Resarch and former facilities

Field of research

The group was working on problems of solid state chemistry and materials science mainly applying modern methods of transmission electron microscopy (TEM). The available methods allow insights to new and long standing unsolved questions such as atomistic structure of poorly crystallised or amorphous products, structure and defects of real crystals, interfaces in solids as well as phase transformations and nucleation of solids.

Materials and material systems were synthesised by the group predominantly by chemical routes. The characterisation of the material was performed with most modern instrumentation using the complete variety of TEM methods. In our interdisciplinary group chemists and physicists fruitfully collaborated at materials related thematic subjects and TEM-related methodical topics.

© WA

real structure of solids and interfaces

Electron microscopy offers the possibility to characterise microscopic defect structures in crystals, and it is the only method available for this task.

© WA

phase transformations

The study of such processes and intermediate products in the reacting regions requires methods with high local sensitivity. For that the various methods of TEM are best suited.

© WA

thin films

Thin films serve as isolating, dielectric, magnetic or electronic components e.g. for integrated antennas and transmitters and radio frequency filters in mobile phones, or for semiconductor elements in integrated circuits of microelectronic products (computer).

© WA

amorphous solids

amorphous (greek: without shape) inorganic solids, without any long range structural order are denoted as glasses. Even metals which have been rapidly cooled from the melt and contain chemical additions can be obtained as (metallic) glasses.

© WA

nanoscale structures

Synthesis and characterization of nanostructuctures are in the focus of our research. To the structures of interest belong two dimensional (thin films), one dimensional (nanowires or -rods) and „zero” dimensional objects such as nanocrystal

© WA

high resolution TEM (HRTEM)

The contrast formation in high resolution TEM (HRTEM) can only be explained by the wave nature of electrons. In HRTEM a virtually planar electron wave transmits a thin specimen (thickness < 20 nm), in most cases a crystal. During transmission the incident electron wave is scattered (or diffracted in the case of a crystal) at the potentials of the atoms, and thereby the phase of the electron wave is changed. 

© WA

electron scattering

Amorphous solids and glasses are produced and studied in the "collaborative research centre SFB 408" at the university of Bonn. Such solids do not exhibit any long range structural order of the atoms. When irradiated by electrons, these materials produce diffuse scattering patterns in which the scattered intensity falls off with increasing scattering angle. 

© WA

electron spectroscopy

Passing a thin specimen, primary electrons can loose energy when they collide with electrons from the atoms of the material. With an energy filter these inelastically scattered electrons can be dispersed as a function of their energy and then detected using either a linear diode array or a CCD camera. As the excited electron will take some kinetic energy with it (which the primary electron must supply) one gets ionization edges on top of an approximately exponentially decaying background, rather than discrete peaks in x-ray microanalysis.

© WA

electron crystallography

Different from the diffraction of X-rays or neutrons, the interaction of electrons with matter is some orders of magnitude stronger. A resulting advantage of electron diffraction is that only small volumes are required for the investigation.

Former facilities

Transmission Electron Microscopes

Philips CM300 FEG/UT - STEM
300 kV acceleration voltage
post column imaging filter (GIF, Gatan)
wide angle ADF-Detector (Fischione/Philips)
2k x 2k MSC-CCD-camera
1k x 1k SSC-CCD-camera
EDS-Detector (HPGe) and analysis system (Noran System Seven, Thermo Fisher Scientific)

Philips CM30 T - STEM I
300 kV acceleration voltage
1k x 1k MSC-CCD-camera
electron energy loss spectrometer (PEELS, Gatan)
EDS-Detektor (Si) and analysis system (Noran System Six, Thermo Fisher Scientific)

Philips CM30 T - STEM II
300 kV acceleration voltage
1k x 1k MSC-CCD-camera

Scanning Electron Microscopes

Philips XL20
EDX-Detector (Si, Tracor) and analysis system (Voyager, Noran)

EDX-Detector (HPGe) and analysis system (Voyager, Noran)

Light Microscope

Zeiss Axiotech

Sample Preparation

Ion Beam Etching
PIPS, Gatan

Coating - Sputtering

saws, grinders, dimple grinders, polishers, etc for mechanical sample preparation

X-Ray Powder Diffraction

Bragg-Brentano Philips P-XRD with AMR post specimen monochromator
Texture diffractomer

Wird geladen