Shigemi Kohiki

Surface characterization and catalytic properties of La1−x-Sr x CoO3

The surface chemical states of the perovskite-type compounds, strontium doped lanthanum cobalt oxides (La1−xSrxCoO3), have been investigated using X-ray photoelectron spectroscopy (XPS). Catalytic oxidations of both methane and CO have also been investigated using flow methods. The chemical composition of the surface of La1−xSrxCoO3 was very different from that in the bulk, which was measured by X-ray fluorescence spectroscopy (XRFS). The catalytic activity of La1−xSrxCoO3 increased with an increase in the quantity of cobalt atoms on the surface.

ENHANCED CONDUCTIVITY OF ZINC OXIDE THIN FILMS BY ION IMPLANTATION OF HYDROGEN ATOMS

Enhancement of the conductivity of zinc oxide through doping with hydrogen atoms was examined by using ion implantation of highly resistive thin films deposited by rf magnetron sputtering at room temperature. With a doping of 1×1017 atoms cm−2, the conductivity after annealing at 200 °C in an N2 atmosphere at 1 atm rose from the initial 1×10−7 Ω−1 cm−1 to 5.5×102 Ω−1 cm−1.

Photoemission from small Pd clusters on Al2O3 and SiO2 substrates

Abstract Positive core-electron binding energy shifts in small palladium clusters supported on Al 2 O 3 and SiO 2 substrates are shown to arise predominantly from an initial-state effect that is more sensitive to cluster size than a final-state effect in lower coverage regions (Pd ⪅ 1×10 15 atoms cm -2 for Al 2 O 3 and ⪅1×10 14 atoms cm -2 for SiO 2 ). The change of the extra-atomic relaxation energy in larger coverage regions directly correlates to the polarizability of the substrates.

Formation of Superconducting Bi-Sr-Ca-Cu-O Thin Films with Controlled c-Axis Lattice Spacings by Multitarget Sputtering

Thin films of the Bi-Sr-Ca-Cu-O system were prepared by sequential deposition of Bi, SrCu, CaCu and SrCu oxides using multitarget sputtering. It was confirmed that the c-axis spacing of lattice planes could be controlled by the variation of the CaCu oxide layer. Also, thin films of the Bi system with the insertion of four Cu-O2 planes were synthesized. The Tcs of the films were found to be 80 K, 110 K and 90 K for the Bi system with two, three and four Cu-O2 planes, respectively.

Enhanced electrical conductivity of zinc oxide thin films by ion implantation of gallium, aluminum, and boron atoms

Effect of ion implantation on the conductivity of zinc oxide was examined by using highly resistive zinc oxide thin films deposited by rf magnetron sputtering at room temperature to reduce the effect of oxygen vacancies. With the doping by 1×1017 atoms/cm2 gallium the conductivity is 1.0×103/Ω cm for as‐implanted film and it increases up to 3.7×103/Ω cm, the highest conductivity reported for zinc oxide films, with raising the annealing temperature in either a nitrogen or oxygen atmosphere. The conductivity of aluminum‐doped films is slightly lower than those of gallium‐doped films. Among the elements gallium, aluminum, and boron, gallium is the most effective in enhancing the conductivity and boron is the least. The order of the effectiveness is explained by the electronegativity of the dopants.

Interaction of hydrogenated amorphous silicon films with transparent conductive films

The effects of the deposition temperature on the interaction of the hydrogenated amorphous silicon films with indium–tin–oxide and tin–oxide films have been investigated in the temperature range 150–300 °C, using Auger electron spectroscopy, secondary ion mass spectrometry, and scanning electron microscopy. It was found that the constituent atoms such as indium and tin are detected in the thin amorphous silicon films deposited. Around the interface between the transparent conductive films and amorphous silicon films the formation of oxidized silicon was also observed. The depth distributions of indium in the amorphous silicon films are strongly dependent upon the deposition temperature while those of tin are almost independent. From results on the observation of the surface morphology of the amorphous silicon films, it has been shown that those depth distributions may be much affected by the initial covering over substrates with the amorphous silicon films.

Ti 2p and Ti 3p X-ray photoelectron spectra for TiO2, SrTiO3 and BaTiO3

Ti 2p and Ti 3p X-ray photoelectron spectra (XPS) were taken for TiO2, SrTiO3 and BaTiO3 single crystals fractured insitu in an electron spectrometer. The inelastic scattering energy loss parts were removed from the observed Ti core level XPS by a deconvolution method using O 1s spectra as a response function. The Ti 2p spectrum for TiO2 has four maxima and it indicates that the final states of the photoemission had quasi continuous energy states. The Ti 2p spectra for SrTiO3 and BaTiO3 had only three maxima. The Ti 3p spectra of the three samples had satellite peaks with energy separation of about 14 eV from the main peaks. The intensity at the higher binding energy side of the main peaks continuously decreased with the relative binding energy from 0 to 8 eV. The spectral features of the Ti 2p and Ti 3p spectra are explained by the charge transfer model after the photoemission.

Ferromagnetism in Transparent Thin Films of Fe-Doped Indium Tin Oxide

Transparent films of Fe-doped indium tin oxide (ITO) were grown at oxygen pressures of 5, 1, 10-1, 10-2, and 10-3 Pa on yttria-stabilized zirconia (001) substrates by a pulsed-laser deposition method. We observed X-ray diffraction peaks from (00h) planes of In2O3 crystalline phase for the films. The films grown at 5 and 1 Pa were paramagnetic and semiconducting, that at 10-1 Pa was ferromagnetic and semiconducting, and those at 10-2 and 10-3 Pa were ferromagnetic and metallic. The Fe-ITO films grown below 10-1 Pa exhibited room-temperature (RT) ferromagnetism. Nanoscale Fe clusters in the highest oxidation state such as γ-Fe2O3 resulted in the RT ferromagnetism.

A new charge-correction method in X-ray photoelectron spectroscopy

Abstract The 2p 3 2 binding energy (242.3 eV) of Ar implanted in insulating materials is available to correct for charging shifts. Argon ions hav materials SiO2 and soda glass. In each case the charging shift for Ar 2p 3 2 electrons agrees exactly with those for core-level elec The charge-corrected binding energies of the insulating materials permit the identification of atomic chemical states. Ion-induced reduction of the ins investigations.

Dilution effect on magnetic properties of Co3O4 nanocrystals

We have prepared diluted systems of Co3O4 nanocrystals dispersed in an amorphous silicate by calcination of molecular sieve soaked in precursor solutions with concentrations of 0.01 and 0.1 mol/l. For both systems we have observed the disappearance of the antiferromagnetic phase transition at 33 K of bulk Co3O4, a difference in the dc susceptibility between field cooling and zero field cooling, and the frequency dependence of the ac susceptibility. Nonlinear susceptibility measurements demonstrated that the systems from the solution of 0.01 and 0.1 mol/l were in superparamagnetic and spin glass phases, respectively. The 0.01 mol/l solution system showed no peaks at any temperature, although the peak temperature for the 0.1 mol/l solution system was 18–22 K. The interparticle interactions were independent and collective for the systems from 0.01 and 0.1 mol/l solutions, respectively.