Ultrathin magnesia films as support for molecules and metal clusters: Tuning reactivity by thickness and composition

• Published in: Physica status solidi. B. Basic research 2010-05, Vol.247 (5), p.1001-1015
• Main Authors: Vaida, Mihai E., Bernhardt, Thorsten M., Barth, Clemens, Esch, Friedrich, Heiz, Ueli, Landman, Uzi
• Format: Article
• Language: English
• Subjects: 68.47.Jn; 79.60.-i; 82.53.Eb; 82.53.St; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Other nonelectronic properties; Physics; Solid surfaces and solid-solid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties)
• ISSN: 0370-1972; 1521-3951
• DOI: 10.1002/pssb.200945579

Ultrathin metal oxide films have attracted considerable interest in recent years as versatile substrate for the design of nanocatalytic model systems. In particular, it has been proposed theoretically and confirmed experimentally that the electronic structure of adsorbates can be influenced by the layer thickness and the stoichiometry, i.e., the type and number of defects, of the oxide film. This has important consequences on the chemical reactivity of the oxide surface itself and of oxide supported metal clusters. It also opens new possibilities to influence and to control chemical reactions occurring at the surface of these systems. The present feature focuses on very recent experiments that illustrate the effects of a proper adjustment of layer thickness and composition of ultrathin MgO(100) films on chemical transformations. On the magnesia surface itself, the photodissociation dynamics of methyl iodide molecules is investigated via femtosecond‐laser pump–probe mass spectrometry. Furthermore, the catalytic oxidation of carbon monoxide at mass‐selected Au20 clusters deposited on magnesia is explored through temperature programmed reaction measurements. In the latter case, detailed first principles calculations are able to correlate the experimentally observed reactivity with structural dimensionality changes that are induced by the changing thickness and composition of the magnesia support. Ultrathin metal oxide films provide the opportunity to influence the electronic structure of adsorbates by varying the layer thickness and the type and number of defects of the film. This has important consequences on the chemical reactivity of the oxide surface itself and of oxide supported metal clusters. This article focuses on selected examples that demonstrate new possibilities to influence and to control chemical reactions occurring at the surface of these systems.