Allgemeines Physikalisches Kolloquium im Sommersemester 2012
Ort:     48149 Münster, Wilhelm-Klemm-Str. 10, IG I, HS 2,
Zeit:    Donnerstag, 19.04.2012 16:00 Uhr c.t.
Kolloquiums-Kaffee ab 15:45 Uhr vor dem Hörsaal

Vortex electron beams in the electron microscope
Prof. Dr. Jo Verbeeck, Universiteit Antwerpen, Fysica – EMAT

Electron vortices were recently created inside a transmission electron microscope. They form the counterpart of the better known optical vortex beams which carry orbital angular momentum caused by their phase signature. The optical wavelength is replaced by the De Broglie matter wavelength which is of the order of picometers in a typical electron microscope. This much smaller wavelength allows us to make vortex probes with diameters of the order of Angstroms. Such small electron vortex probes have much in common with electrons in atomic orbitals except for the fact that the probe electrons are free and propagate in space along the optical axis. The fact that electrons are charged particles leads to more difference with photon vortices in that the spiraling nature of the probability current leads to a magnetic field surrounding the vortex. The result of these differences is a much increased interaction with matter as can be exploited in electron energy loss spectroscopy. Indeed, the spectroscopic signal contains information about the magnetization of a material due to a breaking of symmetry caused by the incoming vortex beam. As such, electron vortex beams hold great promise for magnetic mapping of materials at atomic spatial resolution. A second application of vortex beams that will be discussed is the manipulation of nanoparticles due to the transfer of angular momentum. First experiments will be shown and theoretical arguments towards the strength of this promising effect will be given.

Einladender: Prof. Dr. H. Kohl

Im Auftrag der Hochschullehrer des Fachbereichs Physik

Prof. Dr. Sergej Demokritov