Correction for the calculated XANES spectra of 1,4,7,10-alkyltetracenes considering the total electron yield (TEY) efficiency of sp2- and sp3-carbon atoms.

The calculated X-ray-absorption-near-edge-structure (XANES) spectra in the CK region of 1,4,7,10-alkyltetracenes, which are composed of both sp2-C atoms in the tetracene ring and sp3-C atoms in the alkyl-chains, can be corrected by considering the total electron yield (TEY) efficiency of sp3-C relative to sp2-C. In the correction, the previously measured TEY efficiency of k = 0.51 is applied to the calculated transition probabilities for sp3-C atoms. Then the calculated CK-XANES obtained from density functional theory (DFT) calculations can well reproduce the measured TEY-CK-XANES. Especially, the calculated π*/σ* peak intensity ratios are in good agreement with the measured ones. This suggests that a similar correction for the calculated XANES is necessary for compounds composed of multi-components with different TEY efficiencies.

Total electron yield (TEY) efficiency of sp2 and sp3 carbon atoms in the TEY-X-ray absorption near-edge structure (XANES) of 1,4,7,10-alkyltetracenes.

X-ray absorption near-edge structure (XANES) in the CK region of 1,4,7,10-alkyltetracenes, which are composed of sp2-C atoms in the tetracene ring and sp3-C atoms in the alkyl-chains, are measured using the total electron yield (TEY) and theoretically analyzed by DFT calculations to quantitatively investigate the π* and σ* peak intensities in the TEY-CK-XANES. The calculated π*/σ* peak intensity ratios are well approximated by the linear functions passing through the origin as a function of the sp2-C fraction, which is expressed as sp2-C/(sp2-C + sp3-C). In contrast, the measured π*/σ* peak intensity ratios are well approximated by curve functions passing through the origin, considering the TEY efficiency between sp2-C and sp3-C. The approximated curve functions indicate that the TEY efficiency of sp3-C is lower than that of sp2-C even in molecules. This confirms that the TEY efficiency of sp2-C and sp3-C should be considered in quantitative discussions on the sp2-C and sp3-C fractions from TEY-CK-XANES of carbon materials.

Mass absorption coefficient in the 200-800 eV region of sp3 carbon atoms measured using self-standing polyethylene thin films.

To experimentally determine the mass absorption coefficient (µ) of a sp3-carbon (C) atom in the soft X-ray region, soft X-ray absorption spectra (XAS) in the 200-800 eV and C K regions of 200-nm-thick self-standing polyethylene (PE) films were measured in the transmission and total electron yield (TEY) modes. PE films were prepared by a spin-coating method. Their experimentally measured thickness and density are 200 nm and 0.920 g/cm3, respectively. Soft X-ray absorption measurements were performed in beamline BL-6.3.2 at the Advanced Light Source. Although surface oxygen can be slightly observed in the O K and C K regions in TEY-XAS, it cannot be observed in absorbance-XAS. The absorbance-XAS profiles agree well with the calculated profiles, except in the C K threshold. Hence, it can be confirmed that the absorption-XAS measurements are achieved. From the absorbance, µ of sp3-C in PE is 7 × 104 cm2/g near 288 eV and 294 eV.

C K-XANES of graphitic carbons with oxygenated functional groups.

The X-ray absorption near-edge structure (XANES) in the C K region of graphite oxide (GO) exhibits a complicated and broad profile in the π* (285 eV)-σ* (293 eV) region due to oxygenated carbon atoms. To clarify the oxidation effect on carbon atoms in the spectral profile of GO, we measured the C K-XANES of various oxygenated aromatic compounds and theoretically analyzed them using density function theory (DFT) calculations. From the measured and calculated C K-XANES, the π* peaks of oxygenated carbon atoms shift to the higher-energy range by 0.5-4 eV from 285.5 eV of the typical π* peak of graphite. The energy positions of the shifted π* peaks depend on both the oxygenated functional groups and the molecular structures, confirming that the energy shifts of the π* peaks due to oxygenated carbon atoms cause the broad and complicated peak profiles in the π*-σ* region in C K-XANES of GO.

Heating system for in situ XANES measurements in the soft X-ray region of bulk samples at BL10/NewSUBARU.

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 â„ƒ. For demonstration, the C K- and O K-XANES spectra of sugar (sucrose) whose melting point is approximately 150 â„ƒ are measured while heating from 27 to 180 â„ƒ 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.

Relationship between Width and Height of π* Peak in C K-XANES of Graphitic Carbons.

The relationship between the width and height of the π* peak on X-ray absorption near edge structure (XANES) in the C K region of graphitic carbons is investigated from XANES measurements and theoretical analysis. This relationship is herein named the "characteristic diagram of π* peak profile". Mechanically ground (MG) graphite experimentally exhibits a linear correlation on the diagram. To understand the linear correlation, C K-XANES of the graphitic hexagonal carbon layers are calculated using first-principles calculations by focusing on the edge carbon atoms. The linear correlation is well explained by the ratio of the edge carbon atoms of the graphitic hexagonal carbon layers. The characteristic diagram of π* peak profile is applied to industrial carbon black (CB) for identification. CBs exhibit identical distributions on the diagram, which depend on their uses. It is therefore confirmed that the proposed characteristic diagram of π* peak profile can be a useful tool to identify graphitic carbons from the edge carbon atoms.

Total-Electron-Yield Measurements by Soft X-Ray Irradiation of Insulating Organic Films on Conductive Substrates.

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.

A carbonaceous two-dimensional lattice with FeN4 units.

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 π-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.

Newly Developed Friction Tester for in situ Soft X-Ray Absorption Measurements of Frictional Engine-Oil/Metals Interfaces.

A novel friction tester has been developed to clarify the friction mechanism between engine oil and metals by in situ/operando 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.

Chemical-state analysis of organic semiconductors using soft X-ray absorption spectroscopy combined with first-principles calculation.

The chemical states of organic semiconductors were investigated by total-electron-yield soft X-ray absorption spectroscopy (TEY-XAS) and first-principles calculations. The organic semiconductors, pentacene (C(22)H(14)) and pentacenequinone (C(22)H(12)O(2)), were subjected to TEY-XAS and the experimental spectra obtained were compared with the 1s core-level excited spectra of C and O atoms, calculated by a first-principles planewave pseudopotential method. Excellent agreement between the measured and the calculated spectra were obtained for both materials. Using this methodology, we examined the chemical states of the aged pentacene, and confirmed that both C-OH and C═O chemical bonds are generated by exposure to air. This result implies that not only oxygen but also humidity causes pentacene oxidation.

Pore development in carbonized hemoglobin by concurrently generated MgO template for activity enhancement as fuel cell cathode catalyst.

Various carbon materials with a characteristic morphology and pore structure have been produced using template methods in which a carbon-template composite is once formed and the characteristic features derived from the template are generated after the template removal. In this study, hemoglobin, which is a natural compound that could be abundantly and inexpensively obtained, was used as the carbon material source to produce a carbonaceous noble-metal-free fuel cell cathode catalyst. Magnesium oxide was used as the template concurrently generated with the hemoglobin carbonization from magnesium acetate mixed with hemoglobin as the starting material mixture to enable pore development for improving the activity of the carbonized hemoglobin for the cathodic oxygen reduction. After removal of the MgO template, the substantially developed pores were generated in the carbonized hemoglobin with an amorphous structure observed by total-electron-yield X-ray absorption. The extended X-ray absorption fine structure at the Fe-K edge indicated that Fe was coordinated with four nitrogen atoms (Fe-N(4) moiety) in the carbonized hemoglobin. The oxygen reduction activity of the carbonized hemoglobin evaluated using rotating disk electrodes was dependent on the pore structure. The highly developed pores led to an improved activity.

Distribution of lead in lead-accumulating pteridophyte Blechnum niponicum, measured by synchrotron radiation micro X-ray fluorescence.

The distribution of lead (Pb) accumulated in the pteridophyte Blechnum niponicum, a Pb-hyperaccumulator, was measured using synchrotron-radiation micro X-ray fluorescence (SR-micro-XRF) at BL37XU of SPring-8. From two-dimensional (2D) imagings of Pb at the root, petiole, leaf vein, pinna epidermis and sorus in the Blechnum niponicum, the mechanism for the transportation and accumulation of Pb can be suggested to be as follows: Lead is accumulated in conductive tissues. Most of the Pb solubilized in the rhizosphere is fixed in the conductive tissue, with the remainder being transported with the transpiration stream to the above-ground parts of the plant. Lead transported to the upper parts of the plant ultimately remains at the terminal points of the transpiration stream, including the stomatal apparatus and water pores; it was shown that these sections contain high concentrations of Pb.

Chemical analysis of impurity boron atoms in diamond using soft X-ray emission spectroscopy.

To analyze the local structure and/or chemical states of boron atoms in boron-doped diamond, which can be synthesized by the microwave plasma-assisted chemical vapor deposition method (CVD-B-diamond) and the temperature gradient method at high pressure and high temperature (HPT-B-diamond), we measured the soft X-ray emission spectra in the CK and BK regions of B-diamonds using synchrotron radiation at the Advanced Light Source (ALS). X-ray spectral analyses using the fingerprint method and molecular orbital calculations confirm that boron atoms in CVD-B-diamond substitute for carbon atoms in the diamond lattice to form covalent B-C bonds, while boron atoms in HPT-B-diamond react with the impurity nitrogen atoms to form hexagonal boron nitride. This suggests that the high purity diamond without nitrogen impurities is necessary to synthesize p-type B-diamond semiconductors.

Angle-resolved soft X-ray emission and absorption spectroscopy of hexagonal boron nitride.

Angle-resolved soft X-ray emission and absorption spectra in the BK and NK regions of hexagonal BN were measured using polarized synchrotron radiation. The take-off/incident-angle-dependence on the spectral features in both X-ray emission and absorption is clearly observed. The configuration of the sigma and pi orbitals, which were calculated using discrete variational (DV)-Xalpha molecular orbital calculations, explains the angle-resolved soft X-ray emission and absorption spectra. The relative peak intensity of the 394-eV peak in the NK X-ray emission provides useful information about the BN layer ordering.