Masatoki Ito

Beamline for Surface and Interface Structures at SPring-8

The main components of a new beamline for surface and interface crystal structure determination at SPring-8 are briefly described. Stages for the beamline monochromator are modified for making an incident X-ray intensity more stable for surface X-ray experiments. Absolute photon flux densities were measured with an incident photon energy. A new ultrahigh vacuum system is introduced with preliminary X-ray measurements from an ordered oxygen on Pt (111) surface.

Hydrogen adsorption on Pt(100), Pt(110), Pt(111) and Pt(1111) electrode surfaces studied by in situ infrared reflection absorption spectroscopy

Abstract Hydrogen adsorption on Pt(100), Pt(1111) (6(100) × (111)), Pt(110) and Pt(111) electrode surfaces was studied by both voltammetry and in situ infrared reflection absorption spectroscopy. The terminal hydrogens absorbed on Pt(100), Pt(1111) and Pt(110) electrodes were observed at 1990–2080 cm −1 as bands appearing at potentials more negative than 0.25, 0.1 and 0 V versus SHE, respectively. However, a well-oriented pt(111) electrode did not give a significant absorption of the terminal hydrogens under similar conditions. The terminal hydrogen adsorption was sensitive to the surface crystallographic orientation.

Carbon monoxide oxidation on a Pt(111) electrode studied by in-situ IRAS and STM: coadsorption of Co with water on Pt(111)

Abstract Coadsorption of carbon monoxide (CO) with water on Pt(111) was investigated by cyclic voltammogram (CV), in-situ and non-situ IRAS and STM in order to explore the mechanism of the oxidation of CO to CO 2 on the surface. CO adsorbed on a Pt(111) electrode at 0.4 V (RHE) showed a strong interaction with overlayer water molecules and retarded the oxidation of CO to CO 2 , whereas CO adsorbed at 0.05 V started to oxidize at a lower potential. The structure change from (2 × 2)-3CO ( θ CO = 0.75) to (√19 × √19)R23.4−13CO ( θ CO = 0.685) was followed by an adsorption of water, which played an important role in CO oxidation. Under UHV a c(4 × 2) structure ( θ CO = 0.50) was observed in preference to the compression structures because of the absence of the coadsorbed water molecule.

The vibrational spectra of water cluster molecules on Pt(111) surface at 20 K

Abstract The adsorption of D 2 O on Pt(111) at 20 K has been investigated by infrared reflection absorption spectroscopy (IRAS). Water was found to form as a dimer at low coverages and it grew a tetramer molecule at high coverages. The structures of the cluster water molecules on the surface were derived from the intensities and the frequencies of symmetric and asymmetric ν OD stretching absorptions. The annealing at higher temperatures than 130 K was needed to form an ice bilayer island structure.

Structures of copper and halides on Pt(111), Pt(100) and Au(111) electrode surfaces studied by in-situ scanning tunneling microscopy

Abstract Structures of copper and halide (chloride, bromide or iodide) in a sulfuric acid solution on Pt(111), Pt(100) and Au(111) single-crystal electrode surfaces were systematically investigated by in-situ scanning tunneling microscopy. A (4 × 4) structure was imaged after the first cathodic current peak for Cu + Cl on Pt(111). Distorted (4 × 4) and (√3 × √3)R30° structures were found after the first and the second peaks, respectively, for Cu + Br on Pt(111). For Cu + I on Pt(111), a (√3 × √3)R30° structure was observed after the copper deposition peak. A c(2 × 2) structure was obtained for Cu + Cl, Cu + Br and Cu + I on Pt(100). On a Au(111) surface, a (5 × 5) structure was observed for Cu + Cl after both the first and the second cathodic current peaks. For Cu + Br on Au(111), (√7 × √7)R19.1° was found after the first peak, and (4 × 4) structures were imaged after both the second and third peaks. A (3 × 3) image was obtained for Cu + I after a single peak on Au(111). Structural models for the copper and the halide layers are discussed based on the adsorbate—substrate interaction at these surfaces. Coadsorption structures on platinum surfaces are understandable as those of halide adsorption on a pseudomorphic copper (1 × 1) layer on platinum, while on Au(111) the coadsorption layer is interpreted as an ultrathin crystal of CuX(X = Cl, Br, I).

Electrodeposition processes of palladium and rhodium monolayers on Pt(111) and Pt(100) electrodes studied by IR reflection absorption spectroscopy

Abstract The electrodeposition of palladium on Pt(111) or Pt(100) single-crystal electrodes, and of rhodium on a Pt(111) electrode was carried out in 0.5 M sulfuric acid aqueous solutions containing 1×10 −4 M Pd 2+ or Rh 3+ . Cyclic voltammograms showed the growth of the new sets of adsorption and desorption peaks at 0.22 V (vs. the standard hydrogen electrode) and 0.22 V for Pd/Pt(111), 0.10 and 0.12 V for Pd/Pt(100), and 0.14 and 0.19 V for Rh/Pt(111) respectively. The IR spectra of carbon monoxide on the surfaces during deposition gave evidence for the formation of two-dimensional islands of palladium and rhodium, respectively, by showing the bridge and the threefold absorption bands of carbon monoxide on those atoms. The epitaxial growth of palladium or rhodium monolayers in pseudomorphic (111) structures on Pt(111) and Pt(100) was suggested.

CO adsorption on Pt(111) and Pt(100) single crystal surfaces in aqueous solutions studied by infrared reflection-absorption spectroscopy

Abstract The adsorption of CO on Pt(111) and Pt(100) single crystal surfaces in an aqueous acid solution was studied by IRRAS and CV. On-top and bridge-bonded CO species adsorbed on Pt(111) and Pt(100) electrodes were detected.

Crystal structure of synthetic mordenites

Abstract Crystal structures of synthetic sodium mordenites with different Si Al ratios have been studied by X-ray diffraction methods. Framework geometries of the synthetic mordenites are very similar to those of natural mordenites. Atomic positions and occupancies of extraframework cation and water molecules of synthetic mordenites with different Si Al ratios have been determined.

Comparison of a bisulfate anion adsorbed on M(111) (M=Pt, Rh, Au, Ag and Cu) ☆

Abstract Adsorption of sulfuric acid species on various metal(111) electrodes in a 0.5 M H2SO4 solution was investigated by infrared reflection absorption spectroscopy (IRAS). Pt, Au, Ag, Cu and Rh(111) were used as electrodes. HSO4− is adsorbed on all of the surfaces including Pt, Rh, Au, Ag and Cu in a 0.5 M H2SO4 solution. Considerable amounts of sulfate in addition to bisulfate coexist on Ag(111) in a 0.5 M H2SO4 solution. Also, both DSO4− and SO42− are coadsorbed on Au(111) in 0.5 M D2SO4+D2O solution. The interconversion of HSO4−/H3O+ and H2SO4 that was seen on Pt(111) was not observed on the other electrodes. The frequencies of the SO3 symmetric and S–OH stretching bands of a bisulfate adsorbed on the electrode surfaces are related to the electronic state of each M(111) surface.

The structure of bisulfate and perchlorate on a Pt(111) electrode surface studied by infrared spectroscopy and ab-initio molecular orbital calculation

Abstract In situ infrared reflection absorption spectroscopy yielded the first spectroscopic evidence that perchlorate anion is adsorbed on a Pt(111) electrode surface in a 0.1 M perchlorate acid solution over the potential range, 0.6 to 0.9 V vs. NHE. Both perchlorate and bisulfate anions were chemisorbed reversibly in the form of unidentate or tridentate coordination on the surface. Bisulfate and perchlorate ions started to be adsorbed at 300 and 600 mV vs. NHE, respectively, and these potentials coincided with the onset of hydrogen desorption. The anomalously sharp spike peaks seen in the cyclic voltammetry of the Pt(111) in acid solutions were associated with the structure change of both anions. Ab-initio molecular orbital calculation supported the large frequency shift of bilsufate anions on a positively charged electrode surface.