncorrelated. It is shown that this is usually true in XPS to a good approximation. The method is illustrated on experimental non-monochromatized MgKα spectra of Au acquired at different detection angles but for the same angle of incidence of the X-rays.

Surface excitation effects in elastic peak electron spectroscopy

Abstract Surface electron inelastic excitations, a consequence of electron–surface interaction, effect the measured intensities in surface-sensitive electron spectroscopic methods and distort the quantitative information. This phenomenon is more pronounced at low electron energy and glancing emission angles. In this work we investigate quantitatively the influence of the surface excitation effects on the measured electron elastic backscattering probability. As a model system we used Si, Cu and Al, i.e. materials with different surface excitation properties. Results obtained show that properly corrected measured elastic electron backscattering probabilities lead to inelastic mean free path values which compare well with the theory.

Determination of the inelastic mean free paths of electrons in copper and copper oxides by elastic peak electron spectroscopy (EPES)

Theoretical values of the inelastic mean free path (IMFP) and their electron-energy dependence are available in tbe literature from predictive formulae for various categories of materials, such as elemental solids, inorganic and organic compounds. in contrast, the experimental IMFP values were determined for a more limited number of materials. This refers especially to multicomponent solids. We have measured the IMFP dependence on energy for Cu and two copper oxides, CuO and Cu 2 O, using elastic peak electron spectroscopy. The experiment consisted of measuring the backscattering probabilities for the investigated materials and an Ni standard in the energy range 400-1600 eV. The IMFP values were determined using a theoretical model describing the phenomenon of elastic backscattering. The IMFP values determined in this work are in reasonable agreement with experimental and theoretical values published in the literature.

Elastic Electron Backscattering from Surfaces at Low Energies

A novel experimental method, involving reverse-view LEED optics, is proposed for simultaneous determination of the angular distribution of elastically backscattered electrons and the energy dependence of elastically backscattered intensity. Extensive measurements in the energy range 50–500 eV were performed for Al, Cu, Pt and Au. The experimental energy and angular dependences of the backscattered intensity were found to compare very well with results of Monte Carlo simulations performed in the energy range considered. This indicates that the procedure of determining the inelastic mean free path from the elastically backscattered intensities can also be used in the low electron energy region. The performance of theory is somewhat worse in the case of aluminium, and thus the use of this metal as standard is not recommended.

Determination of the electron inelastic mean free path in polyacetylene by elastic peak electron spectroscopy using different spectrometers

Abstract The inelastic mean free path (IMFP) values for organic materials are very limited. Numerous data have been published mainly for elemental solids, binary alloys and semiconductors. Generally, the IMFP values for different energies can be determined from the theoretical models involving the optical data, from predictive formulas, and from the experimental method called the elastic peak electron spectroscopy (EPES). In the present work the IMFPs in N–(CH)x polyacetylene (unstretched), synthesised according to Naarmann and Theophilou, and this polyacetylene doped with Pd were determined. The IMFPs energy dependence for the above samples has been obtained from the EPES in the primary electron energy range of 200–5000 eV. The experimental data have been recorded using three different spectrometers and compared with the theoretical data available.

Inelastic mean free path measurements of electrons near nickel surfaces

The inelastic mean free path of electrons near solid surfaces is a key parameter in quantitative analyses by commonly used surface-sensitive methods. There are experimental and theoretical methods to determine reliable inelastic mean free path values. The elastic peak electron spectroscopy method allows the determination of the inelastic mean free path values in agreement with the ASTM definition. This method is based on a theoretical relationship between elastic backscattering probability and the inelastic mean free path. In the present contribution, we study statistical and systematic uncertainties of the measured backscattered intensities from Ni foils prepared by rolling and cutting of the bulk material and of annealing. Depending on the sample preparation, the measured intensities vary by a factor of 2 for 200 eV electron energy, whereas at >1000 eV the deviations are much smaller. This behaviour, explained by the different surface morphology and different grain sizes, has an important impact on measured inelastic mean free path values. Investigation of Ni foils is of a great interest due to frequent use of this metal as a standard material in the elastic peak electron spectroscopy method.

Measurements of the escape probability of photoelectrons and the inelastic mean free path in silver sulphide

The escape probabilities of S 2s and S 2p photoelectrons leaving an Ag2S surface in a direction parallel to the photon flux and the inelastic mean free path values in the range 200-1600 eV have been determined experimentally. The escape probability as a function of depth of origin for the S 2s photoelectrons exhibits non-monotonic behaviour, with a maximum at a depth of 0.6-0.8 nm. In contrast, the escape probability of the S 2p photoelectrons leaving the surface in the same direction can be approximated by an exponential function. The inelastic mean free path values determined by elastic peak electron spectroscopy agree well with the values resulting from the G1 predictive formula of Gries.