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The atomic structure of low-index surfaces of the intermetallic compound InPd

DOI: 10.1063/1.4928650 DOI Help
PMID: 26298146 PMID Help

Authors: G. Mcguirk (Institut Jean Lamour) , J. Ledieu (Institut Jean Lamour) , E. Gaudry (Institut Jean Lamour) , M. C. De Weerd (Institut Jean Lamour) , M. Hahne (Department of Earth and Environmental Sciences, Germany) , P. Gille (Department of Earth and Environmental Sciences, Germany) , D. C. A. Ivarsson (Faculty of Natural Sciences, Institute of Chemistry, Germany) , M. Armbrüster (Faculty of Natural Sciences, Institute of Chemistry, Germany) , J. Ardini (Department of Chemistry, University of Reading) , G. Held (Department of Chemistry, University of Reading) , F. Maccherozzi (Diamond Light Source) , A. Bayer (University of Erlangen-Nuremberg) , M. Lowe (University of Liverpool) , K. Pussi (Department of Mathematics and Physics, Lappeenranta University of Technology, P.O. Box 20, FIN-53851 Lappeenranta, Finland) , R. D. Diehl (Department of Physics, Penn State University) , V. Fournee (Institut Jean Lamour)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: The Journal Of Chemical Physics , VOL 143 (7)

State: Published (Approved)
Published: August 2015
Diamond Proposal Number(s): 8821

Abstract: The intermetallic compound InPd (CsCl type of crystal structure with a broad compositional range) is considered as a candidate catalyst for the steam reforming of methanol. Single crystals of this phase have been grown to study the structure of its three low-index surfaces under ultra-high vacuum conditions, using low energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). During surface preparation, preferential sputtering leads to a depletion of In within the top few layers for all three surfaces. The near-surface regions remain slightly Pd-rich until annealing to ∼580 K. A transition occurs between 580 and 660 K where In segregates towards the surface and the near-surface regions become slightly In-rich above ∼660 K. This transition is accompanied by a sharpening of LEED patterns and formation of flat step-terrace morphology, as observed by STM. Several superstructures have been identified for the different surfaces associated with this process. Annealing to higher temperatures (≥750 K) leads to faceting via thermal etching as shown for the (110) surface, with a bulk In composition close to the In-rich limit of the existence domain of the cubic phase. The Pd-rich InPd(111) is found to be consistent with a Pd-terminated bulk truncation model as shown by dynamical LEED analysis while, after annealing at higher temperature, the In-rich InPd(111) is consistent with an In-terminated bulk truncation, in agreement with density functional theory (DFT) calculations of the relative surface energies. More complex surface structures are observed for the (100) surface. Additionally, individual grains of a polycrystalline sample are characterized by micro-spot XPS and LEED as well as low-energy electron microscopy. Results from both individual grains and “global” measurements are interpreted based on comparison to our single crystals findings, DFT calculations and previous literature

Journal Keywords: Low Energy Electron Diffraction; Surface Structure; X-Ray Photoelectron Spectroscopy

Subject Areas: Physics


Instruments: I06-Nanoscience