Kenji Tabata

Surface characterization of LaMnO3+δ powder annealed in air

Abstract Perovskite-type LaMnO3+δ, synthesized using poly(acrylic acid) (PAA), was annealed at 400 and 700°C in air for 6–54 hr. The crystallite size, the specific surface area, the La/Mn ratio, and the catalytic activity of LaMnO3+δ were measured to characterize the surface. The specific surface area decreased slightly with increasing annealing time, while the La/Mn ratio of the surface, calculated from the XPS measurements, was independent of annealing time. The catalytic activity for the oxidation of CO increased with annealing. These results suggest that annealing improved the crystallinity (regularity of the ions) of the LaMnO3+δ surface.

Catalytic application of Mo-incorporated SBA-1 mesoporous molecular sieves to partial oxidation of methane

Abstract Mo-incorporated SBA-1 mesoporous molecular sieves have been synthesized under acidic conditions using cetyltriethylammonium bromide as a surfactant and used as catalysts for partial oxidation of methane with oxygen as an oxidant. In the partial oxidation of methane the catalytic performance of Mo–SBA-1 materials directly synthesized from the Mo-containing gel were superior to those of Mo-impregnated pure siliceous SBA-1 and amorphous silica.

Effects of PLT-buffer layer on microstructures of sputtered PLZT thin films epitaxially grown on sapphire

The microstructures of sputtered thin films of lead-lanthanum zirconate-titanate (PLZT) on (0001) sapphire substrate have been studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thin films of polycrystalline PLZT (9/65/35), Pb 0.91 La 0.09 Zr 0.65 Ti 0.35 O 3 , were prepared on a (0001) sapphire substrate by reactive sputtering, using the dc-magnetron system with a multitarget, Pb, La, Zr, and Ti at the substrate temperature of 700 °C. The PLZT thin films comprised (111) oriented small crystallites of PLZT. Although the average direction of the crystal orientation corresponded to the ideal epitaxial relationship (111) PLZT ‖ (0001) sapphire, the individual crystallites showed misalignment in both the growth direction and the film plane. The thin films could not be considered epitaxially grown films. From analysis of the TEM images, there exists an interfacial region between the PLZT thin film and the substrate. The interfacial region comprises ordered clusters of (111), disordered (101), and/or (110) PLZT crystallites. The presence of the interfacial region will suppress ideal epitaxial growth with uniform crystal orientation. It is confirmed that the addition of the buffer layer of graded composition of PLT-PLZT, between the substrate and the PLZT thin film, will suppress the formation of the disordered interfacial region and will enhance the epitaxial growth of the (111) PLZT on (0001) sapphire with three-dimensional crystal orientations.

The enhancement effects of added methanol on methane-selective oxidation in the gas phase reaction of CH4-O2-NO2

The reactivity of the selective oxidation of methane in the gas phase reaction of CH4–O2–NO2 was enhanced by the addition of a small amount of methanol. The selectivity of methanol produced at the same level of methane conversion was enhanced by adding a small amount of methanol in the feed gas. The enhanced effect of methanol addition was restricted to methane conversion in the presence of NO2. The enhancement effect was obtained more effectively when the ratio of methanol to NO2 was near to 1, at which higher concentration of both methanol and NO2 a significant enhancement was shown. Theoretical calculations concluded as follows: CH3OH + NO2→CH2OH + HNO2 was the predominant step of hydrogen abstraction from methanol. HO2 was then produced by CH2OH + O2→CH2O + HO2. CH4 + HO2→CH3 + H2O2 was the key reaction to enhance the reactivity of methane. HO2 + OH→H2O + O2 brought about an OH radical dissipation reaction to stabilize the produced methanol from the following decomposition reaction: CH3OH + OH→CH2OH + HO2 .

Morphological effects of SnO2 thin film on the selective oxidation of methane

The morphological effects of SnO 2 thin film on catalytic activities and selectivities for the selective oxidation of CH 4 were investigated with X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). Dense texture type and a columnar texture type SnO 2 thin films were prepared by the sputtering method. The measured proportion of adsorbed oxygen species (O 2- , O 2 2- , O 2 - and O b ) on these two types of samples with XPS were different from each other, and the proportion of a highly reactive oxygen species O - was larger on the dense sample. The TDS data of the products (HCHO, CH 3 OH, CO, CO 2 and H 2 O) were obtained on the two different structured film samples after CH 4 exposure at room temperature. The obtained TPD data were explained appropriately by considering several reaction pathways. The dense texture type SnO 2 film showed a higher reactivity for the oxidation of CH 4 than that of the columnar texture type one. The selective formation of HCHO was especially observed for the dense texture film. The oxidation of CH 4 was therefore strongly affected by the surface morphology of SnO 2 film.

Microstructures of sputtered PbTiO3 thin films

Ultrathin stoichiometric PbTiO3 films, 10–100 nm thick, were deposited on (001) SrTiO3 substrate at 600 °C by rf planar magnetron sputtering to understand the microstructure of initial film growth. The electron microscopy and x‐ray diffraction analysis suggested epitaxial growth of (001) PbTiO3/(001) SrTiO3 with three‐dimensional crystal orientation; however, the PbTiO3 films still included crystal boundaries. Miscut (001) SrTiO3 substrates reduced the crystal boundaries and provided continuous ultrathin films of single crystal PbTiO3. Rapid thermal annealing at 600 °C for 10 s further improved their crystallinity.

Methanol adsorption on an oxidized and a reduced SnO2 thin film

Abstract The effects of surface structures of SnO 2 thin films on the selective dissociation of methanol have been investigated with X-ray photoelectron spectroscopy. A pre-oxidized surface of SnO 2 was in favor of the abstraction of hydrogen from methanol while a highly defective surface of SnO 2 prepared by Ar-ion etching favored the dissociation of the CO bond in methanol. The surface, therefore, of pre-oxidized SnO 2 reacted as Bronstead base sites but the surface of highly defective SnO 2 reacted as Bronstead acid sites. These results clearly show the importance of surface structures in the selection of the acid/base interaction of methanol on the SnO 2 surface.

Photoemission study of the subsequential oxidation of dissociatively adsorbed methane on an SnO2 thin film

The subsequent oxidation steps for direct methane selective oxidation with oxygen were examined with x-ray photoelectron spectroscopy (XPS). The intermediate hydrocarbon species, i.e. methoxide, methanol and dioxymethylene species, were observed in the C 1s level spectrum after CH4 exposure at 473 K onto an SnO2 thin film. These chemical species were not oxidized with oxygen even after additional O2 exposure at 473 K, but molecularly adsorbed methane and its carbonaceous intermediates were oxidized mainly to dioxymethylene species. This result agreed with the expectation from the values of theoretically calculated transition barriers of their oxidation reactions. The dioxymethylene species produced seemed to be partly decomposed to methoxide and formate species during heat treatment up to 773 K. Copyright

Topmost surface analysis of a z-cut LiNbO3 by coaxial impact-collision ion scattering spectroscopy

Abstract Topmost structure of a z-cut (001) single crystal of LiNbO 3 has been examined and simulated by Coaxial Impact Collision Ion Scattering Spectroscopy (CAICISS). The measured and the simulated spectra of polar angle dependency of Nb signal intensities for the as-supplied sample were consistent with each other at the [210] azimuthal directional face which was composed of metals (Li and Nb), but inconsistent at the [100] azimuthal directional face, which was composed of metals and oxygen. We suspected that the O-terminated model represented the right model, but the simulation of two directional displaced models was insufficient to express the measured spectrum.

Study of the topmost surface structure of a y-cut LiNbO3 single crystal with coaxial impact collision ion scattering spectroscopy (CAICISS)

Abstract The topmost surface structures of a y -cut LiNbO 3 single crystal were studied with coaxial impact collision ion scattering spectroscopy (CAICISS). The observed CAICISS spectra of the azimuthal intensity variation of Nb atoms of that had mirror plane symmetry which was unexpected from the space group of LiNbO 3 ( R 3 c , C 3 v 6 ) itself. By the simulation of CAICISS, it was strongly suggested that Nb atoms at the topmost few layers of y -cut LiNbO 3 single crystal were rearranged to give a mirror plane of symmetry in their three-dimensional atomic configuration rather than to form other related oxides.