Organic molecules/metal interface structures studied by x-ray scattering
Coati1, M. Sauvage-Simkin1, A. Vlad1, A. Resta1, K. Müller2, A. Kara3, A. Bendounan1,
C. Fourmental1,4, A. Bellec4, V. Repain4, Y. Garreau1,4
1.Synchrotron SOLEIL, L’Orme des Merisiers, St Aubin BP48, 91192 Gif-sur-Yvette Cedex, France
2.Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747 AG Groningen, The Netherlands
3.Department of Physics, University of Central Florida, Orlando, Florida 32816, United States
4.Laboratoire Matériaux et Phénomènes Quantiques, UMR 7162, CNRS – Université Paris Diderot, case courrier 7021, 10 rue A. Domon et L. Duquet, 75205 Paris Cedex 13, France.
Organic molecules on metallic surfaces constitute nowadays a huge field of studies due to their potential applications in various fields, depending on their properties: semiconductor devices, spintronics… A particular role in the properties of the devices is played by the interfaces between the molecular film and the metal.
Surface x-ray scattering techniques (grazing incidence x-ray diffraction – GIXD- and small angle x-ray scattering – GISAXS- and x-ray reflectivity are powerful tools to study the structural properties of organic/metal interfaces. In this presentation I will show how these x-ray scattering techniques can be used to address the structure and the morphology of these interfaces. Two examples will be shown and commented:
- The pentacene (Pn)/copper system, showing long-range ordered molecular arrays when deposited on Cu(110) [1,2]. Ab-initio calculations have confirmed the changes occurring in the electron density  and distortions in the molecule and substrate upper layers have been proposed, however, no direct determination of the actual atomic displacements had been attempted. GIXD measurements supported by state-of-the-art DFT calculations  could determine the atomic structure of the Pn/Cu(110) interface for coverages at and just below one monolayer.
- Organic molecules can be used as a non-magnetic spacer between two magnetic layers, attracting interest for spintronics applications. Promising results have already been obtained on C60 based spin-valves at room temperature  and nano-junction devices at low temperature even present large magneto-resistance value . GIXD, XRR and GISAXS are used to monitor the structure, the morphology and and the stability of thin C60 films grown on a Co(0001) substrate. A subsequent Co thin film growth on C60 completes the sample structure Co/C60/Co.
All the experiments were conducted in-situ under ultra high vacuum at the UHV end-station of the SixS (Surfaces and Interfaces x-ray scattering) beamline at Synchrotron SOLEIL.
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