also be observed in the absence of adsorbed oxygen
containing species, suggesting that it can be associated
with the defect sites themselves [27,40]. In our
unmilled NiO sample, the ratio between the area of the
lattice oxygen peak and the 531.0 eV oxygen peak is
1.2:1. After the NiO is milled with no additive, the
same two O 1s peaks are present, but the ratio of the
lattice oxygen to the 531.0 eV oxygen peak is 1:1.1,
indicating an increase in defect or adsorbate sites upon
milling (Fig. 3(b)(ii)). When NiO is dry milled in the
presence of carbon, the shape of the O 1s peak changes
such that it can no longer be fitted solely by the states
used to describe unmilled NiO. The peak at 531.1 eV
has a larger FWHM (2.8 eV) as compared to the
unmilled NiO and the NiO milled without any additive.
This is likely due to a greater variety of defect sites
arising on the particles milled with carbon. In addition,
there is a new low binding energy feature centered at
528.5 eV (FWHM = 1.9 eV). This peak has been
observed previously for the early stages of solution
processed NiO film growth [41] and AgO film growth
[42]. In both cases, it is ascribed to a transient oxygen