A group of scientists from Ohio University, Argonne National Laboratory, and the University of Illinois-Chicago, among others, led by Ohio University Professor of Physics, and Argonne National Laboratory scientist, Saw Wai Hla, have achieved a groundbreaking feat – capturing the world’s first X-ray signature of a single atom. The U.S. Department of Energy, Office of Basic Energy Sciences has funded this project which could potentially revolutionize the way scientists detect materials.
Since their discovery by Roentgen in 1895, X-rays have been widely used – from medical examinations to security screenings in airports. Even NASA’s Mars rover, Curiosity, has an X-ray device to examine the composition of rocks on Mars. One important use of X-rays in science is to identify the type of materials in a sample.
Over time, the quantity of materials required for X-ray detection has been greatly reduced by the development of synchrotron X-ray sources and new instruments. Presently, the smallest amount of a sample that can be X-rayed is in an attogram, which is roughly 10,000 atoms or more. This is because the X-ray signal produced by an atom is extremely weak, making it impossible to detect with conventional X-ray detectors. Hla says a long-standing goal of scientists to X-ray just one atom has now been achieved.
Hla, who is also the director of the Nanoscale and Quantum Phenomena Institute at Ohio University, said:
“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. Once we are able to do that, we can trace the materials down to the ultimate limit of just one atom. This will have a great impact on environmental and medical sciences and maybe even find a cure that can have a huge impact on humankind. This discovery will transform the world.”
The research team chose an iron atom and a terbium atom, which they inserted in respective molecular hosts, for demonstration. To detect the X-ray signal of one atom, they used a specialized detector made of a sharp metal tip positioned extremely close to the sample to collect X-ray excited electrons. This technique is known as synchrotron X-ray scanning tunneling microscopy or SX-STM and was supplemented with conventional detectors in X-rays. The X-ray spectroscopy in SX-STM is triggered by photoabsorption of core-level electrons, which constitutes elemental fingerprints and is effective in identifying the elemental type of the materials directly.
Hla explained that the spectrums are like fingerprints, each one being unique and able to precisely identify the elemental type of the materials.
“The technique used, and concept proven in this study, broke new ground in X-ray science and nanoscale studies. 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.”
Hla has spent the past 12 years working with Volker Rose, a scientist at the Advanced Photon Source at Argonne National Laboratory, on developing an SX-STM instrument and its measurement methods.
“I have been able to successfully supervise four OHIO graduate students for their Ph.D. theses related to SX-STM method development over a 12-year period. We have come a long way to achieve the detection of a single atom X-ray signature.”
Hla’s study is centered on nano and quantum sciences, with a specific focus on comprehending the chemical and physical properties of materials on an atomic level. The team aimed to achieve the X-ray signature of one atom and use this technique to explore the environmental impact on a single rare-earth atom.
“We have detected the chemical states of individual atoms as well. 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.”
Rare-earth materials play a crucial role in modern technology, from cell phones and computers to televisions and beyond. Scientists can now identify elements’ chemical states and manipulate atoms within different material hosts to meet evolving needs across fields. Furthermore, they have developed “X-ray excited resonance tunneling” (X-ERT), a new method that uses synchrotron X-rays to detect how a single molecule’s orbitals orient on a material surface.
“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 using synchrotron X-rays.”
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 gathering critical materials research and more.
