Synthesis, Electrical Measurement, and Field Emission Properties of α-Fe2O3Nanowires

α-Fe2O3nanowires (NWs) were formed by the thermal oxidation of an iron film in air at 350 °C for 10 h. The rhombohedral structure of the α-Fe2O3NWs was grown vertically on the substrate with diameters of 8–25 nm and lengths of several hundred nm. It was found that the population density of the NWs per unit area (DNWs) can be varied by the film thickness. The thicker the iron film, the more NWs were grown. The growth mechanism of the NWs is suggested to be a combination effect of the thermal oxidation rate, defects on the film, and selective directional growth. The electrical resistivity of a single NW with a length of 800 nm and a diameter of 15 nm was measured to be 4.42 × 103 Ωcm using conductive atomic force microscopy. The field emission characteristics of the NWs were studied using a two-parallel-plate system. A low turn–on field of 3.3 V/μm and a large current density of 10−3 A/cm2(under an applied field of about 7 V/μm) can be obtained using optimal factors ofDNWsin the cathode

Influence of surface atomic structure demonstrated on oxygen incorporation mechanism at a model perovskite oxide

Perovskite oxide surfaces catalyze oxygen exchange reactions that are crucial for fuel cells, electrolyzers, and thermochemical fuel synthesis. Here, by bridging the gap between surface analysis with atomic resolution and oxygen exchange kinetics measurements, we demonstrate how the exact surface atomic structure can determine the reactivity for oxygen exchange reactions on a model perovskite oxide. Two precisely controlled surface reconstructions with (4 × 1) and (2 × 5) symmetry on 0.5 wt.% Nb-doped SrTiO3(110) were subjected to isotopically labeled oxygen exchange at 450 °C. The oxygen incorporation rate is three times higher on the (4 × 1) surface phase compared to the (2 × 5). Common models of surface reactivity based on the availability of oxygen vacancies or on the ease of electron transfer cannot account for this difference. We propose a structure-driven oxygen exchange mechanism, relying on the flexibility of the surface coordination polyhedra that transform upon dissociation of oxygen molecules.Austrian Science Fund (SFB “ Functional Oxide Surfaces and Interfaces ” - FOXSI, Project F 45)European Research Council Advanced Grant (“OxideSurfaces” (Project ERC-2011-ADG_20110209))National Science Foundation (U.S.). Division of Materials Research (CAREER Award Grant No. 1055583