Precise Electron Control Enables Single-Atom Imaging and Dynamic Measurement

The manipulation of matter at the atomic level represents a significant challenge in materials science and nanotechnology, with implications for advancements in energy storage and quantum technologies. Achieving precise control necessitates overcoming limitations imposed by sample damage, positional drift and inherent scan distortions within analytical techniques such as scanning transmission electron microscopy (STEM). Researchers at Oak Ridge National Laboratory and the Massachusetts Institute of Technology, led by Kevin M. Roccapriore, Frances M. Ross and Julian Klein, detail a new technique, termed ‘atomic lock-on’ (ALO), which facilitates sub-20 picometre precision targeting of the electron beam in STEM. Their work, published under the title ‘Quantitative electron beam-single atom interactions enabled by sub-20-pm precision targeting’, demonstrates the ability to repeatedly measure weak electron energy loss signals from a single atomic column, even during sample drift, and quantitatively assess electron beam-matter interactions with microsecond resolution, revealing previously unobserved atomic dynamics.

Atomic Lock-On (ALO) represents a significant advancement in material analysis, achieving sub-angstrom precision in targeting individual atoms within layered materials such as monolayer tungsten disulphide (WS₂) and chromium tribromide sulphide (CrSBr). Quantitative measurements demonstrate a targeting accuracy of 28 ± 18 picometres for tungsten atoms in WS₂, exceeding the limitations imposed by sample drift and scan distortions inherent in conventional scanning transmission electron microscopy (STEM). STEM utilises a focused electron beam to scan across a sample, creating an image based on the transmitted electrons, but is susceptible to inaccuracies due to sample movement and distortions in the scanning process.

ALO markedly improves both the speed and dose efficiency of spectroscopic data acquisition compared to conventional raster-scanning methods. It collects equivalent spectroscopic data in approximately 40 times less time, crucially reducing radiation damage to sensitive materials. Electron energy loss spectroscopy (EELS), a technique employed within ALO, analyses the energy lost by electrons as they interact with the sample, providing information about the material’s elemental composition and bonding. By focusing the beam directly onto the atom of interest, rather than scanning a larger area, ALO minimises unnecessary irradiation and preserves the material’s integrity.

Observations utilising ALO reveal dynamic atomic behaviour, including atom ejection and subsequent recapture, atom diffusion across material surfaces, and beam-induced lattice distortions. These observations provide direct insight into the fundamental interactions between electrons and matter. Researchers directly witness the creation of nanopores, tiny holes in the material, through a process akin to atomic ‘blast off’, offering a unique window into material response to focused electron irradiation. These time-resolved observations, captured with microsecond resolution, provide a detailed understanding of atomic-scale processes and open new avenues for controlling material properties.

ALO achieves comparable, and in some instances superior, precision to targeting methods employing Deep Convolutional Neural Networks (DCNNs). DCNNs are a type of machine learning algorithm used to analyse images and identify patterns, and have been applied to electron beam positioning. ALO represents a viable, and potentially advantageous, alternative to these computationally intensive machine learning approaches. The technique’s ability to lock onto a specific atomic location without prior irradiation further distinguishes it from other targeting strategies, simplifying the experimental setup and reducing the risk of damaging the sample.

Researchers now extend ALO’s capabilities to a wider range of materials and explore its potential for deterministic manipulation of individual atoms. Investigations focus on the limits of precision and dose efficiency, and the development of automated routines for target identification and beam locking. Integrating ALO with advanced spectroscopic techniques promises to unlock new insights into the relationship between atomic structure, dynamics, and material properties, ultimately advancing nanotechnology and materials science.

Dynamic atomic processes become observable through time-resolved observations facilitated by ALO, allowing researchers to directly witness atom ejection from lattice sites, subsequent recapture, and diffusion across the material’s surface. The electron beam also induces local lattice distortions and, in some instances, creates nanopores through material removal, providing insights into the fundamental interactions between the electron beam and the material at the atomic scale. These observations offer a unique opportunity to study the dynamic behaviour of atoms and understand how materials respond to external stimuli.