The scope of the service is the characterization of materials and the structure determination of chemical substances with crystallographic and microscopic methods. This includes single crystal structure determination, transmission and scanning electron microscopy in connection with different methods for sample preparation. Our research areas are electron density determination, polymorphism and crystal-engineering studies.
The electron density of a molecule is the key for the understanding of chemical interactions. On one hand, the electron density can be calculated directly from the wave function. On the other hand, the electron density - in contrast to the wave function - can be observed experimentally. Of special interest for us are transition metal catalysts, co-ordination polymers and organic molecules with special photonic properties. The optical properties of these so-called push-pull chromophores change sometimes drastically between being in solution or forming a crystalline solid. Since the crystalline state usually forms the basis for applications, crystallographic methods are especially useful for these investigation.
Polymorphism describes the ability of a chemical substance to form more than one crystalline state. These different crystalline states have different properties with respect to solubility, colour, or melting point. This phenomenon is known for inorganic and organic molecules. Polymorphism is especially interesting in cases of pigments and pharmaceuticals. X-ray powder diffraction is exceptionally suited to distinguish between different polymorphs. The high transmission of the X-rays allows investigation even of formulated and packaged tablets and can be used to detect counterfeits.
Currently, there are three single crystal diffracometers in use: (Bruker AXS Mach3) with area detectors (Apex II, KappaCCD, Proteum). The X-rays are generated by rotating anodes (Bruker AXS FR591) with Molybdenum and Copper anodes, respectively.
For powder diffraction there is one Stoe STADI P diffractometer, equipped with a primary monochromator and Cu-Kα1 radiation in Debye-Scherer-Geometry, plus a position sensitive image plate detector.
Transmission electron microscopy of nano particles and nano structured materials (zeolites and mesoporous silicates and their replica) reveals structural details in the sub nanometer range.
Scanning electron microscopy is employed to visualize details of the sample surface on the nano meter scale.
The sample preparation for electron microscopy is of utmost importance. Delicate structures must not be destroyed or changed; the sample should be representative for the whole material.
Becker, Benjamin Benno
Bock, Dominique Anna
PhD Student, 10/2010 - 03/2013
Dr. Goddard, Richard
Prof. Dr. Lehmann, Christian W.
Dr. Mondal, Swastik