X-ray photoelectron spectroscopy (XPS or ESCA) curve fitting procedures, reference materials and useful notes are listed here to provide a starting point for the consistent interpretation of XPS spectra. These reference pages contain tips and techniques that are designed to help both the novice and advanced XPS user.
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Titanium
Initial fitting parameters for the titanium 2p peak were developed using averaged binding energy (BE) data and 2p1/2 – 2p3/2 splitting data from the NIST XPS Database[1] (Table 1). As well, data from readily available standard samples (metal, TiO2) [2,3] were used to clarify the peak-widths, splitting (Δ=6.05 eV for Ti(0), Δ=5.72 eV for Ti(IV)) and shapes (asymmetric for the metallic component) (Table 2) [3]. An example of the use of these parameters is presented for a mixed oxidation state titanium-containing sample in Figure 1. Although C 1s set to 284.8 eV can be used as an internal charge correction it is also possible in this case to use the Ti 2p3/2 metal peak set at 453.7 eV or the clearly defined Ti(IV) (TiO2) 2p3/2 peak set at 458.6 eV. This removes the uncertainty associated with charge correcting to adventitious C especially in situations where the adventitious overlayer is not in good electrical contact with the titanium containing species underneath. The Ti 2p1/2 peak for each species is constrained to be at a fixed energy above the Ti 2p3/2 peak. The intensity ratio of the Ti 2p3/2 and Ti 2p1/2 peaks are also constrained to 2:1. The FWHM’s for the metal and Ti(IV) peaks are derived from the standard sample analyses. The FWHM’s for Ti(II) (at a BE of 455.4 eV) and Ti(III) (at a BE of 457.2 eV), which are likely structurally loosely ordered, are constrained to have equal width to each other and are generally slightly broader than the well ordered Ti(IV) oxide peaks [2,3]. A CasaXPS ready (.vms file) of mixed titanium species can be downloaded here. Further information and expanded discussion can be found in reference [3]. Figure 1. Ti 2p spectrum of a heat-treated Ti-apatite composite using peak fittings derived from Tables 1 and 2.Table 1. Literature values (from [1]) for Ti 2p3/2 spectra.Table 2. Spectral fitting parameters for Ti 2p: binding energy (eV), percentage of total area, FWHM value (eV) for each pass energy, and spectral component separation (eV).
Figure 1. Ti 2p spectrum of a heat-treated Ti-apatite composite using peak fittings derived from Tables 1 and 2.
Table 1. Literature values (from [1]) for Ti 2p3/2 spectra.
Table 2. Spectral fitting parameters for Ti 2p: binding energy (eV), percentage of total area, FWHM value (eV) for each pass energy, and spectral component separation (eV).