Seminars

PIER Photon Science Colloquium: New Concepts of Parallel Data Acquisition in Photoemission and Spin Detection

by Gerd Schönhense (Johannes Gutenberg-Universität Mainz)

Europe/Berlin
DESY Auditorium, Bldg. 05 (DESY Hamburg)

DESY Auditorium, Bldg. 05

DESY Hamburg

Description
Owing to the translational symmetry of crystalline solids, their electronic band structure is periodic in k-space and is fully described in the 1st Brillouin zone (BZ). ARPES (mostly with hemispherical analyzers) is established as standard method for the analysis of k-space topologies. In cooperation with MPI für Mikrostrukturphysik (Halle), we develop a novel 3D-technique (time-of-flight k-microscopy) for simultaneous detection of the E(kII)-dispersion in the full surface BZ. The method exploits a basic principle of electron microscopy: A reciprocal (or Fourier) image occurs in the backfocal plane of a special objective lens (strong electrostatic immersion lens). This image in Fourier space is nothing else that the kII-distribution, which is conserved in the photoemission process. k-microscopy thus provides a direct look into the E(kII) bandstructure on a linear k-scale in a range exceeding the first BZ. Parallel energy acquisition is facilitated by implementation of an imaging time-of-flight spectrometer. The 3D acquisition causes minimum radiation damage to delicate samples, because all electrons are detected in parallel. The status of the development is demonstrated by the example of an anomalous surface state discovered on Mo(110), see figure (taken in 20 min. at fixed setting of the microscope). 3D dichroism maps yield information on the band symmetries. An imaging spin filter will open an extremely fast way of spin-resolved band mapping. A high-energy version will establish a novel way of HAXPES.