Scientists just X-rayed a single atom for the first time

A team of US researchers has taken the world’s first X-ray of a single atom.

Although this isn’t an image, it is a huge step down the size chart. Before this, the smallest object that could be X-rayed would be in the realm of attograms – but that is still the size of 10,000 atoms.

“Atoms can be routinely imaged with scanning probe microscopes, but without X-rays one cannot tell what they are made of,” says Argonne National Laboratory physicist, Saw Wai Hla.

“We can now detect exactly the type of a particular atom, one atom-at-a-time, and can simultaneously measure its chemical state.”

“Once we are able to do that, we can trace the materials down to ultimate limit of just one atom.”

As you can see (below on the left) scanning tunnelling microscopy (STM) has been around since the 80s and is specifically made for imaging at the atomic level.

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(Left) An image of a ring shaped supramolecule where only one Fe atom is present in the entire ring. (Right) X-ray signature of just one Fe atom. Credit: Ajayi et al., Nature 2023

But STM can just see the atoms, it’s harder to glean information about them. 

To be able to x-ray just one atom the team started by using the technology from STM. Both STM and the new X-ray system the researchers have used get the tip of the device incredibly close to the surface, and then run a small voltage between the two. Electrons can then tunnel through the vacuum between them in what is called quantum tunnelling.

Then, in the x-ray version, the team beams special synchrotron X-rays from the side to glean information about the atoms themselves.

“This achievement connects synchrotron X-rays with quantum tunneling process to detect 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,” Hla said.

The research has been published in Nature.

In this paper, the team looked specifically at an iron atom and a terbium atom, gaining information about both by using this technique.

“We have detected the chemical states of individual atoms as well,” Hla explained.

“By comparing the chemical states of an iron atom and a terbium atom inside respective 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 surrounding.”

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