As a comparison, we also simulated an O1s spectrum with a linewidth of 0.9eV, as shown in Figure and 6d, which can be well fitted by both one peak and two peak models. This poses an important question for the fitting procedure in experiments. Apparently, when Δ B.E.(0.36eV) is much smaller than the experimental linewidth (0.9eV), there is no justification for the kind of deconvolution as shown in Figure and including an additional peak should be avoided unless necessary, to prevent overfitting and overinterpreting the data.