An anonymous reader quotes a report from Ars Technica: Atomic-scale imaging emerged in the mid-1950s and has been advancing rapidly ever since — so much so, that back in 2008, physicists successfully used an electron microscope to image a single hydrogen atom. Five years later, scientists were able to peer inside a hydrogen atom using a “quantum microscope,” resulting in the first direct observation of electron orbitals. And now we have the first X-ray taken of a single atom, courtesy of scientists from Ohio University, Argonne National Laboratory, and the University of Illinois-Chicago, according to a new paper published in the journal Nature.
“Atoms can be routinely imaged with scanning probe microscopes, but without X-rays one cannot tell what they are made of,” said co-author Saw-Wai Hla, a physicist at Ohio University and Argonne National Laboratory. “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.” […] Hla has been working for the last 12 years to develop an X-ray version of STM: synchrotron X-ray-scanning tunneling microscopy, or SX-STM, which would enable scientists to identify the type of atom and its chemical state. X-ray imaging methods like synchrotron radiation are widely used across myriad disciplines, including art and archaeology. But the smallest amount to date that can be X-rayed is an attogram, or roughly 10,000 atoms. That’s because the X-ray emission of a single atom is just too weak to be detected — until now.
SX-STM combines conventional synchrotron radiation with quantum tunneling. It replaces the conventional X-ray detector used in most synchrotron radiation experiments with a different kind of detector: a sharp metal tip placed extremely close to the sample, the better to collect electrons pushed into an excited state by the X-rays. With Hla et al.’s method, X-rays hit the sample and excite the core electrons, which then tunnel to the detector tip. The photoabsorption of the core electrons serves as a kind of elemental fingerprint for identifying the type of atoms in a material. The team tested their method at the XTIP beam line at Argonne’s Advanced Photon Source, using an iron atom and a terbium atom (inserted into supramolecules, which served as hosts). And that’s not all. “We have detected the chemical states of individual atoms as well,” said Hla. “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.” Also, Hla’s team has developed another technique called X-ray-excited resonance tunneling (X-ERT), which will allow them to detect the orientation of the orbital of a single molecule on a material surface.
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Source: Slashdot – The First X-Ray Taken of a Single Atom