Department: Condensed Matter – Experiment and Theory
The research of our group is focussed on photoelectron spectroscopy and microscopy, in particular parallel imaging and spin-resolving techniques. We operate several different types of photoemission electron microscopes, several UHV spectrometers and a field emission scanning electron microscope (Jeol 8400 F). The group has access to the clean room facilities of the department including a FIB/SEM combination and an AFM/MFM. The PEEM instruments comprise a femtosecond-laser excited PEEM, a time-of-flight PEEM with delay line detector, an X-ray transmission-type PEEM and two instruments for a spin filtered imaging: one with ultra thin ferromagnetic transmission foil and another one with a laterally resolving SPLEED analyser crystal. The research group participates in the Graduate School of Excellence Materials Science in Mainz (MAINZ) and Centre for Complex Materials (COMATT).
Research Group: KOMET 334
PEEM for magnetic imaging
One class of experiments exploits the X-ray magnetic circular dichroism XMCD as contrast mechanism, both in static imaging and dynamic imaging . Besides circular dichroism in the X-ray range other contrast mechanisms for magnetic imaging are investigated. In threshold photoemission a linear and circular dichroism occurs that can be exploited for image formation. Spin-filtering bears a high future potential establishing "parallel imaging SEMPA" . Femtosecond laser sources open the way to an unprecedented time resolution.
XANES-PEEM / XPEEM
A second class of experiments deals with spectroscopic imaging employing various techniques. Chemical imaging can either be implemented exploiting the X-ray near edge structure in photoemission spectromicroscopy (XANES-PEEM). Alternatively, the spectroscopic information can be obtained by discrimination of electron energies. A special development of spectroscopic imaging is the Nano-ESCA, a joint development of two university groups and two companies . As particularly simple device we developed an imaging high-pass retarding-field analyser retaining a linear electron optical column. Finally, electron energy discrimination can be obtained by time-resolved image detection making use of the time-of-flight technique .
PEEM imaging with high time resolution, in particular observation of fast magnetic processes can either utilise a stroboscopic approach by synchronisation of a pulsed light source with a repetitive process or, alternatively, time-resolved detection e.g. using a delay line detector .
Special applications of cathode-lens microscopes
Topics of high current interest are the observation of optical near fields , a novel way of defect inspection on masks for a EUVL lithography or the use of sphere-on-plane resonators as optical nanoantennas . A current project deals with the transfer of angular momentum to special near-field resonators by circularly polarized radiation.
A special topic of our group is the meteoritic research using various spectromicroscopic techniques . These investigations are performed in collaboration with Max-Planck-Institut für Chemie, Mainz (U. Ott).
Spectromicroscopy of macromolecules is carried out by X-ray absorption or fluorescence spectroscopy of respiratory proteins in an in-vivo-like arrangement, in cooperation with Institute for Biophysics (Prof. Decker) and the HZB (Prof. Aziz).
Charge transfer systems are studied by various spectroscopic methods (UPS, HAXPES, NEXAFS) in the framework of the transregio SFB TR49.
Photoelectron spectroscopy in the hard X-ray range with spin resolution (Spin-HAXPES) is performed in close collaboration with the Institute of Anorganic and Analytical Chemistry (C. Felser) in the framework of the DFG research unit 559 "New materials with high spin polarization" and a joint DFG / JST (Japan) project at SPring8.
Novel types of imaging or multichannel spin analysers are being developed . A SPLEED-based laterally resolving spin detector is developed in collaboration with the Max Planck Institute for Microstructure Physics, Halle (J. Kirschner). As alternative method of imaging spin detection the transmission through ultrathin ferromagnetic foils is investigated.
Cooperations with companies
The research group was and is involved in cooperations and joint developments with various companies. Among these are four spin-offs of the University group (FOCUS GmbH, FOCUS electronics GmbH, GST mbH, Surface Concept GmbH). Joint developments were also carried out with OMICRON Nanotechnology GmbH (NanoESCA) and SPECS GmbH (Multichannel Spin Polarimeter).