Facile fabrication of Ag-Pd bimetallic nanoparticles in ultrathin TiO(2)-gel films: nanoparticle morphology and catalytic activity

Ag-Pd bimetallic nanoparticles were prepared directly in ultrathin TiO(2)-gel films by a stepwise ion-exchange/reduction approach. Ion-exchange sites were created in ultrathin films using Mg(2+) ions as template. Ag(+) ion was then incorporated by ion exchange, and converted into metallic nanoparticles by low-temperature H(2) plasma, regenerating ion-exchange sites. The same procedure was then carried out for Pd(2+) ion, producing Pd-on-Ag bimetallic nanoparticles, as TEM observation and plasmon resonance absorption indicate. By contrast, reversed metal incorporation procedure appeared to give a mixture of individual Ag and Pd nanoparticles, as confirmed by TEM, absorption spectroscopy and X-ray photoelectron spectroscopy. For hydrogenation of methyl acrylate, the catalytic activity of the Pd-on-Ag nanoparticle is 367 times as large as that of commercial Pd black and 1.6 times as large as that of Pd monometallic nanoparticle. The outstanding catalytic activity was explicable by the large fraction of the surface-exposed Pd atoms. The formation process of the bimetallic nanoparticle and their general morphological feature are discussed.     

Structure of activated complex of CO2 formation in a CO + O2 reaction on Pd(110) and Pd(111)

Examinations of CO2 formed during steady-state CO oxidation reactions were performed using infrared (IR) chemiluminescence. The CO2 was formed using a molecular-beam method over Pd(110) and Pd(111). The CO2 formation rate is temperature dependent under various partial pressure conditions. The temperature of the maximum formation rate is denoted as TSmax. Analyses of IR emission spectra at surface temperatures higher than TSmax showed that the average vibrational temperature (TVAV) is higher for Pd(111) than for Pd(110). The antisymmetric vibrational temperature (TVAS) is almost equal on both surfaces. These results suggest that the activated CO2 complex is more bent on Pd(111) and straighter on Pd(110). Furthermore, the difference in the TVAV value was small for surface temperatures less than TSmax. The TVAS value was much higher than TVAV on both surfaces. These phenomena were observed only when the surface temperature was lower than TSmax: they became more pronounced at lower temperatures, suggesting that the activated complex of CO2 formation is much straighter on both Pd surfaces than that observed at higher surface temperatures. Combined with kinetic results, the higher CO coverage at the lower surface temperatures is inferred to be related to the linear activated complex of CO2 formation.     

A local second-order Møller-Plesset method with localized orbitals: a parallelized efficient electron correlation method

Using orthogonal localized occupied orbitals we have developed and implemented a parallelized local second-order M?ller-Plesset (MP2) method based on the idea developed by Head-Gordon and co-workers. A subset of nonorthogonal correlation functions (the orbital domain) was assigned to each of the localized occupied orbitals using a distance criterion and excitations from localized occupied orbitals that were arranged into subsets. The correlation energy was estimated using a partial diagonalization and an iterative efficient method for solving large-scale linear equations. Some illustrative calculations are provided for molecules with up to 1484 Cartesian basis sets. The orbital domain sizes were found to be independent of the molecular size, and the present local MP2 method covered about 98%-99% of the correlation energy of the conventional canonical MP2 method.     

Influence of Si doping on the optical and structural properties of InGaN films

Influence of Si doping on the optical and structural properties of InGaN epilayers with different Si concentrations was investigated in detail by means of high-resolution X-ray diffraction (HRXRD), scanning electron microscope (SEM), Cathodoluminescence (CL) and photoluminescence (PL). It was found that a small amount of Si doping in InGaN could enhance luminescence intensity, improve the crystal quality of InGaN and suppress the formation of V-defects in InGaN. Further investigation by CL showed that V-defects act as nonradiative center, which lower the luminescence efficiency of InGaN. Based on above-mentioned results, one possible mechanism of influence of Si doping on the formation of V-defects in InGaN was also proposed in this paper.     

Metal–insulator transition in quantum dot arrays

We present evidence for a re-entrant metal–insulator transition that arises in quantum dot arrays as the gate voltage is used to sweep their density of states past the Fermi level. The form of the temperature variation of the conductance observed in these arrays can be accounted for using a functional form derived from studies of the metal–insulator transition in two dimensions, although the values obtained for the fit parameters suggest that the behavior we observe here may be quite distinct to that found in two dimensions.     

Fiber-in-tube solid-phase microextraction: a fibrous rigid-rod heterocyclic polymer as the extraction medium

A novel “fiber-in-tube” configuration has been applied to the extraction tube of solid phase microextraction (SPME), and the direct coupling of the extraction process to liquid chromatography (LC) has been accomplished for the analysis of n-butylphthalate in wastewater. By using this fiber-in-tube SPME/LC system the preconcentration factor for the phthalate was about 160 with 20 min extraction and no interference peak was observed in the chromatogram. The results also showed the potential applications of this fiber-in-tube SPME/LC for the analysis of sub-ppb level (i.e., lower than 1 ng/mL) of various organic analytes in aqueous sample matrix without a large solvent consumption during the preconcentration process.     

Development and validation of a liquid chromatographic method for the analysis of positron emission tomography radiopharmaceuticals with Ru(bpy)(3)(2+)-KMnO(4) chemiluminescence detection.

A sensitive, selective and rapid high-performance liquid chromatographic (HPLC) method with chemiluminescence (CL) detection was developed and validated for the analysis of positron emission tomography (PET) radiopharmaceuticals. This method is based on the CL reaction of PET compounds with tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)] and acidic potassium permanganate [KMnO(4)]. After optimization of the reaction conditions, 12 of the 14 PET compounds investigated could be successfully detected and showed good performance in terms of sensitivity, linearity and reproducibility. In particular, for compounds with a tertiary amine functional group, the limits of detection were ppb levels for a 20 microL injection volume. Finally, this method was used to determine PET compounds for calculating of specific radioactivity in pharmaceutical samples.     

Numerical verifications of solutions for elliptic equations in nonconvex polygonal domains

Summary In this paper, methods for numerical verifications of solutions for elliptic equations in nonconvex polygonal domains are studied. In order to verify solutions using computer, it is necessary to determine some constants which appear in a priori error estimations. We propose some methods for determination of these constants. In numerical examples, calculating these constants for anL-shaped domain, we verify the solution of a nonlinear elliptic equation.     

Fabrication of GaAs hole array as a 2D-photonic crystal and their application to photonic bandgap waveguide

A two dimensional (2D) GaAs hole array with a high aspect ratio was successfully fabricated by dry etching techniques using a highly ordered alumina membrane as a mask. The reflection spectra of the GaAs hole array shows characteristics of the photonic bandgap (PBG) calculated by using the 2D triangular lattice structure. Various defect lines were formed etching in the GaAs hole array using focused ion beam. The defect-type PBG waveguide was experimentally demonstrated.