Spatial and temporal resolution limits for techniques used to probe domain structures and dynamics. Note: this is not an all-inclusive list but compares methods discussed in this article. Asterisk denotes recent work on improving PFM spatial and temporal resolution.38,39
BFO device geometry for in situ biasing. (a) Plan view of device looking down the  direction showing the patterned SRO electrodes (green) and BFO trenches between them (blue). (b) A magnified view of the boxed region in (a) which illustrates the direction of the applied electric field, principal crystallographic directions, and the projection of the ferroelectric (arrows) and ferroelastic (rhombi) domains in the BFO trench. (c) Isometric front view of same BFO device. Samples are tripod polished to remove most of the bulk STO and then electron transparent channels are milled underneath the BFO trenches using FIB.
Comparison of a BF TEM images (a) and an in-plane phase PFM image (b), revealing the ability of TEM to probe domains.
A sequence of bright field TEM images taken during in situ biasing of a BFO device structure at +45 V (115 kV/cm). Crystallographic and electric field directions are indicated lower left. “Pre” and “Post,” indicated as t = 0 and t = 5 s, denote the domain morphology before the field was applied and 5 s after the field was turned off, respectively. Images from 166 ms (b) and 566 ms (c) are selected frames extracted from the in situ video. Images (e)-(g) contain colored overlays (color online) to guide the eye in viewing the many changes in domain morphology during switching events.
Domains shown in Figure 4 are grouped into four different regions (a) and the cumulative domain areas in each of the four regions versus time are plotted (b). Region I is comprised of domains (blue highlight) nucleating at the electrode edge and along the network of existing dislocations. Region II includes a larger cluster of nuclei and two smaller, individual nuclei (red highlight). Region III consists of one small nuclei and one larger domain (green highlight). The larger domain in region III has nucleated and propagated off an existing domain wall. Region IV is composed of a single, large domain which has also nucleated and propagated from an already present domain wall (purple highlight).
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