(Nanowerk News) In the world’s most powerful X-ray facility, scientists can analyze samples so small as to contain only 10,000 atoms. The smaller size has proved extremely difficult to achieve, but a multi-institutional team has brought it down to one atom.
“X-rays are used everywhere, including security scanning, medical imaging, and basic research,” said Saw Wai Hla, physicist at the US Department of Energy’s (DOE) Argonne National Laboratory and professor at Ohio University. “But since the discovery of X-rays in 1895, scientists have not been able to detect and analyze just one atom. It’s been a dream of scientists to be able to do it for decades. Now we can.”
As recently announced Natural (“Characterization of just one atom using synchrotron X-rays”), scientists from Argonne and several universities reported being able to characterize the elemental types and chemical properties of just one atom using X-ray beams. This new capability will impact fundamental research in multiple disciplines and the development of new technologies.
The results of the X-ray beam produce a kind of fingerprint for the types of elements in a material. For example, NASA’s Curiosity rover collected a small sample of sand on the surface of Mars, then determined by X-ray analysis that its content was similar to the volcanic soils of Hawaii.
Using powerful X-ray machines called synchrotron light sources, scientists can analyze samples as small as a billionth of a billionth of a gram. The sample contains about 10,000 atoms. Smaller sizes proved extremely difficult to achieve, but in an astonishing leap, the team managed to scale down their observations to a single atom.
“The word transformative gets talked about a lot, but I believe this discovery is truly a major breakthrough,” said Hla. “I am so excited I can barely sleep at the thought of possible uses in the development of batteries and microelectronic devices and even in environmental and medical research.”
In order to characterize only one atom with X-rays, it is necessary to isolate it from the same type of atoms. To do so, the team first intertwined a single iron atom in nanometer-sized molecules made up of various elements.
They then took samples for analysis with a strong X-ray beam at an Argonne light source, the Advanced Photon Source (APS). The team detected single atoms in samples on a beamline (XTIP) shared by APS and the Center for Nanoscale Materials (CNM). Both are user facilities of the DOE Office of Science in Argonne. The beam line includes a scanning tunneling microscopy (STM) probe.
“The DOE Early Career Research Program Award I received in 2012 allowed me to assemble a passionate team of scientists and engineers to develop the microscopy techniques used in this research,” said Volker Rose, physicist at APS and at CNM. “Together, we developed and manufactured this one-of-a-kind microscope on the XTIP beamline thanks to additional funding from DOE.”
A rush of photons from the X-ray beam bombards the sample, causing it to release electrons. Positioned less than a nanometer above the surface of the sample, the STM probe collects an electrical signal due to the emitted electrons. The resulting spectrum (a plot of current versus photon energy) is the “fingerprint” for the elements in the periodic table. Each element has a unique fingerprint. By probing the sample surface, scientists can identify specific atomic elements and their exact locations.
There is more. They can also determine the chemical state of atoms from the same spectrum. Chemical state deals with the fact that atoms can lose a certain number of electrons; for example, iron can lose two, three or four electrons. The chemical state reflects the number of electrons lost and is important for scientists to know because it affects the physical, chemical and electronic properties of atoms.
To prove the wider applicability of the new capability, the team successfully repeated the same X-ray analysis with terbium, a rare earth element. Rare earths are essential for microelectronics, batteries, aircraft structures and more. This technique applies to elements other than metals as well. By knowing the properties of single atoms, scientists can then exploit their uses in materials in new ways.
“Being able to study one atom at a time will revolutionize X-ray applications to unprecedented levels, from quantum information technology to environmental and medical research,” said Hla.