For first time, scientists
X-Ray the atom

For the first time since X-rays were discovered in 1895, researchers have successfully performed X-ray spectroscopy to identify the element of a single atom at a time. The achievement takes advantage of improvements to synchrotron X-ray light sources, a type of X-ray produced using a particle accelerator that was invented in the mid-twentieth century. These improvements have increased the resolution of X-rays and reduced the size of the sample needed to identify that sample’s material. Until now however, the smallest usable sample was at least 10,000 atoms. This was because a single atom produces a signal too small to be detectable using X-rays. Therefore, X-rays could not be used to determine the element type of a single atom until now.

The Impact

This work connects synchrotron X-rays to quantum tunneling, a processes that relies on the quantum mechanics of how photons and other particles move. This combination lets researchers simultaneously detect an atom’s element and its chemical state—its ability to react with other elements. The result creates new ways for scientists to study materials. It could be important in applications from environmental studies to medicine to quantum information science.

Summary

Since their discovery in 1895, X-rays have been a key scientific tool. X-ray characterisation requires a large number of atoms, and reducing this quantity has been a long-standing goal for scientists. In this research, scientists showed that X-rays can be used to characterise the elemental and chemical state of just one atom. The research was performed at the XTIP beamline at the Advanced Photon Source and the Center for Nanoscale Materials at Argonne.

Using a specialised tip as a detector, the method detected X-ray-excited currents generated from an iron and a terbium atom coordinated to organic ligands. The X-ray absorption spectra clearly indicated the fingerprints of a single atom of iron and terbium. The researchers characterised the chemical states of these atoms using near-edge X-ray absorption signals, in which X-ray-excited resonance tunnelling (X-ERT) is dominant for the iron atom. The X-ray signal can be sensed only when the tip is located directly above the atom in extreme proximity, which confirms atomically localised detection in the tunnelling regime. The work connects synchrotron X-rays with a quantum tunnelling process and opens future X-rays experiments for simultaneous characterizations of elemental and chemical properties at the single-atom limit. The work was selected as one of the 10 breakthroughs of the year 2023 by Physics World magazine.

Funding

This research was funded by the 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.