Metal Aggregates on Oxide Surfaces: Structure and Adsorption

The growth of metals on oxide substrates has been the subject of many studies in the past (e.g. see the review article of Campbell (Campbell 1997) and references cited therein). One of the reasons for the interest in these systems results from the potential they have as model systems for supported metal catalysts, since they facilitate a detailed investigation of the interplay between the structure of such composite systems and their interaction with adsorbates. There are several examples showing that it is within reach to establish correlations between particle size and electronic properties on the one hand and adsorption behavior or catalytic activity on the other hand (Lambert 1997, Freund 1997-1). Typical metal support systems are those in which the metal is a transition metal, and the support is, for example, composed of SiO2, Al2O3, or MgO. We can produce wellordered layers of MgO (Wu 1992 and 1993, He 1992, Heidberg 1993, Henzler 1993, Schwennicke 1993, Truong 1993, Vesecky 1994, Zecchina 1996, Schr oder) and Al2O3 (Jaeger 1991, Wuttig 1991, Jaeger 1993-1 and -2, Libuda 1994-1 and -2, Chen 1994, Wu 1995, Wu). The preparation of ordered SiO2 layers still gives difficulties (Stempel). We have focused our attention until now on the support system Al2O3, and, thus in the following, initially the structure and properties of the support (Jaeger 1991, Libuda 1994-2) as well as the possibilities of its chemical modification by functionalization (Libuda 1996-1) will be considered, and, thereafter, the growth, morphology, electronic and magnetic structure as well as adsorption and reaction behavior of the metal films deposited (Libuda 1995, Libuda 1996-1 and -2, Freund 1993, Winkelmann 1994, Wohlrab 1996, Bertrams 1995, B aumer 1995, Sandell 1995, 1996, 1997 and 1998).