As for the widely reported defect-related peak at ~1eV higher than the O 2-lattice peak, O interstitial (Oi) is a very likely origin. It has been found that Oi and Zn vacancy (VZn) compete for most stable native defect under O-rich conditions, depending on the position of the Fermi level. However, for O atoms around VZn, the local environment is similar to that of bare surface O atoms, which are not supposed to induce positive CLS. Therefore, Oi can be considered as a credible cause for the defect peak. containing a dumbbell configuration Oi in neutral state, which has been proved to be the most stable Oi configuration. Charge analysis indicates that O1 and O2 form a covalent bond, leading to "diatomic molecule", which jointly take the normal O lattice site. The O-O bond length is 1.47 Å, in accordance with previous reports. Figure shows the CLS as a function of distance to Oi atom. As can be seen, O1 and O2 atom contribute to a distinctly higher CLS, which is 1.27 eV and 1.22 eV, respectively. The remaining O atoms have only small shifts and are indistinguishable from one another. Figure illustrates the simulated XPS spectrum, which can be well fitted by two peaks. As a comparison, the fitting result from the single peak model is given in the inset and shows a poorer fit. The derived Δ B.E. is 1.1eV, which is consistent with the observed defect peaks.