M. Ritter

Adsorption of water on FeO(111) and Fe3O4(111): identification of active sites for dissociation

The adsorption of water on epitaxial FeO(111) and Fe3O4(111) films structurally well characterized by STM and LEED was investigated with photoelectron and thermal desorption spectroscopy. On the FeO(111) surface terminated by a close-packed oxygen layer monomeric water spe- cies get physisorbed. On the Fe3O4(111) surface terminated by ¼ monolayer of Fe atoms located over a close-packed oxygen layer underneath water dissociates resulting in adsorbed OH groups. The OH saturation coverage corresponds to the number of surface Fe atoms, which is much larger than the surface defect concentrations. Therefore, the dissociation takes place at Fe sites exposed on the regular Fe3O4(111) surface, and the FeO(111) surface is chemically inert because no Fe sites exist thereon.

Multicomponent surface analysis system combined with high pressure reaction cells for studying metal oxide model catalysts

A three chamber ultrahigh vacuum (UHV) surface analysis system combined with high pressure reaction cells has been designed. It can be used for the preparation and characterization of ordered metal oxide model catalyst surfaces and for the investigation of heterogeneous catalytic reactions there on also under high pressures. The reaction cells are completely separated from the UHV analysis chambers. They can be used for oxidation treatments and reaction studies at total pressures up to 1 bar. A new sample transfer mechanism together with sapphire sample holders and sample heating–cooling stations on the analysis chamber manipulators provides electron beam and resistive sample heating, liquid nitrogen sample cooling, and precise thermocouple temperature control. First experimental results obtained on single crystalline iron oxide dehydrogenation films grown onto Pt(111) substrates are presented. These results demonstrate the capability of the system for in situ investigation of a sample surface using scann...

Structure of epitaxial iron oxide films grown on Pt(100) determined by low energy electron diffraction

Abstract Ordered iron oxide films from submonolayer to multilayer thickness were grown layer-by-layer onto a Pt(100) substrate by iron deposition and subsequent oxidation at 900 K and 10 − 6 mbar oxygen. Their structure and composition were determined by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). The hexagonal reconstruction of the clean Pt(100) surface is lifted underneath the iron oxide film. The first monolayer forms a c(2 × 10) coincidence structure with respect to an unreconstructed Pt(100) surface. For this monolayer the best fit structure, as provided by a LEED intensity analysis, consists of a slightly distorted hexagonal close-packed iron-oxygen bilayer with oxygen on top. The average platinum-iron and iron-oxygen interlayer distances are 1.61 and 1.26 A, respectively. The iron and oxygen planes are buckled by 0.5 and 0.3 A, respectively. Thicker films grow in (111) orientation of Fe 3 O 4 and form the same surface structure as Fe 3 O 4 multilayer films grown on Pt(111).