Preparation of silver nanoparticles on zinc oxide nanowires by photocatalytic reduction for use in surface‐enhanced Raman scattering measurements

To increase the sensitivity in surface‐enhanced Raman scattering (SERS) measurements, the high surface area of zinc oxide nanowires (ZnO NWs) was used. ZnO NWs on silicon substrates were prepared and used as substrates for further growth of silver nanoparticles (AgNPs). Ultraviolet (UV) irradiation was used to reduce silver ions to AgNPs on the ZnO wires. With proper growth conditions for both ZnO NWs and AgNPs, the substrates exhibit SERS enhancement factors greater than 10⁶. To understand the influences of the morphologies of the ZnO NWs on the growth of AgNPs, the growing time and temperature were varied. The concentration of silver nitrate and irradiation time of UV radiation were also varied. The resulting AgNPs were probed with para‐nitrothiophenol to quantify the SERS enhancements obtained from the varying conditions. The results indicate that ZnO NWs could be grown at temperatures higher than 490 °C and higher growth temperatures result in smaller diameter of the formed ZnO NWs. Also, the morphologies of ZnO NWs did not significantly alter the SERS signals. The concentration of silver nitrate affects the SERS signals significantly and the optimal concentration was found to be in the range of 10–20 mM. With irradiation times longer than 90 s, the resulting AgNPs showed similar SERS intensities. With optimized conditions, the AgNPs/ZnO substrates are highly suitable for SERS measurements with a typical enhancement factor of higher than 10⁶. Copyright © 2010 John Wiley & Sons, Ltd.     

Polymerization of 7-phenyl-2,6-dimethylquinone methide and its derivatives

7-Phenyl-, 7-chlorophenyl-,7-methylphenyl-, and 7-trifluoromethylphenylquinone methide were synthesized to investigate the anionic polymerization of quinone methide. Novel high molecular weight polymers have been prepared and the substitution effects of the monomers on polymerization kinetics were determined. © 1993 John Wiley & Sons, Inc.     

Determination of nuclear parameters by inelastic electron scattering at low-momentum transfer

The second-order Born-approximation treatment of Cutler and Schucan was applied to inelastic electron scattering data on ⁶Li, ⁶⁰Ni, and ¹¹⁴Cd acquired at low momentum transfers. The form factors as a function of momentum transfer q in the range of 0.25–0.57 fm^?1 were obtained by angular distribution measurements performed at incident energies of 30 to 60 MeV. The correlation between two parameters deduced from the measurements, the reduced transition probability B(E2↑) and the transition radius R⁽²⁾_tr, is discussed. It is suggested that inelastic electron scattering data at low-q is best used either in conjunction with an accurate value of B(EL↑) (available from the model-independent analysis of “photon” experiments at zero momentum transfer) to allow accurate determination of R⁽²⁾_tr, or in conjunction with high-q inelastic electron scattering data to allow accurate determination of B(EL↑) as well as R⁽²⁾_tr.     

Crystallization behavior and morphology of poly(ethylene‐co‐trimethylene terephthalate)s

The melt crystallization behaviors and crystalline structures of poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate), and poly(ethylene‐co‐trimethylene terephthalate) (PETT) were investigated with differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X‐ray diffraction at various crystallization temperatures (T_cs). The PETT copolymers were synthesized via the polycondensation of terephthalate with ethylene glycol and trimethylene glycol (TG) in various compositions. The copolymers with 69.0 mol % or more TG or 31.0 mol % or less TG were crystallizable, but the other copolymers containing 34–56 mol % TG were amorphous. The DSC isothermal results revealed that the addition of a small amount of flexible TG (up to 21 mol %) to the PET structure slightly reduced the formation of three‐dimensional spherulites. A greater TG concentration (91–100%) in the copolyesters changed the crystal growth from two‐dimensional to three‐dimensional. The DSC heating scans after the completion of isothermal crystallization at various T_cs showed three melting endotherms for PET, PETT‐88, PETT‐84, and PETT‐79 and four melting endotherms for PETT‐9 and PETT. The presence of an additional melting endotherm could be attributed to the melting of thinner and imperfect copolyester crystallites. Analyses of the Lauritzen–Hoffman equation demonstrated that PETT‐88 had the highest values of the product of the lateral and folding surface free energies, and this suggested that the addition of small amounts of flexible trimethylene terephthalate segments to PET disturbed chain regularity, thus increasing molecular chain mobility. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4255–4271, 2004     

Preparation,morphology, and thermoresponsive properties of poly(N‐isopropylacrylamide)‐based copolymer microgels

In this research, thermoresponsive copolymer latex particles with an average diameter of about 200–500 nm were prepared via surfactant‐free emulsion polymerization. The thermoresponsive properties of these particles were designed by the addition of hydrophilic monomers [acrylic acid (AA) and sodium acrylate (SA)] to copolymerize with N‐isopropylacrylamide (NIPAAm). The effects of the comonomers and composition on the synthesis mechanism, kinetics, particle size, morphology, and thermoresponsive properties of the copolymer latex were also studied to determine the relationships between the synthesis conditions, the particle morphology, and the thermoresponsive properties. The results showed that the addition of hydrophilic AA or SA affected the mechanism and kinetics of polymerization. The lower critical solution temperature (LCST) of the latex copolymerized with AA rose to a higher temperature. However, because the strong hydrophilic and ionic properties of SA caused a core–shell structure, where NIPAAm was in the inner core and SA was in the outer shell, the LCST of the latex copolymerized with SA was still the same as that of pure poly(N‐isopropylacrylamide) latex. It was concluded that these submicrometer copolymer latex particles with different thermoresponsive properties could be applied in many fields. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 356–370, 2006     

First-principles calculation for bowing parameter of wurtzite AlxGa1-xN

Numerical calculation based on first-principles is applied to study the structural characteristics and the band-energy properties of wurtzite Al_xGa_1-xN. The lattice constants obtained from the equilibrium energy are larger than those obtained from the Vegard’s law. The deviation parameter is 0.040±0.005 Å for the a lattice constant and 0.125±0.009 Å for the c lattice constant. The band gap energy is overestimated with the Vegard’s law. The bowing parameter of direct (indirect) band gap energy of 0.752±0.069 eV (0.889±0.057 eV) is obtained with the equilibrium lattice constants, and 0.352±0.046 eV (0.271±0.056 eV) is obtained with the lattice constants derived from the Vegard’s law. PACS 71.15.-m; 71.20.Nr; 81.05.Ea     

Pulsed resonant laser interaction in three level systems

We present a simple treatment for three level transitions excited by a doubly resonant laser pulse. Explicit solutions are derived in special cases. For the strong pulse case we show that the wavefunction can be expressed as a precessing vector.     

IBA calculations on the even-even Pt isotopes

By performing least-squares-fit calculations on the energy spectra of the even-even ^186–196Pt isotopes, the IBA model I and the IBA model II are compared on an equal footing. It is found that both model I and model II can fit energy spectra and absolute B(E2) transition rates reasonably well. Model II shows a distinct improvement in the energy spectra of β-bands of heavier nuclei in the isotope series. It is suggested that for regions far from the closed shells model I may be used to simulate model II as a useful phenomenological probing tool.