Masao Kamada

Characterization of Hard Diamond-Like Carbon Films Formed by Ar Gas Cluster Ion Beam-Assisted Fullerene Deposition

The coordination of carbon atoms in diamond-like carbon (DLC) thin films formed by Ar gas cluster ion beam (GCIB) assisted deposition using fullerene as the carbon source was investigated by measuring near-edge X-ray absorption fine structure (NEXAFS) spectra of the carbon K-edge over the excitation energy range 275–320 eV, using synchrotron radiation. With attention to the peak corresponding to the transition of the excitation electron from a carbon 1s orbital to a π* orbital, relative sp2 contents of various DLC films were estimated. The sp2 contents of the DLC films formed by the GCIB-assisted deposition were observed to be lower than those of the DLC films formed by other methods. The hardness value measured with a nano-indentation technique was found to be strongly related to the sp2 content of the DLC film.

Development of electron-ion coincidence spectroscopy for the study of surface dynamics combined with synchrotron radiation

Energy-selected electron-ion coincidence spectroscopy for the study of surface dynamics combined with synchrotron radiation (SR) was developed. The equipment consists of an electron gun, a cylindrical mirror analyzer (CMA), and a time-of-flight (TOF) ion mass spectrometer. A sample surface was excited by SR, and energy of the emitted electron was analyzed by the CMA. The TOF spectrum of the desorbed ions was measured taking the energy-analyzed electron signal as the starting trigger. The ions coincidently desorbed with the electron gave a characteristic peak in the TOF spectrum. The apparatus was evaluated on the basis of photoelectron–photoion coincidence (PEPICO) and Auger electron–photoion coincidence (AEPICO) measurements of H2O condensed on gold foil. The results demonstrate that PEPICO and AEPICO combined with SR are powerful methods for investigating the ion desorption induced by core-level excitations.

Phonon Side Bands of UV Absorption in NaNO2

Phonon side bands of u v absorption in NaNO 2 have been studied by the measurement of high resolution spectrum with light polarized along each crystallographic axis at low temperatures. Strong peaks in the side bands are assigned to the phonon branches in the first Brillouin zone by taking account of the selection rules for the optical transitions in which an exciton and a phonon are created simultaneously. The integrated intensities of the E // b and E // c absorptions have been found to increase with temperature obeying the coth ( h ν/2 k T ) law with ν b ≃220 cm -1 and ν c ≃130 cm -1 respectively. The relation between the temperature dependence of the E // b and E // c absorptions and the profiles of their phonon side bands is discussed in terms of the averaged phonon frequency \barν.

Fine Structures in Luminescence Spectra of NaNO2 Crystal in the Ultraviolet Region

Luminescence spectra of NaNO 2 single crystal associated with 1 B 1 → 1 A 1 . transition in NO 2 - have been measured for the E // a , E // b and E // c polarizations. Intensities of the series of sharp vibronic lines are described by a Poisson distribution I n ∝( e - s s n / n !) with s ≃4. These lines are interpreted by a simple configuration coordinate model. It has been found that the profile of the phonon side band of the E // a luminescence is nearly a mirror image of that of the absorption with respect to the zero-phonon line, while the profile of the side band of the E // b luminescence is quite different from that of the absorption. The latter result is interpreted in terms of the exciton-phonon bound state. Two extra series of weak satellite bands have been found and are interpreted as the vibronic lines due to isotopic species N 15 O 2 16- and N 14 O 16 O 18- .

Orientation of oxygen admolecules on a stepped platinum(133) surface

Abstract The orientation of oxygen admolecules on a Pt(113) stepped surface was studied by near-edge X-ray absorption fine-structure (NEXAFS). Their adsorption and desorption were first characterized by thermal desorption combined with an isotope tracer. Direct desorption peaks from oxygen admolecules occur at 218 K ( α 1 -O 2 ), 182 K ( α 2 -O 2 ), and 162 K ( α 3 -O 2 ) the temperature range from 150 to 250 K. The orientation of oxygen admolecules yielding the above three peaks was examined separately with NEXAFS. All admolecules lie on the surface. α 1 -O 2 is parallel to the step edge, whereas part of α 3 -O 2 declines slightly from the bulk surface plane.

Design of a helical undulator for UVSOR

Abstract The design concept and the expected performance of a helical undulator which is to be installed in the 0.75 GeV storage ring, UVSOR, of the Institute for Molecular Science are reported. The undulator should produce perfectly circularly polarized light in the energy range of 2 – 45 eV and elliptically and linearly polarized light with energies up to 300 eV.

Spectral profile of the two-photon absorption coefficients in CaF2 and BaF2

Two-photon absorption spectra due to the valence excitons in CaF2 and BaF2 have been measured using the second harmonic of the output of a XeCl-excimer-laser pumped dye laser as a light source. The band gap energies of CaF2 and BaF2 are obtained as 11.8 and 10.6 eV at 298 K, respectively. The two-photon absorption coefficient β in the spectral region below the 2P exciton is expressed by an exponential function of the photon energy in both crystals. The values of β at the 2P exciton peak are about 2×10−9 cm/W for CaF2 and 3×10−9 cm/W for BaF2.

Desorption of H ions from water chemisorbed on Si(100) by O 1s excitation - an Auger electron-photoion coincidence spectroscopy study

Abstract Auger electron-photoion coincidence (AEPICO) spectroscopy, which has been recently developed and proved to be a very powerful technique for investigating the dynamics of desorption induced by the core-level excitation, is applied to the investigation of Auger-stimulated ion desorption from the chemisorbed-water-Si(100) surface induced by O 1s excitation. It is shown that the fast relaxation of the excited state with a core hole and an excited electron takes place before the core hole decay, and that the desorption yield is enhanced by the shake-up (and/or shake-off) excitation. The relative cross-section for Auger-stimulated ion desorption is estimated, and is shown to increase as holes are created at deeper levels of the valence bands as the final state of the Auger decay. A comparison is also made with condensed H 2 O.

Phonon Side Bands of the Triplet Absorption in NaNO2

Absorption spectra of NaNO 2 associated with the electronic transition 1 A 1 → 3 B 1 in NO 2 - have been measured for the E // a , b and c polarizations. The E // b and E // c spectra show the series of vibronic lines accompanied with the phonon side bands, while the E // a absorption is too weak to be observed. The selection rules are discussed for the modes of phonons which interact with the triplet exciton to give rise to the phonon side band of each polarization. The assignments are given to the prominent peaks and shoulders in the side bands of the E // b and E // c spectra. Two extra series of weak satellite bands have been found on the low energy tails of the vibronic lines and they are interpreted as the lines due to the isotopic species N 14 O 16 O 18- and N 15 O 2 16- .

Surface photovoltage effect and its time dependence in GaAs–GaAsP superlattice studied with combination of synchrotron and laser radiation

The surface photovoltage (SPV) effect and its temporal profiles in a GaAs–GaAsP superlattice (SL) were measured by core-level photoelectron spectroscopy with the combination of synchrotron radiation and laser. It was found that the SPV effect in the SL is remarkably suppressed as compared with that in a bulk GaAs. The difference in the temporal profile of the SPV between SL and bulk samples was observed in microsecond range. The suppression of the SPV effect in the negative electron affinity surfaces of the SL was also observed. It is concluded that the SL with a high-doping surface layer is suitable for the spin-polarized electron source without the SPV effect.