The electron energy loss spectroscopy (EELS) of pristine (*VO₂) and vacuum annealed samples at low (low T) and high (high T) temperatures represented in the first three graphs. For the fair comparison between the oxidation states, the EELS spectra of VO, VO₂, V₂O₃, and V₂O₅ is extracted from Ref. 30 and illustrated here.