Regensburg 2010 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 54: Electronic structure II

O 54.1: Vortrag

Mittwoch, 24. März 2010, 15:00–15:15, H33

Momentum resolved imaging of the surface electronic structure of Cu(111) in multi-photon photoemission — •Christian Tusche, Cheng-Tien Chiang, Ahmet Akin Ünal, Aimo Winkelmann, and Jürgen Kirschner — Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany

We use a Photoelectron Emission Microscope (PEEM), combined with an imaging energy filter, to map the distribution of photoelectrons in energy and momentum space. In this “momentum microscope”, the angular distribution of electrons leaving the sample is transferred from the back focal plane of the objective lens into two hemispherical analyzers. [1] The projected images directly show the parallel momentum component of the photoelectrons at a constant energy, and maps of the band structure are obtained as a series of parallel cuts through the Brillouin zone.

Combined with multi-photon photoemission (mPPE), using ultra short laser pulses (hν=3.1 eV), unoccupied electronic states situated in between the vacuum level and the Fermi energy can also be mapped. For instance, for the adsorption system Cs/Cu(111), 2PPE takes place resonantly through an unoccupied Cs-induced state located ≈2 eV below the vacuum level. This resonant photoemission channel is absent in a 1PPE experiment, using 6 eV photon energy. Using 3PPE, our experiments can be extended to the unoccupied part of the Cu(111) Shockley surface state and the image potential states.

[1] Krömker, Escher, Funnemann, Hartung, Engelhard, Kirschner: Rev. Sci. Instrum. 79, 053702 (2008)