Surface oxidation - oxide film formation on copper alloy materials
In the following figure (a) uniform oxide layer is analyzed by employing inelastic electron backgound analysis method for X-ray Induced O KLL Auger Electron Spectroscopy (XAES) transition. First a 20 Å thick layer is found to match the main peak intensity when assumed that the surface is covered with a uniform oxide layer. At this point inelastic background remains still apart from the reference background. When 68 Å thick oxide layer is applied in the analysis the spectrum background fits well with the reference background, whereas the the main peak intensity remains low. The entire surface is therefore not covered by homogenous oxide layer.
Figure (b) shows that by applying analysis in island mode with 0.65 coverage and 55 Å oxide island thickness a good fit is achieved. As a result, this experiment demonstrates that the XAES O KLL transition along with the inelastic electron background analysis can provide quantitative in depth information about the surface morphology.
Figure (c) shows the experimental Cu LMM XAES signal obtained from the oxidized Cu(100) surface and the fit consisting of Cu, Cu2O and CuO signals as well as Shirley background. Instead of synthetic Gaussian or Lorenzian line shapes our fitting procedure involves the use of experimentally obtained fitting components. Initially sets of component line shape data for Cu LMM, Cu2O LMM and CuO LMM were measured separately from metallic Cu, oxidized Cu2O and oxidized CuO surfaces, respectively. These lineshapes were then utilized as fitting components in data prosessing software (CasaXPS). The relative positions of component line shapes were constrained to reference binding energy values during the fitting process. Relative sensitivity factors (R.S.F.) for various components were obtained from reference peak area ratios.