Time-of-flight aberration correction and spin-filtering of electron beams
1 : Institut für Physik, Johannes Gutenberg Universität, D-55099 Mainz, Germany
Time-dependent electron detection e.g. using a delayline detector paves the way towards a
new way of aberration correction. In this approach Scherzer's Theorem is circumvented by
means of time-dependent fields and detection [1, 2]. A possible approach is to “cut” the
electron image into picosecond time slices and finally mount the aberration-corrected partial
images to a total image. Using a special type of low-energy microscope, all three momentum
components of an electron beam (kx, ky via lateral imaging, kz via the time of flight) can be
resolved simultaneously with unprecedented precision, leading to time-of-flight momentum
microscopy.
An additional imaging spin filter yields high contrast magnetic images or spinfiltered kdistributions
and is suitable for the direct observation of magnetization structures on
ferromagnetic surfaces and their ultrafast dynamics. Stern-Gerlach-type spin filters for
electrons are impossible because of the interplay between Lorentz force and Heisenberg
uncertainty relation [3]. All previous spin polarimeters are based on scattering on high-Z
materials and are inherently single-channel methods characterized by low figures of merit of
typically 10-4 to 10-3. We use a novel imaging polarimeter based on spin dependent lowenergy
electron diffraction from W(100) or Ir(100) under specular reflection. A device built at
the Max Planck Institute in Halle can resolve 3800 pixels and is characterized by a 2D figure
of merit of 8 [4]. Alternatively, the imaging spin filter can be used behind the exit of a
hemispherical energy analyzer [5].
In this contribution all aspects of time-of-flight aberration correction and spin-filtering will be
discussed, with emphasis on the application for the diagnosis of electron beams.
Fruitful cooperation with C. Tusche, A. Krasyuk and J. Kirschner (MPI Halle) and M. Kolbe,
D. Kutniakhov, P. Lushchyk and K. Medjanik (Univ. Mainz) is gratefully acknowledged.
Projects are funded by DFG (Scho341/9) and Stiftung Rheinland Pfalz für Innovation (# 886).
[1] G. Schönhense and H. Spiecker; J. Vac. Sci. Technol. B 20 (2002) 2526-2534
[2] G. Schönhense, H. J. Elmers, S. A. Nepijko, C. M. Schneider; Time-resolved photoemission electron
microscopy, in: Advances in Imaging and Electron Physics (Ed. P. Hawkes) 142 (2006) 159-323
[3] J. Kessler, Polarized Electrons, Springer Berlin (1976)
[4] C. Tusche, M. Ellguth, A. A. Ünal, C. T. Chiang, A. Winkelmann, A. Krasyuk, M. Hahn,
G. Schönhense and J. Kirschner; Appl. Phys. Lett. 99 (2011) 032505
[5] M. Kolbe, P. Lushchyk, B. Petereit, H.J. Elmers, G. Schönhense, A. Oelsner, C. Tusche
and J. Kirschner; Phys. Rev. Lett. 107 (2011) 207601
