Hiroshi Oji

Core hole effect in NEXAFS spectroscopy of polycyclic aromatic hydrocarbons: Benzene, chrysene, perylene, and coronene

Carbon K-edge NEXAFS spectra of chrysene, perylene, and coronene were measured using synchrotron radiation, and the results were analyzed by ab initio molecular orbital (MO) calculations. The spectra do not agree well with the calculated density of unoccupied states (DOUS), indicating significant core-hole effect leading to deviation of the NEXAFS spectra from the DOUS. On the other hand, the observed spectra were well simulated by theoretical calculations taking this effect into account by the improved virtual orbital method. This allowed a detailed analysis of the core-hole effect, which affects both transition energy and intensity. During the course of this analysis, the core-hole effect in benzene was also analyzed. It was found that the magnitude of the core-hole effect is strongly dependent on the combination of the excited site and final vacant orbital. This dependence could be semiquantitatively explained in terms of the combination of the excitation site and the orbital patterns of the final stat...

Electronic structure of organic/metal interfaces

Abstract In this article, studies of two subjects recently carried out in our group on organic/metal interfaces are reported. The first is the examination of the change of the work function of various metals (Ca, Mg, Cu, Ag and Au) at the deposition of TPD [N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (TPD)], which is used as a typical hole-injection layer. The work function change was pursued using Kelvin probe method and UV photoelectron spectroscopy (UPS) up to the film thickness of 100 nm. The results clearly showed that band bending leading to Fermi level alignment is not achieved, at least for systems prepared and measured under ultra high vacuum (UHV) conditions. The results of the exposure of the metal substrate to air was also examined. In the second work, we studied the mode of film growth, chemical interaction and electronic structure for interfaces formed by depositing p-sexiphenyl (6P) on metals (Au and Mg) and metals on 6P, using metastable atom electron spectroscopy (MAES), UPS and X-ray photoelectron spectroscopy (XPS). The results strongly depended on the metal and the order of deposition. The Au surface was easily covered by 6P deposition (equivalent to 0.3 nm thickness), while Mg surface requires much larger amount of 6P. In contrast, metal atoms deposited on 6P diffused into the organic layer. In particular, the surface of 6P was exposed even after depositing Au equivalent to 200-nm thickness. The change of work function in these cases is interpreted based on these modes of interface formation.

Ultrafine Gold Clusters Incorporated into a Metal–Organic Framework

Similar tozeolites, the structures of MOFs are usually microporous. Inaddition, there are advantages in the easily tunable sizes,shapes, and surrounding environments of the pores inMOFs; these endow MOFs with broader properties and ap-plications. Therefore, it is reasonable to apply porous MOFsas supports and/or hard templates for preparation of smallAu NPs. The porous structures in MOFs are expected tolimit the migration and aggregation of Au NPs. However, todate, all reported Au NPs are larger than 1.5 nm because ofthe poor understanding of the ruling factors of the size ofAu particles.

Aerobic oxidative coupling of alcohols and amines over Au–Pd/resin in water: Au/Pd molar ratios switch the reaction pathways to amides or imines

A facile switch of the reaction pathways of aerobic oxidative coupling of alcohols and amines from amidation to imination was realized for the first time by tuning the Au/Pd ratios in ion-exchange resin supported Au–Pd alloy catalysts (Au–Pd/resin). Amides were obtained with high yields on Au6Pd/resin while imines were obtained over AuPd4/resin. Various alcohols and amines underwent oxidative coupling smoothly in water to afford the desired products with good to excellent yields. Further investigation on the reaction mechanism suggested the synergistic effect between Au and Pd determined the adsorption strength of the aldehyde intermediate, which in turn dictated the reaction pathways. That is, on Au-rich alloys (e.g., Au6Pd) absorbed aldehyde species was formed, followed by further oxidation to yield amides, while on Pd-rich alloys (e.g., AuPd4), free aldehyde was generated, which then underwent condensation with amines to produce imines. The discovery might provide avenues to develop new efficient catalysts for the green synthesis of special chemicals.

Interfacial electronic structure of long-chain alkane/metal systems studied by UV-photoelectron and metastable atom electron spectroscopies

Abstract Electronic structure and molecular orientation at the interface formed by depositing a monolayer film of tetratetracontane (TTC, n -CH 3 (CH 2 ) 42 CH 3 ) on metals (Au, Ag and Pb) were investigated by ultraviolet photoelectron (UP) spectroscopy and metastable atom electron (MAE) spectroscopy. The MAE spectra reveal that the TTC molecules lie parallel to the substrate surface. A change in the work function by TTC deposition is observed in the UP spectra. The electronic polarization in the molecule is proposed as a possible origin of this change. In contrast to the change of the work function, the HOMO energy of TTC is found to be independent of the coverage up to the first monolayer.

Crop-Derived Polysaccharides as Binders for High-Capacity Silicon/ Graphite-Based Electrodes in Lithium-Ion Batteries

Rice to power: Amylopectin is a major component of agricultural products such as corn, potato, and rice. Silicon-graphite electrodes are prepared by using slurries of these polysaccharides as binders. Compared to the conventionally used binder PVdF, they exhibit drastically improved electrode performance in Li cells. The improved performance is coupled to the degree of branching.

p-Sexiphenyl/metal interfaces studied by photoemission and metastable atom electron spectroscopy

Abstract p -Sexiphenyl(6P)/metal (Au, Mg) interfaces were studied by ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS), and metastable atom electron spectroscopy (MAES). The vacuum level shifts ( Δ ) at the interface were observed in both 6P/Au ( Δ =−0.8±0.1 eV) and 6P/Mg ( Δ =−0.4±0.1 eV) systems. The MAES spectra indicate that the 6P molecules are on the substrate with their mean molecular plane parallel to the substrate surface in both systems, and that the 6P film on Mg substrate has some disorder. Thickness dependence of UPS, MAES, and XPS spectra suggests no significant chemical interaction for 6P on Au, Mg as well as Au, Mg on 6P interfaces. In the system of Au on 6P/Au, the spectral feature of 6P in MAES spectra did not disappear even when the thickness of evaporated gold reached 20 nm, indicating a penetration of Au atoms (or the clusters) into the 6P film.

Base‐Free Direct Oxidation of 1‐Octanol to Octanoic Acid and its Octyl Ester over Supported Gold Catalysts

The choice of a suitable support for gold nanoparticles (Au NPs) enabled the direct oxidation of unreactive aliphatic alcohol, 1-octanol, to octanoic acid and octyl octanoate in the absence of a base. Under optimized conditions, Au NPs supported on NiO (Au/NiO) exhibited remarkably high catalytic activities and excellent selectivities to octanoic acid (e.g., 97 %) at full conversion. In contrast to Au/NiO, Au/CeO₂ selectively produced octyl octanoate as a major product in a base-free aqueous solution with a maximum selectivity of 82 % under optimized conditions.

Full‐Automatic XAFS Measurement System of the Engineering Science Research II beamline BL14B2 at SPring‐8

The Engineering Science Research II beamline BL14B2 at SPring‐8 is a hard X‐ray bending magnet beamline covering the wide energy range from 3.8 to 72 keV, and has been open to XAFS users since September 2007. The gas distribution and exhaust gas treatment systems have been installed for the in‐situ XAFS measurements. Recent improvements in the speed of XAFS measurements have increased the demand for automated measurements. We have developed such a system, in which the adjustment of X‐ray optics and the XAFS measurement in transmission mode can be performed automatically.

Automatic XAFS measurement system developed at BL14B2 in SPring-8

A novel automatic measurement system has been developed, in which the XAFS measurement of up to 80 samples in transmission and fluorescence modes can be carried out.