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Hydrophobic cluster structures in aqueous ethanol solutions at different concentrations have been investigated by soft X-ray absorption spectroscopy (XAS). In the O K-edge XAS, we have found that hydrogen bond structures among water molecules are enhanced in the middle-concentration region by the hydrophobic interaction of the ethyl groups in ethanol. In the C K-edge XAS, the lower energy features arise from a transition from the terminal methyl C 1s electron to an unoccupied orbital of 3s Rydberg character, which is sensitive to the nearest-neighbor intermolecular interactions. From the comparison of C K-edge XAS with the inner-shell calculations, we have found that ethanol clusters are easily formed in the middle-concentration region due to the hydrophobic interaction of the ethyl group in ethanol, resulting in the enhancement of the hydrogen bond structures among water molecules. This behavior is different from aqueous methanol solutions, where the methanol-water mixed clusters are more predominant in the middle-concentration region due to the relatively weak hydrophobic interactions of the methyl group in methanol.

Soft X-ray absorption spectroscopy (XAS) observes element-specific intermolecular interactions of light elements in liquid phase through the core-to-valence excitation. We have newly developed liqu...

Drug penetration in human skin ex vivo following a modification of skin barrier permeability is systematically investigated by scanning transmission X-ray microscopy. Element-selective excitation is used in the O 1s regime for probing quantitatively the penetration of topically applied rapamycin in different formulations with a spatial resolution reaching

Ge atoms segregating on zirconium diboride thin films grown on Ge(111) were found to crystallize into a two-dimensional bitriangular structure, which was recently predicted to be a flat band material through an embedded kagome lattice. Angle-resolved photoelectron emission experiments together with theoretical calculations pointed out the existence of a nearly flat band in spite of non-negligible in-plane long-range hopping and interactions with the substrate. This provides an experimental verification for the fact that a flat band can emerge from the electronic coupling between atoms and not from the geometry of the atomic structure.

We have designed a new low-pass Fresnel zone plate (LPFZP) to extend soft x-ray absorption spectroscopy (XAS) to the lithium K absorption edge in a scanning transmission x-ray microscope (STXM). The performance of the LPFZP was evaluated in the STXM beamline at the UVSOR-III Synchrotron (Okazaki, Japan); the contribution of the higher-order harmonics is successfully suppressed to 0.1% of the fundamental energy, and a spatial resolution of 72 nm and an energy resolution (E/∆E) above 1000 are achieved as expected. XAS spectra of lithium are measured successfully in an electrode of a lithium-ion battery.

The interaction of an ion with surrounding solvent molecules is revealed by X-ray absorption spectroscopy in transmission mode for the case of calcium dication dissolved in pure water, methanol and ethanol at the Ca K and L2,3-edges. The near-threshold K-shell excitation leads to two distinct solvent-dependent features, the Ca 1s to 3d and 4p electronic transitions, clearly indicating the ligand field decreases as water is changed to methanol and methanol to ethanol. On the other hand, the Ca L2,3-edge excitation leads to small changes in the absorption spectra and the peak assignment – mostly in terms of Ca 2p to eg and t2g transitions for each of the two spin orbit components – is strongly depending on the geometry of the first solvation shell around the dication and on the magnitude of the ligand-field multiplet effects. Our interpretation is supported by ab-initio quantum chemical calculations of the solvent dependence of chemical shifts for the Ca 3d and 4p unoccupied levels of the 1s and 2p excited states, performed on a small cluster including the nearest neighbor solvent molecules surrounding the Ca dication assuming a cubic (8-fold) solvent coordination.

Glyoxal (CHOCHO) and methylglyoxal (CH3C(O)CHO) are well-known components of atmospheric particles and their properties can impact atmospheric chemistry and cloud formation. To get information on their hydration states in aqueous solutions and how they are affected by addition of inorganic salts (sodium chloride (NaCl) and sodium sulfate (Na2SO4)), we applied carbon and oxygen K-edge X-ray absorption spectroscopy (XAS) in transmission mode. The recorded C K-edge spectra show that glyoxal is completely hydrated in the dilute aqueous solutions, in line with previous studies. For methylglyoxal, we identified, supported by quantum chemical calculations, not only C-H, C=O and C-OH bonds, but also fingerprints of C-OH(CH2) and C=C bonds. This implies the presence of both mono- and dihydrated forms of methylglyoxal, as well as products of aldol condensation, and enol tautomers of the monohydrates. The addition of salts was found to introduce only very minor changes to absorption energies and relative intensities of the observed absorption features, indicating that the organic-inorganic interactions at the studied concentrations are not strong enough to affect the spectra in this work. The identified structures of glyoxal and methylglyoxal in aqueous environment support the uptake of these compounds to the aerosol phase in the presence of water and their contribution on secondary organic aerosol formation.

Chemical processes in solution are influenced by microheterogeneity (MH), where two liquids seem to be mixed in a macroscopic scale but are microscopically inhomogeneous. We have investigated one of the simplest MH systems, aqueous acetonitrile solution, using soft X-ray absorption spectroscopy (XAS). Molecular interactions of acetonitrile were revealed by C and N K-edge XAS at different concentrations, and those of solvent water were separately revealed by O K-edge XAS. The energy shift of the C≡N π* peak at the C K-edge shows three characteristic concentration regions and a phase-transition-like behavior between them. By comparing the energy shifts in XAS spectra with ab initio quantum chemical inner-shell calculations, we have determined local structures of acetonitrile-water mixtures in three concentration regions and found that the dipole interaction between acetonitrile and water is the key structure to emerge the MH state in the middle concentration region.

The photoelectron angular distribution of organic thin films is essential in the discussion of the (opto)electronic properties from the viewpoints of the spatial distribution of molecular orbitals and the interaction of molecular electronic states. We discuss the role of the weak intermolecular interaction in highly ordered aromatic molecules on the photoelectron angular distribution obtained by angle-resolved photoemission spectroscopy (ARPES). The experimental and theoretical investigation performed for superstructures of polycyclic aromatic hydrocarbons (PAHs) on Au(111) indicates that at least the intramolecular single-scattering process is necessary to be considered in simulation of the orbital tomography. Furthermore, ARPES spectra for various PAH monolayers reveal that the weak π-band dispersion is dependent on the surface Brillouin zone of the monolayer but not of the substrate. The long-range lateral intermolecular interaction in highly ordered aromatic molecules plays a main role in the π-band d...

In soft X-ray absorption spectroscopy in transmission mode (T-mode XAS), it is necessary to optimize the thickness of thin liquid layers for appropriate absorbance around 0.3–0.7 and keep the sample thickness flat within a photon beam. In the present work at the UVSOR Synchrotron Facility, a thin liquid layer is sandwiched between two 100 nm thick Si 3 N 4 or SiC membranes of 2 × 2 mm 2 in a helium chamber with enough working space, and the liquid thickness is optimized by using the elasticity of the membranes under controlling the helium pressure between 0.1013 and 0.12 MPa. The flatness of the liquid sample within a photon beam is investigated with measuring position-dependent O K-edge T-mode XAS spectra of liquid water. In the case of the beam size of 50 μm and the helium pressure of 0.1090 MPa (0.1038 MPa), it is confirmed that the liquid water layer has flat thickness around 200 nm (320 nm) at the center position of 2 × 2 mm 2 sample area with allowance of ±350 μm (±150 μm), where the thickness is ca 900 nm at the brim of the liquid sample area. The pre-edge vs. main edge (Pre/Main) ratio is 0.38 ± 0.01 for the center of the sample area and becomes considerably larger than 0.38 for the off-center position. The deviation from 0.38 is caused by the inhomogeneous thickness and is evaluated in comparison with a model simulation. The Pre/Main ratio can be used to evaluate the flatness in the liquid sample thickness within the beam area of soft X-rays. Positioning of as small a beam as possible on the center of the liquid sample area is essential to obtain reliable T-mode XAS spectra with the present liquid cells.

Intermolecular interactions of pyridine in liquid and in aqueous solution are studied by using soft X-ray absorption spectroscopy (XAS) at the C, N, and O K-edges. XAS of liquid pyridine shows that the N 1s→π* peak is blue shifted and the C 1s→π* peak of the meta and para sites is red shifted, respectively, as compared with XAS of pyridine gas. These shifts in liquid are smaller than those in clusters, indicating that the intermolecular interaction of liquid pyridine is weaker than that of pyridine cluster, as supported by the combination of quantum chemical calculations of the core excitation and molecular dynamics simulations of the liquid structure. On the other hand, XAS spectra of aqueous pyridine solutions (C5H5N)x(H2O)1−x measured at different molar fractions show that in the pyridine rich region, x>0.7, the C and N 1s→π* peak energies are not so different from pure liquid pyridine (x=1.0). In this region, antiparallel displaced structures of pyridine molecules are dominant as in pure pyridine liquid. In the O K-edge XAS, the pre-edge peaks sensitive to the hydrogen bond (HB) network of water molecules show the red shift of −0.15 eV from that of bulk water, indicating that small water clusters with no large-scale HB network are formed in the gap space of structured pyridine molecules. In the water rich region, 0.7>x, the N 1s→π* peaks and the O 1s pre-edge peaks are blue shifted, and the C 1s→π* peaks of the meta and para sites are red-shifted by increasing molar fraction of water. The HB network of bulk water is dominant, but quantum chemical calculations indicate that small pyridine clusters with the HB interaction between the H atom in water and the N atom in pyridine are still existent even in very dilute pyridine solutions.

The orbital-specific interfacial and intermolecular interactions in crystalline films of iron phthalocyanine (FePc) grown on an Au(111) surface were studied by means of angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation. The temperature-dependent ARPES measurement on the FePc monolayer reveals the formation of the molecule–metal hybrid state together with the Kondo resonance state below the Fermi level. These interface-specific states are derived from the electronic coupling of the Fe 3d orbital in the molecule with the Au(111) surface electron. For the flat-lying FePc multilayer on Au(111), the photon-energy-dependent ARPES spectra reveal the intermolecular valence-band dispersion for the C 2p-derived state, while the Fe 3d-derived state does not show such dispersion, indicating the localized Fe 3d spin state. These orbital-specific interactions play crucial roles in the unique electronic and magnetic properties of FePc.

A series of polymerized high internal phase emulsion (polyHIPE) materials have been prepared by using a water in oil emulsion stabilized by a macro-RAFT agent, 2-(butylthiocarbonothioylthio)-2-poly(styrene)-b-poly(acrylic acid), acting as a polymeric surfactant. The pore structures of the formed polyHIPEs were closed. By removing the RAFT-endgroup of the amphiphilic macro-RAFT agent, the obtained polyHIPEs possessed an open structure with voids. The effect of the RAFT-endgroup of the amphiphilic macro-RAFT agent on the surface chemistry of the polyHIPEs is discussed. The obtained polyHIPEs via this surfactant-assisted functionalization strategies were characterized by FTIR spectroscopy, FTIR mapping, SEM, SEM-EDX, TEM, XPS as well as synchrotron-based scanning transmission X-ray microscopy (STXM). The latter technique revealed the surface chemistry of the obtained polyHIPEs and macro-RAFT agent multicomponents with a surface spatial resolution of the order of 30-100 nm. Refereed/Peer-reviewed

The present study aims at probing the influence of different substituents of sodium carboxylate salts R–COO−:Na+ in aqueous solutions, with R = H, CH3, C2H5, CH2Cl, CF3, and C6H5. X-ray absorption spectroscopy was used in the oxygen K-edge region to highlight the effect of R on the energy position of the O1s-to-πCOO* resonance of the carboxylate ion. Ab initio static exchange and ΔSCF calculations are performed and confirm the experimental observations. We qualitatively discuss the results on the basis of the polar properties of these groups as well as on the basis of the πCOO* orbital energy in the ground states, the oxygen 1s orbital ionization energy, and the O1s-to-πCOO* resonance energy.

The electronic structure of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-TCNQ (F4TCNQ) monolayers on Au(111) has been investigated by means of angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation. In contrast to the physisorbed TCNQ/Au(111) interface, the high-resolution core-level photoemission spectra and the low-energy electron diffraction at the F4TCNQ/Au(111) interface show evidence for the strong charge transfer (CT) from Au to F4TCNQ and for the Au atom segregation from the underlying Au(111) surface, suggesting a possible origin of the spontaneous formation of the two-dimensional F4TCNQ-Au network. The ARPES experiment reveals a low hole-injection barrier and large band dispersion in the CT-induced topmost valence level of the F4TCNQ-Au network with 260 meV bandwidth due to the adatom-mediated intermolecular interaction. These results indicate that strong electron acceptor molecules with metal adatoms can form high hole-mobility molecular layers by contro...

In-situ/operando techniques have been developed for spectromicroscopic studies of heavy elements using hard X-rays with high transmittance in samples and long focal length of optical elements (i.e....

Soft X-ray absorption spectroscopy (XAS) involving excitation processes of a core electron to unoccupied states is an effective method to study local structures around excited C, N, and O atoms in liquid samples. Since soft X-rays are strongly absorbed by air and liquid itself, we have developed transmission-type liquid flow cells, where the absorbance of liquid samples can be easily reduced and optimized by controlling the liquid thickness. By using the transmission-mode XAS techniques, we have investigated local structures of several liquid samples such as concentration dependence of aqueous pyridine solutions and unexpected temperature-dependent structural changes in liquid benzene from the precise energy shift measurements in XAS spectra with the help of molecular dynamics simulation and inner-shell calculations. These XAS techniques are also applied to in situ/operando observation of chemical processes in solutions such as catalytic and electrochemical reactions.

The move toward sustainable hydrogen production from water using renewable energy, a highly efficient oxygen evolution electrocatalyst, is crucial because water-splitting efficiency is restricted to the oxygen evolution capability, which is insufficient compared to the hydrogen evolution reaction. Herein, we report a new method that improves the oxygen evolution activity by integration of active nickel oxide clusters using amino acids, meaning that the amount of electrodeposited nickel oxides is increasing with maintaining the catalytic activity. This method enhances the catalytic activity because the reaction sites drastically increase in three dimensions. The detailed reaction mechanism was investigated using operando UV/vis absorption and Ni K-edge X-ray absorption spectroscopic techniques, which suggested that amino acids such as glycine, alanine, and glutamine promoted the electrodeposition of NiO6 octahedral structure clusters. Meanwhile, the analysis of N and O K-edge X-ray absorption spectra showe...

Label-free detection of core-multishell (CMS) nanocarriers and the anti-inflammatory drug dexamethasone is reported. Selective excitation by tunable soft X-rays in the O 1s-regime is used for probing either the CMS nanocarrier or the drug. Furthermore, the drug loading efficiency into CMS nanocarriers is determined by X-ray spectroscopy. The drug-loaded nanocarriers were topically applied to human skin explants providing insights into the penetration and drug release processes. It is shown that the core-multishell nanocarriers remain in the stratum corneum when applied for 100 min to 1000 min. Dexamethasone, if applied topically to human ex vivo skin explants using different formulations, shows a vehicle-dependent penetration behavior. Highest local drug concentrations are found in the stratum corneum as well as in the viable epidermis. If the drug is loaded to core-multishell nanocarriers, the concentration of the free drug is low in the stratum corneum and is enhanced in the viable epidermis as compared to other drug formulations. The present results provide insights into the penetration of drug nanocarriers as well as the mechanisms of controlled drug release from CMS nanocarriers in human skin. They are also compared to related work using dye-labeled nanocarriers and dyes that were used as model drugs.

In order to discuss the site specificity in the organic/metal interfacial interaction, the electronic structure of the well-ordered interface of cobalt phthalocyanine (CoPc) adsorbed on Au(111) is studied by angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation. The core-level and valence-band ARPES spectra show an evidence for the strong CoPc/Au(111) chemical interaction localized at the Co site and the resultant formation of the interface states. The CoPc/Au(111) interface states are formed around the highest occupied molecular orbital (HOMO) and just below the Fermi level (EF) with the nondispersive and dispersive characteristics, respectively. The nondispersive interface state around the HOMO is attributed to the intramolecular πPc–dCo mixed orbital induced by the site-specific interfacial interaction. The dispersive interface state below EF originates from the adsorbate-induced modification of the Au(111) Shockley state, which shows difference between CoPc and metal-free Pc (H2...

An array of ZnO/Fe2O3 core-shell nanowires (NW) for the highly efficient absorption of light and carrier collection is developed for use in photoelectrochemical (PEC) water-splitting. The oriented NW architecture favors physical matching, providing a direct electron conduction pathway and reducing the diffusion length of photogenerated holes. This work involves a combination of spectral imaging, spectromicroscopy and in situ x-ray absorption spectroscopy; spectra are obtained under operando conditions. Direct investigation of oriented nanowires using polarization-dependent x-ray spectromicroscopy enables the determination of the relationship between anisotropic electronic orbitals and charge carrier water-splitting efficiency. The results of O K-edge STXM demonstrated that the ZnO/Fe2O3 core-shell NW exhibits strong anisotropy and thus provides higher electron-hole transport efficiency than bare ZnO. In situ XAS revealed that interfacial charge transfer between Fe 3d and Zn 4p states enhances the photoelectrochemical reaction in the ZnO/Fe2O3 core-shell NW. The photogenerated electrons of Fe2O3 are transferred from Fe 3d states to the Zn 4p state under photoelectrochemical conditions.

Benzene is the simplest aromatic molecule with intermolecular π–π interactions. Because ordered liquids are key structures used to study chemical and biological phenomena in the liquid state, ordered structures of benzene confined in nanopores have been extensively studied, whereas those in the liquid state are still unknown. In this study, we address fundamental questions regarding whether ordered structures of benzene are formed in the liquid state by using carbon K-edge X-ray absorption spectroscopy (XAS) as a sensitive local probe. By comparing unexpected temperature behaviors of the π* peak in XAS spectra with model calculations, we have investigated temperature-dependent changes of ordered structures in liquid benzene caused by the increase in abundance of the parallel sandwich orientation relative to parallel displaced structures for the higher temperature. These results are confirmed by infrared spectroscopy with additional support of vibrational mode calculations.

Functionalities of organic semiconductors are governed not only by individual properties of constituent molecules but also by solid-state electronic states near the Fermi level such as frontier molecular orbitals, depending on weak intermolecular interactions in various conformations. The individual molecular property has been widely investigated in detail; on the other hand, the weak intermolecular interaction is difficult to investigate precisely due to the presence of the structural and thermal energy broadenings in organic solids. Here we show quite small but essential intermolecular valence band dispersions and their temperature dependence of sub-0.1-eV scale in crystalline films of metal phthalocyanines (H 2 Pc, ZnPc, CoPc, MnPc, and F 16 ZnPc) by using angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation. The observed bands show intermolecular and site dependent dispersion widths, phases, and periodicities, for different chemical substitution of terminal groups and central metals in the phthalocyanine molecule. The precise and systematic band-dispersion measurement would be a credible approach toward the comprehensive understanding of intermolecular interactions and resultant charge transport properties as well as their tuning by substituents in organic molecular systems.

In situ O K-edge X-ray absorption fine structure (XAFS) spectroscopy was applied to investigate the electronic and structural change in the nickel–borate (Ni–Bi) electrocatalyst during the oxygen evolution reaction (OER). An absorption peak was observed around 528.7 eV at 1.0 V versus Ag/AgCl in a potassium borate aqueous solution, which relates with the formation of nanoscale order domains of edge-sharing NiO6 octahedra in the Ni–Bi electrocatalyst. XAFS spectra were measured with variation of the electrode potential from 0.3 up to 1.0 V. The measured absorption peaks suggest that the quantity of NiO6 octahedra increased in correlation with the OER current; however, when the potential was changed downward, the XAFS absorption peak assigned to NiO6 octahedra remained constant, even at the electrode potential for no OER current. This difference implies that the water oxidation catalysis proceeds at the domain edge of NiO6 octahedra. The XAFS technique provides the first successful direct probing of the act...

The structure of interfacial water layers around nanoparticles dispersed in an aqueous environment may have a significant impact on their reactivity and on their interaction with biological species. Using transmission soft X-ray absorption spectroscopy in liquid, we demonstrate that the unoccupied electronic states of oxygen atoms from water molecules in aqueous colloidal dispersions of nanodiamonds have a different signature than bulk water. X-ray absorption spectroscopy can thus probe interfacial water molecules in colloidal dispersions. The impacts of nanodiamond surface chemistry and concentration on interfacial water electronic signature are discussed.

In conventional in situ spectroscopies of solid–liquid heterogeneous catalytic reactions, it is difficult to measure the conversion of liquid substrates on solid catalysts due to the lack of sensitivity and the difficulty in separation of target signals in the mixture of substrates, reactants, products, solvents, and solid catalysts. Element-specific soft X-ray absorption spectroscopy (XAS) is a promising method to detect target substrate and product separately from the other components using chemically different inner shell excitation energies. In the present work, we have developed an in situ sample cell to measure time- and temperature-dependent XAS spectra in transmission mode and applied it to one of the solid–liquid heterogeneous catalytic reactions, cyanopyrazine (PzCN) hydration to produce pyrazinamide (PzCONH2) on the TiO2 catalyst (PzCN + H2O → PzCONH2). We have succeeded in unambiguous observation of the spectral change in the C K-edge and N K-edge XAS due to the production of PzCONH2 from PzCN...

Perfluorocarbons are a family of molecules consisting mainly of carbon and fluorine atoms. They have interesting chemical properties and have diverse applications in biomedicine, physical chemistry and polymer science. In this work, carbon K-edge absorption and emission spectra of liquid decalin are presented and compared to perfluorodecalin. A comprehensive picture of the electronic structure of decalin is provided based on soft X-ray absorption and emission spectroscopies. Experimental data are compared to theoretical time-dependent density functional theory for the hydrocarbon, the perfluorocarbon and the stepwise fluorinated derivatives. We observed a molecular orbital change from unoccupied to occupied orbitals for perfluorodecalin, which was induced through the fluorination process.

Interaction between water molecules and alkali metal ions in aqueous salt solutions has been studied by the oxygen K-edge soft X-ray absorption spectroscopy (XAS) in transmission mode. In the measurement of several alkali halide aqueous solutions with different alkali chlorides (Li, Na, and K) and different sodium halides (Cl, Br, and I), the pre-edge component arising from the hydration water molecules shows a blue shift in peak energy as strongly depending on cations but not on anions. In the temperature dependent measurement, the pre-edge component arising from water molecules beyond the first hydration shell shows the same behavior as that of pure liquid water. On the other hand, the pre-edge component arising from water molecules in the first hydration shell of Li+ ions is not evidently dependent on the temperature, indicating that the hydration water molecules are more strongly bound with Li+ ions than the other water molecules. These experimental results are supported by the results of radial distribution functions of the first hydration shell and their temperature dependence, evaluated by molecular dynamics simulations.

Various synchrotron radiation-based spectroscopic and microscopic techniques are used to elucidate the room-temperature ferromagnetism of carbon-doped ZnO-nanowires (ZnO-C:NW) via a mild C+ ion implantation method. The photoluminescence and magnetic hysteresis loops reveal that the implantation of C reduces the number of intrinsic surface defects and increases the saturated magnetization of ZnO-NW. The interstitial implanted C ions constitute the majority of defects in ZnO-C:NW as confirmed by the X-ray absorption spectroscopic studies. The X-ray magnetic circular dichroism spectra of O and C K-edge respectively indicate there is a reduction in the number of unpaired/dangling O 2p bonds in the surface region of ZnO-C:NW and the C 2p-derived states of the implanted C ions strongly affect the net spin polarization in the surface and bulk regions of ZnO-C:NW. Furthermore, these findings corroborate well with the first-principles calculations of C-implanted ZnO in surface and bulk regions, which highlight the stability of implanted C for the suppression and enhancement of the ferromagnetism of the ZnO-C:NW in the surface region and bulk phase, respectively.

International audience; Nanodiamonds exhibit exceptional colloidal properties in aqueous media that lead to a wide range of applications in nanomedicine and other fields. Nevertheless, the role of surface chemistry on the hydration of nanodiamonds remains poorly understood. Here, we probed the water hydrogen bond network in aqueous dispersions of nanodiamonds by infrared, Raman, and X-ray absorption spectroscopies applied in situ in aqueous environment. Aqueous dispersions of nanodiamonds with hydrogenated, carboxylated, hydroxylated, and polyfunctional surface terminations were compared. A different hydrogen bond network was found in hydrogenated nanodiamonds dispersions compared to dispersions of nanodiamonds with other surface terminations. Although no hydrogen bonds are formed between water and hydrogenated surface groups, a long-range disruption of the water hydrogen bond network is evidenced in hydrogenated nanodiamonds dispersion. We propose that this unusual hydration structure results from electron accumulation at the diamond–water interface.

Liquid methanol shows one- and two-dimensional (1D/2D) hydrogen bond (HB) networks, and liquid water shows three-dimensional (3D) HB networks. We have clearly found three different local structures around the methyl group of methanol-water binary solutions (CH3OH)X(H2O)1-X at different concentrations in C K-edge soft X-ray absorption spectroscopy (XAS). With the help of molecular dynamics simulations, we have discussed the concentration dependence of the hydrophobic interaction at the methyl group in the C K-edge XAS spectra. In the methanol-rich region I (1.0X0.7), a small amount of water molecules exists separately around dominant 1D/2D HB networks of methanol clusters. In the region II (0.7X0.3), the hydrophobic interaction of the methyl group is dominant due to the increase of mixed methanol-water 3D network structures. In the water-rich region III (0.3X0.05), methanol molecules are separately embedded in dominant 3D HB networks of water. On the other hand, the pre-edge feature in the O K-edge XAS shows almost linear concentration dependence. It means the HB interaction between methanol and water is almost the same as that of water-water and of methanol-methanol.

Photoinduced quantum dynamics in molecules have hierarchical temporal structures with different energy scales that are associated with electron and nuclear motions. Femtosecond-to-attosecond transient absorption spectroscopy (TAS) using high-harmonic generation (HHG) with a photon energy below 300 eV has been a powerful tool to observe such electron and nuclear dynamics in a table-top manner. However, comprehensive measurements of the electronic, vibrational, and rotational molecular dynamics have not yet been achieved. Here we demonstrate HHG-based TAS at the nitrogen $K$K-edge (400 eV) for the first time to our knowledge and observe all the electronic, vibrational, and rotational degrees of freedom in a nitric oxide molecule at attosecond to sub-picosecond time scales. This method of employing core-to-valence transitions offers an all-optical approach to reveal the complete molecular dynamics in photochemical reactions with element and electronic state specificity.

Edges on the cleaved graphite crystal surface were found to be preferentially oriented perpendicularly to the hexagonal perimeter facet of the graphite single crystal assigned to the zig-zag-type e...

The application of soft X-ray absorption spectroscopy (XAS) to liquid cells based on microfluidics for chemical state analysis of light elements is much more difficult than hard X-ray absorption since soft X-rays cannot deeply penetrate a microfluidic cell. In this study, we have newly developed a microfluidic cell for spatially resolved XAS, where a 100 nm thick Si3N4 membrane is used for the measurement window to transmit soft X-rays for keeping the microfluidic flow at a width and depth of 50 µm. The π* peak of pyridine near the N K-edge XAS shows characteristic energy shifts near the liquid-liquid interface in a laminar flow of pyridine and water. The distributions of the molar fractions of pyridine and water near the liquid-liquid interface have been determined from the energy shifts of the π* peak probed at different geometric positions, where pyridine is mixed in the water part of the laminar flow and vice versa. The spatial distribution of both species has also been studied by infrared microscopy, using the same microfluidic setup. The present work clearly shows that these spectroscopic techniques are easily applicable to chemical and biological reactions prepared by microfluidics.

We have developed an acceptance-cone-tunable (ACT) electron spectrometer for the highly efficient constant-energy photoelectron mapping of functional materials. The ACT spectrometer consists of the hemispherical deflection analyzer with the mesh-type electrostatic lens near the sample. The photoelectron trajectory can be converged by applying a negative bias to the sample and grounding the mesh lens and the analyzer entrance. The performance of the present ACT spectrometer with neither rotating nor tilting of the sample is demonstrated by the wide-angle observation of the well-known π-band dispersion of a single crystalline graphite over the Brillouin zone. The acceptance cone of the spectrometer is expanded by a factor of 3.30 when the negative bias voltage is 10 times as high as the kinetic energy of photoelectrons.

Change in valence of Fe ions in aqueous iron sulfate solutions at different potentials has been studied by Fe L-edge soft X-ray absorption spectroscopy (XAS) in transmission mode. Each XAS spectrum...

Here we present an overview of recent developments of X-ray and electron spectroscopy to probe water at different temperatures. Photon-induced ionization followed by detection of electrons from either the O 1s level or the valence band is the basis of photoelectron spectroscopy. Excitation between the O 1s and the unoccupied states or occupied states is utilized in X-ray absorption and X-ray emission spectroscopies. These techniques probe the electronic structure of the liquid phase and show sensitivity to the local hydrogen-bonding structure. Both experimental aspects related to the measurements and theoretical simulations to assist in the interpretation are discussed in detail. Different model systems are presented such as the different bulk phases of ice and various adsorbed monolayer structures on metal surfaces.

A whole A549 cell and isolated nuclei of HeLa S3 cells in the apoptotic process were investigated by using a scanning transmission X-ray microscope (STXM) in the UVSOR Synchrotron (Okazaki, Japan). Near edge X-ray absorption fine structures (NEXAFS) of DNA and histone in the N K-edge region were measured as reference and their distribution in the nuclei was determined by using these reference spectra. The four stages of the apoptosis were successfully distinguished.