Incredible milestone: World's first X-ray of single atom reported

The previous benchmark for the smallest amount that can be X-rayed was 10,000 atoms, and in comparison, this achievement is disruptive.
Tejasri Gururaj
First-ever X-ray of a single atom
First-ever X-ray of a single atom.

Saw-Wai Hla/Nature 

The world's first X-ray of a single atom is here, and how.

A new study by scientists from the Argonne National Laboratory at Ohio University and the University of Illinois-Chicago revealed the mind-blowing image of the properties of a single atom, using just the X-ray technique, a press release stated.

Since X-rays were discovered in the late 1800s, they have been an essential tool in many fields. Their ability to penetrate matter makes them very useful for imaging purposes in medicine, material research, archaeology, and astrophysics. X-rays are a type of electromagnetic radiation having very high energy and short wavelength. 

Traditional X-ray detection techniques, however, rely on the interaction of X-rays with many atoms in a sample to generate a detectable signal. This is because the signal produced by a single atom is weak and difficult to distinguish from background noise.

The previous benchmark for the smallest amount that can be X-rayed was 10,000 atoms, and in comparison, this achievement is groundbreaking. It could potentially revolutionize how scientists and researchers detect materials.

Taking an X-ray of a single atom

The team chose an iron and a terbium atom to take the single-atom X-ray. 

Conventional X-ray detectors were modified using a sharp metal tip, in combination with a synchrotron X-ray scanning tunneling microscopy (SX-STEM), primarily used for nanoscale imaging and characterization of materials, to detect the X-ray-excited electrons from the individual atoms.

In simple terms, SX-STM enables scientists to use X-rays to see the elements within a material and understand its chemical makeup. This is done by exciting (or giving energy) to the electrons in the core of an atom. When these electrons absorb the X-rays and get excited, they produce a unique fingerprint. This fingerprint, called an absorption spectrum, helps scientists to identify the type of elements present in the material being studied.

The team found that the X-ray absorption spectra revealed unique fingerprints corresponding to the iron and terbium atoms.

Characterizing the chemical states of the atoms

The team additionally used X-ray-excited resonance tunneling (X-ERT) to characterize the chemical states of the atoms. They found that the X-ERT for the iron atom was dominant, revealing information about the atom's reactivity and interactions. 

Interestingly, the researchers noticed that the X-ray signal could only be detected when the specialized tip was placed in extreme proximity to the atom. This confirmed that the detection was highly localized and focused on the atom of interest, allowing for detailed characterization and analysis of the atom's properties and behavior.

"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 Professor Saw Wai Hla the lead researcher, in a press release.

Their research was published in the journal Nature.

Study Abstract:

Since the discovery of X-rays by Roentgen in 1895, its use has been ubiquitous, from medical and environmental applications to materials sciences. X-ray characterization requires a large number of atoms and reducing the material quantity is a long-standing goal. Here we show that X-rays can be used to characterize the elemental and chemical state of just one atom. Using a specialized tip as a detector, X-ray-excited currents generated from an iron and a terbium atom coordinated to organic ligands are detected. The fingerprints of a single atom, the L2,3 and M4,5 absorption edge signals for iron and terbium, respectively, are clearly observed in the X-ray absorption spectra. The chemical states of these atoms are characterized by means of 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 localized detection in the tunnelling regime. Our work connects synchrotron X-rays with a quantum tunnelling process and opens future X-rays experiments for simultaneous characterizations of elemental and chemical properties of materials at the ultimate single-atom limit.

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