Imperial College London

Dr Michele (Shelly) Conroy

Faculty of EngineeringDepartment of Materials

University Research Fellow
 
 
 
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Contact

 

m.conroy

 
 
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Location

 

Royal School of MinesSouth Kensington Campus

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Summary

 

Electron Beam Manipulation of Dynamic Charged Ferroelectric Topologies

Recently there has been a surge in interest of electron‐beam‐based atom‐by‐atom manipulation. Dr. Conroy was the first to report experimentally how the applied electric field of a STEM probe can be used to controllably move ferroelectric topologies.[1] Thus one can investigate the dynamics of these polar entities while imaging at the sub-atomic scale. As the applied electric field of an electron 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 any changes in deflection and thus the changes in polarisation for each domain and DW, can also be monitored with controlled variants in applied Ef conditions. This allows one to study the influence of the surrounding domain patterns and domain wall types (charged and neutral) on the dynamics of charged topologies, Figure 1.

Figure 1. (a) schematic of STEM DPC mapping using a segmented detector, (b) and (c) DPC polarisation mapping of the domains and DWs with changing scan direction of the applied electric field, (d)-(f) domain pattern change with increased dose.

Figure 1. (a) schematic of STEM DPC mapping using a segmented detector, (b) and (c) DPC polarisation mapping of the domains and DWs with changing scan direction of the applied electric field, (d)-(f) domain pattern change with increased dose.

By controlling the incoming STEM probe direction, neutral domain walls can be moved to form charged higher order topologies thus switching from neutral to charged states. Then in each frame by quantifying the atomic displacement per unit cell using our open access TEMUL Toolkit software package [2] the local polarisation at these topologies can also be monitored, Figure 2.

Figure 2. STEM HAADF image of the four fold charged junction formed under the STEM probe.

Figure 2. STEM HAADF image of the four fold charged junction formed under the STEM probe.


We show how the applied electric field of the electron probe is a viable in situ electron microscopy technique providing a new platform for understanding the fundamentals physics of topologically protected quantum state dynamics. Previously thought energetically unfavorable charged junctions can be formed when the applied electric field can be controlled at these sub-atomic dimensions. The new insights required the resolution allowed by aberration corrected STEM due to the 2D nature of the charged domain walls and higher order topologies, reinforcing the idea that advancements in STEM techniques are essential for the progress of quantum information sciences.

[1] Conroy, M., Moore, K., O'Connell, E., Jones, L., Downing, C., Whamore, R., Gruverman, A., Gregg, M. and Bangert, U., 2020. Probing the Dynamics of Topologically Protected Charged Ferroelectric Domain Walls with the Electron Beam at the Atomic Scale. Microscopy and Microanalysis DOI: 10.1017/S1431927620023594

[2] TEMUL Toolkit, https://temul-toolkit.readthedocs.io/en/latest/, 2020. DOI: 10.5281/zenodo.454.3963

In-situ Transmission Electron Microscopy

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In-situ Transmission Electron Microscopy allows for imaging and physical characterization of a sample's response to a stimulus in real time down to atomic resolution. The stimulus can range from applied heat, voltage, changing gases and liquids. Capturing the dynamic changes of samples in these different states of matter allows for microscopy to move beyond just static vacuum studies.

Liquid Cell in-situ TEM:

Dissolution and reactivity of nanomaterials in an aqueous environment is vitally important to a wide range of disciplines including pharmaceutical chemistry, geochemistry, battery science etc. In the image below AlOOH (boehmite) mineral nanoparticles are suspended in water within a liquid cell and imaged by TEM. In-situ TEM imaging reveals that the dissolution of boehmite is in fact a much more complex multi-step process than previously inferred. The electron beam irradiation destabilises the hydrogen bonding mineral inter-layer network resulting in internal delamination of the particle forming 2D exfoliated boehmite nanosheets prior to the complete dissolution. 

Conroy, M., Soltis, J.A., et al. Importance of interlayer H bonding structure to the stability of layered minerals. 2017 https://doi.org/10.1038/s41598-017-13452-7

Liquid cell -situ TEM imaging showing the internal delamination of boehmite nanoparticles.Figure. Liquid cell in-situ TEM imaging showing the internal delamination of AlOOH nanoparticles.

Heating/Annealing in-situ TEM:

Changes in temperature is one of the most important factors affecting the phase and functional behavior of materials. In situ heating TEM is a powerful tool for understanding such temperature effects.

Examples of in-situ heating TEM of functional electronic materials:

In situ heating

Figure. Bright field TEM image of R2 GaN nanorods after (a) ex-situ 900 °C and (b) in situ 900 °C anneal on the 112̅0 zone, d1 red dotted line shows the end point of the dislocation pre thermal anneal and d2 shows the end point of the same dislocation after prolonged thermal anneal treatment.

  • Smith, M. D., O'Mahony, D., Conroy, M., Schmidt, M., & Parbrook, P. J. InAlN high electron mobility transistor Ti/Al/Ni/Au Ohmic contact optimisation assisted by in-situ high temperature transmission electron microscopy. 2015 https://doi.org/10.1063/1.4930880

In situ heating

Examples of in-situ heating TEM of functional energy materials:

  • Jiang, W., Conroy, M., Kruska, K., Olszta, M. J., Droubay, T. C., Schwantes, J. M., ... & Devanathan, R. In situ study of particle precipitation in metal-doped CeO2 during thermal treatment and ion irradiation for emulation of irradiating fuels. The Journal of Physical Chemistry C 2019 https://doi.org/10.1021/acs.jpcc.8b11027

in situ ceria

Figure. In-situ heating and ion irradiation TEM investigation of metallic particle fission product formation in oxide fuels. (Journal cover)

Biasing in-situ TEM:

In-situ biasing TEM allows researchers to do atomic-scale investigations of nano-electronic devices & materials. 

in situ biasing

Figure. STEM HAADF imaging of (a) low resolution FIB lamella welded on to heating and biasing in situ TEM chip, (b), (c) atomic resolution images showing the domain wall.

  • Conroy, M., Moore, K., Lehane, R., Gamero-Quijano, A., Scanlon, M., & Bangert, U. In-situ TEM Investigation of the Amorphous to Crystalline Phase Change During Electrical Breakdown of Highly Conductive Polymers at the Atomic Scale. 2020 https://doi.org/10.1017/S1431927620024149

in situ biasing pedot

Figure. (a) Photograph of glass vial of PEDOT 2D layers suspended in acetone, showing the highly conducting surface, (b) low resolution BF and DF TEM imaging of the amorphous and fibrous nature of the PEDOT layers, (c) optical microscope image of the ex-situ biasing of PEDOT and (d) the PEDOT layer that was scooped onto the in-situ TEM DENS MEMS chips. (e)  BF TEM imaging during in-situ biasing of phase change from amorphous to crystalline nanoparticles.