The photoresponse of polycrystalline ZnO films generally contains both a true photoconductivity and a contribution from surface structural changes which can alter the surface conductance via the chemisorption and phot...
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The photoresponse of polycrystalline ZnO films generally contains both a true photoconductivity and a contribution from surface structural changes which can alter the surface conductance via the chemisorption and photodesorption of an active ambient-gas component. The surface structural changes can increase the conductance by up to seven orders of magnitude for a 500 nm thick sample when illuminated with an intensity of 4 x 10(16) photon cm(-2) s(-1) UV light, but the response times are very slow. Newly prepared samples exhibit a fast response characteristic such as a true photoconductivity, but after exposure to air for several months the slower response dominates. Thus if used as a photoconductor, oxygen adsorption or desorption from the surface of a ZnO film is particularly problematic, but some surface stability can be achieved by adding nitrogen to the surface layers of the ZnO film and these samples exhibit more normal and improved photoconducting behaviour.
A strong accumulation layer can be produced on the surface of polycrystalline ZnO films when the samples are exposed to ions from an inert gas discharge in Ar or Kr. A combination of surface conductance and surface po...
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A strong accumulation layer can be produced on the surface of polycrystalline ZnO films when the samples are exposed to ions from an inert gas discharge in Ar or Kr. A combination of surface conductance and surface potential measurements show that an accumulation layer is induced by the adsorption of charges from the inert gas plasma which neutralizes and removes chemisorbed oxygen atoms, and this can increase the conductance by more than 6 orders of magnitude, for 500 nm thick films. Electrical neutrality in the ZnO provides the electrons for the accumulation layer, either from the ohmic contacts or the plasma. This accumulation layer can be further enhanced by illumination with UV light.
We calculate the far-infrared absorption spectrum of the endohedral fullerene He@C-70. In this molecule the He inclusion experiences a strongly anisotropic potential V(rho, z). The 2D Schrodinger equation governing it...
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We calculate the far-infrared absorption spectrum of the endohedral fullerene He@C-70. In this molecule the He inclusion experiences a strongly anisotropic potential V(rho, z). The 2D Schrodinger equation governing its rovibrational motion is solved variationally. The spectrum consists of strong P- and R-branches (Delta m = +/-1) and a much weaker Q-branch (Delta m = 0), and peaks near 100cm(-1). Despite its apparent complexity, however, the eigenvalue spectrum is essentially regular, and the system displays little evidence of chaos.
A Fourier cosine transform method, based on the Rayleigh-Gans-Debye thin-shell approximation, was developed to retrieve vesicle size distribution directly from the angular dependence of scattered light intensity. Its ...
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A Fourier cosine transform method, based on the Rayleigh-Gans-Debye thin-shell approximation, was developed to retrieve vesicle size distribution directly from the angular dependence of scattered light intensity. Its feasibility for real vesicles was partially tested on scattering data generated by the exact Mie solutions for isotropic vesicles. The noise tolerance of the method in recovering unimodal and biomodal distributions was studied with the simulated data. Applicability of this approach to vesicles with weak anisotropy was examined using Mie theory for anisotropic hollow spheres. A primitive theory about the first four moments of the radius distribution about the origin, excluding the mean radius, was obtained as an alternative to the direct retrieval of size distributions.
Based on the Rayleigh-Gans-Debye thin shell approximation, a fast Fourier cosine transform method was developed to retrieve vesicle size distributions directly from the light scattering measurement. The method was tes...
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Interfacial structure in the isotropic phase of a liquid-crystalline material near a wall is studied by a mean-field density-functional theory. With increasing strength of the wall anchoring potential, the theory pred...
Interfacial structure in the isotropic phase of a liquid-crystalline material near a wall is studied by a mean-field density-functional theory. With increasing strength of the wall anchoring potential, the theory predicts a first-order transition from incomplete to complete wetting by the smectic-A phase at bulk isotropic-smectic coexistence, with an associated prewetting transition occurring away from bulk coexistence. The incomplete wetting case is accompanied by a small number (between 0 and and 2) of discrete layer transitions, while an infinite number of such transitions occurs at complete wetting. An analysis of the underlying physical mechanisns for layer transitions reveals that these transitions tend to disappear as the system is moved both sufficiently close to and sufficiently far from the bulk isotropic–nematic–smectic-A triple point by varying the model coupling parameters. These results reconcile findings from previous theories and experiments.
We examine a three-dimensional vector lattice model for water, oil, and amphiphile mixtures, using the mean-field and Bethe approximations as well as Monte Carlo methods. The Monte Carlo results exhibit three-phase co...
We examine a three-dimensional vector lattice model for water, oil, and amphiphile mixtures, using the mean-field and Bethe approximations as well as Monte Carlo methods. The Monte Carlo results exhibit three-phase coexistence between water-rich, oil-rich, and microemulsion phases, where the microemulsion has low amphiphile concentration (≊15%) in agreement with experiment. Also present is a floating incommensurate lamellar phase which coexists with the microemulsion at slightly higher amphiphile concentration, similar to lamellar phases observed experimentally. These features are absent in the two mean-field-like approximations and we conclude that, in general, these types of approximations are inappropriate for describing mixtures containing efficient amphiphiles.
We present a renormalization group theory in polymer conformation space to describe randomly branched polymers in which monomers interact with each other through the excluded volume interaction. We make a perturbation...
We present a renormalization group theory in polymer conformation space to describe randomly branched polymers in which monomers interact with each other through the excluded volume interaction. We make a perturbation expansion for the mean square radius of gyration of randomly branched polymers with annealed structures and identify the appropriate scaling variable. We further perform a renormalization group analysis that results in the ε expansion for the critical exponents of the radius of gyration ν=1/4+ε/36 and of the number of configurations θ=5/2-ε/12, which are consistent with the results of an earlier theory.
The behavior of liquid crystalline polymers in the interfacial region between the isotropic and nematic phases is investigated based on an inhomogeneous free-energy functional. A mean-field approximation is used for t...
The behavior of liquid crystalline polymers in the interfacial region between the isotropic and nematic phases is investigated based on an inhomogeneous free-energy functional. A mean-field approximation is used for the system of semiflexible polymers obeying the Saito-Takahashi-Yunoki description and interacting via the Onsager-type repulsive interaction. The density distribution of the polymers crossing the interface is computed by using a spherical-harmonics expansion. The calculated interfacial tension is consistent with the results of the scaling argument which is also presented in this paper.
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