Tougaard Method Research Articles

Validity of background correction algorithms studied by comparison with theory of synchrotron‐radiation‐excited core levels and their corresponding auger peak intensities

AbstractThe validity of the Shirley, the straight line and the Tougaard methods for background correction of electron spectra is studied under variation of the photon energy by using a synchrotron light source. For C and Ag the intensity ratio of the peak from a photon‐excited core level and the corresponding Auger transition is compared with theory. This ratio is independent of the possible error in photo‐ionization cross‐sections. The deviations are found to increase with increasing photon energy. Possible explanations are discussed in terms of errors in the elastic mean free path and energy dependence of the analyser response function as well as the characteristics of the monochromator. The agreement between theoretical and experimental ratios is better for the Shirley method than for the straight line method and significantly best for the Tougaard method.

Background correction in XPS: Comparison of validity of different methods

AbstractWe investigate the validity of methods for background correction in XPS by comparing determined peak intensity ratios with theory. For Ag, Pt and Au, peaks are considered for which possible errors in the inelastic electron mean free path and in the energy dependence of the analyser response function have minimal influence on the accuracy of the theoretical ratios. The straight line method gives a root‐mean‐square (RMS) deviation from theory of ∼34% and ∼60% when the low‐energy point is selected to lie close to or far from the main structure of the peak respectively. The Shirley method gives an RMS deviation from theory of ∼35%, with only a small change between two sets of considered energy ranges. The Tougaard method gives an RMS deviation from theory of ∼3%, which is of the order of the expected uncertainty due to the combined effects of the level of the apparatus stability and the errors in the ratios of photo‐ionization cross‐sections.

The adsorption of alkanethiols on gold studied quantitatively by XPS inelastic background analysis

Organic films of alkanethiols, CH 3 (CH 2) n-1 SH ( n = 2, 6, 8, 11, 16, 18, 22), adsorbed from solution onto gold surfaces are investigated by quantitative XPS. Application of a recent formalism based on inelastic background analysis (the Tougaard method) to the XPS spectra allows information on the thiol film in-depth distribution to be extracted. For the analysis, a knowledge of the product of the inelastic mean free path λ and the inelastic scattering cross-section K( T) in the thiol film is needed. To examine the influence of the thiol λ K( T) function on the result of the analysis, the “universal cross-section” as well as the λ K( T) value for polyethylene evaluated from REELS spectra are applied in the present analysis. Our results show that the polyethylene λ K( T) function is superior to the universal function in describing the thiol λ K( T) function. In the present analysis of the thiol/gold system an in-depth distribution model assuming uniform overlayer growth with the thickness Δ x depending linearly on n was found to match the actual profile. For n = 22 the fractional thiol coverage of the gold surface is shown to be at least 90%.

The Comparison of the Background Removal Methods in XPS Spectra

The comparison of the background lines obtained from Shirley's method and Tougaard's method was made in different energy ranges of the XPS spectrum. Tougaard's method always showed almost the same background line, even when the analyzing energy range of the spectrum was varied.

XPS study of the penetration and reaction speed of polymer derivatization reagents

Functionalized polymer surfaces were prepared by electropolymerizing substituted phenols and were used to study the penetration depth and speed of reaction of derivatization reagents (trifluoroacetic anhydride and pentafluorophenylhydrazine). Depth information was obtained by angular variations of XPS intensities and lineshape analysis according to Tougaard's method. The penetration of both reagents into the test polymers is rapid but the reaction of pentafluorophenylhydrazine with carbonyl groups is slow.