Photoluminescence characterization of vertically aligned ZnO microrods

A detailed optical characterization of vertically aligned ZnO microrods (μRs) grown using a Ni-based catalyst was carried out by excitation-power- and temperature-dependent photoluminescence (PL) measurements. Low-temperature PL spectra of ZnO μRs are dominated by near-band-edge (NBE) emission consisted of a series of sharp lines typical for the bulk ZnO. Starting from the higher energy free exciton (FX) emission feature, the majority of them can be explained by radiative recombination of excitons bound to neutral donors (D⁰X), defect bound exciton (DBX), two-electron satellites emission, free-to-bound, i.e. free electrons to the neutral acceptors (eA⁰) transition, as well as their longitudinal-optical phonon replicas. An additional excitonic line located in between the FX and D⁰X lines, denoted as the surface excitons (SX) for ZnO μRs is observed. The intensity of the SX line is found to be smaller than that of the nanosized counterpart and has been attributed to the surface–volume ratio effects. The excitation-power-dependent results of FX line at low and high power regimes show quite close values corresponding to, respectively, p=2 and p=1 limits of the theoretical power law expression I～L^p and larger deviations for the D⁰X, SX and DBX lines. The temperature-dependent measurements confirmed the presence of eA⁰ line showing kT/2 influence to the position of eA⁰ emission line in comparison with FX. FX emissions persist up to 300 K and together with the dominant eA⁰ emission govern the line shape of the NBE emission range, while D⁰X and SX lines are quenched completely at 150 K.     

Flower-like Cu5Sn2S7/ZnS nanocomposite for high performance supercapacitor

Due to the synergistic effect between ZnS and Cu₅Sn₂S₇, the ZnS can enhance electrochemical performance of pristine Cu₅Sn₂S₇.     

p-character and the polarizability of molecular hydrogen

The polarizability of molecular hydrogen has been calculated over a range of internuclear separations by Hartree-Fock perturbation theory, both coupled and uncoupled, using Gaussian functions as basis set. It is shown that a relatively simple function having the proper admixture of s and p character can yield polarizabilities comparable in accuracy with those obtained from highly sophisticated wave-functions.

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Zusammenfassung Die Polarisierbarkeit des Wasserstoffmoleküls wurde für einen Bereich von Kernabständen mit Hilfe der gekoppelten als auch der entkoppelten Hartree-Fock-Störungstheorie mit einer Basis von Gauss-Funktionen berechnet. Es wird gezeigt, daß eine relativ einfache Funktion mit der geeigneten Beimischung von s- und p-Charakter Polarisierbarkeiten ergibt, deren Genauigkeit solchen aus Rechnungen mit sehr komplizierten Wellenfunktionen vergleichbar ist.

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Résumé Calcul de la polarisabilité de l'hydrogène moléculaire pour un éventail de distances internucléaires par la théorie des perturbations Hartree-Fock, couplée et non couplée, dans une base de fonctions gaussiennes. Une fonction relativement simple présentant un mélange convenable de caractère s et p fournit des polarisabilités, comparables au point de vue précision avec celles obtenues à partir de fonctions d'ondes très élaborées.

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Supported by the National Science Foundation; Grant No. GP-8359.     

Analysis of styrenated methyl esters of linseed oil fatty acids by molecular distillation

The distillation of the reaction product of methyl esters of linseed oil fatty acids and gaseous styrene at 280° C in a highly efficient molecular still is described. From the specific refractions of the fractions obtained it follows that styrene has combined chemically with the esters.     

Synthesis and mesomorphic properties of Schiff base esters possessing terminal chloro substituent

<正>A homologous series of Schiff base esters,4-chlorobenzylidene-4'-n-alkanoyloxyanilines,containing even number of carbons at the end groups of the molecules(C_(n-1)H_(2n-1)COO-,n=4,6,8,10,12,14,16) were synthesized.The mesomorphic properties were investigated by differential scanning calorimetry(DSC) and polarizing optical microscopy(POM).It was found that the end groups of the molecules had an effect on the mesomorphic properties.n-Butanoyloxy was found non-mesogenic,whilst n-hexanoyloxy exhibited monotropic smectic phase.The higher members in this homologous series were enantiotropic smectogens.     

Incident-angle-dependent reflectance in distributed Bragg reflectors fabricated from ZnO/MgO multilayer films

We present the incident-angle-dependent reflectance spectra of the 10-period ZnO/MgO multilayer films deposited on Si by sputtering technique. As increasing the incident angle, the resonant wavelength and bandwidth of the measured reflectance spectra exhibit redshift and narrower, respectively. The theoretical curves using transfer matrix method taken account of transverse electric (TE) and transverse magnetic (TM) polarizations are calculated to well describe the variations in the behavior of the experimental spectra. The simulated TE- and TM-reflection band at different angles can evaluate the bandwidth of the resonance band and provide valuable parameters to design an omnidirectional-reflection band in selected multilayer structure.     

What students value in effective mathematics learning: a ‘Third Wave Project’ research study

Considerations of how mathematics can be effectively taught and learnt may be cognitive, affective or sociocultural in approach. ??What students value in effective mathematics learning?? is a research study of the Third Wave Project, an international consortium of research teams adopting a sociocultural approach to investigate the harnessing of relevant values to optimise school mathematics teaching and learning. This paper seeks to contextualise the study, as part of the study examines what the high-achieving East Asian mathematics students value. The study is framed by knowledge relating to the relative cultural influence on effectiveness in mathematics learning, Alan Bishop??s values in mathematics education and the role of interactions in education, in particular David Tripp??s idea of critical incidents as reflecting professional judgement (and, thus, underlying values). Features of the innovative qualitative research design are also presented, which include the facilitation of photo-voice, the argument for an international collaborative team and focus group interviews for all values research, and a two-stage data analysis process aimed at clarifying both etic and emic perspectives.     

Synthesis,Bonding and Reactivity of a Terminal Titanium Alkylidene Hydrazido Compound

We report a detailed study of the reactions of the Ti?NNCPh₂ alkylidene hydrazide functional group in [Cp*Ti{MeC(NiPr)₂}(NNCPh₂)] ( 8 ) with a variety of unsaturated and saturated substrates. Compound 8 was prepared from [Cp*Ti{MeC(NiPr)₂}(NtBu)] and Ph₂CNNH₂. DFT calculations were used to determine the nature of the bonding for the Ti?NNCPh₂ moiety in 8 and in the previously reported [Cp₂Ti(NNCPh₂)(PMe₃)]. Reaction of 8 with CO₂ gave dimeric [(Cp*Ti{MeC(NiPr)₂}{μ‐OC(NNCPh₂)O})₂] and the “double‐insertion” dicarboxylate species [Cp*Ti‐{MeC(NiPr)₂}{OC(O)N(NCPh₂)C(O)O}] through an initial [2+2] cycloaddition product [Cp*Ti{MeC(NiPr)₂}{N(NCPh₂)C(O)O}], the congener of which could be isolated in the corresponding reaction with CS₂. The reaction with isocyanates or isothiocyanates tBuNCO or ArNCE (Ar=Tol or 2,6‐C₆H₃iPr₂; E=O, S) gave either complete NNCPh₂ transfer, [2+2] cycloaddition to Ti?N_α or single‐ or double‐substrate insertion into the Ti?N_α bond. The treatment of 8 with isonitriles RNC (R=tBu or Xyl) formed σ‐adducts [Cp*Ti{MeC(NiPr)₂}(NNCPh₂)(CNR)]. With Ar^F5CCH (Ar^F5=C₆F₅) the [2+2] cycloaddition product [Cp*Ti{MeC(NiPr)₂}{N(NCPh₂)C(Ar^F5)C(H)}] was formed, whereas with benzonitriles ArCN (Ar=Ph or Ar^F5) two equivalents of substrate were coupled in a head‐to‐tail manner across the Ti?N_α bond to form [Cp*Ti{MeC(NiPr)₂}{N(NCPh₂)C(Ar)NC(Ar)N}]. Treatment of 8 with RSiH₃ (R=aryl or Bu) or Ph₂SiH₂ gave [Cp*Ti{MeC(NiPr)₂}{N(SiHRR′)N(CHPh₂)}] (R′=H or Ph) through net 1,3‐addition of Si? H to the N? N?CPh₂ linkage of 8 , whereas reaction with PhSiH₂X (X=Cl, Br) led to the Ti?N_α 1,2‐addition products [Cp*Ti{MeC(NiPr)₂}(X){N(NCPh₂)SiH₂Ph}].