Takashi Fujikawa

Angle-resolved ultraviolet photoelectron spectroscopy of thin films of bis(1,2,5-thiadiazolo)-p-quinobis (1,3-dithiole) on the MoS2 surface

In this paper we report on the angle-resolved ultraviolet photoelectron spectroscopy on ultrathin films of bis(1,2,5-thiadiazolo)-p-quinobis (1,3-dithiole) (BTQBT) deposited on a MoS2 surface with synchrotron radiation, and describe the quantitative analysis of the angular distribution of photoelectron from the highest occupied state. The observed angular distributions were better explained by those calculated with the single-scattering approximation combined with molecular orbital calculation considering intramolecularly scattered waves than the previously used independent-atomic-center approximation combined with molecular orbital calculation. Further, the low-energy-electron diffraction measurements were performed on the film. From the low-energy-electron diffraction, the two-dimensional lattice of the ultrathin films on the MoS2 was found to be MoS2(0001)−(13×13, R=±13.9°)-BTQBT, and from the analysis of the photoelectron angular distributions, it was found that at the lattice points the molecules lie...

Many-body theory of core-level photoemission by Keldysh Green's functions

Abstract The many-body theory of X-ray photoelectron diffraction (XPD) spectra is developed by using Keldysh’s non-equilibrium Green’s functions, which was basically applied by Caroli et al. We have applied skeleton diagram expansion in terms of dressed one-electron Green’s function G and the screened Coulomb interaction W. The damping photoelectron wave functions under the influence of the optical potential play a central role in the present XPD theory. On the basis of the present theoretical framework, we provide detailed discussion on Debye–Waller and Franck–Condon factors in XPD spectra at finite temperature, resonance effects in particular multiatom resonant photoemission (MARPE) effects, and also on the loss effects. The XPD spectra are simply described by a product of the Franck–Condon factor and the XPD intensity including the Debye–Waller factor. This result is in contrast to the X-ray absorption fine structure (XAFS) where the Franck–Condon factor is smeared out by a convolution product. We have discussed the conditions which give rise to prominent MARPE spectra. In particular, symmetry lowering plays an important role giving rise to prominent MARPE spectra. The angular dependence provides us with useful information on near neighbor atomic arrangement. Some model calculations clarify the basic physical processes of MARPE spectra. To discuss the loss spectra, we stress the importance of the interference effects between the intrinsic and extrinsic losses. The explicit formulas, which include both inelastic and elastic scatterings, are newly derived in the present theoretical framework, and enable us to calculate an XPD pattern associated with losses.

Genome analysis of the kiwifruit canker pathogen Pseudomonas syringae pv. actinidiae biovar 5

Pseudomonas syringae pv. actinidiae (Psa) is a destructive pathogen of kiwifruit bacterial canker disease, causing severe economic losses to kiwifruit industry worldwide. Biovar 5 is the most recently reported biovar of Psa, and is found in only a local area of Japan at present. There is not much information of genetic characteristics of biovar 5. Thus, the genome of biovar 5 was sequenced and analyzed to clarify its detailed genetic characteristics. Here, the genomes of strain MAFF 212056 and MAFF 212061 of biovar 5 were estimated to be about 6.3 Mbp and 6.5 Mbp, respectively, and their phylogenetic positions were proved to be near that of biovar 2 in the phylogenetic tree. However, it was confirmed that biovar 5 had neither the coronatine biosynthetic genes conserved in biovar 2, its phylogenetic neighbor, nor the phaseolotoxin biosynthetic genes conserved in biovar 1, Japanese native pathogen. In addition, 45 genes of type III secreted effectors were identified in biovar 5 genomes, showing that their composition is different from that in the other biovars. Moreover, some biovar 5-specific regions were identified. Then, biovar 5-specific PCR primers for targeting these regions were designed, and proved to be applicable for detecting biovar 5 specifically.

XAFS Theory at Zero and Finite Temperature

Many-body XAFS theory at zero and finite temperature is proposed based on the two different theories, scattering theory and nonequilibrium (Keldysh) Greens function theory. The latter has an advantage to describe finite temperature XAFS, and the former is flexible to include core-hole effects. In the Keldysh Greens function theory, the X-ray absorption intensity is described in terms of the reducible polarization propagator. By applying the skeleton diagram expansion, we obtain useful approximate formulas. Some important problems in XAFS analyses such as Debye-Waller and Franck-Condon factors, the subtle cancellation of loss structures are discussed by using these theoretical tools, and are closely compared with each other. In particular scattering Greens function including optical potential is compared with G > and G r , and the optical potential is compared with the self-energy in the Keldysh theory, Σ > , Σ r and Σ. Based on the nonequilibrium Greens function formula, we obtain the convolution XAFS...

Importance of radiation field screening in XPS and XAFS spectra

Abstract In this work the importance of radiation field screening is stressed in Keldysh’s Green’s function theory to study X-ray photoelectron spectroscopy (XPS) spectra and X-ray absorption fine structure (XAFS). So far these terms have been supposed to be small, however, we have found that these effects play a crucial role to analyze resonance effects. In particular the importance of these vertex correction is important in the analyses of multiatom resonant photoemission (MARPE) spectra and the resonance effects in XAFS. We also investigate the contribution from polarized part Wp of the screened Coulomb interaction W to the resonance effects. We find that W≈v is quite a good approximation. Off the resonance these radiation field screening diagrams are not important. They have no contribution to loss processes even though they include W> and W

Photoelectron diffraction from laser-aligned molecules with X-ray free-electron laser pulses

We report on the measurement of deep inner-shell 2p X-ray photoelectron diffraction (XPD) patterns from laser-aligned I2 molecules using X-ray free-electron laser (XFEL) pulses. The XPD patterns of the I2 molecules, aligned parallel to the polarization vector of the XFEL, were well matched with our theoretical calculations. Further, we propose a criterion for applying our molecular-structure-determination methodology to the experimental XPD data. In turn, we have demonstrated that this approach is a significant step toward the time-resolved imaging of molecular structures.

Debye-Waller and Condon factors in XAFS

Abstract The effects of atomic displacement on XAFS after core hole production are studied within the harmonic approximation for atomic vibration. Within single scattering approximation for photoelectron wave we can accurately include the phonon effects on XAFS with aid of the Schwinger method. We obtain three factors in this treatment, the Debye-Waller factor, the Condon faator and their interference term, but only the first term plays an important role.

C 1s photoelectron angular distributions from fixed-in-space CO molecules in the high-energy continuum ≥50 eV

We measured molecular-frame photoelectron angular distributions (MFPADs) for a carbon 1s level of CO molecules in the kinetic energy range of up to 150 eV. X-ray photoelectron diffraction (XPD) theory was adopted to interpret the profiles of the MFPADs. Computational experiments within the framework of XPD theory were performed to demonstrate the emergence of interference effects between the direct photoelectron and scattered waves in the MFPAD profiles.

Spin orientation transition across the single-layer graphene/nickel thin film interface

The spin-polarized electronic structures across the interface between single-layer graphene and a Ni(111) thin film are explored by employing depth-resolved X-ray absorption and magnetic circular dichroism spectroscopy with atomic layer resolution. The depth-resolved Ni L2,3-edge analysis clarifies that the Ni atomic layers adjacent to the interface show a transition of the spin orientation to the perpendicular one in contrast to the in-plane one in the bulk region. The C K-edge analysis reveals the intensification of the spin–orbit interactions induced by the π–d hybridization at the interface as well as out-of-plane spin polarization in the π band region of graphene. The present study indicates the importance of the interface design at the atomic layer level for graphene-based spintronics.

X‐Ray Absorption Fine Structure Spectroscopy Study of Arsenate Adsorption on Schwertmannite

We studied arsenate adsorption on schwertmannite by means of XAFS. Our results show that arsenate is bound to one or two iron octahedra and individual iron octahedra in schwertmannite become more regular after the adsorption. At the same time there is an increase of disorder in polymeric chains of iron octahedra. This suggests that the release of local strain is related to the overall stability of arsenate‐adsorbed schwertmannite.