Masuaki Matsumoto

Study of the adsorption structure of NO on Pt(111) by scanning tunneling microscopy and high-resolution electron energy-loss spectroscopy

The structure of nitric oxide (NO) on a Pt(111) surface was studied by scanning tunneling microscopy (STM ) and high-resolution electron energy-loss spectroscopy (HREELS ). The coexistence of two species is observed by STM after saturating the surface with NO at 70 K and annealing to 215 K. Two pairs of NMO and PtMN stretching vibrational frequencies are observed in HREELS spectra after annealing, which are assigned to the two species observed by STM. Comparison between the spectra of HREELS and infrared absorption spectroscopy (IRAS) indicates that IRAS is less sensitive to the lower-frequency mode. A new model for the adsorption structure of NO on the Pt(111) surface is proposed and discussed.

Influence of H2-annealing on the hydrogen distribution near SiO2/Si(100) interfaces revealed by in situ nuclear reaction analysis

Employing hydrogen depth-profiling via 1H(15N,αγ)12C nuclear reaction analysis (NRA), the “native” H concentration in thin (19–41.5 nm) SiO2 films grown on Si(100) under “wet” oxidation conditions (H2+O2) was determined to be (1–2)×1019 cm−3. Upon ion-beam irradiation during NRA this hydrogen is redistributed within the oxide and accumulates in a ∼8-nm-wide region centered ∼4 nm in front of the SiO2/Si(100) interface. Annealing in H2 near 400 °C introduces hydrogen preferentially into the near-interfacial oxide region, where apparently large numbers of hydrogen trap sites are available. The amount of incorporated H exceeds the quantity necessary to H-passivate dangling Si bonds at the direct SiO2/Si(100) interface by more than one order of magnitude. The H uptake is strongly dependent on the H2-annealing temperature and is suppressed above 430 °C. This temperature marks the onset of hydrogen desorption from the near-interfacial oxide trap sites, contrasting the thermal stability of the native H, which pre...

Electronic structure of a Pt(111)Ge surface alloy and adsorbed CO

Abstract Angle-integrated photoemission spectra are observed for Pt(111) and a Pt(111) Ge surface alloy. The spectra for Pt(111) Ge show d band filling compared with those for Pt(111). Although the chemisorption energy of CO is noticeably reduced by alloy formation, the binding energies of the occupied levels for adsorbed CO are almost the same as those on pure Pt(111). The results are discussed by the d band filling due to s-d hybridization of Ge s electrons and the Pt d band and by two-level hybridization of the 5σ and 2π states with the modified d band.

Two charged states of hydrogen on the SrTiO3(001) surface

The effects of hydrogen exposure on the electronic structure of two types of SrTiO3(001) surfaces, oxygen-deficient (OD) and nearly-vacancy-free (NVF) surfaces, were investigated with ultraviolet photoemission spectroscopy and nuclear reaction analysis. Upon molecular hydrogen exposure to the OD surface which reveals in-gap states at 1.3 eV below the Fermi level, the in-gap state intensity was reduced to half the initial value at a hydrogen coverage of 0.9 ± 0.7 × 10(14) cm(-2). On the NVF surface which has no in-gap state, on the other hand, atomic-hydrogen exposure induced in-gap states, and the hydrogen saturation coverage was evaluated to be 3.1 ± 0.8 × 10(14) cm(-2). We argue that H is positively charged as H(∼0.3 +) on the NVF surface by being coordinated to the O atom, whereas H is negatively charged as H(-) on the OD surface by occupying the oxygen vacancy site. The stability of H(-) at the oxygen vacancy site is discussed.

Knudsen layer formation in laser induced thermal desorption

Laser induced thermal desorption of Xe atoms into vacuum from a metal surface following the nano-second pulsed laser heating was investigated by the time-of-flight (TOF) measurement. The desorption flow was studied at a wide range of desorption flux by varying the initially prepared Xe coverage Θ (1 ML = 4.5 × 10(18) atoms/m(2)). At Θ = 0.3 ML, the TOF of Xe was well represented by a Maxwell-Boltzmann velocity distribution, which is in good agreement with thermal desorption followed by collision-free flow. At Θ > 0.3 ML, the peak positions of the TOF spectra were shifted towards the smaller values and became constant at large Θ, which were well fitted with a shifted Maxwell-Boltzmann velocity distribution with a temperature TD and a stream velocity u. With TD fixed at 165 K, u was found to increase from 80 to 125 m/s with increasing Θ from 1.2 to 4 ML. At Θ > 4 ML, the value of u becomes constant at 125 m/s. The converging feature of u was found to be consistent with analytical predictions and simulated results based on the Knudsen layer formation theory. We found that the Knudsen layer formation in laser desorption is completed at Knudsen number Kn <0.39.

Apparatus for time-resolved and energy-resolved measurement of internal conversion electron emission induced by nuclear resonant excitation with synchrotron radiation

A high-energy and large-object-spot type cylindrical mirror analyzer (CMA) was constructed with the aid of electron trajectory simulations. By adopting a particular shape for the outer cylinder, an energy resolution of 7% was achieved without guide rings as used in conventional CMAs. Combined with an avalanche photodiode as an electron detector, the K-shell internal conversion electrons were successfully measured under irradiation of synchrotron radiation at 14.4 keV in an energy-resolved and time-resolved manner.

Effects of Hydrogen on the Electronic State and Electric Conductivity of the Rutile TiO2(110) Surface

The adsorption of atomic hydrogen on a rutile TiO2(110) surface was investigated by nuclear reaction analysis (NRA), ultraviolet photoelectron spectroscopy (UPS), and conductivity measurements. The TiO2(110) surface was annealed in O2 of 1 × 10−4 Pa, which is regarded as a quasi-stoichiometric surface. After exposure to atomic hydrogen, UPS showed a localized in-gap state (IGS) at about 0.8 eV below the Fermi level and downward band bending with a decrease in the work function. Along with these changes, the conductivity was increased by 2.9 µS/□. Our results indicate that hydrogen donates electrons to the substrate. The amount of charge transfer and electric conductivity are discussed on the basis of the experimental data.

Photostimulated desorption of Xe from Au(001) surfaces via transient Xe − formation

Photostimulated desorption (PSD) of Xe atoms from the Au(001) surface in thermal and nonthermal regimes was investigated by the time-of-flight measurement at photon energies of 6.4 and 2.3 eV. Xe was desorbed in a thermal way at high laser fluence, which was in good agreement with theoretical simulations. At a low laser fluence, on the other hand, desorption was induced only at a photon energy of 6.4 eV by a nonthermal one-photon process. We argue that the nonthermal PSD occurs via transient formation of Xe

Structure of Iron Silicide film on Si(111) Grown by Solid-Phase Epitaxy and Reactive Deposition Epitaxy

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Mechanism of gate dielectric degradation by hydrogen migration from the cathode interface

on Au(001). The lifetime of Xe