Structure and Magnetism of well-defined cobalt nanoparticles embedded in a niobium matrix

Our recent studies on Co-clusters embedded in various matrices reveal that the co-deposition technique (simultaneous deposition of two beams : one for the pre-formed clusters and one for the matrix atoms) is a powerful tool to prepare magnetic nanostructures with any couple of materials even though they are miscible. We study, both sharply related, structure and magnetism of the Co/Nb system. Because such a heterogeneous system needs to be described at different scales, we used microscopic and macroscopic techniques but also local selective absorption ones. We conclude that our clusters are 3 nm diameter f.c.c truncated octahedrons with a pure cobalt core and a solid solution between Co and Nb located at the interface which could be responsible for the magnetically inactive monolayers we found. The use of a very diluted Co/Nb film, further lithographed, would allow us to achieve a pattern of microsquid devices in view to study the magnetic dynamics of a single-Co cluster.Comment: 7 TeX pages, 9 Postscript figures, detailed heading adde

H and O atom detection for combustion applications: study of quenching and laser photolysis effects

Meier U, Kohse-Höinghaus K, Just T. H and O atom detection for combustion applications: study of quenching and laser photolysis effects. Chemical Physics Letters. 1986;126(6):567-573.A method is in development which should allow the determination of absolute number densities of H and 0 atoms in flames from two-photon laser-excited fluorescence measurements. The calibration will be based on reference experiments in a discharge-flow reactor. In this study, the influence of fluorescence quenching and the generation of additional H and 0 atoms by laser photolysis of the flame gases is investigated. Consequences for typical hydrogen-oxygen flame conditions are discussed

Discussion of two-photon laser-excited fluorescence as a method for quantitative detection of oxygen atoms in flames

Meier U, Bittner J, Kohse-Höinghaus K, Just T. Discussion of two-photon laser-excited fluorescence as a method for quantitative detection of oxygen atoms in flames. PROCEEDINGS OF THE COMBUSTION INSTITUTE. 1989;22(1):1887-1896.Spatially resolved measurements of absolute oxygen atom concentrations in low-pressure H2/O2/Ar-, CH4/O2- and C2H2/O2 flames are performed by two-photon laser excited fluorescence. The measured signals are converted into O atom number densities using a calibration technique, based on the comparison of fluorescence signals in a flame with those in a discharge flow reactor. This procedure requires consideration of quenching processes; furthermore, the influence of photoionization and potential photodissociation of flame gases must be considered. The sensitivity of the derived concentrations to experimental parameters and atomic quantities is discussed