A5035038022- Advanced Chemical Physics Studies
- Catalytic Processes in Materials Science
- Gold and Silver Nanoparticles Synthesis and Applications
- Plasmonic and Surface Plasmon Research
- Electron and X-Ray Spectroscopy Techniques
- nanoparticles nucleation surface interactions
- Molecular Junctions and Nanostructures
- Advanced Fiber Optic Sensors
- Nonlinear Optical Materials Studies
- Optical Coatings and Gratings
- Semiconductor Lasers and Optical Devices
- Photonic and Optical Devices
- Surface and Thin Film Phenomena
- Gas Sensing Nanomaterials and Sensors
- Near-Field Optical Microscopy
- Ammonia Synthesis and Nitrogen Reduction
- Laser-Plasma Interactions and Diagnostics
- Advanced Optical Sensing Technologies
- Photonic Crystal and Fiber Optics
- Nanowire Synthesis and Applications
- Laser-Ablation Synthesis of Nanoparticles
- Advanced Semiconductor Detectors and Materials
- Dye analysis and toxicity
- Quantum Dots Synthesis And Properties
- Electrocatalysts for Energy Conversion
Hirosaki University
2012-2024
Kanazawa Medical University
2023
The University of Tokyo
2003-2016
Science Council of Japan
2016
Fritz Haber Institute of the Max Planck Society
2011-2014
High Energy Accelerator Research Organization
2006-2010
Keio University
2009-2010
Institute for Molecular Science
2006-2010
Sekisui Chemical (Japan)
2006-2010
Freie Universität Berlin
2010
The adsorption structure of methylthiolate (CH3S) adsorbed on Au(111), a long-standing controversial issue, has been unambiguously determined by scanned-energy and scanned-angle S 2p photoelectron diffraction. molecules are found to occupy atop sites with S-Au distance 2.42 +/- 0.03 A. angular distribution the photoelectrons due forward scattering reveals that S-C bond is inclined approximately 50 degrees from surface normal towards both [211] [121] (nearest-neighbor thiolate) directions.
We studied the mechanism of CO oxidation on O-precovered Pd(111) surfaces by means fast x-ray photoelectron spectroscopy (XPS). The oxygen overlayer is compressed upon coadsorption from a p(2 x 2) structure into (square root(3) square root(3))R30 degrees and then 1) with increasing coverage. These three O phases exhibit distinctly different reactivities. (1) phase does not react unless surface temperature sufficiently high (<290 K). (2) In phase, reaction occurs exclusively at island...
We clarified the relationship between near-field optical properties and local structure in monolayer assembly of gold nanoparticles by using scanning microscopy (SNOM) electron (SEM). The success superposition SNOM image with SEM allows us to find that intense electromagnetic field is localized at rim part, especially interstitial site dimerlike structure.
Spatial distribution of surface enhanced Raman activity is visualized for two-dimensional (2D) nearly close-packed and well-ordered monolayer array gold nanoparticles by using scanning near-field optical microscope. The 2D arrays exhibit highly nonuniform enhancement in scattering, i.e., the regions along edge are preferentially enhanced. We demonstrate that spatial localized electric field also agrees well with enhancement.
Ultrafast dynamics of surface-enhanced Raman scattering (SERS) was investigated at cleaved graphite surfaces bearing deposited gold (Au) nanostructures (∼10 nm in diameter) by using sensitive pump–probe reflectivity spectroscopy with ultrashort (7.5 fs) laser pulses. We observed enhancement phonon amplitudes (C═C stretching modes) the femtosecond time domain, considered to be due enhanced electromagnetic (EM) field around Au nanostructures. Finite-difference time-domain (FDTD) calculations...
Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) has been applied to the investigation of NO adsorption on Pt(111) under various pressures (up 1 Torr) at room temperature. Under 10−7 Torr, molecular occupies most stable fcc-hollow sites and partially energetically unfavorable atop sites. reversibly desorbs from after evacuation. At higher than 10−6 however, irreversible atomic oxygen takes place via dissociation, leading formation NO+O domains. This result is consistent with...
The key structural parameter for greater enhancement of infrared absorption on metal nanostructures was identified by systematic and exhaustive surface-enhanced (SEIRA) measurements well-defined periodic gold square column (SC) arrays silicon wafers fabricated using electron beam lithography. SC have size parameters compatible with those vacuum-evaporated thin films, which are used conventionally SEIRA. crucially important determining the factor is ratio gap to nanoparticle size. An...
We studied the mechanism of CO oxidation on O-covered Pt(111) surfaces during exposure by means time-resolved near edge x-ray absorption fine structure spectroscopy. Two distinct reaction processes were found to occur sequentially; isolated O atoms and island-periphery contribute each process. Combination in situ monitoring kinetics Monte Carlo simulations revealed that coadsorption plays a role inducing dynamic change spatial distribution atoms, which switches over two paths.
Phase-change materials based on Ge-Sb-Te alloys are widely used in industrial applications such as nonvolatile memories, but reaction pathways for crystalline-to-amorphous phase-change picosecond timescales remain unknown. Femtosecond laser excitation and an ultrashort x-ray probe is to show the temporal separation of electronic thermal effects a long-lived ($>$100 ps) transient metastable state Ge$_{2}$Sb$_{2}$Te$_{5}$ with muted interatomic interaction induced by weakening resonant...
We studied the mechanism of N + NO reaction on Rh(111) surfaces by means near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Atomic nitrogen layers were titrated with at various temperatures. Below 350 K, chemisorbed monomer does not react N, while dimer formed in second layer acts as an extrinsic precursor to reaction: N(a) (NO)2(a) → N2O(g) NO(a). Because a dominant role precursor-mediated mechanism, proceeds slower increase temperature. Above switches different path: NO(a) N2(g) O(a).
The mechanism of CO oxidation reaction on oxygen-precovered Pt(111) surfaces has been studied by using time-resolved near-edge x-ray absorption fine structure spectroscopy. whole process is composed two distinct paths: (1) a isolated oxygen atoms with adsorbed CO, and (2) island-periphery after the saturation. coadsorption plays role to induce dynamic change in spatial distribution O atoms, which switches over paths. These mechanisms were confirmed kinetic Monte Carlo simulations. effect...
We have studied electromagnetic field on the surface of two-dimensional nanostructure gold nanoparticles through two-photon–induced photoluminescence images by using scanning near-field optical microscope and far-field surface-enhanced Raman scattering measurements. The image shows that strong inhomogeneous enhancement in occurs over nanostructure, representing localized plasmon excitations. results suggest local structure influences distribution excitation.
We visualized the enhanced optical field distributions in one-dimensional linear array structures of gold nanospheres by using scanning near-field microscopy. The characteristic distribution depends on chain length structures. is reproduced qualitatively model calculations based upon finite-difference time-domain (FDTD) method. From analysis, we have found that arises from interparticle interactions, which cause propagation plasmon excitation inner part array, and trapping it a localized...
Abstract The pH dependent structure of thymol blue (TB) in solution, a long-standing controversial issue, has been determined by quantum chemistry with an aid multivariate analysis electronic absorption spectra. It revealed that the TB varies from neutral biprotonated form open-sulton ring showing red to monovalent anion pure quinoid yellow and then quinoid-phenolate on raising for solution.
The catalytic water formation reaction was investigated by the energy dispersive near-edge x-ray absorption fine structure (dispersive NEXAFS) spectroscopy. An oxygen covered Pt(111) surface with (2×2) exposed to gaseous hydrogen (5.0×10−9 Torr) at constant temperatures (120–140 K). O K-edge NEXAFS spectra were measured during a time interval of 35 s. Quantitative analyses provided coverage changes adsorbed species (O, OH, and H2O). is composed three steps, which are characterized an...
The electronic structure of Ni2P(0001) has been investigated by photoelectron spectroscopy utilizing synchrotron radiation. In the valence band spectra, a Ni 3d—P 3p hybrid (main band) and satellite were observed at 0-4 eV 8 eV, respectively. showed resonant behavior around threshold, is associated with photoemission leading to two-hole bound final state. From analysis anti-resonance dip main intensity, 3d component was proved be included in whole binding energy region band. P 2p core-level...
In this study, optical second-harmonic generation (SHG) microscopy of one-dimensional linear arrays spherical Au nanoparticles (NPs) at the submicron scale was performed. Nine NPs with a particle size ∼100 nm were arrayed one-dimensionally in groove on glass substrate, and array structure observed by atomic force (AFM). The (SH) intensity distribution non-uniform varied photon energy. To understand relationship between SH signal local electric field related to surface plasmon (SP) modes...
We studied the mechanism of N+NO reaction on Rh(111) surfaces by means fast near-edge X-ray absorption fine structure spectroscopy. This is important as a basis NOx reduction reactions platinum-group metal surfaces. Atomic nitrogen layers were titrated with NO at various temperatures. N2O exclusively formed and desorbs into gas phase below 350 K. The consumption rate atomic exhibits strange temperature dependence between 100 K; proceeds slower increasing temperature. Reaction kinetics...
We perform model calculations of coherent lattice vibrations in solids driven by ultrashort laser pulses. In order to maximize the amplitude phonon time domain, an evolutionary algorithm optimizes driving field. find that only a Fourier-limited single pulse yields maximum amplitude, irrespective actual physical excitation mechanism (impulsive or displacive). This result is clear contrast widespread intuition train phase with oscillation leads largest oscillator. rationalize this intuitive...