Scientists report world’s first x-ray of a single atom

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When X-rays (blue color) shine on an iron atom (red sphere in the center of the molecule), the electrons in the nucleus are excited. The electrons excited by the X-rays are then tunneled to the detector tip (gray) via overlapping atomic/molecular orbitals, which provide elemental and chemical information of the iron atom. Credit: Saw-Wai Hla

A team of scientists from Ohio University, Argonne National Laboratory, the University of Illinois-Chicago, and others, led by Ohio University physics professor and Argonne National Laboratory scientist, Saw Wai Hla, they detected the world’s first single-atom X-ray SIGNATURE (or SIGNATURE). This groundbreaking result could revolutionize the way scientists detect materials.

Since its discovery by Roentgen in 1895, X-rays have been used in everything from medical exams to airport security checkpoints. Curiosity, NASA’s Martian rover, is also equipped with an X-ray device to examine the material composition of rocks on Mars. An important use of x-rays in science is to identify the type of materials in a sample. Over the years, the amount of materials in a sample required for X-ray detection has been greatly reduced through the development of synchrotron X-ray sources and new instruments. To date, the smallest amount that can be X-rayed of a sample is in attigrams, which is about 10,000 atoms or more. This is because the X-ray signal produced by an atom is extremely weak, such that conventional X-ray detectors cannot be used to detect it. According to Hla, it is a long-standing dream of scientists to x-ray a single atom, which is now being realized by the research team he leads.

“Atoms can be routinely imaged with scanning probe microscopes, but without X-rays you can’t tell what they are made of. We can now detect exactly the type of a particular atom, one atom at a time, and we can simultaneously measure its state.” chemical,” explained Hla, who is also director of the Nanoscale and Quantum Phenomena Institute at Ohio University. “Once we are able to do that, we will be able to trace materials down to the ultimate limit of just one atom. This will have a big impact on environmental and medical sciences and maybe even find a cure that can have a huge impact for humanity. This discovery will transform the world.”

Their article, published in the scientific journal Nature on May 31, 2023, and graces the cover of the print version of the scientific journal on June 1, 2023, details how Hla and many other physicists and chemists, including Ph.D. OHIO students used a purpose-built synchrotron X-ray instrument at the Advanced Photon Source XTIP beamline and the Center for Nanoscale Materials at Argonne National Laboratory.

For the demonstration, the team chose an iron atom and a terbium atom, both inserted into their respective molecular hosts. To detect the X-ray signal of an atom, the research team supplemented conventional X-ray detectors with a specialized detector consisting of a sharp metal tip placed in close proximity to the sample to collect electrons excited by the X-rays with a technique known as synchrotron X-ray scanning tunneling microscopy or SX-STM. X-ray spectroscopy in SX-STM is triggered by electron photoabsorption at the core level, which forms the elemental fingerprints and is effective in directly identifying the elemental type of materials.

According to Hla, ghosts are like fingerprints, each one unique and able to detect exactly what it is.

“The technique used and the concept demonstrated in this study have broken new ground in X-ray science and nanoscale studies,” said Tolulope Michael Ajayi, who is first author of the paper and is doing this work as part of his Ph.D. of research. thesis. “Furthermore, 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 trace element detection in environmental and medical research, to name a few. This The result also paves the way for advanced instrumentation for materials science.”

(Left) An image of a ring-shaped supramolecule in which there is only one Fe atom in the entire ring. (Right) X-ray signature of a single Fe atom. Credit: Saw-Wai Hla

For the past 12 years, Hla has been involved in the development of an SX-STM instrument and its measurement methods together with Volker Rose, a scientist at the Advanced Photon Source at Argonne National Laboratory.

“I was able to successfully supervise four OHIO graduate students on their doctoral theses related to the development of the SX-STM method over a 12-year period. We have come a long way to achieving single-atom X-ray detection signature,” Hla said.

Hla’s study focuses on nano and quantum sciences with an emphasis on understanding the chemical and physical properties of materials at a fundamental level based on a single atom. In addition to obtaining the X-ray signature of an atom, the team’s main objective was to use this technique to study the environmental effect on a single rare earth atom.

“We also detected the chemical states of individual atoms,” Hla explained. “By comparing the chemical states of an iron atom and a terbium atom within their respective molecular guests, we find that the terbium atom, a rare earth metal, is quite isolated and does not change its chemical state while the The iron atom interacts strongly with its surroundings.”

Many rare earth materials are used in everyday devices, such as cell phones, computers and televisions, to name a few, and are extremely important in the creation and advancement of technology. Thanks to this discovery, scientists can now identify not only the type of element but also its chemical state, which will allow them to better manipulate atoms within different host materials to meet ever-changing needs in various fields. In addition, they also developed a new method called ‘X-ray excited resonance tunneling or X-ERT’ which allows them to detect how the orbitals of a single molecule orient themselves on a material surface using synchrotron X-rays.

“This result links synchrotron X-rays with the quantum tunneling process to detect the X-ray signature of a single atom and opens up many interesting research directions, including research into the quantum and spin (magnetic) properties of a single atom using synchrotron X-rays”. Hla said.

In addition to Ajayi, several other OHIO graduate students, including current Ph.D. students Sineth Premarathna in Physics and Xinyue Cheng in Chemistry, as well as Ph.D. in Physics alumni Sanjoy Sarkar, Shaoze Wang, Kyaw Zin Latt, Tomas Rojas, and Anh T. Ngo, currently an associate professor of chemical engineering at the University of Illinois-Chicago were involved in this research. Eric Masson, president of the Roenigk College of Arts and Sciences and professor of chemistry, designed and synthesized the rare earth molecule used in this study.

Going forward, Hla and his research team will continue to use X-rays to detect the properties of just one atom and find ways to further revolutionize their applications for use in critical materials research gathering and more.

More information:
Saw-Wai Hla, Single-atom characterization using synchrotron X-rays, Nature (2023). DOI: 10.1038/s41586-023-06011-w.

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