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  • Structure of Smallest Crystals Made Visible
Sep 2011
MAINZ, Germany, Sept. 21. 2011 — A new way of making structures visible at the nanoscale level makes it possible to determine with precision the arrangement of atoms and molecules in materials ranging from cement to pharmaceuticals. The procedure, still in its infancy, comes from the field of electron microscopy and can resolve the structure of the tiniest crystals.

The method, developed by Ute Kolb’s group at the Institute of Physical Chemistry at Mainz University, is receiving international attention. For example, in cooperation with researchers from Spain and China, the technique has allowed the structure of a new type of fine-pore zeolite to be established.

The arrangement of atoms and molecules in a solid has a decisive influence on the physical properties of that material. The crystalline structure of a material is responsible for the thermal, electrical, visual and mechanical properties of substances.

Electron diffraction tomography, a technique developed at the University of Mainz in Germany, can help analyze some of the smallest crystals known to materials scientists. (Image: Dr. José Louis Jorda, Valencia)

In the age of nanotechnology, the focus increasingly is on very small particles, which can no longer be captured by way of traditional x-ray crystallography; e.g., an x-ray structural analysis of a single crystal is possible only up to a crystal size of around 1 μm. Below this threshold, electron diffraction tomography or automated diffraction tomography allows similar determinations of the structure of individual crystallites.

“It is as if we have switched on a light in the world of nanostructures,” Kolb said. As is the case with electron microscopy, the method is generally based on the concept of an electron beam being directed at an object and diffracted as a result. The diffraction behavior allows the location of the atoms to be established.

With her group, Kolb developed single-crystal electron diffraction tomography, to give it is full name, over the past 10 years. The most recent example of the technique’s use is the determination of the structure of the zeolite ITQ-43 in cooperation with Spanish and Chinese scientists. Zeolites, which are created from a compound of aluminum and silicate, have small pores that make them interesting for energy and environmental technologies because of their potential use as adsorbers, ion exchangers or catalysts. The researchers describe the complex crystal structure of the zeolite in a recent article in Science.

With crystals ~100 nm, automated diffraction tomography often is the only way by which the structure can be fully and clearly resolved. “There is a large number of natural and synthetic solid materials for which our method may be used — materials which are not available or cannot be manufactured in a suitable crystal size,” Kolb said.

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x-ray crystallography
The study of the arrangement of atoms in a crystal by means of x-rays.
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