Quantum Tunneling Enables Single Atom X-Ray Characterization

According to a study published in Nature, researchers have successfully used X-ray spectroscopy to determine the element of a single atom at a time, for the first time since X-rays were discovered in 1895.

The accomplishment makes use of advancements in synchrotron X-ray light sources, a form of X-ray generated by a particle accelerator established in the mid-twentieth century. These advancements have boosted the resolution of X-rays and lowered the amount of the sample required to determine its substance.

Until now, the lowest acceptable sample required at least 10,000 atoms. This is because a single atom emits a signal that is too tiny to be detected by X-rays. As a result, X-rays were previously unable to distinguish the element type of a single atom.

The Impact

This study ties synchrotron X-rays to quantum tunneling, a procedure that uses quantum mechanics to transfer photons and other particles. This combination allows researchers to identify both an atom's element and its chemical state (its ability to react with other elements). The result opens up new avenues for scientists to investigate materials. It might be useful in a variety of fields, including environmental research, health, and quantum information.

Since its discovery in 1895, X-rays have been an important scientific tool. X-ray characterization requires a significant number of atoms, and scientists have long sought to reduce this quantity. In this study, scientists demonstrated that X-rays can be utilized to determine the elemental and chemical state of a single atom. The research was carried out at the Advanced Photon Source's XTIP beamline and Argonne’s Center for Nanoscale Materials.

Using a customized tip as a detector, the approach identified X-ray-excited currents created by an iron and terbium atom coupled to organic ligands. The X-ray absorption spectra clearly showed the fingerprints of a single atom of iron and terbium. The researchers used near-edge X-ray absorption signals to define these atoms' chemical states, with the iron atom dominated by X-ray-excited resonance tunnelling (X-ERT).

The X-ray signal can only be seen when the tip is exactly above the atom in close proximity, confirming atomically targeted detection in the tunneling domain. The study links synchrotron X-rays to a quantum tunneling mechanism, paving the way for future X-ray investigations to characterize elemental and chemical characteristics simultaneously at the single-atom level. Physics World magazine named the work one of the ten most significant accomplishments of 2023.

Funding

Department of Energy (DOE) Office of Science, Office of Basic Energy Sciences, Materials Science and Engineering Division. Work performed at the Center for Nanoscale Materials and Advanced Photon Source, both DOE Office of Science user facilities, was supported by the DOE Office of Basic Energy Sciences. Computing resources were provided on Bebop, a high-performance computing cluster operated by the Laboratory Computing Resource Center at Argonne National Laboratory.

Journal Reference:

Ajayi, T. M., et al. (2023) Characterization of just one atom using synchrotron X-rays. Nature. doi.org/10.1038/s41586-023-06011-w.