Fig. 1: Static electron diffractions of VO₂ by TEM.

a Schematic layout of the VO₂ films for UED experiments. STO represents SrTiO₃(111) which is used as substrate and buffer layer. SAO represents Sr₃Al₂O₆ which is used as sacrificial layer. SAO can be etched by water indicated by black arrows. b Crystal structures of VO₂ in the R phase and M₁ phase. Only V atoms are presented. Red solid lines in the M₁ phase represent V–V dimers. Hexahedrons with black lines are the unit cells. c Static electron diffraction pattern measured at 300 K by TEM. The incident electron beam is along [010] direction of VO₂. d Simulated TEM diffraction pattern in the M₁ phase with three domains and twinning. Red/green/black colors represent the contributions from three 120° domains, respectively. For convenience, we use smaller dots to present the superstructure spots. The subscript “T” means the contribution from a twin domain.