Probing the Atomic-Scale Internal Phases with the Electron Beam of Multiferroic Domain Walls Formed During Dynamics

Session

EMAG - In-situ EM Techniques & Analysis

Authors

Shelly Conroy (1), Eoghan O'Connell (4), Kalani Moore (3), Lewys Jones (2), Quentin Ramasse (6, 7), Sinéad Griffin (5), Colin Ophus (5)

Affiliations

1. Department of Materials, London Centre of Nanotechnology, Henry Royce Institute, Imperial College London
2. Department of Physics, Advanced Microscopy Laboratory, Trinity College Dublin
3. Direct Electron
4. Max Planck Institute for the Science of Light
5. Molecular Foundry, Lawrence Berkeley National Laboratory
6. SuperSTEM
7. University of Leeds

Keywords

in-situ STEM, in-situ EELS, 4D-STEM, in-situ biasing

Abstract text

Dynamic multiferroic domain wall topologies overturn the classical idea that our nanoelectronics need to consist of fixed components of hardware. To harness the true potential of domain wall-based electronics, we must take a step back from the device design level, and instead re-look at the subatomic internal properties. With recent advances in experimental characterization and theoretical calculation approaches, in the last 5 years reports of non-classic internal structures and functionalities within domain walls have become a common occurrence.^1-3 As the region of interest is at the nanoscale and dynamic, it is essential for the physical characterization to be at this scale spatially and time resolved.

This presentation focuses on using the applied electric field of aberration corrected scanning transmission electron microscopy (STEM) probes to move domain walls, and thus investigate their dynamics while imaging at the subatomic scale. As the STEM probe can be controlled in terms of dose, probe size, direction and speed, a diverse set of experiments is possible without complicated sample preparation. Using a segmented STEM detector (or 4DSTEM CoM experimental set-up) any changes in deflection and thus the changes in polarisation for each domain, can also be investigated with controlled variants in applied field conditions. By controlling the incoming STEM probe direction, parallel domain walls could be moved around to form stable vertex junctions, thus switching from a neutral to charged state. Then in each frame by quantifying the atomic displacement per unit cell using our open-source python based TopoTEM software package,⁴ the local polarisation at these charged topologies can also be monitored. Finally, we will show how changes in band structure can be monitored via ultrahigh energy resolution electron energy loss spectroscopy (EELS) as the domain walls switch from neutral to charge states. By combining the local atomic resolution structure, strain, charge density and band structure measurements we can resolve all the measurable parameters of interest within domain walls and thus start unravelling the fundamental physics governing their formation, dynamics and resulting functionality. We will show that this technique can be used for several different types of multiferroic oxide and oxy halide material systems, such as improper ferroelectric boracites and hyper-ferroelectric lead germanate. 

Acknowledgements:

Conroy acknowledges funding from the Royal Society Tata University Research Fellowship (URF\R1\201318) and the Royal Society Research Fellows enhanced research grant (RF\ERE\210200). Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy, DE-AC02-05CH11231.

References

[1] Z Hong, et al., Nano letters 8 (2022) p. 3533-3539. doi: 10.1021/acs.nanolett.1c0040

[2] K Moore, et al., ACS Appl. Mater. Interfaces 4 (2022) p 5525–5536. doi:10.1021/acsami.1c17383

[3] S Cherfi-Hertel, et al., Nature Comms 8 (2017) doi: 10.1038/ncomms15768

[4] E N O'Connell, et al., Microscopy and Microanalysis 28.4 (2022) p. 1444-1452. doi: 10.1017/S1431927622000435