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 (La_1?x Sr _x CoO₃), 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 La_1?x Sr _x CoO₃ was very different from that in the bulk, which was measured by X-ray fluorescence spectroscopy (XRFS). The catalytic activity of La_1?x Sr _x CoO₃ increased with an increase in the quantity of cobalt atoms on the surface.     

Temperature-dependent change of Cu-O bond in La2CuO4 and YBa2Cu3O7

Valence-band spectra of La₂CuO₄ and YBa₂Cu₃O₇ were obtained by using X-ray photoemission varying the temperature of the measurement (35, 260, 300, and 500 C). In La₂CuO₄ the broad band centred around 4eV splits into two peaks at 260 C. At both 35 and 500 C the spectra show almost similar shape. In YBa₂Cu₃O₇ the broad peak centred around 4eV splits into two peaks at 500 C. Below 300 C the spectra show almost similar shape. These splittings of the valence-band spectra may be due to the rearrangement of the crystal structure accompanying the phase transition from the orthorhombic to tetragonal symmetry.     

Correlation between resistivity and oxygen vacancy of hydrogen-doped indium tin oxide thin films

Thin films of indium tin oxide (ITO) sputter-deposited by dc-plasma containing deuterium on glass substrate without any heat treatments exhibited gradual lowering in electrical resistivity with increasing the deuterium content [D₂] in plasma gas by 1% and then demonstrated a jump in resistivity by further increase of [D₂] than 1%. X-ray photoelectron spectroscopy revealed that hydroxyl-bonded oxygen in ITO grew continuingly with [D₂]. Deuterium positioned at the interstitial site increased almost quantitatively with increasing [D₂]. Rutherford backscattering spectroscopy showed gradual reduction in the oxygen content of ITO with increasing [D₂] by 1% and then demonstrated an abrupt increase of the oxygen content with the increase of [D₂] than 1%. The films with [D₂] < 1% were oxygen deficient, but those with [D₂] > 1% were excess of oxygen. The most oxygen deficient film of [D₂] = 1% was the most conductive. Behavior in the resistivity with [D₂] looks parallel to that in the oxygen content. A lower resistivity of the films corresponded well to oxygen vacancy rather than hydrogen interstitial.     

Growth of β-Ga2O3 nanocolumns crossing perpendicularly each other on MgO (1 0 0) surface

β-Ga₂O₃ nanocolumns straightened and crossed perpendicularly each other were deposited on MgO (1 0 0) substrate by vapor phase transport method. Growth of the nanocolumns was examined at steps of 1000, 1050, and 1200 °C in elevation of source-boat temperature. We have drawn out the substrate from deposition-tube at each source-boat temperatures of 1000, 1050, and 1200 °C. Scanning electron microscopy of the sample with source-boat temperature of 1200 °C demonstrated that the straightened and elongated nanocolumns are crossing perpendicularly each other. Typical lengths of the nanocolumns were in the range of several hundreds nanometers below 1050 °C, and those of 1200 °C were in the range of ten to fifteen hundreds nanometers. Diameters of the nanocolumns stayed in the range of few hundreds nanometers, notwithstanding variation of the source temperature. X-ray diffraction and transmission electron microscopy with energy dispersive X-ray spectroscopy revealed that the nanocolumns are monoclinic β-Ga₂O₃ crystal, and the (4 0 0) plane of β-Ga₂O₃ nanocolumns is parallel to the (1 0 0) plane of MgO substrate.     

Optical and electrical properties of indium tin oxide thin films sputter-deposited in working gas containing hydrogen without heat treatments

Polycrystalline thin films of indium tin oxide sputter-deposited in the working gas containing hydrogen of 0.3–1.5% exhibited transmittance of ≥ 80% for visible lights and blue-shift of ≥ 0.1 eV in the optical absorption energy. The film deposited in the gas containing hydrogen of 1% demonstrated almost flat temperature-dependent resistivity and the lowest resistivity of ≈ 1.5 × 10^? 4 Ω cm at room temperature. The carrier density showed an inverse V-shaped behavior with the maximum at the hydrogen concentration of 1%. The mobility stayed at almost constant below the hydrogen concentration of 1% and dropped rather rapidly above 1%.     

Catalytic properties and surface states of La1−x (Th,Sr) x CoO3

The surface chemical states of the perovskite-type thorium- or strontium-doped lanthanum cobalt oxides (La_1–x Th _x CoO₃, La_1–x Sr _x CoO₃) have been investigated using X-ray photoelectron spectroscopy. Catalytic oxidations of CO have been also investigated by flow methods. The ionicity between cobalt and lattice oxygen was increased by substituting thorium for lanthanum, and had a peak atx = 0.02. The catalytic activity also had a peak atx = 0.02. However, the ionicity decreased for the case of strontium substitution, and the activity also decreased.