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Mg2NiH4 thin films have been prepared by activated reactive evaporation in a molecular beam epitaxy system equipped with an atomic hydrogen source. The optical reflection spectra and the resistivity of the films are measured in situ during deposition. In situ grown Mg2NiH4 appears to be stable in vacuum due to the fact that the dehydrogenation of the Mg2NiH4 phase is kinetically blocked. Hydrogen desorption only takes place when a Pd cap layer is added. The optical band gap of the in situ deposited Mg2NiH4 hydride, 1.75 eV, is in good agreement with that of Mg2NiH4 which has been formed ex situ by hydrogenation of metallic Pd capped Mg2Ni films. The microstructure of these in situ grown films is characterized by a homogeneous layer with very small grain sizes. This microstructure suppresses the preferred hydride nucleation at the film/substrate interface which was found in as-grown Mg2Ni thin films that are hydrogenated after deposition. [ABSTRACT FROM AUTHOR]

In order to develop optical fiber hydrogen sensors, thin film materials with a high optical contrast between the metallic and hydrided states are needed. Magnesium exhibits such a contrast but cannot be easily hydrogenated at room temperature. However, thin films of Pd-doped Mg (MgPdy with 0.023<=y<=0.125) prepared by magnetron dc sputtering can easily be hydrided at room temperature and 0.5 bar H2 within a few minutes. The rate of first hydrogenation increases linearly with increasing Pd concentration. Hydrogenation induces high variations of transmission (ΔT up to 20%) and reflection (ΔR up to 70%) of light (0.5 eV<=hω<=6.0 eV corresponding to 2500 nm>=λ>=210 nm). The optical properties can be understood by considering Pd as a deep donor in semiconducting MgH2. [ABSTRACT FROM AUTHOR]

A triple layer thin film (30 nm Mg2Ni/100 nm Ti/10 nm Pd sputtered on glass) switches reversibly from a shiny metallic to a “black” state upon exposure to moderate hydrogen pressure (≈5.103 Pa). This black state resembles that obtained in thick Mg2NiHx layers and has the great advantage of being stable and easily controlled. Both the reversible high optical contrast (Rreflective/Rblack≈10 in the red wavelength range) and the fast kinetics of hydrogen absorption and desorption make this material interesting for applications as optical hydrogen sensors. [ABSTRACT FROM AUTHOR]

Presents a study which examined the growth and properties of bilayer structures consisting of insulating epitaxial copper[sub3]nitride films grown on epitaxial ferromagnetic iron[sub4]nitride films. Experiment; Results and discussion; Conclusion.

Copper nitride films were grown by molecular-beam epitaxy of copper in the presence of nitrogen from a radio-frequency atomic source on (001) γ[sup ′]-Fe[sub 4]N/(001)MgO or directly on MgO substrates. The structural properties of the Cu[sub 3]N films were found to be very dependent on the substrate and on the deposition temperature. At optimal growth conditions, the Cu[sub 3]N films grow epitaxial on both substrates. The Cu[sub 3]N films grown on MgO were characterized optically to be insulators with an energy gap of 1.65 eV. On γ[sup ′]-Fe[sub 4]N, Cu[sub 3]N films with a thickness of only 6 nm, were grown as closed layers, epitaxial and rather smooth (root-mean-square roughness of 0.7 nm). This material has ideal properties to be used as a barrier in low resistance magnetic tunnel junctions. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]