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Measuring picometers to advance nanotechnology

Getting the most from nanotechnology sometimes requires measuring at a scale a thousand times smaller—the scale of picometers. Technologically important properties of some nanostructures—for example, certain complex metal oxide crystals—dependent strongly on knowing atomic positions very precisely—to within a few percent of an atomic diameter. A recent review describes the advantages to nanotech of advances in electron microscopy that allow mapping electron states localized at or between atoms, when coupled with extensive quantum-mechanical calculations. From a press release of the Helmholtz Association of German Research Centres, via AAAS EurekAlert “Electron microscopy enters the picometer scale

Jülich scientists have succeeded in precisely measuring atomic spacings down to a few picometres using new methods in ultrahigh-resolution electron microscopy. This makes it possible to find out decisive parameters determining the physical properties of materials directly on an atomic level in a microscope. Knut Urban from Forschungszentrum Jülich, a member of the Helmholtz Association, reports on this in the latest issue (25 July) of the scientific high-impact journal Science [abstract].

Progress in research in the area of physics is very frequently connected to an increase in the accuracy of measurements, which help researchers to track natural phenomena. With the aid of new methods in electron optics, researchers were able to microscopically measure atomic displacements precisely to a few picometres. A picometre corresponds to a billionth of a millimetre a distance that is one hundred times smaller than the diameter of an atom. This is one of the highlights that Knut Urban, director of the Ernst Ruska-Centre in Jülich, reports on in Science as part of a review of ten years of electron microscopy with aberration-corrected lenses.

Jülich scientists investigated, for example, the configuration of atoms in orthogonal grain boundaries of the oxide superconductor YBa2Cu3O7. These atoms mark the boundary between two areas of the crystalline material with atomic structures that are tilted at an angle of exactly 90° to each other. From microscopic images taken under different conditions, the physicists succeeded in using computers to calculate the quantum-mechanical wave function of the electrons, which served as a basis for determining the exact position of the atoms.

In doing so, it became apparent that the relatively heavy atomic species barium, copper and yttrium are systematically displaced a few picometres from their ideal position in the grain boundary and that the lighter oxygen atoms follow this displacement. This provides an explanation for the attenuation of superconducting properties, which can be observed when electric current flows over such a grain boundary. This phenomenon is undesired if the superconductor is intended to be used for a loss-free current transport. However, it is useful for the construction of so-called SQUIDs (superconducting quantum interference devices), which exploit the magnetic field dependency of this disturbance to measure smallest magnetic fields, for example, to measure brain waves (magnetoencephalography).

…Knut Urban explains: “This is the beginning of a new physics of materials which enables researchers to determine physical parameters and properties in the nano range through highly precise measurements of the atomic spacings. This will also provide clues on how these properties may be manipulated in order to gain new functions and better functional performance.”

—Jim

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