Formation of Iron Oxide Nanoparticles and Thin Films on Au(111)
(Result of the month 05/2007)

Iron-based catalysts, including iron oxides, are an important class of materials with relevance to Fischer-Tropsch catalysis and gas-sensing applications. The controlled growth of nanoparticles and atomically thin films on single crystal surfaces allows for systematic studies of how size, shape, and atomic structure affect the chemical reactivity of these materials. We have studied the formation of monolayer thick iron oxide nanoparticles and thin films on the reconstructed Au(111) surface. A variety of interesting structural and chemical properties are noted with these novel materials.

A 50  x 50 nm STM scan of iron deposited on the reconstructed Au(111) surface at room temperature. Fe particles are one monolayer thick and form triangular shapes. Evidence of 2nd layer formation prior to the completion of the 1st layer is also seen.

A 9 X 10 nm scan of an FexOy particle formed on a Au(111) surface. The particle is formed by exposing Fe particles similar to those shown in Image 1 to molecular oxygen at ~325 K followed by vacuum annealing at 500-700 K. FexOy particles formed in this manner tend to be a monolayer high, are hexagonal in shape, and have a well-formed crystalline structure.

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A 18 X 18 nm scan of an FexOy particle grown on a Au(111) surface. Larger particles show evidence of a long range periodicity seen as brighter spots in the image. This effect is believed to result from a non-coincidence periodicity between the FexOy monolayer and the underlying Au(111) substrate, which creates different tunneling environments depending on the registration of the FexOy and Au(111) lattice sites.

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