title: To tilt or not to tilt: correction of the distortion caused by inclined sample surfaces in low-energy electron diffraction.
abstract: Low-energy electron diffraction (LEED) is a widely employed technique for the structural characterization of crystalline surfaces and epitaxial adsorbates. For technical reasons the accessible reciprocal space is limited at a given primary electron energy E. This limitation may be overcome by sweeping E to observe higher diffraction orders decisively enhancing the quantitative examination. Yet, in many cases, such as molecular films with rather large unit cells, the adsorbate reflexes become less pronounced at energies high enough to observe substrate reflexes. One possibility to overcome this problem is an intentional inclination of the sample surface during the measurement at the expense of the quantitative interpretability of then severely distorted diffraction patterns. Here, we introduce a correction method for the axially symmetric distortion in LEED images of tilted samples. We provide experimental confirmation for micro-channel plate LEED and spot-profile analysis LEED instruments using the (7×7) reconstructed surface of a Si(111) single crystal as a reference sample. Finally, we demonstrate that the correction of this distortion considerably improves the quantitative analysis of diffraction patterns of adsorbates since substrate and adsorbate reflexes can be evaluated simultaneously. As an illustrative example we have chosen an epitaxial monolayer of 3,4,9,10-perylenetetracarboxylic dianhydride on Ag(111) that is known to form a commensurate superstructure.
authors.affiliation: Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 5, 07743 Jena, Germany. Electronic address: falko.sojka@uni-jena.de.
authors.forename: Falko
authors.initials: F
authors.lastname: Sojka
authors.forename: Matthias
authors.initials: M
authors.lastname: Meissner
authors.forename: Christian
authors.initials: C
authors.lastname: Zwick
authors.forename: Roman
authors.initials: R
authors.lastname: Forker
authors.forename: Michael
authors.initials: M
authors.lastname: Vyshnepolsky
authors.forename: Claudius
authors.initials: C
authors.lastname: Klein
authors.forename: Michael
authors.initials: M
authors.lastname: Horn-von Hoegen
authors.forename: Torsten
authors.initials: T
authors.lastname: Fritz
mesh_terms: D003460:Crystallization / Q000379:methods; D004583:Electrons; D046529:Microscopy, Electron, Transmission / Q000379:methods*; D013499:Surface Properties
keywords: Distortion correction; Micro-channel plate LEED (MCP-LEED); Off-axis; Spot-profile analysis low-energy electron diffraction (SPA-LEED); Tilted samples