Continuity approach, metal deposition

Deposition of small clusters using a STM tip can be used [183]. It could also position metal clusters at desired locations on a flat substrate. The technique can be scaled up using the millipede approach to deposit a large number of clusters simultaneously [184]. Potentially, it can be coupled with dip-pen technology for a continuous supply of the metal precursor [185]. At present, however, these techniques have not yet achieved atomic control. In other words, there is no technique yet to generate supported metal clusters of uniform composition, shape, and size. 

Noble metal particles of Au, Pt, and Ir were deposited on nanostructured Ti02 films using an electrophoretic approach [189], The improved photoelectrochemical performance of the semiconductor-metal composite film was attributed to the shift in the quasi-Fermi level of the composite to more negative potentials. Continuous irradiation of the composite films over a long period causes the photocurrent to decrease as the semiconductor-metal interface undergoes chemical changes. 

Another approach to preparing model catalysts is the preparation of inverse supported catalysts . In this approach, the catalytically active metal (usually single crystal) is used as a substrate upon which an oxide is deposited, presumably leaving patches of exposed metal. This approach has been used to study reduction of ceria, and methanation kinetics on Rh as promoted by deposited ceria, and chemisorption of various molecules. As stated above, it is generally assumed that thick enough ceria layers will continuously cover the metal substrate, placing a limit on the thickness of the ceria islands that can be achieved for an inverse supported catalyst. The different procedures used for the inverse and metal particle on bulk oxide model catalysts is expected to produce differences in thermal stability, morphology and surface structure which may have consequences for the reactivity of the model catalyst. 

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