Emerging Electron Microscopy Techniques for Quantum Research

Quantum technologies, and in particular quantum computing, are often heralded foundational to the next Industrial Revolution.¹ The exploitation of quantum effects in devices, such as entanglement and coherences, is being explored to create new devices like quantum sensors, which may offer better detection limits and faster responses than traditional sensing technology.²

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The development of these new technologies necessitates new characterization tools that can capture and quantify the material properties responsible for quantum effects. Electron microscopy has been widely used in materials research, specifically for the development of quantum materials.^3,4

Quantum materials encompass superconductors, topological insulators, 2D materials like graphene, and quantum spin liquids.³

Although all materials exhibit quantum properties to some extent, as they are composed of nuclei and electrons, quantum materials are defined by properties that can only be described by quantum mechanics. This includes phenomena like collective excitations, which can be described by quasiparticles like phonons or skyrmions.⁵

Traditional Electron Microscopy Techniques and Limitations

Traditional electron microscopy techniques include scanning electron microscopy (SEM) and transmission electron microscopy (TEM), where electrons that interact with the sample are imaged.⁴

The primary difference between SEM and TEM lies in the detection of electrons: SEM measures scattered electrons, while TEM captures those that pass directly through the sample.

SEM and TEM are often used in conjunction, as each has distinct advantages. For example, it is easier to image larger sample areas with SEM, but TEM can achieve higher-resolution images.⁵ SEM instruments are typically more cost-effective, with more straightforward sample preparation requirements than TEM—which requires the sample to be sufficiently thin to allow the electron beam to pass through.⁶

There have been various modifications to both SEM and TEM to enhance their applications, such as measuring liquids or performing time-resolved measurements. These adaptations allow researchers to observe how a system interacts with an external stimulus over very short timescales.^7,8

Despite these advancements, one of the biggest limitations of electron microscopy has been the issue of sample damage from the intense electron beams, which made it historically challenging to measure any live biological specimens or more fragile quantum materials.⁹

Applications of Advanced Electron Microscopy in Quantum Materials and Devices

Cryogenic-electron microscopy (cryo-EM) has been a revolutionary advancement in the life sciences. Reduced sample temperatures help minimize electron beam damage, enabling the imaging of new swathes of biological species.¹⁰ Many fragile materials also benefit from being measured at cryogenic temperatures.

Cryo-EM has, therefore, facilitated numerous investigations of quantum materials, including direct visualization of the atomic, electronic, and spin structures, as well as characterization of the lattice structures and the impact of defects or interfaces.¹¹

The power of electron microscopy in materials analysis lies in its outstanding spatial resolutions and the ability to combine with methods for elemental analysis and identification. For many materials, the high spatial resolution of electron microscopies is critical for answering many open questions in the field.

To achieve material design with ‘properties on demand,’ there remains a need for continued research and characterization into the unique structures of quantum materials. This includes exploring structure-function relationships, such as the role of interfaces in van der Waals materials.¹²

Another technique that uses electron microscopy platforms is electron holography, which offers great insights into the properties of quantum materials, including as a direct probe of the electromagnetic fields.¹³ This method uses the interference between a known reference wave and one that has interacted with the sample to reconstruct the signal of interest.

For electron microscopy, electron holography methods offer a route to very high spatial and temporal resolution measurements, which can be challenging with other methods due to the inherent space-charge in the electron beam. Holography is also well-suited to probing quantum mechanical effects, such as coherences in the emitted photoelectrons.¹³

The Future of Electron Microscopy in Quantum Research

Electron microscopy has become a standard, essential technique in all areas of material science. New modalities are continually developed to overcome issues such as electron beam deflection in magnetic samples and other phenomena that can degrade image resolution.¹⁴

The increasing popularity and accessibility of cryo-EM are enhancing quantum materials research by enabling the characterization of more fragile materials.

Other approaches, such as electron holography, look promising for achieving greater spatiotemporal resolutions and probing quantum phenomena. There are also several approaches using more traditional electron microscopy measurements to explore correlations and electron coherence.¹⁵

Quantum materials are utilized across various application areas, from sensing to photovoltaics. While the exploitation of properties such as electron coherence in fields outside of quantum information is still being explored, theoretical predictions suggest these phenomena could be used to control the quantum mechanical properties of materials.

Electron microscopy will undoubtedly play a key role in understanding these mechanisms and advancing our knowledge of quantum materials.

More from AZonNano: What Are Electron Microscopy Grids Made From?

References and Further Reading

1. Senekane, M., Maseli, M., Taele, MB. (2020). Noisy, intermediate-scale quantum computing and industrial revolution 4.0. The Disruptive Fourth Industrial Revolution: Technology, Society and Beyond. doi.org/10.1007/978-3-030-48230-5_9
2. Degen, C. L., Reinhard, F., Cappellaro, P. (2017). Quantum sensing. Reviews of Modern Physics. doi.org/10.1103/RevModPhys.89.035002
3. Keimer, B., Moore, JE. (2017). The physics of quantum materials. Nature Physics. doi.org/10.1038/nphys4302
4. Wang, ZL. (2003). New Developments in Transmission Electron Microscopy for Nanotechnology. Advanced Materials. doi.org/10.1002/adma.200300384
5. Cava, R., De Leon, N., Xie, W. (2021). Introduction: Quantum Materials. Chemical Reviews. doi.org/10.1021/acs.chemrev.0c01322
6. Brodusch, N., Brahimi, SV., Barbosa De Melo, E., Song, J., Yue, S., Piché, N., Gauvin, R. (2021). Scanning Electron Microscopy versus Transmission Electron Microscopy for Material Characterization: A Comparative Study on High-Strength Steels. Scanning. doi.org/10.1155/2021/5511618
7. Ross, FM. (2015). Opportunities and challenges in liquid cell electron microscopy. Science. doi.org/10.1126/science.aaa9886
8. Alcorn, FM., Jain, PK., van der Veen, RM. (2023). Time-resolved transmission electron microscopy for nanoscale chemical dynamics. Nature Reviews Chemistry. doi.org/10.1038/s41570-023-00469-y
9. Nicholls, D., Lee, J., Amari, H., Stevens, AJ., Mehdi, BL., Browning, ND. (2020). Minimizing damage in high-resolution scanning transmission electron microscope images of nanoscale structures and processes. Nanoscale. doi.org/10.1039/d0nr04589f
10. Hattne, J., et al. (2018). Analysis of Global and Site-Specific Radiation Damage in Cryo-EM. Structure. doi.org/10.1016/j.str.2018.03.021
11. Zhu, Y. (2021). Cryogenic Electron Microscopy on Strongly Correlated Quantum Materials. Accounts of Chemical Research. doi.org/10.1021/acs.accounts.1c00131
12. Basov, DN., Averitt, RD., Hsieh, D. (2017). Towards properties on demand in quantum materials. Nature Materials. doi.org/10.1038/NMAT5017
13. Madan, I., et al. (2019). Holographic imaging of electromagnetic fields via electron-light quantum interference. Science Advances. doi.org/10.1126/sciadv.aav8358
14. Nordahl, G., Jones, L., Christiansen, EF., Hunnestad, KA., Nord, M. (2023). Correcting for probe wandering by precession path segmentation. Ultramicroscopy. doi.org/10.1016/j.ultramic.2023.113715
15. Mechel, C., Kurman, Y., Karnieli, A., Rivera, N., Arie, A., Kaminer, I. (2021). Quantum correlations in electron microscopy. Optica. doi.org/10.1364/optica.402693

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