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O in CoO, Co3O4 and CoOOH

O-K Edges for different cobalt oxides. The first peak is from O-p/Co-d bonded empty states, so is larger for Co atoms with lower electron counts. The Co formal valences are 2+, 2.667+ and 3+ for CoO, Co3O4 and CoOOH respectively, and the peak increases roughly with the increase in formal valence.

By: Yao Yang

Microscope: Nion UltraSTEM (100 keV)

Energy Resolution: 0.5 eV

Note: The energy axis of the O edge has been calibrated using dual EELS map. 

Ref: Yang, PNAS, 2019, 116, 24425