ECM27 | The 27th Meeting of the European Crystallographic Association
Saturday, 30 March 2019
Laue Centennial

The year 2012 represents the centennial of the first single crystal X-ray experiments, performed at the Ludwig Maximilian Universit├Ąt, Munich, Germany, by Paul Knipping and Walter Friedrich under the supervision of Max Laue.

Max von Laue was awarded the Nobel prize in Physics 1914 "for his discovery of the diffraction of X-rays by crystals".

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This fundamental achievement will be highlighted at the ECM27.

Laue's experiment in 1912 of the diffraction of X-rays by crystals is one of the most influential discoveries in the history of science, with monumental consequences. Confirming crystal structures to be periodic, as had been postulated 100 years earlier, and showing X-rays to be short-wavelength light, was of great importance at that time.

But the impact of the diffraction of X-rays, and later of electrons and neutrons, exceeds enormously these immediate results. For the first time, the visualization of the structure of matter at the atomic level became possible. Atoms were no longer somewhat nebulous entities postulated in various theories. They could be seen directly, they became observable physical objects. X-ray diffraction provided a microscope with atomic resolution. In addition, the absorption and emission of X-rays by matter could be analyzed by diffraction from a crystal, and this elucidated atomic structure and atomic energy levels, and was later used for chemical analysis.

All branches of science concerned with matter, solid state physics, chemistry, materials science, mineralogy and biology, could now be firmly anchored on the spatial arrangement of atoms. Simple ionic checkerboard-like structures such as the one of rock salt, NaCl, demonstrating the absence of molecules, were in 1913, and even decades later, revolutionary for many chemists. Another simple structure determined very early, the one of silicon (and diamond), became the basis of modern electronic devices. Organic molecules were shown to possess definite three-dimensional shapes. The structures of silicates enabled a rational classification of minerals and rocks. The development of macromolecular crystallography elucidated the stereochemistry of processes in living organisms, the genetic code (double helix of DNA), the spatial form and function of proteins and the machinery for the production of proteins from DNA.

Many results from X-ray diffraction and spectroscopy are today common knowledge and are found in introductory chapters of textbooks for first year undergraduates and even high school students. Structure determination has developed into a mature science, and its scientific drive is towards applications. Modern crystallographic research covers an extremely wide domain, and is no longer always explicitly referred to as Crystallography.

Diffraction of X-rays, of electrons in electron microscopes and of neutrons is an indispensible tool applied to all sorts of matter and not only to periodic crystals. The need to know the structure of matter at atomic resolution provides the powerful drive for the development and construction of new international and national high-intensity radiation sources, synchrotrons, free-electron lasers and neutron spallation sources.

Dieter Schwarzenbach, Professor emeritus

Laboratory of Crystallography, EPFL, Lausanne, Switzerland