Photoelectron diffraction studies of Ag(001), MnO(001) and epitaxial MnO films A. Chassé a, ⁎, Ch. Langheinrich a , M. Nagel b , T. Chassé b a Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle, Germany b Instut für Physikalische und Theoretische Chemie, Universität Tübingen, D-72074, Tübingen, Germany abstract article info Article history: Received 16 June 2010 Accepted 15 October 2010 Available online 29 October 2010 Keywords: Angle-resolved photoemission Low energy electron diffraction Photoelectron diffraction MnO epitaxial films Single crystal surfaces Interface strain Computer simulations Green's function method A joint experimental and theoretical investigation of epitaxial MnO films on Ag(001) also including the reference systems Ag(001) and MnO(001) is presented using photoelectron diffraction (XPD) supported by photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED). MnO films have been grown with thicknesses 1 to 5 nm. The conditions of film growth (temperature and time) have been chosen to obtain information on the development of film structure with thickness and to permit comparison regarding film absorption and diffraction studies. Experimental angular distribution patterns (ADP) and angular distribution curves (ADC) have been recorded and analyzed by comparing the results to multiple scattering cluster calculations. Excellent agreement was obtained for the description of the ADCs of Ag(001) and MnO(001) surfaces, and fine structures due to multiple scattering effects have been clearly identified. The multiple scattering analysis has been found to be indispensable in particular for a structural analysis of the oxide material. ADPs of MnO films grown on Ag(001) have supported the epitaxial growth of the films from the beginning. The analysis of the ADCs in dependence on growing MnO film thickness has provided clear evidence for strained, tetragonally distorted MnO films for the first few nm, while the thicker films of about 5 nm have evidently adopted bulk structure and bulk lattice constants. These results are discussed in comparison to recent structural studies of MnO on non-lattice matched metal substrates resulting in a rather similar plot for the oxide growth. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The preparation and characterization of thin films in the nanoscale range is a challenge in surface science. The reduced dimensionality of the film may lead to different or new chemical and physical properties in comparison to the bulk material. These properties depend strongly on the chemistry and structure of the interface region [1,2]. More recently there has been growing interest in the preparation and characterization of thin metal-oxide films, which serve as model systems in the development of novel magnetic multilayer struc- tures [3] and the application in heterogeneous catalysis [4]. Besides thin films of transition-metal oxides (TMOs) are very interesting for fundamental studies of electron correlation in solids [5]. For all applications the control of the film structure and the morphology at the atomic scale is a crucial point. In a multitechnique approach the methods of low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), X-ray photoelectron diffraction (XPD) and scanning tunneling microscopy (STM) may be combined in order to investigate ultrathin oxide films grown on a single crystal surface [6]. These methods may give complementary results about the growth and structure of a thin film. In short form, LEED gives information about the surface structure, XPS about the chemical composition of the interface region, XPD about the short-range order and STM a detailed image of the surface. The main advantage of photoelectron diffraction (as well as Auger electron diffraction) in comparison to LEED is the local character of the method [13,14]. A core electron is excited from a deep core level which is related to a specific atom within the sample. The diffraction pattern arises due to the interference of the directly emitted and the elastically scattered outgoing photoelectrons. Besides different chemical states of one species and the spin of photoelectrons may be resolved. Therefore, photoelectron diffraction or Auger electron diffraction is a local structural probe of the system. Usually the experimental data should be accompanied by complex scattering calculations to get the structure of the system. But, there is a focusing effect if photoelectrons or Auger electrons are emitted with kinetic energies of several hundred eV by means of enhanced intensities along directions of interatomic axes in the crystal. During the last few years this method (XPD or AED in forward scattering conditions) has been developed into a powerful technique of the structural study of epitaxial films of simple metals or more complex oxide systems grown on single crystal surfaces [15,16]. There are contributions in the study of TiO x films on Pt(111) [17,18] and Pt(100) [19], NiO films on Pd(100)[20] and on Ag(001) [21], CoO films Surface Science 605 (2011) 272–281 ⁎ Corresponding author. Tel.: +49 345 5525436. E-mail address: angelika.chasse@physik.uni-halle.de (A. Chassé). 0039-6028/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2010.10.028 Contents lists available at ScienceDirect Surface Science journal homepage: www.elsevier.com/ locate/susc