Co metal, CoO, Co(OH)2 and Co3O4 spectra are presented in Figure 1 with spectral fitting parameters given in Table 1 [1]. Fitting parameters for CoOOH from a fit of a digitized spectrum from the recent work of Yang et al.[2] are also presented. As for Fe, the binding energy overlap of the various oxide and hydroxide forms will greatly increase the absolute error in speciation quantitation. However, curve fitting procedures such as those presented here, should be useful for a more meaningful interpretation for a series of similar Co containing samples. A second concern is the overlap of the higher binding energy 2p3/2 multiplet or satellite structures of the various oxides and hydroxides with the metal 2p1/2 peak at 793.1 eV. This overlap, when the metal is present, requires the use of an offset for the higher binding energy background endpoint similar to
that used for Ni as described in reference [3].
Figure 1. Co 2p spectra for (bottom to top) Co metal, CoO, Co(OH)2 and Co3O4.

Table 1. Co 2p3/2 spectral fitting parameters: binding energy (eV), percentage of total area, FWHM value (eV) for each pass energy, and spectral component separation (eV).

Obtaining a pure CoO specimen for analysis is problematic. Initial analysis of a commercial CoO sample showed the surface to be extensively oxidized to Co3O4 even though the bulk powder XRD spectrum showed only CoO. This appears to be a common problem with two published databases [4,5] showing similar Co3O4 oxidized surfaces for CoO. Note: Be forewarned that this has caused some confusion in the literature.

[1] M.C. Biesinger, B.P. Payne, A.P. Grosvenor, L.W.M. Lau, A.R. Gerson, R.St.C. Smart, Appl. Surf. Sci. 257 (2011) 2717.
[2] J. Yang, H. Liu, W.N. Martens, R.L. Frost, J. Phys. Chem C 114 (2010) 111.
[3] M.C. Biesinger, B.P. Payne, L.W.M. Lau, A.R. Gerson, R.St.C. Smart, Surf. Interface Anal. 41 (2009) 324.
[4] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Corp., Eden Prairie, MN, 1992.
[5] B.V. Crist “Handbook of Monochromatic XPS Spectra, Vol. 2 Commercially Pure Binary Oxides” XPS International Inc. (1999) pg 72-78.