Figure 1: Phases of VO₂.

(a) Crystal structures of different VO₂ phases with the corresponding band structures. Left of panel: metal rutile phase, Middle of panel: insulating monoclinic (M1) phase, Right of panel: intermediates of metal-like monoclinic (M1*) phase with the proposed band diagram from ref. 20. (b) Room temperature optical images of the AA-treated VO₂ nanobeams with increasing treatment time, showing the phase evolution. The treatment time from left to right is: 0, 1, 3, 5 and 8 h. The stabilized M1* lies between R and the M1 host. (c) Schematic of the phase transition induced by AA treatment. The portion marked in the red rectangular frame is the M1* phase with high-density itinerant electrons.