Fig. 1.

Atomic-scale observation of polarization in 2- and 3-u.c. BFO. a Atomic-resolution HAADF-STEM image of 2-u.c. BFO. The scale bar is 2 nm. b Superposition of a magnified image and B-site atomic displacement vector map from the area marked with a white dashed rectangle in a. c Schematic of the unit cell of ferroelectric BFO, D_Fe denotes the relative displacement of the Fe atoms. d HAADF-STEM image of 3-u.c. BFO film. The scale bar is 2 nm. e Superposition of a magnified image and B-site atomic displacement vector map from the area marked with a white dashed rectangle in d. In the insets of b, e, yellow arrows represent the displacement vectors of B-site atoms and white dashed lines are drawn to guide visually. The length and direction of the arrows represent the magnitude and direction of the displacement vectors concerning the scale bar in the upper right corner, respectively. f–j The false-color Bi, Fe, Sr, Ru, and overlaid EDX elemental maps of e, respectively. The scale bar is 0.5 nm