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Oxysulfide semiconductors have narrow bandgaps suitable for water splitting under visible-light irradiation, because the electronegative sulfide ions negatively shift the valence band edges of the corresponding oxides1,2. However, the instability of sulfide ions during the water oxidation is a critical obstacle to simultaneous evolution of hydrogen and oxygen3. Here, we demonstrate the activation and stabilization of Y2Ti2O5S2, with a bandgap of 1.9 eV, as a photocatalyst for overall water splitting. On loading of IrO2 and Rh/Cr2O3 as oxygen and hydrogen evolution co-catalysts, respectively, and fine-tuning of the reaction conditions, simultaneous production of stoichiometric amounts of hydrogen and oxygen was achieved on Y2Ti2O5S2 during a 20 h reaction. The discovery of the overall water splitting capabilities of Y2Ti2O5S2 extends the range of promising materials for solar hydrogen production. The instability of sulfide ions during water oxidation prevents simultaneous evolution of hydrogen and oxygen. An oxysulfide semiconductor photocatalyst, Y2Ti2O5S2, is shown to evolve H2 and O2 via a water-splitting reaction under visible-light irradiation.

High-quality needle-like crystals of La5Ti2CuS5O7 (a ternary transition-metallic oxysulfide) as long as 1 mm and a few μm in diameter were grown in CsCl molten-salt flux. This synthesis process was performed in a Bridgman furnace with slow motion of charge across the heating zone. Transmission electron microscopy/diffraction analysis indicated that they are product crystallites without crystalline intergrowth, and that the longitudinal direction of needle crystals is parallel to crystallographic b axis of La5Ti2CuS5O7. Optical polarized ultraviolet–visible reflectance spectroscopy provided the first experimental evidence of the one-dimensional electronic excitation along the b axis of this material. The spectroscopic peaks are assigned to the transitions between the electronic bands aided by numerical calculations on the basis of density functional theory (DFT). The advantages of this synthetic process will be applicable in general for oxysulfides that are useful as optical and photocatalytic materials.

Thin films of a solid solution of ZnSe and CuIn0.7Ga0.3Se2 ((ZnSe) x (CIGS) 1–x ) are prepared by co-evaporation. Structural characterization reveals that the ZnSe and CIGS form a solid solution with no phase separation. (ZnSe)0.85(CIGS)0.15-based photocathodes modified with Pt, Mo, Ti, and CdS exhibit a photocurrent of 7.1 mA cm−2 at 0 VRHE, and a relatively high onset potential of 0.89 VRHE under simulated sunlight. A two-electrode cell containing a (ZnSe)0.85(CIGS)0.15 photocathode and a BiVO4-based photoanode has an initial solar-to-hydrogen conversion efficiency of 0.91%, which is one of the highest values reported for a photoanode–photocathode combination. Thus, (ZnSe)0.85(CIGS)0.15 is a promising photocathode material for efficient photoelectrochemical water splitting.

The surface phonon dispersion of a deuterium-terminated Si(110)-(1 × 1) surface [D:Si(110)-(1 × 1)] is investigated by using high-resolution electron-energy-loss spectroscopy (HREELS) and first-principles calculations based on the density functional theory (DFT) with the local density approximation (LDA). The characteristics of D:Si(110)-(1 × 1) are unique compared to those of H:Si(110)-(1 × 1) (Matsushita et al., 2015) in terms of the resolved vibrational modes. By the HREELS, one-dimensional surface phonons consisting of D–Si stretching vibrations are observed above the bulk-phonon band energy edge of 64.5 meV. Ten modes are observed below this value, classified as surface, surface resonant, and bulk phonons according to the calculated energy dispersion as well as the depth profile of spectral density and displacement vectors. In particular, five D–Si bending modes are observed out of the seven theoretically predicted modes. The bending modes are strongly coupled with the displacements across the D and five Si layers. The DFT-LDA surface phonon dispersion is in good agreement with the experimental results except a few frequency/dispersion mismatches, as the structure optimized by DFT-LDA mismatches with the previous scanning tunneling microscopy (STM) results (Matsushita et al., 2015). D:Si(110)-(1 × 1) elucidates the nature of covalently bonded phonons and their characteristics both experimentally and theoretically.

A mixed monolayer of 1,2-dihexanoyl-sn-glycero-3-phospho-l-serine (DHPS) and 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) on an 1-octanethiol-modified gold substrate was visualized on the nanometer scale using in situ scanning tunneling microscopy (STM) in aqueous solution. DHPS clusters were evident as spotty domains. STM enabled us to distinguish DHPS molecules from DHPC molecules depending on their electronic structures. The signal of the DHPS domains was abolished by neutralization with Ca(2+). The addition of the PS + Ca(2+)-binding protein of annexin V to the Ca(2+)-treated monolayer gave a number of spots corresponding to a single annexin V molecule.

We have measured the macroscopic and microscopic surface morphology of hydrogen-terminated Si(110)-(1 × 1) [H:Si(110)-(1 × 1)] surfaces prepared by an improved wet chemical process. The observations were performed by high-resolution electron-energy-loss spectroscopy (HREELS), low-energy-electron diffraction (LEED), and scanning tunneling microscopy (STM). At macroscopic scale, it was found that the surface is a mono-hydride terminated surface with a two-dimensional p2mg space group, thus, being a well-defined H:Si(110)-(1 × 1) surface. At microscopic scale, elongated terraces were observed along the [1 1 ¯ 0] direction reflecting surface anisotropy. The terraces extend in frames with sizes up to a few micrometers. We discussed the macroscopic and microscopic surface morphology by combining our LEED and STM results.

In situ dynamic observation of model biological cell membranes, formed on a water/gold substrate interface, has been performed by the combination of electrochemical scanning tunneling microscopy and reflection infrared absorption vibrational spectroscopy. Monolayers of 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) were formed on alkanethiol-modified gold surfaces in a buffer solution, and the microscopic phase transitions driven by electrochemical potential control were observed more in detail than our previous study on the same system [Electrochem. Commun. 2007, 9, 645-650]. This time the transitions were associated with the chemistry of DHPC by the aid of vibrational spectroscopy and the utilization of deuterium-labeled DHPC molecules. A negative potential shift solidifies the fluidic lipid layers into static striped or grainy features without notable chemical reactions. The first positive potential shift over the virginal DHPC monolayer breaks DHPC into choline and the corresponding phosphatidic acid (DHPA). This is the first case of a phospholipid electrochemical reaction microscopically detected at the solid surface.

A tip-enhanced Raman spectroscopy (TERS) set-up added on a scanning tunneling microscope (STM) was constructed and was used to study the molecular arrangement of 4,4′-bipyridine (4,4′-BiPy) and 4,4′-bipyridine N,N' -dioxide (4,4′-BiPyO 2 ) adsorbed on Au(111). Over a monolayer of 4,4′-BiPy, in the ambient atmosphere, intense TERS signals were recorded, involving Au N stretching vibration at 185 cm − 1 . At the early stage of 4,4′-BiPy adsorption, the Au N stretching signal was not detected. By the aid of the theoretical calculations of the Raman scattering intensities for each vibrational normal mode, a standing-up, tilted orientation at monolayer coverage and a vertical orientation with the longitudinal molecular axis parallel to the surface at low surface coverage was concluded. Adsorption of 4,4′-BiPyO 2 on Au(111) resulted in formation of a (6 × 9) adlattice. Moderately intense TERS signals were observed, containing the N O stretching modes and the in-plane ring vibrational modes. Neither Au O nor Au N stretching modes were observed. 4,4′-BiPyO 2 was laid with the longitudinal axis parallel to the surface, and the molecular plane vertical to the surface. These results demonstrate that STM-TERS is an effective method for simultaneous imaging and vibrational analysis, facilitating identification of the adsorbed layers with the nanometer-scale spatial resolution and monolayer sensitivity.

UTokyo Research掲載「太陽光を用いて水を分解できる粉末光触媒シート」 URI: http://www.u-tokyo.ac.jp/ja/utokyo-research/research-news/solar-water-splitting-using-particulate-photocatalyst-sheets.html, UTokyo Research "Solar water splitting using particulate photocatalyst sheets" URI: http://www.u-tokyo.ac.jp/en/utokyo-research/research-news/solar-water-splitting-using-particulate-photocatalyst-sheets.html

We studied the light emission induced by tunneling electrons of scanning tunneling microscopy (STM) from well-defined 3,4,9,10-perylenetertracarboxylic dianhydride (PTCDA) bilayer, vapor deposited under ultrahigh vacuum condition on Au(111) single crystal surface. We detected visible fluorescence over the second layer of PTCDA. The light emission spectrum contained a fluorescence peak at 1.75 eV of photon energy at STM bias voltages below 2.5 V. When the bias voltage was set above 2.5 V, another fluorescent peak was observed at 2.35 eV. This peak is out of the range of Au local plasmon excitation, and is attributed to the transition from S 1 excited state to S 0 ground state of PTCDA molecule excited by direct electron injection. The fluorescence near 2.35 eV was reported in dilute solution of PTCDA by optical excitation. This intrinsic molecular fluorescence indicates that the 2nd layer PTCDA molecules were significantly isolated from environment over the presence of the 1st layer on Au(111).

Duramycin is a small tetracyclic peptide which binds specifically to ethanolamine phospholipids (PE). In this study, we used lipid monolayers consisting of 1-palmitoyl-2-oleoyl phosphatidylethanolamine (POPE) and various phosphatidylcholines (PC) to investigate the effect of duramycin on the organization of lipids and its influence on surrounding water molecules, using vibrational sum-frequency generation spectroscopy in conjunction with surface pressure measurements and fluorescence microscopy. The results show that while duramycin has no effect on the PC lipid monolayers, it induces significant disorder of PE molecules and causes an increase of the PE monolayer surface pressure. Duramycin adopts a β-sheet conformation and is well-ordered at the air-water interface as well as after binding to PE. Our results are consistent with duramycin inserting into the PE monolayer via its hydrophobic end, exposing phenylalanine residues to the lipid. Binding of duramycin to PE broadens the hydrogen-bond distribution of lipid-bound water molecules, notably increasing the fraction of the less strongly hydrogen-bonded, possibly undercoordinated, water molecules. Fluorescence microscopy reveals that the interaction of duramycin with PE causes a change in the shape of the liquid-condensed domains of the PE monolayer from circular to horseshoe-like, indicating a reduction of line tension at the boundary of the two lipid phases. These results reveal that the first steps in the disruption of membrane integrity by duramycin consist of a reduction of the line tension, a decrease in the lipid order, and a weakening of the hydrogen bonding network of water around PE.

We review a wet chemical process to prepare the high quality hydrogen-terminated Si(111)-(1×1) surface and show that the two key issues for the high reproducibility are the etching time and the oxygen in the etching solution. We add ammonium sulfite to remove the oxygen according to the previous report [Appl. Surf. Sci. 130, 146 (1998)]. To elucidate the optimal etching time, the vibrational properties and the surface morphology are investigated by high-resolution electron-energy-loss spectroscopy (HREELS), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The HREELS spectra and images of AFM and STM reveal the precise aqueous NH4F etching process of Si(111) and indicate the high controllability of steps and terraces with atomic scale. The surface cleanliness and morphology strongly depend on the etching time. At the etching time of 10 min, we obtain an ultra-clean and atomically ordered surface with wide terraces of 36 ± 7 nm step distance. It is confirmed by AFM and STM that the 1.0% ammonium sulfite is useful to remove dissolved oxygen in the 40% NH4F etching solution and to prepare a high quality H:Si(111)-(1×1) surface with low density of etch pits. The measurement of scanning tunneling spectroscopy(STS) shows the Schottky diode character of the surface. This surface is well applied to the initial stages of the nano-particle and film growth of Ag atoms and Pentacene molecules. [DOI: 10.1380/ejssnt.2009.557]

It was revealed that electrostatic forces between electrodes under the applied bias are almost completely suppressed by an electrochemical potential control. The force operating between n-decanethiol self-assembled monolayers (SAMs) on gold was examined by atomic force microscopy in liquid n-dodecane and in an aqueous solution of HClO4. In inert n-dodecane, the bias voltage was simply applied between the tip and the sample, and the force curve exhibited a long-range attractive force in accordance with the simple capacitance model. Meanwhile under the independent control of the tip and sample potentials in HClO4, the force curve did not depend on the applied potentials due to the small double-layer capacitance. [DOI: 10.1380/ejssnt.2009.731]

Adsorption of purine DNA bases (guanine and adenine) on Cu(1 1 0) was studied by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine-structure spectroscopy (NEXAFS), and density-functional theory (DFT) calculation. At coverages near 0.2 monolayers, Angular-resolved NEXAFS analysis revealed that adenine adsorbates lie almost flat and that guanine adsorbates are tilted up on the surface with the purine ring parallel to the atom rows of Cu(1 1 0). Referring to the previous studies on pyrimidine DNA bases [M. Furukawa, H. Fujisawa, S. Katano, H. Ogasawara, Y. Kim, T. Komeda, A. Nilsson, M. Kawai, Surf. Sci. 532–535 (2003) 261], the isomerization of DNA bases on Cu(1 1 0) was found to play an important role in the adsorption geometry. Guanine, thymine and cytosine adsorption have an amine-type nitrogen next to a carbonyl group, which is dehydrogenated into imine nitrogen on Cu(1 1 0). These bases are bonded by the inherent portion of –NH–CO– altered by conversion into enolic form and dehydrogenation. Adenine contains no CO group and is bonded to Cu(1 1 0) by participation of the inherent amine parts, resulting in nearly flatly-lying position.

The covalent attachment of alkyl groups to silicon surfaces, via carbon–silicon bond formation, has been attempted using gas-surface reactions starting from Cl-terminated Si(1 1 1) or H:Si(1 1 1) under ultraviolet light irradiation. The formation of Cl-terminated Si(1 1 1) and its resulting stability were examined prior to deposition of organic molecules. High-resolution electron energy loss spectroscopy (HREELS) was utilized for detecting surface-bound adsorbates. The detection of photo-deposited organic species on Cl:Si(1 1 1) from gas-phase CH4 or CH2CH2 was not significant. On H:Si(1 1 1), it was evident that after the photoreaction with gas-phase C2H5Cl, C2H5 groups were chemically bonded to the surface Si atoms through single covalent bonds. The C2H5 groups were thermally stable at temperatures below 600 K. Alkyl monolayers prepared on silicon surfaces by dry process will lead to a new prospective technology of nanoscale fabrication and biochemical applications.

The molecular internal vibration modes and orientation of the DNA base molecules (cytosine, thymine, guanine and adenine) adsorbed on copper(1 1 0) clean single crystal surface were investigated by infrared reflection adsorption spectroscopy in ultrahigh vacuum. The adsorption was performed by thermal evaporation of powder of each species onto Cu(1 1 0) at room temperature. The surface uptakes of the molecules were determined by Auger electron spectroscopy. Cytosine exhibited characteristic asymmetric and symmetric NH2 stretching signal. The asymmetric stretching signal was missing in the submonolayer region, indicating that the whole molecule was standing upright, with the NH2 group sticking out of the surface. Thymine was also proved to stand upright at surface. Guanine exhibited weakened infrared signals, indicating that the core purine ring was tilted on the surface, with an interaction of NHCO side of the molecule. Adenine at coverages below one monolayer gave no absorption signals, evidencing the molecules laid flat along the surface. The vibrational information obtained will be helpful in developing the future methods of surface DNA sequencing.

The processes of thermal desorption and photo-induced desorption were investigated for nitric oxide (NO) molecules from the adlayers on bare diamond C(1 1 1) (2×1) surface formed at 110 K. The surface coverage of NO was monitored by X-ray photoelectron spectroscopy (XPS). The kinetics of thermal desorption of NO was of first-order (the activation energy of desorption=9.8 kcal mol −1 ) at coverages below one monolayer, and of zeroth-order (9.2 kcal mol −1 ) for multilayer. Time-of-flight (TOF) detection of photo-induced desorption of NO was performed by laser beams of wavelengths 193, 248 and 308 nm. The photo-excitation that drives NO desorption was attributed to the band-gap excitation of substrate and/or surface for the NO coverages below one monolayer, and to the direct absorption by NO multilayer consisting of (NO) 2 species.

La5Ti2Cu1−x Ag x S5O7, a solid solution of La5Ti2CuS5O7 and La5Ti2AgS5O7, is a semiconductor studied for sunlight-driven water splitting. In this study, the band structure and effective mass of La5Ti2Cu1−x Ag x S5O7 solid solutions are analyzed on the basis of density functional theory (DFT) calculations to reveal the effect of the composition on the band structure and the anisotropy in the conductivity. The band gap of La5Ti2Cu1−x Ag x S5O7 materials exhibits a bowing with respect to the value of x. The effective masses of holes and electrons in La5Ti2Cu1−x Ag x S5O7 are estimated from the band structure. Both holes and electrons have smaller effective masses in the b-axis direction than in the other directions, testifying the highly anisotropic electronic properties. The wave functions at the valence band maximum and the conduction band minimum are both delocalized along the b-axis only, forming parallel channels for electron and hole conduction. These results support the experimental observation that photoexcited carriers tend to migrate one dimensionally. The outcome of the theoretical calculation is qualitatively consistent with the experimental observations and helps to understand the electronic properties of La5Ti2Cu1−x Ag x S5O7 with varying compositions.

We have measured the surface phonon dispersion curves on the hydrogen-terminated Si(110)-(1×1) surface with the two-dimensional space group of p2mg along the two highly symmetric and rectangular directions of ΓX and ΓX' using high-resolution electron-energy-loss spectroscopy. All the essential energy-loss peaks on H:Si(110) were assigned to the vibrational phonon modes by using the selection rules of inelastic electron scattering including the glide-plane symmetry. Actually, the surface phonon modes of even-symmetry to the glide plane (along ΓX) were observed in the first Brillouin zone, and those of odd-symmetry to the glide plane were in the second Brillouin zone. The detailed assignment was made by referring to theoretical phonon dispersion curves of Graschus et al. [Phys. Rev. B 56, 6482 (1997)]. We found that the H-Si stretching and bending modes, which exhibit highly anisotropic dispersion, propagate along ΓX direction as a one-dimensional phonon. Judging from the surface structure as well as our classical and quantum mechanical estimations, the H-Si stretching phonon propagates by a direct repulsive interaction between the nearest neighbor H atoms facing each other along ΓX, whereas the H-Si bending phonon propagates by indirect interaction through the substrate Si atomic linkage.

Photochromism of 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene (1a) and 1,2-bis(2-methyl-6-nitro-1-benzothiophen-3-yl)perfluorocyclo-pentene (2a) in single-crystalline phases was investigated. Upon irradiation with 366 nm light the colorless crystals of 1a and 2a turned red and green, respectively. The colored crystals are due to the formation of the closed-ring isomers, 1b and 2b. The colored crystals were bleached by irradiation with visible light. The direction of the electronic transition moment of 1b in crystal was estimated from the absorption anisotropy of 535 nm band. When the photogenerated green colored crystal of 2a was observed under polarized light, the colored crystal showed dichroism of yellow and blue. The yellow and blue colors were attributed to two perpendicular electronic transitions of 2b at 465 and 600 nm, respectively.

A diarylethene having a chiral substituent underwent a diastereoselective photocyclization reaction in the crystalline phase, while the selectivity was not observed in solution.

The deposition of metallic nickel on n-Si(100) wafers was performed without external potential control in aqueous NiSO 4 solutions of different compositions at pH 8.0. Without giving any catalyzation treatment, the deposition of nickel on hydrogen-terminated Si(100) was confirmed in a conventional electroless plating bath containing NaH 2 PO 2 as the reducing agent, sodium citrate as the complexing agent, and (NH 4 ) 2 SO 4 as the buffering agent. The deposition of nickel was found to take place also in a bath without the reducing agent, and even in a simple solution consisting of NiSO 4 and (NH 4 ) 2 SO 4 . By using a transmission electron microscope equipped with an energy dispersive X-ray spectrometer, the cross sections of the films deposited from these solutions were examined, which revealed formation of silicon oxide between the Ni deposit and Si substrate. Based on these results, the mechanism of the entire process of electroless Ni deposition on Si is discussed.

The structure of the iodine adlattice formed on Ag(111) in aqueous solutions containing iodide ions has been determined as a function of the electrode potential by in situ scanning tunneling microscopy (STM) and ex situ low energy electron diffraction (LEED). In KI solutions buffered with KF-KOH at pH 10, continuous compression of the iodine adlattice from square (√3 × √3R-30°), via (√3qRβ° × √3R-30°), to (√3 × √3)R30° was observed as the electrode potential was increased; this was then followed by an abrupt phase transition into a rotated hexagonal (√3r × √3r)R(30° + α°) phase. Coadsorption of K was observed by Auger electron spectroscopy (AES) at potentials negative of that for the phase transition. In acid solutions (0.1mM HI) the continuous compression from (√3 × √3)R30°, via c(p × √3R-30°), into (√3r × √3r)R(30° + α°) was observed. The Moire pattern observed for the (√3r × √3r)R(30° + α°) adlattice, as well as the flatness of other adlattices observed in STM images, is explained in terms of lattice registry on the basis of a “hard ball contact model”.

It was observed by X-ray single crystal analysis that trans-2-buten-1-y1 cobaloxime complex with pyridine or 4-bromopyridine as a axial ligand isomerizes to the cis isomer with retaining the single crystal form on exposure to a Xe lamp. The complex with 3-chloropyridine or methylsulfide as a axial ligand did not show the isomerization. The reaction cavities for the trans-2-butenyl groups calculated from four crystal structures showed that those of reactive crystals are significantly larger than those of non-reactive ones.

In-situ scanning tunneling microscopy (STM) and ex-situ low-energy electron diffraction (LEED) have been employed to characterize an iodine-coated Au(111) electrode surface in perchloric acid solution in the absence of iodide ions. Iodine forms a well-ordered monolayer with two distinguished sets ofincommensurate lattices (phases) : a centered rectangular c(p x √3R-30°) phase and a rotated hexagonal (rot-hex) phase in the range of electrode potentials between 0.3 and 1.4 V vs a reversible hydrogen electrode (RHE). Both lattices become more compressed with increasing electrode potential. The (√3 x √3)R30° phase was found to have the most open structure for the iodine monolayer on the Au(111) surface. Uniaxial compression of the c(p x √3R -30°) phase (p decreases from 3 to ca. 2.5) resulting from an increase in electrode potential was successfully observed by LEED. In the range of the electrode potential between 0.5 and 1.2 V vs RHE, LEED and in-situ STM measurements indicate a small change in the p value around 2.5. Isometrical electrocompression of the rot-hex-I phase was successfully monitored using in-situ STM by following changes in Moire patterns resulting from an increase in electrode potential. A detailed characterization of the rot-hex-I phase was achieved with the aid of computer- simulated STM images. The reversible phase transition between c(p x √3R-30°) and rot-hex occurred at potentials more positive than ca. 1.3 V vs RHE. Atomic size vacancies were observed at the early stages ofelectrooxidation of the rot-hex-iodine adlayer.

Iodine adlayers formed on Au(111) in aqueous KI solution have been studied by ex situ Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and in situ scanning tunneling microscopy (STM). The LEED patterns are described as c ( p × 3 R − 30 ° ) where p decreases continuously with increasing emersion potential. By in situ STM, a series of rotated hexagonal structures was observed at positive potentials in addition to the c ( p × 3 R − 30 ° ) structures. This rotated hexagonal adlattice was also compressed with increasing electrode potential. These results in general confirm the phenomenon of electrocompression of the iodine adlayer on Au(111) observed by in situ surface X-ray scattering.

Deuteration of macromolecules is an important technique in neutron protein crystallography. Solvent deuteration of protein crystals is carried out by replacing water (H(2)O) with heavy water (D(2)O) prior to neutron diffraction experiments in order to diminish background noise. The effects of solvent deuteration on the crystallization of proteinase K (PK) with polyethylene glycol as a precipitant were investigated using high-resolution X-ray crystallography. In previous studies, eight NO(3)(-) anions were included in the PK crystal unit cell grown in NaNO(3) solution. In this study, however, the PK crystal structure did not contain NO(3)(-) anions; consequently, distortions of amino acids arising from the presence of NO(3)(-) anions were avoided in the present crystal structures. High-resolution (1.1 A) X-ray diffraction studies showed that the degradation of PK crystals induced by solvent deuteration was so small that this degradation would be negligible for the purpose of neutron protein crystallography experiments at medium resolution. Comparison of the nonhydrogen structures of nondeuterated and deuterated crystal structures demonstrated very small structural differences. Moreover, a positive correlation between the root-mean-squared differences and B factors indicated that no systematic difference existed.

AES, XPS, TDS and LEED have been used to study the interactions of F, H and CH x species with the diamond C(111)-(2 × 1) surface. It is found that a small quantity of chemisorbed H atoms can induce the (2 × 1) to (1 × 1) phase transformation and uphold the sp3 structure to nearly 1400K. In contrast, F atoms and CH x species are unable to do so. The distinct bonding characteristics of these adsorbates manifest clearly the diverse effects on the surface electronic and geometrical structures. It is further shown that H can react with and replace the preadsorbed CH x , while subsequent exposure to CH x can do the same to the preadsorbed H atoms. The results are relevant to a better understanding of the basic mechanisms involved in the diamond CVD process.

We visualized nanometer-scale phospholipid particle fusion by scanning tunneling microscopy (STM) on an alkanethiol-modified gold substrate, induced by duramycin, a tetracyclic antibiotic peptide with 19 amino residues. Ultrasonic homogenization generated a suspension mainly consisting of minimal lipid particles (MLP) from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) in a phosphate buffer solution, confirmed by dynamic light scattering (DLS). In situ STM discerned individual MLP as particles (diameter approximately 8 nm) spread on Au(111), modified with alkanethiol, within the suspension. The MLP became fragile by the presence of duramycin, and the MLP were easily scratched by the scanning tip into multilayers along the surface. This process of particle fusion on the gold surface coincides with the aggregation of MLP in the suspension, observed by DLS. It was demonstrated that STM is capable of discerning and monitoring the nanometer-scale features of phospholipid particles altered by antibiotics with biochemical impact. STM might allow in situ, real-space, nanometer-scale observations of minute particles composed of phospholipids within the real cells with the highest magnification ratio.

Pd(100), Rh(100) and PtRh(100) are inert for the dissociative adsorption of N 2 . We succeeded to prepare a surface nitride with a c(2 × 2) structure on Pd(100), Rh(100) and Pt-Rh(100) surfaces by performing the catalytic reaction of NO + H 2 → N(a) + H 2 O. On Pt(100), however, the accumulation of N atoms was difficult. Formation of c(2 × 2)-N on a PtRh(100) surface indicates equal affinity of N atoms to the Pt and Rh atoms on the alloy surface. When the c(2 × 2)-N surface is exposed to H 2 . a prominent loss-peak appears at 3200–3240 cm −1 . In situ EELS experiments of the c(2 × 2) surfaces in 10 −7 -10 −8 Torr of H 2 showed that the loss peak intensity for the N-H vibration obeys to a half order dependence in hydrogen pressure, which suggests that the predominant N-hydrogen adsorption complex is NH and not NH 2 . The isotope effect for equilibrium of NH and ND is very small on Pd(100), Rh(100) and Pt-Rh(100) surfaces.

The phonon dispersion relations of monolayer graphite on Ni(111) and on Ni(001) were measured by using electron energy loss spectroscopy. Both samples gave almost the same results. The data were analysed with a force constant model in a slab geometry, and it was revealed that the vertical bond bending force constant and the bond twisting force constant were greatly softened. These force-constant changes are comparable with the previously reported case of monolayer graphite on (111) surfaces of transition-metal carbides. However, the interaction between the Ni substrate and the graphite overlayer is not so strong as that on the carbide (111) surface. The similar phonon structures between graphitic layers on Ni(111) and on Ni(001) suggest that both substrates have similar charge transfer capability.

A nitrogen overlayer (N(a)) was synthesized on Pd(100) by catalytic reduction of NO by CO or H 2 in the total pressure range of 10 −7 −10 1 Torr at crystal temperatures higher than 500 K. The process of the formation of N(a) was monitored by AES, LEED, HREELS and TDS. N(a) formed a c (2 × 2) superlattice, and desorbed at 600–700 K. N(a) was hydrogenated by gas-phase H 2 . HREELS revealed the reversible formation of NH x (a) species on the surface.

The catalytic reduction of NO by H 2 on a Pt 0.25 Rh 0.75 (100) alloy single crystal was investigated by monitoring the surface species while the reaction was proceeding. Adsorption of NO at 500 K formed an O-covered surface with p(3 × 1) structure. Enrichment of Rh on the surface induced by adsorption of O was observed, and a Rh-rich alloy surface forms the p(3 × 1)-O faster. The nature of the p(3 × 1) overlayer is discussed. The NO + H 2 reaction formed a c(2 × 2) overlayer of N(a). The hydrogenated adsorbate NH x (a) was observed under the presence of gas-phase H 2 . The hydrogenation reaction of N(a) to NH x (a) was reversible, and faster than complete hydrogenation to NH 3 (g).

The surface phonon dispersion was investigated by high-resolution electron-energy-loss spectroscopy on the deuterium-terminated $\mathrm{Si}(111)\text{\ensuremath{-}}(1\ifmmode\times\else\texttimes\fi{}1)$ prepared by an improved wet chemical method. The phonon modes were recorded over the entire surface Brillouin zone and compared with the theoretical phonon dispersion curves derived on the basis of semiempirical total-energy scheme calculated by Sandfort et al. [Phys. Rev. B 51, 7139 (1995)] and by Gr\"aschus et al. [Surf. Sci. 368, 179 (1996)]. The present results of the observation fairly agree with the theoretical curves, except a discrepancy for ${\mathrm{B}}_{3}$ and ${\mathrm{R}}_{1}$ branches exhibiting a sizable dispersion between 35 and $55\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, which was predicted to have no dispersion by the theory. The suface-projected bulk phonon is distributed below $65\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ of the vibration energy, and the Si-D modes with higher energies than that are independent of SPBP. The Si-D vibrations with energies between 35 and $65\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ strongly intermix with bulk phonons, and below $35\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, the Si-D's move together in phase and the surface phonons are the same as those of hydrogen-terminated $\mathrm{Si}(111)\text{\ensuremath{-}}(1\ifmmode\times\else\texttimes\fi{}1)$.

Phytobilins are linear tetrapyrrole compounds used as chromophore for light harvesting and photoreceptor proteins in higher plants, algae, and cyanobacteria. Phytobilins are synthesized from biliverdin IX(alpha) (BV). Phycocianobilin:oxidoreductase (PcyA) is an enzyme to produce phycocyanobilin (PCB) used as chromophore for light harvesting and photoreceptor proteins. PcyA is unique because it catalyzes the reduction of BV by two sequential steps; the first step is the reduction of the vinyl of the BV D-ring to produce 18(1)-18(2)-dihydrobiliverdin (18EtBV), and the second step is the reduction of the A-ring. In these reduction steps, four hydrogen atoms are delivered to BV. The earlier studies showed that the carboxyl group of Asp105 showed dual conformations. This has been attributed to the difference of its protonation states. The catalytically essential His88 was suggested to be protonated (i. e. His88 is a proton donor) to donate the proton to BV. BVH+ (N-protonated) state, in which four pyrrole N atoms of BV were fully protonated, was proposed to be partially formed when BV was bound to PcyA. Further, another tautomeric BVH+ state in which three of four pyrrole N atoms of BV were protonated and the lactam (C=O) group of BV D-ring was protonated as lactim (C-OH; O-protonated) was proposed. Additionally, newly identified water molecule near BV has been suggested to be a proton donor. To elucidate the H atom positions of these molecules, we determined the neutron crystal structure of the PcyA-BV complex at 1.95 Å resolution. Crystal with approximately 2.2 X 1.8 X 0.8 mm3 size, which was soaked into the deuterium-exchanged crystallization solution, was used in the diffraction experiment. The neutron diffraction intensity data was collected using IBARAKI Biological Crystal Diffractometer (iBIX) in J-PARC. In this conference, we report the protonation states of catalytically important residues and BV as well as orientations of water molecules in the PcyA-BV complex.

α-Thrombin is a serine protease, which plays the central role in the coagulation system. Investigating the protonation states of the enzyme is useful to reveal the reaction mechanism and to design anticoagulant drugs. We have studied the protonation states of the α-Thrombin-bivalirudin complex using neutron diffraction method. The complex is regarded as the enzyme-product complex, because the hydrolyzed bivalirudin fragments keep staying in the binding sites in the crystal. Previously we had performed a neutron crystallographic analysis of α-Thrombin-bivalirudin complex at pD 5.0 (space group P21212) at 2.8 Å resolution.[1] To observe the protonation states of the active site more clearly, we carried out time-of-flight neutron diffraction experiments for a different crystal form of this complex (space group C2 at pD 7.9) using IBARAKI biological crystal diffractometer, iBIX, installed in J-PARC. Using improved 30 neutron detectors with high-efficiency, we have succeeded in collecting the reflections at around 2.0 Å resolution. XN-joint refinements were performed using PHENIX program. The neutron scattering length OMIT map showed a density on the hydroxyl group of serine 195, which could be a deuterium. Since the density was not observed for P21212 crystal at pD 5.0 and the position was too far from an acceptor atom to form a stiff hydrogen bond, currently we are confirming the result. In this presentation, details of the neutron crystallographic analysis and the comparison between the structures, especially, the protonation states of amino acid residues in the active site of the complex at pD 5.0 and pD 7.9 will be given.

Introduction Recent high resolution (better than 1A) X-ray protein crystallographic analysis requires high quality protein crystals. High quality crystals in turn produce a highresolution diffraction data set. In protein crystallography the quality of the crystal is usually defined as follows: an often-used alternative criterion is whether the crystal produces a high resolution Bragg reflection data set or not. One possible explanation of the quality of protein crystals is whether the protein molecules are orientationally ordered within the unit cell. In that case, the overall B-factor obtained by the Wilson plot technique [1] becomes a good measure of the quality of the protein crystals. As a matter of the fact, we have already made such a proposal and we have proved that the overall B-factors obtained from Wilson plots correlate much better with the quality of the crystals experimentally [1]. In other words, the quality of the protein crystals is discussed by the degree of the disorder of the protein molecules in the unit cell. Generally in X-ray diffraction phenomena it is well known that the disorder of molecules in unit cells provides diffuse scattering under a Bragg reflection profile. In the past such a diffuse scattering from a protein crystal has been often observed and this phenomenon has been discussed from the view point of molecular dynamics. We do not deny that one part of the diffuse scattering is the contribution of molecular dynamics, but we think that the main part is one of the disorder of molecules, incompleteness of crystals. The diffraction pattern on the imaging plate observed at 77K shows very distinctive diffuse scattering under Bragg reflections, which do not depend on temperature. We tried to measure the accurate profile of diffuse scattering in order to analyze the relation between the crystal quality and the molecular disorder.

When a clean Pt-Rh(100) alloy surface was exposed to NO at T > 440 K, the LEED pattern changed sequentially as p(1 × 1) → c(2 × 2) → c(2 × 2) + p(3 × 1) → p(3 × 1), where the c(2 × 2) pattern appeared immediately after the exposure to NO. In contrast to this, the appearance time for the p(3 × 1) depends strongly on the initial Rh concentration on the surface adjusted by annealing. When the p(3 × 1) surface was exposed to H2 by mixing H2 into NO gas, the AES intensity of O(a) decreased and of N(a) increased markedly and the LEED pattern changed from p(3 × 1) to c(2 × 2). These results suggest that N(a) has equal affinity to Pt and Rh atoms so that the N(a) does not distinguish the Pt and Rh sites on the alloy surface. On the other hand, O(a) makes a stronger bond with Rh atoms so that Rh atom segregation onto the surface is induced. By reacting randomly distributed Rh atoms on the Pt-Rh(100) surface with oxygen, a surface compound in a p(3 × 1) arrangement is built on the surface.

The thermal desorption spectra, the adsorption isotherms, and the absolute rates of adsorption and desorption of carbon monoxide were measured on the (100) plane of palladium modified with sulfur adatoms. A small amount of S adatoms reduced the thermal desorption energy from ~ 34 kcal mol −1 to ~ 9 kcal mol −1 . During adsorption, the absolute desorption rate increased with increasing ambient CO pressure. This kind of pressure dependency was depressed by a quarter monolayer of S. The absolute adsorption rate as a function of CO coverage did not depend on the crystal temperature of the clean surface, but it showed a negative temperature-dependence with increasing sulfur coverage.

A Ni(100) single crystal surface modified by sulfur catalyzes the H 2 −D 2 isotope exchange reaction, which is completely arrested upon the formation of a hexagonal oxygen overlayer.

Two new ultrahigh vacuum instruments were designed and constructed to study chemical reactions on single‐crystal surfaces. These instruments allow samples to be cycled between high‐pressure gas cells for treatment of the samples, and ultrahigh vacuum, for electron spectroscopies. By using newly developed ‘‘rod‐through‐chamber’’ devices, the ultrahigh vacuum and high pressure are completely separated, while the sample is smoothly transferred between those parts. We are utilizing them to prepare surface chemical compounds and to observe heterogeneous catalysis on solid surfaces.

The isotope scrambling reaction of dihydrogen H 2 + D 2 → 2HD in the medium pressure range was investigated on a Ni(100) single crystal surface modified by sulfur. This reaction was completely suppressed by adding a 10 −6 part of dioxygen in the reactant, when the surface was covered by a hexagonal overlayer containing oxygen. The hexagonal overlayer reacted with hydrogen to form water. The lattice structure and thermal stability of this overlayer were examined by LEED, AES, TDS and a medium-pressure reaction cell.