Am Freitag, den 02.03.18 um 13:00 Uhr
spricht in unserem Institutskolloquium
Dr. Carsten Richter
X-ray Nanoprobe Group, The European Synchrotron
"Characterization of atomic displacements in crystals
using resonant x-ray diffraction techniques"
Gäste sind herzlich willkommen.
Leibniz-Institut für Kristallzüchtung
Raum 316, Geb. 19.31,
Leibniz-Institut für Kristallzüchtung, Berlin, Deutschland
Mittwoch, 12. Oktober - Freitag, 15. Oktober 2016
Gastdozent: Elias Vlieg, Radboud University, IMM, Nijmegen, Niederlande
The growth of crystals, whether this is a large and highly-perfect silicon boule or powder-like material of an active pharmaceutical ingredient, always takes place at the interface with its growth medium and (nearly) always atom by atom (or molecule by molecule). A complete understanding of crystal growth, and a subsequent control of the crystal properties, therefore requires an atomic-scale knowledge of the processes and structure at the interface. This series of lectures describes attempts to understand several topics from this atomic-scale perspective.
The faceted nature of a crystal (like quartz) makes anyone curious about the origin of this shape and understanding and predicting the morphology (habit) of a crystal is, therefore, a very classic subject. Both old and new models for this will be discussed.
At the growth interface, both the crystal and the growth medium will typically have a structure that is different from the bulk. Assessing such interfaces, in particular when growing from a solution or melt, is quite difficult, but a combination of techniques like Atomic Force Microscopy, computer simulations, and X-ray diffraction, has yielded significant insights. A number of examples will be discussed, including the ordering of Ga at the GaN-Ga interface at high pressure and temperature as observed using high-energy X-rays from synchrotron radiation sources.
In many applications, one aims to grow highly perfect crystals. In the case of protein crystals, the perfection is needed to achieve a high resolution of the protein structure. Growth without convection has several advantages in this context and a number of routes to achieve convection-free growth will be discussed. The resulting slow growth leads to better crystals and to a reduced uptake of impurities. This thus also yields lessons for the growth of other types of crystals.
Nature is homochiral; for example, nearly all natural amino acids are left-handed. This not only raises the fundamental question of why nature made this particular choice but also has practical consequences for pharmaceutical ingredients because the left-handed version can have very different effects than the right-handed one. Crystallization is one route to obtain chirally pure material. In the last decade, a number of new and surprising routes have been found. In Viedma ripening, for example, grinding a slurry of left- and right-handed crystals lead to a complete conversion of all the solid material to single chirality. This process involves interesting growth routes in which growth appears to take place by the incorporation of small clusters
Elias Vlieg is a professor of Solid State Chemistry at the Institute for Molecules and Materials (IMM) at Radboud University, Nijmegen, The Netherlands. The research theme of his group is the fundamental understanding of crystal growth, for which a wide range of experimental, computational and theoretical methods are applied to a wide range of crystals. His current interests include chiral separation, additives, nucleation, polymorphism, self-assembly and the atomic-scale structure of solid-liquid interfaces. As head of the Applied Materials Science group, he is further involved in the practical applications of III-V semiconductors for thin film solar cells, including a role as CEO of a small spin-off company.
Vorlesung am Lehrstuhl für Kristallzüchtung
an der Brandenburgischen Technischen Universität Cottbus-Senftenberg
Wachstum einkristalliner Materialien und ausgewählte Anwendungen
Vorlesung am Institut für Physik
der Mathematisch Naturwissenschaflichen Fakultät I der
Humboldt - Universität zu Berlin
Röntgenstreuung: Grundlagen und Anwendungen in der Materialwissenschaft und Materialwissenchaftlichen Analytik