Annealing effect of absorbing property for Cs and CsI in fullerene investigated by synchrotron X-ray photoelectron spectroscopy

Sekiguchi, Tetsuhiro; Yokoyama, Keiichi; Yaita, Tsuyoshi

e-Journal of Surface Science and Nanotechnology (Internet), 20(3), p.186 - 195, 2022/07

https://doi.org/10.1380/ejssnt.2022-030

Cesium-135 having long life, 2.3 million y, that is contained in nuclear wastes may cause long-term pollution. Technology of isotopic separation of such long lived nuclide is indispensable not only for its volume reduction but also annihilation by nuclear transmutation. The recovery of atomic Cs from molecular CsI is mandatory. We have investigated fullerene C as a potential absorber for Cs. Angle-resolved X-ray photoelectron spectroscopy, AR-XPS has been used to analyze the depth concentration distribution of Cs. Experiments were performed at soft X-ray beamline BL27A at KEK PF facility. We report on the annealing effect after deposition of Cs and the effect of heating substrate during deposition. For Cs/C sample, the intensity ratio of Cs-3d/C-1s increased in double at the high temperature. This suggests that Cs atoms remain in the material at high temperatures. On the other hand, for CsI/C, the intensity ratio does not change much by elevating temperatures.

Investigation of hydration and adsorption structures on clay minerals of radium by EXAFS

Yamaguchi, Akiko; Nagata, Kojiro*; Tanaka, Kazuya; Kobayashi, Keita; Kobayashi, Toru; Shimojo, Kojiro; Tanida, Hajime; Sekiguchi, Tetsuhiro; Kaneta, Yui; Matsuda, Shohei; et al.

Hosha Kagaku, (45), p.28 - 30, 2022/03

no abstracts in English

Absorbent property of fullerene for cesium isotope separation investigated using X-ray photoelectron spectroscopy

Sekiguchi, Tetsuhiro; Yokoyama, Keiichi; Uozumi, Yuki*; Yano, Masahiro; Asaoka, Hidehito; Suzuki, Shinichi; Yaita, Tsuyoshi

Progress in Nuclear Science and Technology (Internet), 5, p.161 - 164, 2018/11

https://doi.org/10.15669/pnst.5.161

For nuclear transmutation of cesium-135 (Cs), which is long-lived fission product, we are developing selective absorbent which takes only Cs atom in, but does not CsI. In this study, absorbing property of Cs atom onto the surface of fullerene (C) film has been investigated using synchrotron-based angle-dependent X-ray photoelectron spectroscopy (XPS). The results were compared with those of CsI. It was found that Cs penetrates into C deep bulk. In contrast, CsI deposits on shallow surface. Furthermore, XPS spectra were measured as a function of Ar-sputtering time in order to know Cs concentration profiles in deep region. Results showed that Cs penetrates into deep region of several hundreds .

Observation of oriented organic semiconductor using Photo-Electron Emission Microscope (PEEM) with polarized synchrotron

Sekiguchi, Tetsuhiro; Baba, Yuji; Hirao, Norie; Honda, Mitsunori; Izumi, Toshinori; Ikeura, Hiromi*

Molecular Crystals and Liquid Crystals, 622(1), p.44 - 49, 2015/12

BB2014-1632.pdf:0.71MB

https://doi.org/10.1080/15421406.2015.1096989

The molecular orientation is one of the important factors for controlling various properties in organic semiconductor materials. Films are usually heterogeneous. Thus they exist as a mixture of microscopic domains which have a variety of orientation directions. Therefore, it is essential to observe selectively microscopic domains with different orientation direction. In this work, we have developed the photoelectron emission microscopy (PEEM) system combined with the linearly polarized vacuum ultraviolet (VUV) light or synchrotron radiation (SR) X-rays. PEEM images (FOV = ca.50 micro m) for poly(3-hexylthiophene), P3HT thin films were observed under the UV irradiation with various polarization angles, including in-plain and out-of-plain polarization. Morphologies at some bright parts are different each other. The resultant observation suggests that it enables us to distinguish oriented micro-domains with specific directions of polymer chain axis from other amorphous parts.

Investigation of unoccupied electronic states near the fermi level of polysilane using resonant Auger spectroscopy

Ogawa, Hiroshi*; Ikeura, Hiromi*; Sekiguchi, Tetsuhiro

Molecular Crystals and Liquid Crystals, 622(1), p.164 - 169, 2015/11

https://doi.org/10.1080/15421406.2015.1105081

Unoccupied electronic states near the Fermi level of poly(dimethylsilane) were probed using Si 1s X-ray absorption spectroscopy (XAS) and Si KLL resonant Auger spectroscopy (RAS). The measured resonance peaks of XAS spectra near Si K-edge have been assigned in comparison with the discrete variational (DV)-X molecular orbital calculations. The rapid delocalization of Si 1s core-excited electron through the empty conduction band was observed along the polymer chain with the energy dependent RAS measurement, and the electron delocalization time was estimated based on the core-hole clock method.

A Fluorescence XAFS measurement instrument in the Soft X-ray region toward observation under operando conditions

Honda, Mitsunori; Baba, Yuji; Shimoyama, Iwao; Sekiguchi, Tetsuhiro

Review of Scientific Instruments, 86(3), p.035103_1 - 035103_5, 2015/03

https://doi.org/10.1063/1.4913653

A Polarization rule on atomic arrangements of graphite-like boron carbonitride

Shimoyama, Iwao; Baba, Yuji; Sekiguchi, Tetsuhiro

Carbon, 71, p.1 - 10, 2014/05

https://doi.org/10.1016/j.carbon.2013.11.066

B and N K-edge near-edge X-ray absorption fine structure (NEXAFS) spectra of boron carbonitride (B-C-N) films prepared by ion beam deposition are interpreted by molecular orbital calculations with the core-hole effect. Model clusters with different atomic arrangements are compared in terms of photoabsorption cross section (PACS) and net charge, and they are classified into two groups, i.e., polarization and non-polarization types. PACS of peaks near the lowest unoccupied molecular orbital (LUMO) state increase at B K-edge and decrease at N K-edge for polarization type and vice versa for non-polarization type. Based on a comparison between experimental and theoretical results, we propose a rule for atomic arrangements of boron, carbon, and nitrogen atoms in graphite-like B-C-N. Finally, the relationship between the rule and structural stability is discussed.

Structure of ultra-thin silicon film on HOPG studied by polarization-dependence of X-ray absorption fine structure

Baba, Yuji; Shimoyama, Iwao; Hirao, Norie; Sekiguchi, Tetsuhiro

Chemical Physics Letters, 594, p.64 - 68, 2014/02

https://doi.org/10.1016/j.cplett.2014.01.025

Structures of mono-layered silicon on a highly oriented pyrolytic graphite (HOPG) have been investigated by X-ray photoelectron spectroscopy and X-ray absorption near edge structure (XANES). For the Si K-edge XANES spectrum of the 0.15 mono-layered film, two distinct peaks were observed, which were assigned to the resonant excitations from the Si 1s into the valence unoccupied orbitals with and characters. On the basis of the polarization dependences of the peak intensities, it was concluded that a part of the Si film lies flat on the HOPG surface, which supports the existence of two-dimensional graphene-like structure in mono-layered silicon.

Focusing of soft X-rays using poly-capillary with precise adjustment mechanism and its application to quick chemical-state analysis

Hirao, Norie; Baba, Yuji; Sekiguchi, Tetsuhiro; Shimoyama, Iwao

Bunseki Kagaku, 63(1), p.53 - 58, 2014/01

AA2013-0769.pdf:1.16MB

https://doi.org/10.2116/bunsekikagaku.63.53

A method for quick and real-time observations of a solid surface at nanometer scale is described. The principle of the method is as follows. Soft X-rays from a synchrotron light source are irradiated on a solid surface and the total photoelectrons are expanded and focused on a screen using electrostatic lenses. When the energy of X-rays is scanned and the brightness is plotted, we can obtain micro X-ray absorption (micro-XAFS) spectra in all regions of the image. The spacial resolution of the method was 40 nm. In order to more quickly observe a microscopic image and measure micro-XAFS spectra, the soft X-rays from the bending magnet were focused using a newly developed poly-capillary. As a result, the photon flux of 3 keV X-rays was increased about 60 time higher than that before the focusing. Using focused X-rays, we succeeded in observing one image at 10 ms for a bulk sample. We have also tried to shorten the measuring time of the micro-XAFS spectrum. For a Si-SiO sample, it has been demonstrated that micro-XAFS spectra in all regions of an image can be obtained within 1 min. It is concluded that real-time observations of chemical-states at nanometer scale are possible by the present method.

Molecular orientation of pentacene derivative

Ikeura, Hiromi*; Sekiguchi, Tetsuhiro

Photon Factory Activity Report 2013, Part B, P. 518, 2014/00

Organic electrically conducting -stacked small molecules are widely regarded as promising materials for future application of low-cost and flexible nanoelectronics. Pentacene is one of the most promising organic semiconductors because of its excellent device performance. Direct measurements of electronic structures of unoccupied states of organic semiconductors lead to better understanding of mechanism of electron conduction. For probing unoccupied partial density of states (DOS), X-ray absorption spectroscopy (XAS) is commonly used, where selective excitation of the 1s core electron to the unoccupied conduction band is possible. The molecular orientation of pentacene derivative has been investigated by angle dependent XAS measurements. Electronic states were calculated by DVX method.