Tokihisa Hikita

Surface structure of SrTiO3(001) with various surface treatments

Three kinds of SrTiO3(001) surfaces, TiO2 terminated, SrO terminated, and a mixture of these surfaces, are selectively formed and their surface structures are examined by means of reflection high energy electron diffraction, x‐ray photoelectron spectroscopy, and x‐ray photoelectron diffraction. The TiO2 terminated surface is obtained under a moderate temperature (<700 K) cleaning by the Bi deposition/desorption method and subsequent oxidation, where the distance between the first TiO2 plane and the SrO plane underneath is 1.95+0.07 A and the oxygen of the first TiO2 plane is pulled out 0.10 A. The SrO terminated surface is obtained by growing one monolayer of SrO on the TiO2 terminated surface, where the distance between the first SrO plane and TiO2 plane underneath is 1.95+0.10 A and the oxygen of the first SrO plane is pulled out 0.16 A. These two surfaces are different from the surface obtained by Ar+ sputtering and annealing, which is found to be the mixture of TiO2 and SrO terminated surfaces.

The reaction of copper and calcium dipivaloylmethanates (Cu(DPM)2 and Ca(DPM)2) with hydroxyls on oxide surface

Abstract Selective and stoichiometric reactions between surface hydroxyl groups (OH) on SiO 2 and calcium dipivaloylmethanate (Ca(DPM) 2 ) were investigated by infrared (IR) and photoelectron (XPS) spectroscopies. The stoichiometric ratio of initial surface OH and adsorbed Ca(DPM) 2 is estimated from IR absorbance to be ca. (2–3): 1. Introduction of water vapor at 673 K to this surface results in the removal of ligand DPM from the adsorbed Ca(DPM) 2 , leaving the Ca on the surface. The reactive property of Ca(DPM) 2 is identical to that of Cu(DPM) 2 , previously reported by us. A similar reaction on the surface of single crystal SrTiO 3 (100) with the Cu(DPM) 2 is also carried out.

Adsorbed structure of copper and calcium dipivaloylmethanates on SiO2

Abstract Adsorbed states of copper and calcium dipivaloylmethanate [M(DPM)2 (M = Cu, Ca)] complexes on SiO2 are determined by means of infrared (IR) spectroscopy and extended X-ray absorption fine structure (EXAFS). Since the H atom of surface OH moves into the DPM ligands, the structure of the DPM ligand changes into the structure in adsorbed M(DPM)2. No significant changes in the MO bond length and the oxygen coordination numbers around M are observed between isolated M(DPM)2 and adsorbed M(DPM)2 by EXAFS. In spite of the difference in the metals included, the complexes adsorb on SiO2 in a basically identical mechanism, where the adsorbates are stabilized by the ligand-surface interaction.

Reaction between copper dipivaloylmethanate Cu(DPM)2 and H2O adsorbed on SrTiO3(100)

Abstract Selective reaction of copper dipivaloylmethanate (Cu(DPM) 2 , β-diketonate complex) with H 2 O adsorbed on the SrTiO 3 (100) surface is investigated. Adsorption of H 2 O on SrTiO 3 (100) occurs on Ti 3+ sites produced by prior Ar + ion bombardment. It is found that the β-diketonate complex, Cu(DPM) 2 , reacted selectively with the adsorbed H 2 O at room temperature. Further reaction of the adsorbed Cu(DPM) 2 with H 2 O vapor results in the removal of the ligand, DPM, leaving elemental copper on the surface.

Alkali nitrate promoted Raney Ru catalyst as a superior catalyst for ammonia synthesis

Alkali nitrate promoted Raney Ru catalysts were prepared by hydrogenolysis of alkali nitrates (CsNO3, RbNO3, KNO3, and NaNO3) over Raney Ru. These catalysts were even more active in ammonia synthesis than Raney Ru promoted with metallic potassium. The promotion behaviour was different from that for the supported Ru catalysts, where metallic potassium was more effective than CsNO3. Per-weight activity of CsNO3 promoted Raney Ru was higher than that for any catalysts so far reported in ammonia synthesis under 80 kPa and at 573 K.

Structure of Dipivaloylmethanate Complexes Adsorbed with Hydroxyls on SiO2 Surface by EXAFS

Adsorbed structure of copper and calcium dipivaloylmethanates [M(DPM)2, M=Cu and Ca] complexes on amorphous SiO2 are determined by extended X-ray absorption fine structure (EXAFS). There are no significant changes in the M–O bond length and the oxygen coordination numbers around M between the isolated M(DPM)2 and the adsorbed M(DPM)2. Furthermore clear existence of Cu C coordination is observed for the adsorbed Cu(DPM)2. Therefore, it is concluded that the M–O bond and the ring structure of DPM ligand remain unchanged after the adsorption. Introducing water vapor at 673 K to the Cu(DPM)2/SiO2 system results in the removal of ligand DPM from the adsorbed Cu(DPM)2. The remained species is found to be Cu metal particle by the EXAFS and the X-ray absorption near-edge strueture(XANES).

Selective surface reaction between metal compounds and surface functional groups

Reactivity of copper dipivaloylmethanate (Cu(DPM) 2 ) adsorbed selectively on the H 2 O on a SrTiO 3 (1 0 0) surface is discussed. Reaction of the adsorbed (Cu(DPM) 2 with H 2 O vapor at 473 K results in the removal of the ligand, DPM, leaving the highly dispersed copper atoms in the +1 oxidation state on the surface. Dispersed copper is found to aggregate to form particulates at 673 K.