村松 康司

A heating system for in situ XANES measurements in the soft X-ray region of bulk samples is newly developed and installed in BL10 at NewSUBARU. The system employs Joule heating, which can heat various bulk samples up to 250 ℃. For demonstration, the C K- and O K-XANES spectra of sugar (sucrose) whose melting point is approximately 150 ℃ are measured while heating from 27 to 180 ℃ under a vacuum pressure of 10-5 Pa. The in situ XANES spectra of heated sugars can successfully observe the thermal transformation of sucrose molecules and their hydrogen bonds.

The photocurrent (sample current) of insulating 0.7-μm thick polyethylene terephthalate (PET) films on conductive substrates (C, Au, Cu) was clearly measured through the substrates during soft X-ray irradiation on the PET films. X-ray absorption measurements of the PET/conductive-substrates using the total-electron-yield (TEY) method by measuring sample current easily provide the X-ray absorption spectra (XAS) of PET films, which are independent of the substrates. From additional X-ray absorption measurements using self-standing PET/Au and Au/PET-films, I-V measurements, and thickness-dependent sample current measurements, it can be confirmed that electrically conductive paths form in the insulating PET film in thickness direction along the soft X-ray beam trajectory. Such phenomena enable easy and simple TEY-XAS measurements of insulating μm-order-thick samples.

© 2020 Elsevier Inc. Simple molecules such as formaldehyde and ammonia were expected to be incorporated into small bodies with water ice in the early accretion history. These molecules would have reacted to produce various organic compounds during aqueous alteration which most of the primitive carbonaceous chondrite parent bodies have experienced. Our previous hydrothermal experiments involving formaldehyde and ammonia have already shown formations of amino acids and organic solids that resemble to macromolecular organic matter in primitive meteorites. Here we focus on the characterization in liquid phases with various analytical methods including high-resolution mass spectrometry (HRMS), X-ray absorption near edge structure (XANES), and Fourier-transform infrared spectroscopy (FTIR), in addition to kinetic analyses of the reactions using in-situ FTIR spectroscopy with a heatable liquid cell. The HRMS results showed that soluble fractions contain various carbohydrates (CHO molecules) and these with nitrogen (CHON molecules). The mass defect plots of the reaction products suggested the reactions involving CH2O addition, CH2 addition, dehydration and decarboxylation. C[dbnd]C and C[dbnd]N bonds increased with temperature by condensation reactions. Behaviors of oxygen-bearing functional groups showed high complexity. In general, carboxyl/ester/aldehyde compounds formed at the early stage of the reactions, then some of these decomposed by decarboxylation. N-XANES indicated the presence of amide-bearing compounds that could be precursors of amino acids. The in-situ FTIR spectra showed that formaldehyde and ammonia reacted and formed hexamethylenetetramine (HMT) before starting the heating experiments at room temperature. Kinetic analyses showed that the apparent activation energy of decreases in HMT is ~130–140 kJ mol−1. The decrease in HMT is faster than the other reactions, indicating that the reactions involving HMT occurred at the early stage of the aqueous alteration. The kinetics of the ammonia–aldehyde system suggested that the reactions involving formaldehyde, ammonia and HMT are efficient for aqueous alteration in parent bodies of CI, CM, and CR chondrites.

© Published under licence by IOP Publishing Ltd. In order to analyze the local structure of graphitic carbons by soft X-ray absorption spectroscopy, CK-XANES spectra of polycyclic aromatic compounds having 5-membered pentagonal or 7-membered heptagonal rings were theoretically analyzed by first-principles calculations. Pentagonal rings in the bent graphitic structure take different π∗ orbital states. Hence, pentagonal rings split the π∗ peak into two peaks in CK-XANES spectra. Heptagonal rings create electrostatic potential holes in graphitic structures, and the carbon atoms in the heptagonal ring can be regarded as conjugated edge carbon atoms. Hence, heptagonal rings also split the π∗ peak into two peaks. Edge-carbon atoms split the π∗ peak into two peaks in CK- XANES spectra. Consequently, carbon atoms in non-benzenoid rings and the edge-carbon atoms in graphitic structures make the π∗ peak profile wider when compared to graphite.

While activated carbons are used as electrode materials in commercial supercapacitors, they are not stable under high voltage operation especially at a positive-electrode side, and this limits the working voltage of supercapacitors to about 2.8 V in organic electrolytes. Thus, revealing the specific carbon chemical structures causing the corrosion is of great significance to come up with ideas of avoiding the corrosion reactions and eventually to achieve high energy density by expanding the working voltage. In this work, a variety of carbon materials are analyzed with many characterization techniques such as X-ray diffraction, Raman spectroscopy, N-2 adsorption, magnetic susceptibility measurement, and temperature programmed desorption up to 1800 degrees C, to find out the origin of corrosion reactions in an organic electrolyte. While carbon crystallinity and porosity are not directly related to the positive-electrode corrosion, a good correlation is found between the corrosion charge and the number of carbon edge sites terminated by H and oxygen-functional groups which are decomposed and release CO. It is thus concluded that the H-terminated edge sites, phenol, ether and carbonyl groups are electroactive sites for the carbon materials used in the positive electrode of supercapacitors.

A metal-containing carbonaceous two-dimensional lattice was formed on a graphene plane by sublimation, deposition, and pyrolysis of Fe phthalocyanine (Pc). The formation and growth of the FePc-derived pi-conjugated planar system were reflected by its orientation conversion from the perpendicular to horizontal mode and by the N K-edge X-ray absorption near-edge structure.

A novel friction tester has been developed to clarify the friction mechanism between engine oil and metals by in situloperando measurements of the X-ray absorption near edge structure (XANES) using the total electron yield (TEY) method. The tester can perform frictional motion with engine oil and metals in a vacuum chamber under a vacuum of 10(-7) Torr during TEY-XANES measurements in BL-6.3.2 at the Advanced Light Source (ALS). From in situ XANES measurements in the C K and Fe L regions, the organic molecule layers at the oil/metals interfaces have been successfully observed.

Low-energy Ar ions (0.5-2 keV) were irradiated onto vertically aligned multiwalled carbon nanotube (VA-MWCNT) films, and the chemical states, orientation, and oxygen content of the irradiated VA-MWCNT films were investigated by soft X-ray absorption spectroscopy (XAS). After irradiation, two additional peaks appeared in the XAS spectra in the C K region, indicating a significant change in the electronic structure. Furthermore, it was found that the VA-MWCNT films were oxidized after irradiation. The results of chemical-state analyses of the XAS spectra in both the C K and 0 K regions indicated the formation of carboxyl groups (-COOH) on the surface of the VA-MWCNT films upon irradiation. The oxygen content of the VA-MWCNT films increased with increasing ion energy and fluence. (C) 2016 Elsevier B.V. All rights reserved.

The structure of carbon obtained from the thermal reduction of graphite oxide at 900 degrees C after electrochemical storage sodium ions was investigated. X-ray diffraction measurement of the carbon sample after charged to various potentials indicated that sodium ions are stored between the layers of carbon below 0.3V vs. Na/Na+ though the interlayer spacing of it was similar to that of graphite. The lower LUMO energy as revealed from the broad pi* peak in the region of CK observed in soft X-ray absorption measurement was responsible for the intercalation of a large amount of sodium ions into the present carbon material. (C) The Electrochemical Society of Japan, All rights reserved.