A Single Atom’s X-Ray Signature Has Been Recorded for the First Time

Scientists have measured the X-ray signature from a single atom for the first time. The effort was published in Nature and was authored by a multi-center team including researchers from Ohio University, Argonne National Laboratory, the University of Illinois-Chicago and others. The study could have a huge impact on how scientists detect the chemical makeup of materials.

Stuck at the attogram

X-rays are used in a multitude of fields – from scanning broken bones to detecting security risks at airports. In scientific research, X-rays are used to analyze the properties of materials. Advances in analysis instrumentation, such as the advent of the X-ray synchrotron, have decreased the sample size required to produce an accurate reading. Currently, the smallest quantity of a substance required for X-ray analysis is an attogram – which is roughly 10,000 atoms or more. The new advance represents a step change in our detection abilities.

Until now, the attogram limit has existed due to the weakness of the X-ray signal produced by smaller atomic quantities. Saw Wai Hla, a researcher at Argonne National Laboratory and a professor of physics at Ohio University, said that scientists have long targeted a technique to image smaller numbers of atoms. “Atoms can be routinely imaged with scanning probe microscopes, but without X-rays, one cannot tell what they are made of. We can now detect exactly the type of a particular atom, one atom at a time, and can simultaneously measure its chemical state,” said Hla.

To limbo under this physical barrier, Hla and team used a custom-built X-ray synchrotron housed at the Center for Nanoscale Materials at Argonne National Laboratory.

Elemental fingerprints

In the paper, the researchers showed off their technique by characterizing the signals from an iron and a terbium atom. The researchers added a specialized detector to conventional X-ray equipment. This bonus scanner featured a sharp metal rod placed immediately next to the sample. The rod’s extreme proximity allowed it to hoover up excited electrons produced when the sample was scanned. This method is called synchrotron X-ray scanning tunneling microscopy or SX-STM. The energy emitted by the atoms is tied to their core physical properties, meaning that they represent unique elemental “fingerprints”, allowing the atom to be identified.

When X-rays (blue color) illuminate an iron atom (red ball at the center of the molecule), core-level electrons are excited. X-ray excited electrons are then tunneled to the detector tip (gray) via overlapping atomic/molecular orbitals, which provide elemental and chemical information about the iron atom. Credit: Saw-Wai Hla

“The technique used, and concept proven in this study, broke new ground in X-ray science and nanoscale studies,” said Tolulope Michael Ajayi, a PhD student and the study’s first author. “More so, using X-rays to detect and characterize individual atoms could revolutionize research and give birth to new technologies in areas such as quantum information and the detection of trace elements in environmental and medical research, to name a few. This achievement also opens the road for advanced materials science instrumentation.” 

A rare discovery

The team then went on to characterize how the atoms were affected by being stored inside different molecular hosts. “We find that the terbium atom, a rare-earth metal, is rather isolated and does not change its chemical state while the iron atom strongly interacts with its surroundings,” said Hla.

The applications of this new knowledge span many fields. Rare-earth metals like terbium are key components of everyday devices like TVs and phones, but also in advanced technology like lasers and aerospace alloys. The new findings will allow scientists working with these materials to better understand how their chemical properties are modified by their environment, which should open up even more potential uses for these elements.

Additionally, the team devised a novel technique called X-ray excited resonance tunneling (X-ERT). This method enables the detection of lone molecular orbital orientations on a material surface using synchrotron X-rays.

“This achievement connects synchrotron X-rays with the quantum tunneling process to detect the X-ray signature of an individual atom and opens many exciting research directions including the research on quantum and spin (magnetic) properties of just one atom using synchrotron X-rays,” said Hla.

Hla concluded, “This will have a great impact on environmental and medical sciences and maybe even find a cure that can have a huge impact for humankind. This discovery will transform the world.”

Reference: Ajayi TM, Shirato N, Rojas T, et al. Characterization of just one atom using synchrotron X-rays. Nature. 2023;618(7963):69-73. doi:10.1038/s41586-023-06011-w

This article is a rework of a press release issued by Ohio University. Material has been edited for length and content.