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:

  1. 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 [3] 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 [4] could determine the atomic structure of the Pn/Cu(110) interface for coverages at and just below one monolayer.
  2. 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 [5] and nano-junction devices at low temperature even present large magneto-resistance value [6]. 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.

[1] S. Söhnchen et al., J. Chem. Phys. 121 (2004) 525

[2] K. Müller et al., Phys. Rev. B 79 (2009) 245421

[3] K. Müller et al., J. Phys. Chem. C 116 (2012) 23465

[4] M. Sauvage-Simkin et al., J. Phys. Chem. C 118 (2014) 27815

[5] M. Gobbi et al., Adv. Mater. 23 (2011) 1609

[6] C. Barraud et al., Nat. Phys. 6 (2010) 615