Scientists take first X-ray of a single atom

A team of scientists from Ohio University, Argonne National Laboratory, the University of Illinois-Chicago, and other institutions, led by Professor Saw Wai Hla, has achieved a groundbreaking milestone by capturing the world’s first X-ray signature of a single atom. This remarkable accomplishment has the potential to revolutionize material detection methods.

Since their discovery in 1895 by Roentgen, X-rays have found widespread applications, from medical imaging to airport security screenings. Even NASA’s Mars rover, Curiosity, employs X-ray technology to analyze the composition of Martian rocks. X-rays are particularly valuable in scientific research for identifying materials in a sample. Through advancements such as synchrotron X-ray sources and innovative instruments, the quantity of material required for X-ray detection has significantly decreased over time. Currently, the smallest amount that can be X-rayed is around 10,000 atoms or more, known as an attogram. This limitation arises from the exceptionally weak X-ray signal produced by a single atom, making it undetectable by conventional X-ray detectors. Professor Hla and his research team have now fulfilled the long-standing scientific aspiration of capturing the X-ray signature of just one atom.

“While atoms can be routinely imaged using scanning probe microscopes, X-rays are essential for determining their composition,” explained Professor Hla, who also serves as the director of the Nanoscale and Quantum Phenomena Institute at Ohio University. “We can now identify the precise type of atom, one atom at a time, while simultaneously measuring its chemical state. This breakthrough allows us to trace materials down to the ultimate limit of a single atom, which will have profound implications for environmental and medical sciences. It may even lead to significant breakthroughs that benefit humanity. This discovery will truly transform the world.”

The team’s research, detailed in their paper published in the prestigious journal Nature on May 31, 2023, and featured on the cover of the print edition on June 1, 2023, outlines how they employed a specialized synchrotron X-ray instrument at the XTIP beamline of the Advanced Photon Source and the Center for Nanoscale Materials at Argonne National Laboratory.

To demonstrate their achievement, the researchers selected an iron atom and a terbium atom, both embedded in molecular hosts. In order to detect the X-ray signal of a single atom, the team utilized a custom-made synchrotron X-ray scanning tunneling microscopy (SX-STM) instrument. This instrument combined conventional X-ray detectors with a sharp metal tip positioned extremely close to the sample to collect X-ray excited electrons. The resulting technique, known as SX-STM, relied on X-ray spectroscopy triggered by the absorption of core-level electrons, providing elemental fingerprints and enabling direct identification of the materials’ elemental composition.

Professor Hla likened the obtained spectra to fingerprints, each unique and capable of precisely identifying the material.

“The technique and concept presented in this study have pushed the boundaries of X-ray science and nanoscale research,” commented Tolulope Michael Ajayi, the paper’s first author and a Ph.D. student at Ohio University. “Furthermore, using X-rays to detect and characterize individual atoms could revolutionize research and pave the way for new technologies in fields such as quantum information, as well as the detection of trace elements in environmental and medical research. This achievement also sets the stage for advanced materials science instrumentation.”

(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: Saw-Wai Hla

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

“Over a 12-year period, I have successfully mentored four Ph.D. students from OHIO who focused on the development of the SX-STM method. Our journey has been long, but we have finally achieved the detection of a single atom’s X-ray signature,” Hla shared.

Hla’s research primarily centers on nano and quantum sciences, with a specific focus on understanding the chemical and physical properties of materials at the fundamental level, even down to individual atoms. In addition to capturing the X-ray signature of a single atom, the team’s primary objective was to employ this technique to study the environmental effects on rare-earth atoms.

“We have successfully detected the chemical states of individual atoms as well,” explained Hla. “By comparing the chemical states of an iron atom and a terbium atom within their respective molecular hosts, we observed that the terbium atom, a rare-earth metal, remains relatively isolated and does not undergo changes in its chemical state, whereas the iron atom strongly interacts with its surroundings.”

Rare-earth materials find widespread use in everyday devices like cell phones, computers, and televisions, making them crucial for technological advancements. With this discovery, scientists can now not only identify the type of element but also determine its chemical state. This breakthrough will enable them to manipulate atoms within different material hosts more effectively, meeting the evolving demands across various fields. Additionally, the research team has developed a novel method called “X-ray excited resonance tunneling” or X-ERT, which utilizes synchrotron X-rays to detect how the orbitals of a single molecule align on a material surface.

“This achievement establishes a connection between synchrotron X-rays and quantum tunneling processes, enabling the detection of an individual atom’s X-ray signature. It opens up exciting research avenues, including investigations into the quantum and spin (magnetic) properties of single atoms using synchrotron X-rays,” added Hla.

Apart from Tolulope Michael 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, contributed to this research. Professor Eric Masson, the College of Arts and Sciences Roenigk Chair and Professor of Chemistry, designed and synthesized the rare-earth molecule employed in the study.

Moving forward, Professor Hla and his research team will continue utilizing X-rays to investigate the properties of individual atoms, aiming to further revolutionize their applications for critical materials research and beyond.

Source: Ohio University

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