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

G. M. McGuirk, J. Ledieu, É. Gaudry, M.-C. de Weerd, M. Hahne, P. Gille, D. C. A. Ivarsson, M. Armbrüster, J. Ardini, G. Held, F. Maccherozzi, A. Bayer (+4 others)
2015 Journal of Chemical Physics  
Structure and morphology of the As-rich and the stoichiometric GaAs(114)A surface J. Appl. Phys. 95, 7645 (2004); 10.1063/1.1707212 Tin-oxide overlayer formation by oxidation of Pt-Sn(111) surface alloys J. 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
more » ... cuum 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. C 2015 AIP Publishing LLC. [http://dx.
doi:10.1063/1.4928650 pmid:26298146 fatcat:yk6a5fvzivgczd2ul7x3vbelpq