US scientists have obtained information about the state of a single atom for the first time by combining tunneling microscopy with synchrotron X-rays. The new method allows you to determine the type of a particular atom at a time, as well as measure its chemical state. This is reported in an article published in the journal Nature.

So far, the smallest scale that could be characterized using X-rays includes 10,000 atoms or more. This is because the X-ray signal produced by the atoms is extremely weak, so conventional detectors cannot be used to detect it. The new approach is aimed at recording the currents generated when atoms are irradiated with X-rays.

During the experiment, scientists aimed at the iron atom and the terbium atom in the composition of complex compounds, that is, organic molecules, ligands, are attached to the metal atom. Conventional X-ray detectors were supplemented with a detector consisting of a sharp metal tip located in close proximity to the sample to collect electrons excited by synchrotron X-rays. This technique is known as Synchrotron X-ray Scanning Tunneling Microscopy, or SX-STM.

There are two SX-STM measurement modes: tunnel and far field. In the first mode, the needle is located above the sample in the tunneling area, at a distance of about 0.5 nanometers. In the far-field mode, the needle is located at a distance of about five nanometers from the sample, which is outside the tunneling zone, and only the electrons ejected by the X-ray radiation contribute to the measurements.

Using the new method, scientists were able not only to determine the type of atoms, but also to identify their chemical states. It turned out that the atom of terbium, a rare earth metal, is rather isolated and does not change its chemical state, while the iron atom closely interacts with its environment.