Fig. 2

Evolution of the polar vortex structure. a–c PFM images and 3D domain patterns of the same region at 1, 5, and 22 h after poling, respectively. The yellow squares indicate the polarized regions. The red (blue) lines represent the 71o (109o) domain walls. The yellow (light blue) arrows indicate vortex (antivortex) structure. The dotted (dash) arrows mean the OP polarization of the domain is downward (upward)