Theory of quasicrystal surfaces: Probing the chemical reactivity by atomic and molecular adsorption
- Author(s)
- Marian Krajci, Juergen Hafner
- Abstract
The adsorption of oxygen and carbon atoms and of carbon monoxide molecules on a fivefold surface of icosahedral Al–Pd–Mn quasicrystals has been investigated using ab initio density-functional calculations. The quasicrystalline surface has been modeled by periodically repeated slabs cut from rational approximants to the quasicrystalline structure. Atomic and molecular adsorption have been studied for a large number of possible adsorption sites by performing three-dimensional static relaxations of the adsorbate/substrate complex. Four different scenarios for the dissociative adsorption of the CO molecule have been investigated via nudged-elastic band calculations of the transition states. Al and Mn-metal atoms present at the surface bind C and O atoms rather strongly, while Pd atoms are unstable adsorption sites: during relaxation, the adsorbate drifts to the nearest strong-binding site. The chemical reactivity with respect to a CO molecule varies very strongly across the surface. The adsorption close to Mn sites is promoted by rather strong covalent effects, but CO is only physisorbed at Al sites via weak polarization forces. On the basis of the observed local variations of the adsorption strength, we develop scenarios for dissociation and determine the potential energy barriers for this processes. We find that CO adsorbed close to a transition-metal atom can dissociate via an activated process, but the dissociation rate is expected to be rather low because of a high dissociation barrier and a “late” transition state. CO adsorbed close to Al atoms will desorb before dissociation. Surface vacancies present as a consequence of the irregular coordination of the Mackay cluster in the quasiperiodic structure will act as strongly attractive traps for diffusing molecules. Mn surface atoms are located in the center of truncated Mackay clusters. In scanning tunneling electron microscopy (STM) these truncated clusters are imaged as “white flowers”. Surface vacancies are responsible for the “dark stars” in the STM images. Since both are molecular adsorption sites, our study predicts that these characteristic features should be affected by CO adsorption.
- Organisation(s)
- Computational Materials Physics
- External organisation(s)
- Slovenian Academy of Sciences and Arts (SASA)
- Journal
- Surface Science
- Volume
- 602
- Pages
- 182–197
- No. of pages
- 16
- ISSN
- 0039-6028
- DOI
- https://doi.org/10.1016/j.susc.2007.10.003
- Publication date
- 2008
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 103015 Condensed matter
- Portal url
- https://ucris.univie.ac.at/portal/en/publications/theory-of-quasicrystal-surfaces-probing-the-chemical-reactivity-by-atomic-and-molecular-adsorption(0d755cab-03ec-47c1-b9dd-e64b11d2549b).html