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O: Oberflächenphysik

O 46: Adsorption VI

O 46.2: Vortrag

Freitag, 31. März 2006, 11:30–11:45, TRE Phys

The p(4 × 4) structure of Ag(111): A soft O-induced reconstruction — •Michael Schmid¹, Georg Kresse², Jan Klikovits¹, Orest Dubay², and Peter Varga¹ — ¹Inst. f. Allgemeine Physik, TU Wien — ²Inst. f. Materialphysik and CMS, Universität Wien

Silver is a well-known catalyst for selective oxidation reactions, e.g., of ethylene (epoxidation). The phase on the (111) surface usually associated with this reaction is a p(4 × 4) superstructure, which has been studied since 1972 [1] and considered a surface oxide similar to a layer of the Ag₂O bulk structure since 1974. An X-ray diffraction study by A. Stierle et al. [2] has disproved essentially all Ag₂O-based models [3] so far. We have studied the mass transport during reduction of the p(4 × 4) structure by scanning tunneling microscopy (STM) to determine the number of Ag atoms per cell. Based on this input and the STM images, a structural model very different from Ag₂O emerges. The model is compatible with high-resolution core level spectroscopy data and was confirmed by surface x-ray diffraction [4]. The structure does not have the lowest energy of all possible models in density functional theory (DFT) calculations, a fact attributed an inherent problem of today’s DFT calculations. Nevertheless, DFT is valuable for a detailed study of this structure and shows that it is very soft, exhibiting extremely high vibration amplitudes.

[1] G. Rovida et al., J. Vac. Sci. Technol. 9, 796 (1972).

[2] A. Stierle et al., contribution at DPG Frühjahrstagung 2004.

[3] A. Michaelides et al., J. Vac. Sci. Technol. A 23, 1487 (2005).

[4] A. Stierle et al., contribution at this conference.