Publisher：Journal of Physical Chemistry C  

The development of an electrocatalyst with high bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performances using non-precious-metal/metal oxides is highly important as a future energy material. NiFe-layered double hydroxides (LDH) are well-known catalysts that have high OER activity, while their ORR activity is low. We here present a method to enhance the ORR of NiFe-LDH. We first synthesized a polybenzimidazole (PBI)-coated multiwalled carbon nanotube (MWNT)-based NiFe-LDH catalyst (MWNT/PBI-NiFe-LDH), then by sulfurization of the LDH, sulfur-doped catalysts, MWNT/PBI/NiFeS-xh (x is sulfurization time) were synthesized, which were characterized by TEM, STEM, EDX, thermogravimetry, X-ray diffraction analysis, XPS, and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). After sulfurization, the nanoplate structure of MWNT/PBI-NiFe-LDH changed to nanoparticles that were composed of Ni-Fe-S composites. The valency of Ni and Fe is suggested to be +2 and +3, respectively. MWNT/PBI/NiFeS-xh provided a higher ORR (E1/2= 0.80 V vs RHE) than that (E1/2= 0.70 V vs RHE) of MWNT/PBI-NiFe-LDH with no sulfurization, while the sulfurization did not change their OER activities. This study provides an efficient and simple method for enhancing ORR of LDH catalysts, and the method is useful for designing a non-precious-metal-based ORR/OER bifunctional catalyst with high performance.

DOI： 10.1021/acs.jpcc.3c02321

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：International Journal of Hydrogen Energy  

For the development of small-scale desulfurization processes such as fuel cell systems, catalytic decomposition of dimethyl sulfide (DMS) to H2S without H2 addition was investigated using a Co/H-Beta zeolitic catalyst, with its acidity controlled via post-synthesis modification. The protonated zeolite (H-Beta) exhibited little catalytic activity at 400 °C, but Co modification significantly promoted DMS decomposition, with a high H2S yield of 50% observed. The optimum Co amount was equivalent to half of the ion-exchange capacity of the original H-Beta zeolite. While the Co/SiO2 did not display catalytic activity, and thus, the coexistence of acid and Co ion sites is necessary in DMS decomposition. The Co species were introduced at the cation sites of the zeolite, suppressing Co sulfurization, which contributed to the high catalytic activity.

DOI： 10.1016/j.ijhydene.2023.04.052

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Journal of Power Sources  

Polymer electrolyte fuel cells (PEFCs) have been commercialized as fuel cell vehicles, but high oxygen transport resistance (OTR) needs to be improved for the operation at high current density. OTR is deeply related to oxygen transport to the Pt catalyst through the proton conduction ionomer. In this study, reduction of OTR has simply demonstrated by mixing a high oxygen permeable polymer, poly[1-phenyl-2[p(trimethylsilyl)phenyl]acetylene] (PTMSDPA), and a commercial Nafion® ionomer. Although the resulting blend ionomers have lower proton conductivity than Nafion® itself, they have contributed to increase in PEFC performance in the higher current density region. With small addition of PTMSDPA like 2.5%, local OTR around the Pt catalyst (RPt), is found to decrease as the amount of PTMSDA increases owing to high oxygen permeability of PTMSDPA. However, OTR inside the pore of the catalyst layer (Rpore) rather keeps increasing because of a hydrophilic character of PTMSDPA, leading to oxygen blockage by trapped water. Therefore, only the small amount of addition like 2.5% of PTMSDPA results in the best, and Rpore and Rpt are significantly lowered compared those of Nafion® ionomer by 29% and 43%, respectively, suggesting that utilizing high oxygen permeable polymer is effective for reducing OTR in PEFC.

DOI： 10.1016/j.jpowsour.2022.232500

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Publishing type：Research paper (scientific journal)   Publisher：International Journal of Hydrogen Energy  

To improve the catalytic activity of Pt catalysts for methylcyclohexane (MCH) dehydrogenation, which is utilized for hydrogen transportation, the effects of the addition of Se on the performance of Pt/TiO2 catalysts were investigated. In Se/Pt/TiO2 catalysts, even a small amount of Se addition (Se/Pt = 0.01) improved the catalyst stability. Se was highly dispersed on the Pt/TiO2 surface, without volatilizing in a reducing atmosphere at temperatures below 450 °C, and did not form an alloy with Pt. The analysis of adsorption-desorption characteristics revealed that the addition of Se promoted the desorption of products, including the main product, toluene. Moreover, an electron donation effect from Se to Pt was observed by FT-IR measurement after the reduction. The desorption characteristic caused by the electron donation effect suppressed the deterioration of the catalyst and allowed stable catalytic activity toward the MCH dehydrogenation reaction.

DOI： 10.1016/j.ijhydene.2022.09.055

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Journal of Membrane Science  

Decomposition of polymer electrolyte membranes (PEMs) by radical species is a significant issue related to the chemical durability of polymer electrolyte fuel cells (PEFCs). A major contributor to radical formation is the oxygen crossover through the membrane from cathode to anode. Therefore, suppression of oxygen diffusion through the PEM is predicted to effectively mitigate the chemical degradation via radical formation. To confirm this, a simple high oxygen barrier PEM is prepared by sandwiching a thin gas barrier interlayer in between two Nafion 211 membranes. The interlayer consists of poly (vinyl alcohol) (PVA) and poly (vinyl sulfonic acid) (PVS) with various molar ratio. The sandwich PEM can show 286 times lower oxygen permeability than Nafion 212 membrane, which corresponds to 1.7 times longer survival time than Nafion 212 in a chemically accelerated stress test for PEMs known as open circuit voltage (OCV) holding test. Furthermore, the SEM image of the sandwich PEM cross-section shows that the interlayer could survive the OCV holding test despite its lower resistance against radical attack. The results in this study indicate that the addition of high oxygen barrier interlayer can reduce radical formation in PEFC and improve chemical durability.

DOI： 10.1016/j.memsci.2022.120734

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DOI： https://doi.org/10.1016/j.ijhydene.2022.09.055

Publishing type：Research paper (scientific journal)   Publisher：Materials Advances  

As efficient electrodes in energy conversion and storage devices, we focus on the development of a polymer-type non-precious metal-coordinated eco-friendly catalyst with high performance, which is of importance in flexible wearable energy storage electronic devices with adaptable shapes. In the present study, we describe the design and synthesis of a nickel (Ni)-coordinated poly(thiourea-formaldehyde) polymer, then a nanocarbon (Vulcan, porous nanocarbon CNovel™, 2-different multi-walled carbon nanotubes, or single-walled carbon nanotubes) as the conducting support was combined to prepare seven different molecular catalysts. The chemical structure of the Ni-coordinated polymer was characterized by elemental analysis, 13C NMR, FT-IR and XPS. Furthermore, EXAFS studies and theoretical calculations revealed that this polymer consists of two Ni-O (2.17 Å) and two Ni-S (2.17 Å) coordination bonds. This Ni-coordination polymer was stable in an oxidative and reductive environment in an alkaline medium over a long term due to its strong Ni-coordination. The catalysts were found to act as an efficient catalyst for an oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Especially, among the catalysts, the CNovel™-based catalyst showed the highest oxygen electrode performance for the ORR: E1/2: 0.81 V vs. RHE, and OER: 1.57 V vs. RHE at 10 mA cm−2. The catalyst acted as an efficient and durable cathode for a rechargeable Zn-air battery (charge-discharge overpotential gap of 0.45 V). Such outstanding air-cathode performance is explained by the cooperative mechanism between water on the axial site of the Ni in the polymer and superoxide ion on the porous carbon. The present study is of importance for the development of advanced energy materials in batteries and molecular catalysts.

DOI： 10.1039/d2ma00450j

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DOI： DOI https://doi.org/10.1039/D2MA00450J

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Electrochemical reduction of CO2 (ECO2R) is gaining attention as a promising approach to store excess or intermittent electricity generated from renewable energies in the form of valuable chemicals such as CO, HCOOH, CH4, and so on. Selective ECO2R to CH4 is a challenging target because the rate-determining step of CH4 formation, namely CO* protonation, competes with hydrogen evolution reaction and the C–C coupling toward the production of longer-chain chemicals. Herein, a Cu-TiO2 composite catalyst consisting of CuOx clusters or Cu nanoparticles (CuNPs), which are isolated on the TiO2 grain surface, was synthesized using a one-pot solvothermal method and subsequent thermal treatment. The Cu-TiO2 catalyst exhibited high selectivity for CH4, and the ratio of FE for CH4 to total FE for all products in ECO2R reached 70%.

DOI： 10.3390/catal12050478

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

The oxygen evolution reaction (OER) is a critical element for all sorts of reactions that use water as a hydrogen source, such as hydrogen evolution and electrochemical CO2 reduction, and novel design principles that provide highly active sites on OER electrocatalysts push the limits of their practical applications. Herein, Au-cluster loading on unilamellar exfoliated layered double hydroxide (ULDH) electrocatalysts for the OER is demonstrated to fabricate a heterointerface between Au clusters and ULDHs as an active site, which is accompanied by the oxidation state modulation of the active site and interfacial direct O-O coupling (“interfacial DOOC”). The Au-cluster-loaded ULDHs exhibit excellent activities for the OER with an overpotential of 189 mV at 10 mA cm−2. X-ray absorption fine structure measurements reveal that charge transfer from the Au clusters to ULDHs modifies the oxidation states of trivalent metal ions, which can be active sites on the ULDHs. The present study, supported by highly sensitive spectroscopy combining reflection absorption infrared spectroscopy and modulation-excitation spectroscopy and density functional theory calculations, indicates that active sites at the interface between the Au clusters and ULDHs promote a novel OER mechanism through interfacial DOOC, thereby achieving outstanding catalytic performance.

DOI： 10.1002/adma.202110552

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/adma.202110552

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：ACS Applied Energy Materials  

Photocatalytic reactions to produce hydrogen from water under visible-light irradiation are an important key process for solar energy utilization. Because Cu-doped ZnS undergoes redox reactions upon irradiation with visible light, these materials have been applied to hydrogen production. In this study, Cu-doped ZnS catalysts were prepared by a solvothermal method, and their structures were investigated using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and ultraviolet-visible spectroscopic studies. Cu-doped ZnS consists of nanospherical particles with a diameter of 50 nm. Cu2+ doping in ZnS causes structural distortion of the ZnS. The local structures were analyzed by X-ray absorption fine structure studies. As the amount of Cu added to ZnS increased, the degree of distortion of the ZnS structure also increased, and this degree of distortion reached a maximum when the Cu/Zn ratio was 0.07 (7% Cu doping). Cu-doped ZnS exhibited high activity in the hydrogen production reaction from water using Na2S and Na2SO3 as sacrificial agents under visible-light irradiation (λ > 420 nm), and the highest activity was observed at 7% Cu doping.

DOI： 10.1021/acsaem.1c03323

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Language：Japanese   Publisher：The Japan Institute of Energy  

<p>Microwave irradiation accelerated hydrogen production by catalytic pyrolysis of crystalline cellulose and bamboo via Ni-SiO₂-Al₂O₃. The Debye-Waller factor measured by microwave in situ XAFS suggested that the reaction was accelerated due to the localized high temperature of Ni nanoparticles formed by microwave irradiation. We demonstrated that synergy of the microwave-enhanced pyrolysis of biomass and localized high temperature of Ni nanoparticles accelerate the catalytic pyrolysis of lignocellulose to produce hydrogen.</p>

DOI： 10.20550/jiebiomassronbun.17.0_29

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/d0ta11287a

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.jpcc.0c08349

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.colsurfa.2020.125314

Language：English   Publishing type：Research paper (scientific journal)  

Biomass-derived gas and unused industrial byproducts are resources for H₂ production with low CO₂ emission; however, they contain > 1000 ppm H₂S, which necessitates the use of H₂S-tolerant catalysts. Herein, a pure CeO₂ catalyst demonstrated stable and efficient H₂ production via the dry reforming reaction in the presence of 2000 ppm H₂S. No impurity phases and carbon deposition appeared on the catalyst after the reaction. Moreover, CeO₂ catalytic activity improved with H₂S concentration. The effect of H₂S on CeO₂ was determined by in situ infrared spectroscopy and S K-edge X-ray absorption near-edge structure studies. The re-oxidation of CeO₂ by CO₂, a key step of the dry reforming reaction, was accelerated by the rapid redox cycle of sulfur, which promoted CH₄ activation and decreased the apparent activation energy from 125 to 101 kJ/mol. The redox cycle of S made the pure CeO₂ catalyst resistant to high concentration of H₂S.

DOI： 10.1016/j.jcat.2020.06.040

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1111/jace.17101

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2320/matertrans.M-M2019858

Language：English   Publishing type：Research paper (scientific journal)  

An effective method for removing selenium (Se) from water is required from the viewpoint of environmental preservation. To establish this method, a cation exchange resin that adsorbed ferric ions was applied as an adsorbent. In this study, the adsorption behavior of Se to the adsorbent was examined by both batch and column methods. The batch experiment confirmed that selenite ions (Se(IV)) are effectively adsorbed but selenate ions (Se(VI)) are hardly adsorbed. To elucidate the adsorption mechanism, the Fe in the adsorbent and the Fe in the adsorbent after the adsorption of Se(IV) were characterized by Fe K-edge X-ray absorption spectroscopy and ⁵⁷Fe Mӧssbauer spectroscopy. The analytical result of Se K-edge EXAFS spectra for the Se(IV) adsorbed on the adsorbent suggests that Se(IV) are adsorbed specifically to the adsorbent through the formation of Fe-O-Se bonds. The breakthrough curve obtained by the column experiment showed that Se(IV) in 3 tons of synthetic solution containing 0.1 ppm Se can be efficiently removed using a column in which 12.8 g (10.4 cm³) of the adsorbent was packed.

DOI： 10.1016/j.jhazmat.2019.04.076

Language：English   Publishing type：Research paper (scientific journal)  

Iridium oxide (IrO_x)-based materials are the most suitable oxygen evolution reaction (OER) catalysts for water electrolysis in acidic media. There is a strong demand from industry for improved performance and reduction of the Ir amount. Here, we report a composite catalyst, IrO_x-TiO₂-Ti (ITOT), with a high concentration of active OH species and mixed valence IrO_x on its surface. We have discovered that the obtained ITOT catalyst shows an outstanding OER activity (1.43 V vs RHE at 10 mA cm^-2) in acidic media. Moreover, no apparent potential increase was observed even after a chronopotentiometry test at 10 mA cm^-2 for 100 h and cyclic voltammetry for 700 cycles. We proposed a detailed OER mechanism on the basis of the analysis of the in situ electrochemical X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements as well as density functional theory (DFT) calculations. All together, we have concluded that controllable Ir-valence and the high OH concentration in the catalyst is crucial for the obtained high OER activity.

DOI： 10.1021/acscatal.9b01438

Language：English   Publishing type：Research paper (scientific journal)  

Boron-incorporated ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were deposited by coaxial arc plasma deposition with boron-blended graphite targets. The effects of boron incorporation on the electrical properties of the films were investigated by hard X-ray photoelectron spectroscopy. Their electrical conductivity increased from 10⁻⁷ to 10⁻¹ Ω⁻¹ cm⁻¹ with increasing boron content up to 5 at.%. From the temperature dependence of electrical conductivity, hopping conduction due to localized states produced by boron atoms is predominant in carrier transport. X-ray photoelectron spectra showed the shifts of Fermi levels toward the top of the valence band with increasing boron content. It implies that boron atoms in the films lead to form localized states, which results in enhanced electrical conductivity.

DOI： 10.1007/s00339-019-2607-8

Language：English   Publishing type：Research paper (scientific journal)  

Performance of a polymer electrolyte alcohol electrosynthesis cell (PEAEC) using a glycolic acid (GC)/oxalic acid (OX) redox couple was enhanced via the multiscale approach, i.e., increase of reaction rate on an anode by employing nanometer-scale (nanoscale) IrO2 catalysts and increase of selectivity for GC production via optimization of cell structures, i.e., a millimeter-scale approach. We prepared nanoscale IrO2 anode catalyst, which is mixture of IrO2 nanoparticles (d = 3.7 ± 1.8 nm) and their agglomerates (d < 200 nm). The linear sweep voltammetry measurement for water oxidation revealed that the nanoscale IrO2 catalyst deposited on a porous carbon paper reduces overpotential for water oxidation by 196 mV from that obtained with an anode composed of commercial microscale IrO2 grans. Furthermore, application of the nanoscale IrO2 catalyst on porous titanium paper not only improved durability but also doubly enhanced water oxidation performance. We examined various PEAEC architectures composed of the nanoscale IrO2 applied Ti anode. Both nanometer- and millimeter-scale approaches realized the best PEAEC performance for GC production, i.e., 59.4% of energy conversion efficiency with 97.1% of Faradaic efficiency for the GC production at 1.8 V and 98.9% of conversion for 3 M OX, which is an almost saturated aqueous solution at operating temperature of the PEAEC (60 °C).

DOI： 10.1016/j.cattod.2019.03.071

Language：English   Publishing type：Research paper (scientific journal)  

Face-centered cubic (fcc) Ru nanoparticles (NPs) have been recently synthesized by reducing Ru(III) acetylacetonate, despite bulk Ru having a hexagonal close-packed (hcp) structure. We observed the formation processes of fcc and hcp Ru NPs using X-ray diffraction and X-ray absorption fine structure. We concluded that the strong RuO bond between Ru and the acetylacetonate ligand leads to the formation of the fcc structure.

DOI： 10.1246/cl.190338

Language：English   Publishing type：Research paper (scientific journal)  

The palladium–hydrogen system is one of the most famous hydrogen-storage systems. Although there has been much research on β-phase PdH(D)_x, we comprehensively investigated the nature of the interaction between Pd and H(D) in α-phase PdH(D)_x (x<0.03 at 303 K), and revealed the existence of Pd−H(D) chemical bond for the first time, by various in situ experimental techniques and first-principles theoretical calculations. The lattice expansion, magnetic susceptibility, and electrical resistivity all provide evidence. In situ solid-state ¹H and ²H NMR spectroscopy and first-principles theoretical calculations revealed that a Pd−H(D) chemical bond exists in the α phase, but the bonding character of the Pd−H(D) bond in the α phase is quite different from that in the β phase; the nature of the Pd−H(D) bond in the α phase is a localized covalent bond whereas that in the β phase is a metallic bond.

DOI： 10.1002/anie.201805753

Language：English   Publishing type：Research paper (scientific journal)  

Hard X-ray photoemission spectroscopy (HAXPES) was employed for the structural evaluation of ultrananocrystalline diamond/amorphous carbon (UNCD/a-C) composite films deposited on cemented carbide substrates, at substrate temperatures up to 550 °C by coaxial arc plasma deposition. The results were compared with those of soft X-ray photoemission spectroscopy (SXPES). Since nanocrystalline diamond grains are easily destroyed by argon ion bombardment, the structural evaluation of UNCD/a-C films, without the argon ion bombardment, is preferable for precise evaluation. For samples that were preserved in a vacuum box after film preparation, the sp³ fraction estimated from HAXPES is in good agreement with that of SXPES. The substrate temperature dependencies also exhibited good correspondence with that of hardness and Young's modulus of the films. On the other hand, the sp³ fraction estimated from SXPES for samples that were not preserved in the vacuum box had an apparent deviation from those of HAXPES. Since it is possible for HAXPES to precisely estimate the sp³ fraction without the ion bombardment treatment, HAXPES is a feasible method for UNCD/a-C films, comprising nanocrystalline diamond grains.

DOI： 10.3390/COATINGS8100359

Language：English   Publishing type：Research paper (scientific journal)  

We report on hexagonal close-packed (hcp) palladium (Pd)–boron (B) nanocrystals (NCs) by heavy B doping into face-centered cubic (fcc) Pd NCs. Scanning transmission electron microscopy–electron energy loss spectroscopy and synchrotron powder X-ray diffraction measurements demonstrated that the B atoms are homogeneously distributed inside the hcp Pd lattice. The large paramagnetic susceptibility of Pd is significantly suppressed in Pd–B NCs in good agreement with the reduction of density of states at Fermi energy suggested by X-ray absorption near-edge structure and theoretical calculations.

DOI： 10.1002/anie.201703209

Language：Japanese   Publishing type：Research paper (scientific journal)  

We report depth-resolved structural measurements in symmetric PS-b-P2VP thin films, using grazing incidence small angle X-ray scattering (GISAXS) in the tender X-ray region. The nanostructures in thin films show cylindrical structures although lamellar structures are expected, thermodynamically, as equilibrium state. It has been reported that, when the thin films are annealed at temperatures greater than the T_g, lamellar structures formed, parallel to the substrate. We prepared as-cast and annealed thin films on silicon substrates. From GISAXS measurements, we concluded that vertical cylindrical nanostructures in as-cast thin films are formed, oriented from surface toward substrate interface. Annealing changed the vertical cylindrical nanostructures at the surface. Even after very long annealing, like 12 hours above T_g, we found that vertical nanostructures still remained at the substrate interface, due to the lower mobility of polymer chains near the substrate interface.

DOI： 10.1295/koron.2016-0058

Language：English   Publishing type：Research paper (scientific journal)  

A laboratory hard X-ray photoelectron spectroscopy (HXPS) system equipped with a monochromatic Cr Kα (hν = 5414.7 eV) X-ray source was applied to an investigation of the core-level electronic structure of La_1-xSr_xMnO₃. No appreciable high binding-energy shoulder in the O 1s HXPS spectra were observed while an enhanced low binding-energy shoulder structure in the Mn 2p_3/2 HXPS spectra were observed, both of which are manifestation of high bulk sensitivity. Such high bulk sensitivity enabled us to track the Mn 2p_3/2 shoulder structure in the full range of x, giving us a new insight into the binding-energy shift of the Mn 2p_3/2 core level. Comparisons with the results using the conventional laboratory XPS (hν = 1486.6 eV) as well as those using a synchrotron radiation source (hν = 7939.9 eV) demonstrate that HXPS is a powerful and convenient tool to analyze the bulk electronic structure of a host of different compounds.

DOI： 10.7567/JJAP.54.083201

Language：English   Publishing type：Research paper (scientific journal)  

Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) films were deposited in hydrogen atmospheres by coaxial arc plasma deposition, and the effects of hydrogenation on the mechanical properties were studied on the basis of spectroscopic structural evaluations. The existence of UNCD grains in the films was confirmed by transmission electron microscopy and X-ray diffraction. Non-hydrogenated films prepared in no hydrogen atmosphere exhibited a 22 GPa hardness and 222 GPa Young’s modulus, and the sp³/(sp² + sp³) ratio estimated from the X-ray photoemission spectra was 41 %. For the films prepared in a 53.3-Pa hydrogen atmosphere, whereas the hardness increases to 23 GPa, the modulus decreases to 184 GPa. The UNCD grain size estimated using Scherrer’s equation and the sp³/(sp² + sp³) ratio were 2.3 nm and 64 %, respectively, both of which are remarkably increased as compared with those of the non-hydrogenated films. From the near-edge X-ray absorption fine structure spectra, it is considered that σ*C–H bonds are alternatively formed instead of π*C=C, which probably results in the enhanced hardness and reduced modulus by hydrogenation. In addition, it was found that the formation of olefinic and aromatic structures remarkably softens the UNCD/a-C:H film.

DOI： 10.1007/s00339-014-8949-3

Language：English   Publishing type：Research paper (scientific journal)  

Poly(3-hexylthiophene) (P3HT) is an important basic material that is widely used in p-type semiconductor devices for organic solar cells and transistors. time. However, the change is dramatically suppressed in comparison with the initial reaction. This supports that there is polymer adsorption on the ferric chloride particles that regulates formation of the radical cation on the 3HT. In short, the adsorbed polymer appears to poison the catalytic behavior. To clarify the effect of solvent on the polymerization, researchers replaced chloroform with hexane and carried out the reaction under similar conditions. The polymerization is initiated when two radical cations react. A pair of protons departs at the extended part of the dimer to form a neutral structure. Another radical cation is then generated at the end of the extended polymer chain due to reduction of Fe(II), propagating the reaction. Through this reaction, a polymer with high molecular weight is formed.

DOI： 10.1002/pola.27720

Language：English   Publishing type：Research paper (scientific journal)  

We investigate the electronic structure of a perovskite-type Pauli paramagnet SrMoO
₃
(t
₂
g
₂
) thin film using hard x-ray photoemission spectroscopy and compare the results to realistic calculations that combine density functional theory within the local-density approximation (LDA) with dynamical mean-field theory (DMFT). Despite the clear signature of electron correlations in the electronic specific heat, the narrowing of the quasiparticle bands is not observed in the photoemission spectrum. This is explained in terms of the characteristic effect of Hund's rule coupling for partially filled t2g bands, which induces strong quasiparticle renormalization already for values of Hubbard interaction which are smaller than the bandwidth. This interpretation is supported by DMFT model calculations including Hund's rule coupling, which show a renormalization of low-energy quasiparticles without affecting the overall bandwidth. The photoemission spectra show additional spectral weight around -2.5 eV that is not present in the LDA+DMFT results, pointing to a source of correlations that is not present in our calculations that include only on-site interactions. We interpret this weight as a plasmon satellite, which is supported by the measured core-level spectra that all show satellites at this energy.

DOI： 10.1103/PhysRevB.90.205131

Language：English   Publishing type：Research paper (scientific journal)  

We studied the charge-orbital ordering in the superlattice of charge-ordered insulating Pr_0.5Ca_0.5MnO₃ and ferromagnetic metallic La_0.5Sr_0.5MnO₃ by resonant soft x-ray diffraction (RSXD) and hard x-ray photoemission spectroscopy (HXPES). A temperature-dependent incommensurability is found in the orbital ordering by RSXD. In addition, a large hysteresis is observed that is caused by phase competition between the insulating charge ordered and metallic ferromagnetic states. No magnetic phase transitions are observed in contrast to pure Pr_0.5Ca_0.5MnO₃ thin films, confirming the unique character of the superlattice. Mn HXPES spectra revealed a hysteresis in the metalicity, supporting the picture of phase competition. The deviation from the commensurate orbital order can be directly related to the decrease of ordered-layer thickness that leads to dimensional crossover from three-dimensional to two-dimensional orbital ordering.

DOI： 10.1088/1367-2630/16/7/073044

Language：English   Publishing type：Research paper (scientific journal)  

We have investigated the electronic and magnetic properties of Co-doped Pr_0.8Ca_0.2MnO₃ thin films using various spectroscopic techniques. X-ray absorption and hard x-ray photoemission spectroscopy revealed that the substituted Co ions are in the divalent state, resulting in hole doping on the Mn atoms. Studies of element-selective magnetic properties by x-ray magnetic circular dichroism found a large orbital magnetic moment for the Co ions. These spectroscopic studies reveal that the substituted Co ions play several roles of hole doping for Mn, ferromagnetic superexchange coupling between the Co2⁺ and Mn4⁺ ions, and orbital magnetism of the Co2⁺ ions. Competition among these complex interactions produces the unique electronic and magnetic behaviors including enhanced coercivity of the Co-doped Pr_0.8Ca_0.2MnO ₃.

DOI： 10.1103/PhysRevB.88.174423

Language：English   Publishing type：Research paper (scientific journal)  

In this study, we have realized a high lateral resolution and wide-angle-resolved hard X-ray photoelectron spectroscopy (HAXPES) facility at BL47XU in SPring-8. The system uses Kirkpatrick-Baez focusing mirrors to achieve a beam size of 1.0 μm (horizontal) × 0.98 μm (vertical) at the photon energy of 7.94 keV and a wide-acceptance-angle objective lens installed in front of the electron energy analyzer. The objective lens system, which we had been developed originally and has achieved a total acceptance angle of ±34 with a resolution better than that of an acceptance angle of 1.5. The performance of this system was evaluated through core spectra measurements of a typical multi-layered sample of Ir (8 nm)/HfO₂ (2.2 nm)/thickness-graded SiO₂ (0-10 nm)/Si(0 0 1).

DOI： 10.1016/j.elspec.2013.04.004

Language：English   Publishing type：Research paper (scientific journal)  

By using laboratory x-ray photoemission spectroscopy (XPS) and hard x-ray photoemission spectroscopy (HX-PES) at a synchrotron facility, we report an empirical semi-quantitative relationship between the valence/core-level x-ray photoemission spectral weight and electrical conductivity in La _1-xSr_xMnO₃ as a function of x. In the Mn 2p_3/2 HX-PES spectra, we observed the shoulder structure due to the Mn³⁺ well-screened state. However, the intensity at x = 0.8 was too small to explain its higher electrical conductivity than x = 0.0, which confirms our recent analysis on the Mn 2p_3/2 XPS spectra. The near-Fermi level XPS spectral weight was found to be a measure of the variation of electrical conductivity with x in spite of a far lower energy resolution compared with the energy scale of the quasiparticle (coherent) peak because of the concurrent change of the coherent and incoherent spectral weight.

DOI： 10.1063/1.4811372

Language：English   Publishing type：Research paper (scientific journal)  

We report the detailed electronic structure of a hole-doped delafossite oxide CuCr
_1-x
Mg
_x
O
₂
(0≤x≤0.03) studied by photoemission spectroscopy (PES), soft x-ray absorption spectroscopy (XAS), and band-structure calculations within the local-density approximation +U (LDA+U) scheme. Cr/Cu 3p-3d resonant PES reveals that the near-Fermi-level leading structure has primarily the Cr 3d character with a minor contribution from the Cu 3d through Cu 3d-O 2p-Cr 3d hybridization, having good agreement with the band-structure calculations. This indicates that a doped hole will have primarily the Cr 3d character. Cr 2p PES and L-edge XAS spectra exhibit typical Cr3
⁺
features for all x, while the Cu L-edge XAS spectra exhibited a systematic change with x. This indicates now that the Cu valence is monovalent at x=0 and the doped hole should have Cu 3d character. Nevertheless, we surprisingly observed two types of charge-transfer satellites that should be attributed to Cu
⁺
(3d10) and Cu2
⁺
(3d9) like initial states in Cu 2p-3d resonant PES spectrum of at x=0, while Cu 2p PES spectra with no doubt shows the Cu
⁺
character even for the lightly doped samples. We propose that these contradictory results can be understood by introducing not only the Cu 4s state, but also finite Cu 3d,4s-Cr 3d charge transfer via O 2p states in the ground-state electronic configuration.

DOI： 10.1103/PhysRevB.87.195124

Language：English   Publishing type：Research paper (scientific journal)  

We report normal and superconducting properties of the Rashba-type noncentrosymmetric compound CaIrSi ₃ using single crystalline samples with nearly 100% superconducting volume fraction. The electronic density of states revealed by the hard x-ray photoemission spectroscopy can be well explained by the relativistic first-principles band calculation. This indicates that strong spin-orbit interaction indeed affects the electronic states of this compound. The obtained H-T phase diagram exhibits only approximately 10% anisotropy, indicating that the superconducting properties are almost three dimensional. Nevertheless, strongly anisotropic vortex pinning is observed.

DOI： 10.1103/PhysRevB.86.184510

Language：English   Publishing type：Research paper (scientific journal)  

Although amorphous InGaZnO ₄ has intensively been studied for a semiconductor channel material of thin-film transistors in next-generation flat-panel displays, its electronic structure parameters have not been reported. In this work, the electron affinities (χ) and the ionization potentials (I _p) of crystalline and amorphous InGaZnO ₄ (c-IGZO and a-IGZO) were measured using bulk-sensitive hard x-ray photoelectron spectroscopy. First, the χ and I _p values of c-IGZO and a-IGZO thin films were estimated by aligning the Zn 2p _3/2 core level energies to a literature value for ZnO, which provided χ 3.90 eV and I _p 7.58 eV for c-IGZO and 4.31 eV and 7.41 eV for a-IGZO. It was also confirmed that the escape depth of the photoelectrons excited by the photon energy of 5950.2 eV is 3.3 nm for a-IGZO and large enough for directly measuring the interface electronic structure using a-IGZO/c-Si heterojunctions. It provided the valence band offset of ∼2.3 eV, which agrees well with the above data. The present results substantiate that the a-IGZO/c-Si interface follows well the Schottky-Mott rule.

DOI： 10.1063/1.4744983

Language：English   Publishing type：Research paper (scientific journal)  

The spin-resolved electronic structure of buried magnetic layers is studied by hard X-ray photoelectron spectroscopy (HAXPES) using a spin polarimeter in combination with a high-energy hemispherical electron analyzer at the high-brilliance BL47XU beamline (SPring-8, Japan). Spinresolved photoelectron spectra are analyzed in comparison with the results of magnetic linear and circular dichroism in photoelectron emission in the case of buried Co
₂
FeAl
_0.5
Si
_0.5
layers. The relatively large inelastic mean free path (up to 20nm) of fast photoelectrons enables us to extend the HAXPES technique with electron-spin polarimetry and to develop spin analysis techniques for buried magnetic multilayers and interfaces.

DOI： 10.1143/JJAP.51.016602

Language：English   Publishing type：Research paper (scientific journal)  

The electronic band structure of thin films and superlattices made of Heusler compounds with NiTiSn and NiZr_0.5Hf_0.5Sn composition was studied by means of polarization dependent hard x-ray photoelectron spectroscopy. The linear dichroism allowed to distinguish the symmetry of the valence states of the different types of layered structures. The films exhibit a larger amount of "in-gap" states compared to bulk samples. It is shown that the films and superlattices grown with NiTiSn as starting layer exhibit an electronic structure close to bulk materials.

DOI： 10.1063/1.3665621

Language：English   Publishing type：Research paper (scientific journal)  

This work reports the measurement of magnetic dichroism in angular-resolved photoemission from in-plane magnetized buried thin films. The high bulk sensitivity of hard x-ray photoelectron spectroscopy (HAXPES) in combination with circularly polarized radiation enables the investigation of the magnetic properties of buried layers. HAXPES experiments with an excitation energy of 8 keV were performed on exchange-biased magnetic layers covered by thin oxide films. Two types of structures were investigated with the IrMn exchange-biasing layer either above or below the ferromagnetic layer: one with a CoFe layer on top and another with a Co₂FeAl layer buried beneath the IrMn layer. A pronounced magnetic dichroism is found in the Co and Fe 2p states of both materials. The localization of the magnetic moments at the Fe site conditioning the peculiar characteristics of the Co₂FeAl Heusler compound, predicted to be a half-metallic ferromagnet, is revealed from the magnetic dichroism detected in the Fe 2p states.

DOI： 10.1103/PhysRevB.84.054449

Language：English   Publishing type：Research paper (scientific journal)  

The surface structure of a single-crystal ZnO wafer was studied by angle-resolved x-ray photoelectron spectroscopy (ARXPS) using synchrotron radiation. As a result, well-defined x-ray photoelectron diffraction (XPD) patterns were obtained for the (0001) and (0001̄) polar surfaces using the photoemission from the Zn 2p_3/2 and O 1s core levels. The XPD patterns were indexed assuming forward scattering of photoelectrons by neighboring ions. Further, the XPD patterns for the (0001) and (0001̄) surfaces were different from each other, indicating the possibility for using the XPD technique for polarity determination.

DOI： 10.1016/j.susc.2011.04.036

Language：English   Publishing type：Research paper (scientific journal)  

This study reports on the linear dichroism in angular-resolved photoemission from the valence band of the Heusler compounds NiTi _0.9Sc_0.1Sn and NiMnSb. High-resolution photoelectron spectroscopy was performed with an excitation energy of hν=7.938keV. The linear polarization of the photons was changed using an in-vacuum diamond phase retarder. The valence band spectra exhibit the typical structure expected from first-principles calculations of the electronic structure of these compounds. Noticeable linear dichroism is found in the valence band of both materials, and this allows for a symmetry analysis of the contributing states. The differences in the spectra are found to be caused by symmetry-dependent angular asymmetry parameters, and these occur even in polycrystalline samples without preferential crystallographic orientation.

DOI： 10.1103/PhysRevLett.107.036402

Language：English   Publishing type：Research paper (scientific journal)  

Photoelectron spectroscopy and diffraction have been used to investigate structural changes during the annealing process of Ga_1-xMn _xAs samples. Hard x-ray radiation helped in observing photoelectron core-level spectra and electron diffraction from the bulk underlying the oxidized surface layer. High electron-energy resolution enabled us to separate the components due to substitutional and interstitial Mn atoms in the intrinsic Mn 2p_3/2 photoemission profile, resulting in two peaks at 638.8 and 639.5 eV binding energy, respectively. The peaks display the known characteristic behavior after annealing, that is, an almost complete reduction of the interstitial component and preservation of the substitutional component. In the photoelectron diffraction, a sensitivity of high-energy polar plots to the incorporation sites of photoemitting atoms into the atomic lattice has been shown. As a consequence, the experimental polar plots from substitutional and interstitial Mn atoms, which are supported theoretically, show characteristic features that provide structural information. From the similarities and differences of the polar plots for Mn and Ga, we have confirmed the assignment of components within the intrinsic part of the photoemission Mn 2p_3/2 signal suggested by photoelectron spectroscopy.

DOI： 10.1103/PhysRevB.83.235327

Language：English   Publishing type：Research paper (scientific journal)  

A highly adherent Cu-Ni-P film was successfully grown on a UV-irradiated liquid-crystal-polymer (LCP) film. Irradiation from a UV light under an atmospheric condition created hydrophilic nanometer-scale roughness on the LCP film surface by introducing hydrophilic groups on the surface. The high adhesion strength of more than 0.8 kN/m was obtained because of the anchoring effect of the nanometer-scale roughness developed at the interface between the deposited metal and the LCP film. Copper circuit patterns formed on the LCP film showed satisfactory performance for various reliability tests. Fine circuit formation and selective plating facilitated by UV irradiation could lead to a manufacturing approach for the next generation of flexible-printed-circuit technology.

DOI： 10.1149/1.3156638

Language：English   Publishing type：Research paper (scientific journal)  

The surface of an Al plate was treated with a combination of chemical and electrochemical processes for fabrication of surface nanoscale structures on Al plates. Chemical treatments by using acetone and pure water under supersonic waves were conducted on an Al surface. Additional electrochemical process in H
₂
S O
₄
solution created a finer and oriented nanoscale structure on the Al surface. Dynamic force microscopy (DFM) measurement clarified that the nanoscale highly oriented line structure was successfully created on the Al surface. The line distance was estimated approximately 30-40 nm. At the next stage, molecular patterning on the highly oriented line structure by functional molecules such as copper phthalocyanine (CuPc) and fullerene C
₆₀
was also conducted. CuPc or C
₆₀
molecules were deposited on the highly oriented line structure on Al. A toluene droplet containing CuPc molecules was cast on the nanostructured Al plate and was extended on the surface. CuPc or C
₆₀
deposition on the nanostructured Al surface proceeded by evaporation of toluene. DFM and x-ray photoemission spectroscopy measurements demonstrated that a unique molecular pattern was fabricated so that the highly oriented groove channels were filled with the functional molecules.

DOI： 10.1116/1.3125264

Language：English   Publishing type：Research paper (scientific journal)  

A chemical and electrochemical multistage process was conducted on an Al surface in order to create new types of nanostructures on the Al surface. The multistage processing was a combination of fabrication processes of linked crater and highly oriented line types of nanostructures on an Al surface. At the first stage, a highly oriented line structure was fabricated by treatment with acetone and subsequent anodization. The line separation was estimated approximately 30-40 nm. At the second stage, the nanostructure formed from the first stage was modified by treating with the chemical agent Semiclean and ultrasonic agitation. Dynamic force microscopy measurements showed that a tilted-step structure, or sawtoothed structure, was created from the highly oriented line structure. In the sawtooth structure, nanoscale sawtooth-shaped structures, which were composed of tilted steps, were created over 5 μ m2 areas and were aligned along the original highly oriented lines. Furthermore, molecular and polymer patterns were created on this unique nanostructure using copper phthalocyanine (CuPc) and polyaniline. The CuPc molecules were deposited on the nanostructure from toluene droplets containing CuPc while aniline monomers were polymerized on the sawtooth structure. In the case of CuPc deposition, a nanoscale pattern was created along the original sawtooth structure. In the case of polyaniline deposition resulted in a lot of grain-shaped polyaniline structures were grown on the tilted steps while a large tree-shaped polyaniline fiber was found crossing the tilted steps.

DOI： 10.1116/1.3098495

Language：English   Publishing type：Research paper (scientific journal)  

A linked-crater structure was fabricated on an Al surface by chemical and electrochemical combination processes. The surface of an Al plate was treated with semiClean and was successively processed in anodization in H2 S O4. Dynamic force microscopy image showed that a linked-crater structure was formed on the Al surface. The crater size ranged from 80 to 200 nm. It turned out that a lot of pores with 9 nm in diameter were created inside each crater. The depth of each crater was approximately 7-17 nm. At the next stage, the thin film growth of polythiophene on the linked-crater structured Al surface was conducted by an electrochemical synthetic method. The electrochemical polymerization on the Al surface was performed in acetonitrile containing thiophene monomer and (Et)4 NB F4 as a supporting electrolyte. After being electrochemically processed, the contour image of each crater was still recognized implying that the polymer nanofilm was grown on the nanoscale structured Al surface. The cross section analysis demonstrated that the nanofilm was grown along the linked-crater structure because the contour of each crater became thick. The average thickness of the polymer film was estimated as 10-20 nm. Furthermore, copper phthalocyanine molecules were successfully injected into the polymer nanofilm on the Al surface in order to functionalize the nanoscale material.

DOI： 10.1116/1.2889420

Language：English   Publishing type：Research paper (scientific journal)  

Nanowire fabrication was implemented on the nanoscale highly-oriented line-structure of Al surface. An Al plate was chemically and successively electrochemically processed by applying dc voltage in H2SO4 solution in order to fabricate a nanoscale highly-oriented line structure on the surface. The line width was estimated under 50 nm. As a nanowire polymerization process, aniline monomer solved in pure water and oxidizing agent APS solved in HC1 successively dropped on the nanostructured Al surface. The Dynamic force microscopy (DFM) measurements and cross section analysis clarified that the line-structure still remained and the depth of the row became shallow after the polymerization process was applied. Since N Is core-level lines appeared after the aniline polymerization by X-ray photoemission spectroscopy (XPS) measurements, the aniline monomers were polymerized along the line and filled in the row channel.

DOI： 10.1088/1742-6596/100/5/052Q55

Language：English   Publishing type：Research paper (scientific journal)  

The surface of an Al plate was treated with a combination of chemical and electrochemical processes for fabrication of surface nanoscale structures on Al plates. Chemical treatments by using acetone and pure water under supersonic waves were conducted on an Al surface. Additional electrochemical process in H
₂
SO
₄
solution created a finer and oriented nanoscale structure on the Al surface. DFM measurement clarified that the nanoscale highly oriented line-structure was successfully created on Al surface. The line distance was estimated approximately 30-40 nm. Molecular patterning on the highly oriented line-structure by copper phthalocyanine (CuPc) was also conducted. The CuPc molecules were put on the nanoscale structure by casting a toluene droplet containing CuPc. DFM and X-ray photoemission spectroscopy (XPS) measurements demonstrated that a molecular pattern that the groove channels were filled with CuPc molecules was fabricated.

DOI： 10.1088/1742-6596/100/5/052018

Language：English   Publishing type：Research paper (other academic)  

A nanoscale linked-crater structure was fabricated on an Al surface by chemical and electrochemical combination processes. The surface of an Al plate was treated with Semi Clean and was successively processed in anodization in H₂SO₄. Dynamic force microscopy image (DFM) showed that a linked-crater structure was formed on the Al surface. At the next stage, the authors conducted the thin film growth of conducting polymer polythiophene on the Al surface by an electrochemical method. The electrochemical polymerization on the Al surface was performed in acetonitrile containing thiophene monomer and (Et)₄NBF₄ as a supporting electrolyte. After being electrochemically processed, the contour image of each crater was still recognized implying that the polymer nanofilm was grown on the nanoscale structured Al surface. The cross section analysis demonstrated that the nanofilm was grown along the linked-crater structure because the contour of each crater became thick. X-ray photoemission spectroscopy measurement also supported the polymer nanofilm growth because C 1s and S 2p lines were detected. Furthermore, copper phthalocyanine (CuPc) molecules are injected into the polymer nanofilm grown on the nanoscale structured Al surface by diffusing method in order to functionalize the nanoscale hybrid material.

DOI： 10.1117/12.733602

Language：English   Publishing type：Research paper (scientific journal)  

Photoemission spectra and images of titanyl phthalocyanine films formed on graphite surfaces have been measured with 0.3 μm lateral and 30 meV energy resolutions. Islands of bilayer films were found to be formed in areas of monolayer films. Photoemission spectra revealed similarity/difference of molecular configurations between the bilayer islands and the well-annealed uniform bilayer films. The islands decayed slowly by migration of molecules. The results demonstrate the capability of photoemission microspectroscopy to resolve complicated electronic structures of realistic organic films.

DOI： 10.1016/j.cplett.2007.10.088

Language：English   Publishing type：Research paper (scientific journal)  

Dye molecules doped polythiophene (PT) films prepared by electrochemical doping were investigated by Fourier transform infrared spectroscopy (FTIR) reflection absorption spectroscopy (RAS) and transmission in order to investigate whether the presence of an electric field could control the ordering of the dye molecule assembly in the polymer. The present work focuses on organic dye molecules, which contain three benzene rings in plane with a high symmetry such as crystal violet (CV) and brilliant green (BG) as a dopant. In the case of CV doped PT by applying triangle-shaped negative voltage, the orderings of CV molecules were found by FTIR measurements. Since the ring stretching mode due to the componential benzene ring around 1585 cm^-1 was observed only in the FTIR transmission spectra while not observed in the spectrum of FTIR RAS spectra, this result shows that CV molecules are doped in the polymer so that the ring plane of CV is inclined to be parallel to the polymer film plane. In the case of CV doped PT samples by field-free casting method, the ring stretching modes were observed in both spectra of FTIR RAS and transmission, indicating that the dopant molecules were randomly oriented.

DOI： 10.1116/1.2784722

Language：English   Publishing type：Research paper (scientific journal)  

An electrochemical anodization technique associated with wet surface cleansing processes was applied for fabrication of surface nanoscale structures on Al plates. Dynamic force microscopy (DFM) measurements clarifies that different wet cleansing processes create different initial surface structures on Al such as a linked-crater pattern and a groove pattern on Al surfaces and induce finer and well-ordered characteristic surface nanoscale patterns. Based on those structures, anodization proceeds in the fabrication of well-ordered characteristic nanoscale patterns with quite unique secondary structures on Al surface. One is a crater-array structure with small pores in each crater. The other is a hut-shaped structure with a well-oriented line structure in each hut structure. Further anodization assists in fabrication of more ordered finer nanoscale structures such as well-oriented row-aligned pattern and a well-defined lattice pattern. Deposition of copper phthalocyanine (CuPc) molecules on anodized crater-arrayed Al surface is conducted by casting CuPc resolved toluene. DFM and x-ray photoemission spectroscopy measurements clarify that an organic-inorganic nanoscale patterned material is fabricated.

DOI： 10.1116/1.2747619

Language：English   Publishing type：Research paper (scientific journal)  

A conducting polymer polythiophene (PT) film incorporated with copper phthalocyanine (CuPc), which was a highly functional molecule, was synthesized and characterized by Fourier transform infrared (FTIR) spectroscopy and x-ray photoemission spectroscopy (XPS). Electrochemical and casting processes were developed as a doping method of CuPc molecules in a PT film. In the XPS measurements of the CuPc doped PT, CuPc-origin peaks on the higher energy side appeared in the C 1s spectrum. The C 1s spectral profiles between electrochemically doped and cast samples were different in the higher binding energy region. S 2p and N 1s core-level spectra of CuPc doped compounds also showed the difference of the spectral profile between electrochemically doped and cast samples, which suggested the dopant-polymer interaction. A split of Cu 2p spectra indicates the charge transfer between CuPc and the polymer chains. In the FTIR measurements, characteristic vibrational modes to CuPc, in-plane, out-of-plane, and ring stretching modes were observed. A central metal-origin peak was also observed. New peaks at 1545 and 1680 cm-1 suggest the polymer-PcCu linkage.

DOI： 10.1116/1.2731347

Language：English   Publishing type：Research paper (scientific journal)  

An electrochemical anodization technique associated with wet surface cleansing processes was applied for fabrication of surface nanoscale structures on Al plates. Dynamic force microscopy (DFM) measurements clarifies that different wet cleansing processes create different initial surface structures on Al such as a linked-crater pattern and a groove-pattern on Al surfaces and induce finer and well-ordered characteristic surface nanoscale patterns. Based upon those structures, anodization proceeds in the fabrication of well-ordered characteristic nanoscale patterns on Al surface such as a well-oriented row-aligned pattern and a well-fined lattice pattern. Deposition of copper phthalocyanine (CuPc) molecules upon anodized craterarrayed Al surface is conducted by casting CuPc resolved toluene. DFM and X-ray photoemission spectroscopy (XPS) measurements clarify that an organic-inorganic nanoscale patterned material is fabricated.

DOI： 10.1088/1742-6596/61/1/105

Language：English   Publishing type：Research paper (scientific journal)  

The authors have applied photoemission microspectroscopy to copper phthalocyanine films grown on a graphite surface with a lateral resolution of 0.3 μm and an energy resolution of 30 meV. The photoemission peak due to the highest occupied molecular orbital was found to be at binding energies of 1.13, 1.23, 1.38, and 1.5 eV, depending on film thickness. From the thickness and light-polarization dependence, the peaks were assigned to originate from isolated molecules, the first layer, the second layer, and multilayer, respectively. They demonstrate the capability of photoemission microspectroscopy to resolve electronic states modified by fine differences of molecular environments.

DOI： 10.1063/1.2388922

Language：English   Publishing type：Research paper (other academic)  

We have constructed a laser-based microspot photoemission spectrometer which achieved lateral resolution of 0.3 μm and energy resolution of 30 meV. The light source at wavelength of 140 nm (photon energy of 8.86 eV) was generated as the 6-th harmonics of a titanium sapphire laser of 100 fs pulse duration. The high-energy resolution is the characteristics of our apparatus. The space-charge effect which affects the energy resolution and limits the sensitivity was described. The apparatus was applied to reveal spatial inhomogeneity of copper phthalocyanine films caused by intermolecular interaction and inter-layer interaction. We found that the highest occupied molecular orbital is peaking at the binding energies of 1.13, 1.23, and 1.38 eV depending on the film thickness and the sample positions. The peaks were assigned to originate from isolated molecules, ordered monolayer, and the second layer, respectively. The apparatus can also be operated as microspot two-photon photoemission spectrometer which probes unoccupied electronic states. A surface image due to the unoccupied first image potential state of Cu(111) facets showed that the lateral resolution for two photon photoemission with a light of 280 nm wavelength was 0.4 μm, smaller by 1/√2 than the diffraction limited spot size.

DOI： 10.1117/12.679894

Language：English   Publishing type：Research paper (scientific journal)  

Performance of our micro-spot photoemission spectrometer based on fs-laser radiation has been applied to observe (a) surface images due to an unoccupied electronic state and (b) inhomogeneous electronic structure of a thin organic film. Two-photon photoemission spectroscopy was performed with lateral resolution of 0.6 μm for a polycrystalline copper plate. We have observed lateral distribution of the unoccupied image-potential state of Cu(1 1 1) surface. In addition to μm-scale information from the surface image, the high-energy resolution spectroscopy provides insight on the step size of nm-scale. By employment of focused VUV light of 8.86 eV, one-photon photoemission spectroscopy was performed for a copper phthalocyanine film grown on the polycrystalline copper plate with a lateral resolution of 0.3 μm and an energy resolution of 30 meV. The photoemission band due to the highest occupied molecular orbital peaked at the binding energy of either 1.6 or 1.2 eV depending on the sample positions. Polarization dependence of the band showed that molecules are poorly oriented even on the (1 1 1) surface. The results demonstrate that a large inhomogeneity exists in the interface electronic structure.

DOI： 10.1016/j.susc.2005.06.043

Language：English   Publishing type：Research paper (scientific journal)  

We have applied microspot photoemission spectroscopy to the surface imaging of a polycrystalline Cu plate with a lateral resolution of 0.3 μm and an energy resolution of 30 meV. The images of the crystalline islands with the (1 1 1) surface were measured by detecting photoelectrons due to the Shockley surface state (SS) and the sp-band specific to the (1 1 1) surface. The dependence of the images on the photoelectron energies was related to the mean length of the (1 1 1) terrace. The (1 1 1) island measured with the photoelectron close to the work function cutoff was found to be shifted from that measured with the Shockley state. The result demonstrates that the very high-energy resolution is essential for precise understanding of the surface images.

DOI： 10.1016/j.elspec.2005.01.245

Language：English   Publishing type：Research paper (scientific journal)  

We have applied photoemission microspectroscopy to copper phthalocyanine film grown on a polycrystalline copper with a lateral resolution of 0.3 μm and an energy resolution of 30 meV. The photoemission band due to the highest occupied molecular orbital peaked at the binding energy of either 1.6 or 1.2 eV depending on the sample positions, while the work functions were 4.3 and 4.5 eV for the respective positions. The band was intense when the binding energy was low. The results demonstrate that a large inhomogeneity exists in the interface electronic structure.

DOI： 10.1063/1.1808494

Language：English   Publishing type：Research paper (scientific journal)  

A photoemission microspectroscopy of 30meV energy resolution and 0.3μm lateral resolution has been applied to observe crystalline domains formed on a polycrystalline copper plate. Surface images based on the Shockley state specific to the (111) surface clearly showed many crystalline islands composed of the (111) surface. Similarly, surface images based on the unoccupied image-potential state were measured by employing two-photon photoemission spectroscopy. The high-energy resolution spectroscopy provides insight on the nm-scale surface morphology. The Shockley state was observed even on a poorly crystallized area, while the image-potential state was observed only on an area where mean (111) terrace length is sufficiently long.

DOI： 10.1016/j.elspec.2004.02.032

Language：English   Publishing type：Research paper (scientific journal)  

Microbeam photoemission spectroscopy of 30-meV energy resolution and 0.3-μm lateral resolution has been applied to observe (111) surface domains formed on a polycrystalline copper plate. The light source was fs-coherent radiation at a wavelength of 140 nm (8.9 eV). The images based on the intensity of the Shockley-surface-state feature clearly show many crystalline domains, exposing the (111) surface. The energy of the surface-state feature was distributed in the range from -−0.3 to −0.1 eV with respect to the Fermi level (E_F). In addition to the μm-scale information, the high-energy-resolution spectroscopy provides detailed insight on the nm-scale surface morphology. Surface images based on the unoccupied image-potential state were also measured by employing two-photon photoemission with uv light at a wavelength of 280 nm (4.43 eV). The image state was always at 4.10 eV, which is very close to the state of single-crystalline Cu(111). The Shockley state was observed even on poorly crystallized areas, while the image-potential state was observed only on areas where mean (111) terrace lengths are sufficiently long.

DOI： 10.1103/PhysRevB.68.165404

Language：English   Publishing type：Research paper (scientific journal)  

The lateral resolution of our laser-based microspot photoemission spectrometer [Surf. Sci. 507-510 (2002) 434] has been improved to 0.3 μm by focusing VUV light of 140 nm wavelength (8.9 eV photon energy). The VUV light is generated by frequency tripling a second-harmonic output of a regeneratively amplified titanium:sapphire laser of 250 kHz repetition rate, and is focused on a sample surface by a Schwarzschild objective of 0.29 NA. Time-of-flight (TOF) photoelectron spectra of energy resolution better than 40 meV are accumulated for 0.4 s during scanning the sample position by 0.1 μm/step. Measurement on a Ta-striped Si sample revealed that the lateral resolution is 0.3 μm, which is very close to the diffraction-limited spot diameter. The present microspectrometer is characterized with the simultaneous realization of the diffraction-limited lateral resolution and the high-energy resolution, which is close to the Fourier transform of the pulse width of the laser light (100 fs).

DOI： 10.1016/S0039-6028(03)00196-1

Language：English   Publishing type：Research paper (scientific journal)  

Femtosecond transient reflectivity measurements were performed for Au(111) electrode/aqueous solution interfaces under electrochemical potential control. Electrode interfaces modified with and without a self-assembled monolayer of alkanethiols were studied in aqueous solutions of HClO
₄
and H
₂
SO
₄
. Dependence on electrochemical potential, interface modification, and kind of solute anions are observed concerning the transient reflectivity response in 3ps. For Au electrodes in an aqueous HClO
₄
solution, the rate of the initial relaxation at an unmodified interface, 6-10 ps
^-1
, decreased with the electrochemical potential at the potential range where a water dipole rearranged. The rate for alkanethiol-modified interfaces showed a tendency depending on the hydrocarbon chain length. A relative deposited energy from absorbed photon energy was estimated, indicating that interface modification with alkanethiols restricted energy dissipation from the interface. Our trial could contribute not only to develop a study of interaction between a substrate and adsorbed molecules in an ultrafast time scale but also to elucidate elementally processes of electrochemical reactions such as oxidation/reduction reactions at an electrode interface.

DOI： 10.1021/jp015562z

Type：Competition, symposium, etc.