The appropriate background offset is determined using an iterative approach while monitoring a residual plot of the 2p3/2 area. In many cases an offset of the higher binding energy end of the background can be used to improve the fit of the peak shapes. This work has shown that a Shirley background applied across the entire 2p (2p3/2 and 2p1/2) portion of the spectrum works reasonably well (even though fitting of only the 2p3/2 portion of spectrum is carried out). Overlap of the high binding energy satellite structure from Ni(OH)2 (and to a lesser extent NiO) with the 2p1/2 metal peak, which is composed of an asymmetric main peak and contributions from plasmon loss structure, can make the definition of an appropriate spectral background using only the 2p3/2 portion of the spectrum problematic. The absolute binding energy values were allowed to vary by ± 0.1 to 0.2 eV to allow for error associated with charge referencing to adventitious C 1s. The binding energy differences, FWHM and area ratios are constrained for each species. Spectra are fitted with the asymmetric line shape and loss/satellite peaks for Ni metal (Table 1 and Figure 1) and an empirical fit of the NiO and Ni(OH)2 line shapes from parameters derived from standard samples (Table 1 and Figure 2). Curve fitting techniques for nickel species use specified empirical fitting parameters that take into account the unique peak shapes of the various Ni compounds.
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