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

Journal Article · Fri Aug 21 00:00:00 EDT 2015 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4928650· OSTI ID:22493554

McGuirk, G. M.; Ledieu, J.; Gaudry, É.; Weerd, M. -C.; Hahne, M.; Gille, P. ^[1]; Ivarsson, D. C. A.; Armbrüster, M. ^[2]; Ardini, J.; Held, G. ^[3]; Maccherozzi, F. ^[4]; Bayer, A. ^[5]; Lowe, M. ^[6]; Pussi, K. ^[7]; Diehl, R. D. ^[8]

---

1. Department of Earth and Environmental Sciences, Crystallography Section, Ludwig-Maximilians-Universität München, Theresienstrasse 41, D-80333 München (Germany)
2. Faculty of Natural Sciences, Institute of Chemistry, Materials for Innovative Energy Concepts, Technische Universität Chemnitz, D-09107 Chemnitz (Germany)
3. Department of Chemistry, University of Reading, Reading RG6 6AD (United Kingdom)
4. Diamond Light Source Ltd, Didcot OX11 0DE (United Kingdom)
5. Lehrstuhl für Physikalische Chemie II, Universität Erlangen-Nürnberg, Egerlandstraße 3, D-91058 Erlangen (Germany)
6. Surface Science Research Centre and Department of Physics, The University of Liverpool, Liverpool L69 3BX (United Kingdom)
7. Department of Mathematics and Physics, Lappeenranta University of Technology, P.O. Box 20, FIN-53851 Lappeenranta (Finland)
8. Department of Physics, Penn State University, University Park, Pennsylvania 16802 (United States)

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.

• OSTI ID: 22493554
• Journal Information: Journal of Chemical Physics, Vol. 143, Issue 7; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ANNEALING
CATALYSTS
CESIUM CHLORIDES
CRYSTAL STRUCTURE
DENSITY FUNCTIONAL METHOD
ELECTRON DIFFRACTION
ELECTRON MICROSCOPY
ETCHING
INDIUM
INTERMETALLIC COMPOUNDS
LAYERS
METHANOL
MONOCRYSTALS
MORPHOLOGY
PALLADIUM
POLYCRYSTALS
SCANNING TUNNELING MICROSCOPY
SURFACE ENERGY
SURFACES
X-RAY PHOTOELECTRON SPECTROSCOPY