Researchers at the Faculty of Physics, University of Vienna, have discovered a method to create single atomic vacancies in the atomically thin insulator hexagonal boron nitride (hBN) using a scanning transmission electron microscope (STEM) under ultra-high vacuum conditions. This breakthrough, detailed in the journal Small, could have significant implications for applications in quantum computation, information networks, and sensors.

Transmission electron microscopy is a powerful tool for visualizing atomic structures and material defects. However, the electron beam used in this technique can also cause damage to the structure. Additionally, residual gases in the vacuum environment can contribute to further damage by etching away atoms. Previous studies on hBN were conducted under poor vacuum conditions, leading to rapid damage and hindering the controllable creation of vacancies.

The researchers at the University of Vienna overcame these challenges by employing aberration-corrected STEM in near ultra-high vacuum conditions. They irradiated the hBN material at various electron-beam energies and observed the resulting damage rates. At lower energies, damage occurred significantly slower than previous measurements under poorer vacuum conditions. By manipulating the electron energies, the researchers created single vacancies in both boron and nitrogen atoms, with boron being twice as likely to be ejected due to its lower mass. The findings also suggest that nitrogen vacancies can be selectively created by adjusting the electron energies, potentially enabling the controlled production of vacancies that emit single photons.

The study relied on meticulous experimental work and the development of new theoretical models. Lead author Thuy An Bui spent significant time collecting data at different electron energies. Machine learning techniques were employed to analyze the data accurately. The research team also developed an approximate model combining ionization and knock-on damage to understand the mechanism of vacancy creation and extrapolate to higher energies.

The study revealed that monolayer hBN exhibits unexpected stability under electron irradiation when chemical etching is prevented. This allows for purposefully creating specific vacancies that emit single photons by selectively irradiating desired lattice sites with a focused electron probe. Furthermore, as demonstrated previously in impurity atoms in graphene and bulk silicon, the ability to manipulate atoms with atomic precision may also be extended to hBN.

This research showcases the potential for advancing the field of quantum technologies by harnessing the properties of single photons emitted from defects in hBN. By controlling vacancies using STEM, scientists can explore novel applications in quantum computation, information networks, and sensors. The findings also highlight the importance of combining experimental techniques with theoretical models to comprehensively understand defect creation and manipulation in materials.

References

• Bui, T. A., Leuthner, G. T., Madsen, J., Monazam, M. R. A., Chirita, A. I., Postl, A., Mangler, C., Kotakoski, J., & Susi, T. (2023). Creation of single vacancies in hbn with electron irradiation. Small, 2301926. https://doi.org/10.1002/smll.202301926
• University of Vienna. (2023, June 14). Single-atom vacancies in atomically thin insulators created in ultra-high vacuum. Phys.org; University of Vienna. https://phys.org/news/2023-06-single-atom-vacancies-atomically-thin-insulators.html