New experimental technique of photoelectron holography applied to Bi trimers on Si(111)

The branching ratio, the photoemission intensity ratio of two spin-orbit-split components, has been applied for the first time as a means for obtaining a photoelectron holographic image. Angle-resolved photoemission from a monolayer of Bi adsorbed on Si(111) shows fine-structure oscillations in the branching ratio of the Bi 5d core level due to diffraction effects. These oscillations as a function of photon energy are recorded for a number of emission angles. Three-dimensional holographic inversion of the data yields an atomic image which shows that the Bi adatoms are arranged in a trimer structure.     

Prediction of oscillating thick cambered aerofoil aerodynamics by a locally analytic method

A complete first-order model and locally analytic solution method are developed to analyse the effects of mean flow incidence and aerofoil camber and thickness on the incompressible aerodynamics of an oscillating aerofoil. This method incorporates analytic solutions, with the discrete algebraic equations which represent the differential flow field equations obtained from analytic solutions in individual grid elements. The velocity potential is separated into steady and unsteady harmonic parts, with the unsteady potential further decomposed into circulatory and non-circulatory components. These velocity potentials are individually described by Laplace equations. The steady velocity potential is independent of the unsteady flow field. However, the unsteady flow is coupled to the steady flow field through the boundary conditions on the oscillating aerofoil. A body-fitted computational grid is then utilized. Solutions for both the steady and the coupled unsteady flow fields are obtained by a locally analytic numerical method in which locally analytic solutions in individual grid elements are determined. The complete flow field solution is obtained by assembling these locally analytic solutions. This model and solution method are shown to accurately predict the Theodorsen oscillating flat plate classical solution. Locally analytic solutions for a series of Joukowski aerofoils demonstrate the strong coupling between the aerofoil unsteady and steady flow fields, i.e. the strong dependence of the oscillating aerofoil aerodynamics on the steady flow effects of mean flow incidence angle and aerofoil camber and thickness.     

Multiphonon resonant Raman scattering in GaSe

Multiphonon resonant Raman scattering up to 4 phonons in GaSe has been measured. The results are interpreted by a simple cascade theory. It is shown that the dispersion of RRS here is dominated by resonances with the exciton states.     

A modified Marton-type electron interferometer

It is shown that the original Marton-type electron interferometer is based on the Fresnel diffraction of two coherent beams by a crystal. The modified Marton-type electron interferometer presented here is based on the Fraunhofer diffraction. The advantages of the proposed interferometer are given in the text along with a simplified sketch of the major components.     

Photoluminescence studies of vacancies and vacancy-impurity complexes in annealed GaAs

Photoluminescence measurements made at various depths below the surface of annealed GaAs single crystals are compared with vacancy distribution profiles obtained from electrical measurements. Results on undoped n-GaAs indicate that isolated Ga or As vacancies form non radiative centers. A broad-band emission at 1.20 eV, arising from V_Ga-donor complexes, is observed in spectra taken from n-type samples doped with Si, Sn or Te. The intensity of the 1.20eV band varies with depth and reaches its maximum value in the region where Ga vacancies are dominant. These results show the consistency between photoluminescence and electrical measurements. A band at 1.37eV has previously been assigned to V_As-acceptor complexes. This band was observed in this study only when the samples had been annealed in ampoules prepared from quartz containing traces of Cu. It is concluded that the 1.37eV band is due to Cu contamination rather than V_As-acceptor complexes.     

Quantitative analysis of a mixture of cresols by carbon-13 NMR spectroscopy

The suitability of ¹³C NMR as a technique for determining o-, m, and p-cresols in their mixtures was investigated. Spectra were determined in methanol, containing o-toluidine as an internal standard, without nuclear Overhauser suppression. Ratios of peak areas of each cresol isomer to o-toluidine were determined by means of the standard calibration method, and then mixtures of cresol isomers were prepared and quantified in varying concentrations from 8.30 to 66.84 mol% for each isomer, with an average absolute error of 0.78% for all isomers. The method described was convenient and the results were generally satisfactory.     

Spectroscopic characterization of the matrix–silane coupling agent interface in fiber-reinforced composites

The copolymerizations of anhydride-cured epoxy resin on fiberglass surfaces treated with a N-methylaminopropyltrimethoxysilane coupling agent has been investigated using Fourier-transform infrared spectroscopy. The structure of the interface of the silane and the resin in fiber-reinforced composites is composed of copolymers of the epoxy resin with the organofunctionality of the deposited silanes. The number of interfacial bonds formed depends on the amount of silane coupling agent deposited on the fiberglass and the reaction conditions. The silane induces additional esterification and increases the curing density of the epoxy matrix near the fiber surface by about 5–10% relative to the bulk resin.     

Polymer-monomer conversion in anthracene thin films as a switching and memory device

The switching and memory phenomenon in anthracene thin films is explained by assuming the polymerization of anthracene molecules to a graphite-like polymer. When the voltage is a threshold point, the energetic electron and the secondary ionization may initiate the process similar to the polymerization. Since the polymer-like entity has graphite-like structure, it has higher conductivity, thus the film is switched to ON state. Since the molecule in a thin film can not rotate as freely as in liquid, the polymer-like entity formed is under great bond strain, thus it may readily switch back to monomer anthracene molecule. However, if with repeated cycles, the polymer is at a relatively stable configuration with less bond strain, then it is in the memory state. Many experimental data of Elsharkawi and Kao may be explained with this model.