Bulk sensitive hard x-ray photoemission electron microscopy

ROM 2015-01
Author: Marten Patt (1), m.patt@fz-juelich.de
Institute: 1) Peter Grünberg Institute (PGI-6) and JARA-FIT, Research Center Jülich, D-52425 Jülich, Germany 2) Focus GmbH, Neukirchner Str. 2, D-65510 Hünstetten, Germany 3) DESY Photon Science, Deutsches Elektronen-Synchrotron, D-22603 Hamburg, Germany 4) Fakultät f. Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universität Duisburg-Essen, D-47048 Duisburg, Germany
Publication: Citation(s)
Instrument: NanoESCA

Hard x-ray photoelectron spectroscopy (HAXPES) has now matured into a well-established technique as a bulk sensitive probe of the electronic structure due to the larger escape depth of the highly energetic electrons. In order to enable HAXPES studies with high lateral resolution, we have set up a dedicated energy-filtered hard x-ray photoemission electron microscope (HAXPEEM) working with electron kinetic energies up to 10 keV. It is based on the NanoESCA design and also preserves the performance of the instrument in the low and medium energy range. In this way, spectromicroscopy can be performed from threshold to hard x-ray photoemission.

In our publication we study the capabilities of this microscopic approach and present measurements on specially designed test-samples to quantify the bulk-sensitivity and the resolution power of the instrument for covered structures or multilayer-devices, but also discuss challenges which are associated with the used techniques.

The HAXPEEM approach is of high interest for the study of new material systems and complex device structures like nonvolatile memory cells, spin-transistors, photovoltaic elements or batteries, because it allows a spatial resolved chemical analysis of the used materials (and their electronic intermediate states) even if they are covered by electrodes which are compulsive for the functionality of these devices. Our results show, that the chemically resolved photoemission imaging through even 15 nm thick cover layers is possible with a good sub-micrometer spatial resolution. The precision of the setup is even adequate to perform a new approach for determining the effective attenuation length of a cover-material: in a one shot experiment we acquired the photoemission signal excited under a cover layer with a thickness-gradient. The evaluated results match the theoretical predictions of the inelastic mean free path pretty well. This underlines the feasibility of the instrument for quantitative studies if the new single-event counting data acquisition is used.

Images:
M.Patt et al., Rev. Sci. Instrum. 85, 113704 (2014))

Authors
Marten Patt1, Carsten Wiemann1, Nils Weber2, Matthias Escher2, Andrei Gloskovskii3, Wolfgang Drube3, Michael Merkel2 and Claus M. Schneider1,4

URL of Institute web-pages
(1) http://www.fz-juelich.de/pgi/pgi-6
(2) http://www.focus-gmbh.com
(3) http://photon-science.desy.de/
(4) https://www.uni-due.de/cenide/

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