X-ray photoelectron spectroscopic study on initial oxidation of hafnium hydride fractured in an ultra-high vacuum

The initial oxidation of hafnium hydride was studied by X-ray photoelectron spectroscopy (XPS). The clean surface of hafnium hydride was obtained by fracturing the specimen in an XPS measurement chamber under a background pressure of 2.7 × 10⁻⁶ Pa. The fractured surface was oxidized in situ with the exposure to high-purity oxygen and the residual gases in an ultra-high vacuum chamber. The XPS spectra for the oxidized surfaces had the shoulder due to the oxidation, and the shoulder grew up with increase in exposure time even in the ultra-high vacuum. The factor analysis for the XPS spectra of the oxidized surface showed that the oxide formed in the chamber consists of only the hafnium dioxide, and no suboxide states are contained. The result corresponded to the oxide observed on hafnium hydride fractured in air.     

Study of chemical states at intergranular fracture planes of iron-phosphorus alloys by auger and electron energy-loss spectroscopies

Auger and electron energy-loss spectroscopies (ELS) have been used to study chemical states at the fracture surfaces of iron-phosphorus alloys. The transgranular (TG) and intergranular (IG) fracture planes have similar Auger P LVV transition energies and similar Fe 3p loss energies. These indicate that phosphorus and iron atoms are dispersed atomically in layers segregated at IG planes. The energy separations between the inter-and intra-atomic Auger transition peaks in P LVV show that the TG and IG planes and Fe₃P have similar energy separations between the P 3p and Fe 3p levels. The layers segregated at IG planes are estimated to be equivalent to a monolayer, as indicated by the dependence of the loss energy of the valence-conduction-band transition on primary-electron kinetic energy from 200 to 500 eV. The phosphorus concentration in the segregated layers is saturated to ~ 20 at.% above a bulk phosphorus concentration of 2 at.%.     

Determination of the thickness of a covering layer on a solid by Auger and electron energy-loss spectra without a standard sample

A semi-quantitative method is proposed for determining the thickness of a covering layer on a solid. The thickness is calculated from the intensity ratios between Auger electron spectra (AES) and core-electron energy-loss spectra (ELS) for the uncovered and covered surfaces. This method needs no standard sample or ion sputtering to estimate the thickness, although it involves a number of assumptions. It has been applied to the determination of the thickness of segregated phosphorus layers on intergranular fracture planes of FeP alloys, using a cylindrical-mirror electron analyzer.     

Optical resolution of mandelic acid derivatives by column chromatography on crosslinked cyclodextrin gels

Crosslinked α- and β-cyclodextrin gels (α-CD-E and β-CD-E) were used for the chromatographic resolution of racemic mandelic acid and its derivatives. β-CD-E bound L -(+)-isomers preferentially over D -(?)-isomers and resolved DL -methyl mandelate to give a D -(?)-isomer of 100% optical purity in the first fraction. Mandelic acid, ethyl mandelate, and O-methylated mandelic acid yielded resolutions of 65–83% in initial fractions. α-CD-E, on the contrary, bound D -(?)-isomers more strongly than L -(+)-isomers, resolving DL -methyl mandelate to a smaller extent than β-CD-E. Binding of DL -mandelic acid and DL -methyl mandelate on β-CD-E was studied quantitatively by the equilibrium method. β-CD-E has a similar binding capacity to starch with 1:1 stoichiometry but bound much more strongly than starch. β-CD-E has the same mode of selectivity as starch for the asymmetric binding of the mandelic acid derivatives, but α-CD-E has a reverse selectivity to β-CD-E and starch.     

Incorporation of organic groups within the channel wall of spin-on mesostructured silica films by a vapor infiltration technique

Organically functionalized mesoporous silica films have been prepared by a novel synthetic procedure that involves spin-coating of mesostructured silica films and a vapor infiltration (VI) technique, using organosiloxanes, before the removal of surfactant. The VI-treated mesostructured films were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and a field emission scanning electron microscope (FE-SEM). Nitrogen adsorption/desorption measurements were performed using films attached with a silicon substrate. The XRD and FE-SEM measurements show that the mesochannel wall, densified and modified with organosilyl groups by the VI treatment, hardly contracts under calcination. FE-SEM observations for the films' cross section support the view that organosiloxane vapor is not deposited on the surface of the film. These results show that organosiloxane molecules penetrate the film and are selectively incorporated into the silica wall. Thus, hydrophobic mesoporous silica films can be synthesized without a reduction in pore size, a result that cannot be attained by conventional grafting and co-condensation methods. The excellent high porosity and hydrophobicity of the mesostructured composite films may be of advantage for next-generation low-k dielectric films.     

Enantioselective Lewis acid-catalyzed Mukaiyama-Michael reactions of acyclic enones. Catalysis by allo-threonine-derived oxazaborolidinones

allo-Threonine-derived O-aroyl-B-phenyl-N-tosyl-1,3,2-oxazaborolidin-5-ones 1g,n catalyze the asymmetric Mukaiyama-Michael reaction of acyclic enones with a trimethylsilyl ketene S,O-acetal in high enantioselectivity. A range of alkenyl methyl ketones is successfully employed as Michael acceptors affording ee values of 85-90% by using 10 mol % of the catalyst. The use of 2,6-diisopropylphenol and tert-butyl methyl ether as additives is found to be essential to achieve high enantioselectivity in these reactions. The effects of the additives are discussed in terms of the retardation of an Si(+)-catalyzed racemic pathway, which seriously deteriorates the enantioselectivity of asymmetric Mukaiyama-Michael reactions. A working model for asymmetric induction is proposed based on correlation between catalyst structures and enantioselectivities.     

Architecture of supramolecular metal complexes for photocatalytic CO2 reduction: ruthenium-rhenium bi- and tetranuclear complexes

We study the electrochemical, spectroscopic, and photocatalytic properties of a series of Ru(II)-Re(I) binuclear complexes linked by bridging ligands 1,3-bis(4'-methyl-[2,2']bipyridinyl-4-yl)propan-2-ol (bpyC3bpy) and 4-methyl-4'-[1,10]phenanthroline-[5,6-d]imidazol-2-yl)bipyridine (mfibpy) and a tetranuclear complex in which three [Re(CO)3Cl] moieties are coordinated to the central Ru using the bpyC3bpy ligands. In the bpyC3bpy binuclear complexes, 4,4'-dimethyl-2,2'-bipyridine (dmb) and 4,4'-bis(trifluoromethyl)-2,2'-bipyridine ({CF3}2bpy), as well as 2,2'-bipyridine (bpy), were used as peripheral ligands on the Ru moiety. Greatly improved photocatalytic activities were obtained only in the cases of [Ru{bpyC3bpyRe(CO)3Cl}3]2+ (RuRe3) and the binuclear complex [(dmb)2Ru(bpyC3bpy)Re(CO)3Cl]2+ (d2Ru-Re), while photocatalytic responses were extended further into the visible region. The excited state of ruthenium in all Ru-Re complexes was efficiently quenched by 1-benzyl-1,4-dihydronicotinamide (BNAH). Following reductive quenching in the case of d2Ru-Re, generation of the one-electron-reduced (OER) species, for which the added electron resides on the Ru-bound bpy end of the bridging ligand bpyC3bpy, was confirmed by transient absorption spectroscopy. The reduced Re moiety was produced via a relatively slow intramolecular electron transfer, from the reduced Ru-bound bpy to the Re site, occurring at an exchange rate (DeltaG approximately 0). Electron transfer need not be rapid, since the rate-determining process is reduction of CO2 with the OER species of the Re site. Comparison of these results with those for other bimetallic systems gives us more general architectural pointers for constructing supramolecular photocatalysts for CO2 reduction.