Characterization of Co-evaporated Cu-Ag-In-Se Thin Films

In this study, annealing effect on the structural, electrical, and optical characteristics of the quaternary Cu-Ag-In-Se (CAIS) thin films was investigated. These samples were deposited by co-evaporation of the Cu, Ag, In₂Se₃, and Se sources at the substrate temperature of 300 °C. The structural properties of the thin films were analyzed by means of X-ray diffraction, and the results indicated that all of the films were in the polycrystalline structure with the preferred orientation along (112) direction. From the optical measurements, the band gap values were found to vary between 1.38 and 1.45 eV with annealing processes. The temperature-dependent electrical conductivity of the samples was measured in the temperature range of 90–400 K. The films gained degenerate behavior with increasing annealing temperature. The carrier conduction mechanism was determined at high- and low-temperature regions by comparing thermionic emission and hopping parameters. Photoconductivity of the as-grown film showed that there was an increase in conductivity with increasing illumination intensity. From this measurement, the variation of photocurrent as a function of illumination intensity was determined.     

Kaluza–Klein reduction of a quadratic curvature model

Palatini variational principle is implemented on a five dimensional quadratic curvature gravity model, rendering two sets of equations, which can be interpreted as the field equations and the stress-energy tensor. Unification of gravity with electromagnetism and the scalar dilaton field is achieved through the Kaluza–Klein dimensional reduction mechanism. The reduced curvature invariant, field equations and the stress-energy tensor are obtained in the actual four dimensional spacetime. The structure of the interactions among the constituent fields is exhibited in detail. It is shown that the Lorentz force density naturally emerges from the reduced field equations and the equations of the standard Kaluza–Klein theory are demonstrated to be intrinsically contained in this model.     

On the mechanism of the N,N‐dimethyl amination of Grignard reagents: a kinetic study

A direct kinetic study is reported for the electrophilic amination of substituted phenylmagnesium bromides with N,N‐dimethyl O‐(mesitylenesulfonyl)hydroxylamine in THF. Rate data, Hammett relationship, and activation entropy are consistent with a S_N2 displacement involving the attack of carbanions to sp³N in the amination reagent (AR). Copyright © 2007 John Wiley & Sons, Ltd.     

Simulating listener errors in using genetic algorithms for perceptual optimization

The genetic algorithm (GA) was previously suggested for fitting hearing aid or cochlear implant features by using listener's subjective judgment. In the present study, two human factors that might affect the outcome of the GA when used for perceptual optimization were explored with simulations. Listeners with varying sensitivity in discriminating sentences of different intelligibility and with varying error rates in entering their judgment to the GA were simulated. A comparison of the simulation results with the results from human subjects reported by Ba?kent et al. Ear Hear. 28(3) 277-289 (2007) showed that these factors could reduce the performance of the GA considerably.     

Non-gravitating scalars and spacetime compactification

We discuss role of partially gravitating scalar fields, scalar fields whose energy–momentum tensors vanish for a subset of dimensions, in dynamical compactification of a given set of dimensions. We show that the resulting spacetime exhibits a factorizable geometry consisting of usual four-dimensional spacetime with full Poincaré invariance times a manifold of extra dimensions whose size and shape are determined by the scalar field dynamics. Depending on the strength of its coupling to the curvature scalar, the vacuum expectation value (VEV) of the scalar field may or may not vanish. When its VEV is zero the higher-dimensional spacetime is completely flat and there is no compactification effect at all. On the other hand, when its VEV is nonzero the extra dimensions get spontaneously compactified. The compactification process is such that a bulk cosmological constant is utilized for curving the extra dimensions.     

Fiber Optic Excitation of Silicon Microspheres in Amorphous and Crystalline Fluids

ABSTRACT

This study investigates the optical resonance spectra of free-standing monolithic single crystal silicon microspheres immersed in various amorphous fluids, such as air, water, ethylene glycol, and 4-Cyano-4’-pentylbiphenyl nematic liquid crystal. For the various amorphous fluids, morphology-dependent resonances with quality factors on the order of 10⁵ are observed at 1428 nm. The mode spacing is always on the order of 0.23 nm. The immersion in various amorphous fluids affects the spectral response of the silicon microsphere and heralds this technique for use in novel optofluidics applications. Even though the nematic liquid crystal is a highly birefringent, scattering, and high-index optical medium, morphology-dependent resonances with quality factors on the order of 10⁵ are observed at 1300 nm in the elastic scattering spectra of the silicon microsphere, realizing a liquid-crystal-on-silicon geometry. The relative refractive index and the size parameter of the silicon microsphere are the parameters that affect the resonance structure. The more 4-Cyano-4’-pentylbiphenyl interacting with the silicon microsphere, the lower the quality factor of the resonances is. The more 4-Cyano-4’-pentylbiphenyl is interacting with the silicon microsphere, the lower the mode spacing Δλ of the resonances is. The silicon microspheres wetted with nematic liquid crystal can be used for optically addressed liquid-crystal-on-silicon displays, light valve applications, or reconfigurable optical networks.     

Multi‐crystalline silicon solar cells with metal‐assisted nano‐texturing using HNO3 as hole injection agent

In this study, metal‐assisted etching (MAE) with nitric acid (HNO₃) as a hole injecting agent has been employed to texture multi‐crystalline silicon wafers. It was previously proven that addition of HNO₃ enabled control of surface texturing so as to form nano‐cone shaped structures rather than nanowires. The process parameters optimized for optically efficient texturing have been applied to multi‐crystalline wafers. Fabrication of p‐type Al:BSF cells have been carried out on textured samples with thermal SiO₂/PECVD‐SiN_x stack passivation and screen printed metallization. Firing process has been optimized in order to obtain the best contact formation. Finally, j_sc enhancement of 0.9 mA/cm² and 0.6% absolute increase in the efficiency have been achieved. This proves that the optimized MAE texture process can be successfully used in multi‐crystalline wafer texturing with standard passivation methods.

J –V curves and SEM images of the nano and iso‐textured samples. j_sc enhancement of 0.9 mA/cm² together with 0.6% absolute efficiency gain was observed on nano‐textured samples.     

Vibrational dynamics of the organometallic compound triarylorganoantimony (V) SbPh<Subscript>3</Subscript>[O<Subscript>2</Subscript>CC(OH)Ph<Subscript>2</Subscript>]<Subscript>2</Subscript>

A complete normal coordinate analysis was performed for five-coordinate non-rigid triarylantimony diester SbPh₃(O₂CR)₂, known to be a bioactive molecule, using Wilson G-F matrix method and Urey Bradley force field. The study of vibrational dynamics was performed using the concept of group frequencies and band intensities.      

Sound velocities of compressed Fe3C from simultaneous synchrotron X‐ray diffraction and nuclear resonant scattering measurements

The applications of nuclear resonant scattering in laser‐heated diamond anvil cells have provided an important probe for the magnetic and vibrational properties of ⁵⁷Fe‐bearing materials under high pressure and high temperature. Synchrotron X‐ray diffraction is one of the most powerful tools for studying phase stability and equation of state over a wide range of pressure and temperature conditions. Recently an experimental capability has been developed for simultaneous nuclear resonant scattering and X‐ray diffraction measurements using synchrotron radiation. Here the application of this method to determine the sound velocities of compressed Fe₃C is shown. The X‐ray diffraction measurements allow detection of microscale impurities, phase transitions and chemical reactions upon compression or heating. They also provide information on sample pressure, grain size distribution and unit cell volume. By combining the Debye velocity extracted from the nuclear resonant inelastic X‐ray scattering measurements and the structure, density and elasticity data from the X‐ray diffraction measurements simultaneously obtained, more accurate sound velocity data can be derived. Our results on few‐crystal and powder samples indicate strong anisotropy in the sound velocities of Fe₃C under ambient conditions.