Enhancement of near-band-edge photoluminescence of ZnO thin films in sandwich configuration at room temperature

ZnO/ITO/ZnO sandwich structure films were fabricated. The effects of buffer layer on the structure and optical properties of ZnO films were investigated by x-ray diffraction (XRD), photoluminescence, optical transmittance, and absorption measurements. XRD spectra indicate that a buffer layer has the effects of lowering the grain orientation of ZnO films and increasing the residual stresses in the films. The near-band-edge emissions of ZnO films deposited on both single indium tin oxide (ITO) buffer and ITO/ZnO double buffers are significantly enhanced compared with that deposited on a bare substrate due to the quantum confinement effect. (C) 2006 American Institute of Physics.

The topological configuration and conformational analysis of mRNA in translation

The theoretical model construction of mRNA hairpin structure and single-stranded structure as well as the simulation studies on RNA structure determined by the X-ray crystal diffraction and nuclear magnetic resonance revealed that in translation, after mRNA being unfolded into single-stranded structure, its topological configuration was closely correlative with the original hairpin structure. The conformational features of single-stranded mRNA appeared as helical regions alternating with curly regions to different extents, which might exert the influence on the folding of nascent polypeptide by various regulating effects including different translational rates.

The quantum tunnelling between two-component Bose-Einstein condensates in a double-well configuration

We examine in terms of exact solutions of the time-dependent Schrodinger equation, the quantum tunnelling process in Bose-Einstein condensates of two interacting species trapped in a double well configuration. Based on the two series of time-dependent SU(2) gauge transformations, we diagonalize the Hamilton operator and obtain analytic time-evolution formulas of the population imbalance and the berry phase. the particle population imbalance (a(L)(+)aL - a(R)(+)a(R)) of species A between the two wells is studied analytically.

The quantum tunneling between two-component Bose-Einstein condensates in a double-well configuration

In terms of exact solution of the time-dependent Schrodinger equation. we examine the quantum tunneling process in Bose condensates of two interacting species trapped in a double well configuration. We use the two series of time-dependent SU(2) gauge transformation to diagonalize the Hamilton operator obtain analytic time-evolution formulas of the population imbalance and the berry phase. The particle population imbalance (a(L)(+)a(L) - a(R)(+)a(R)) of species A between the two wells is studied analytically.

A high-performance Si-based MOS electrooptic phase modulator with a shunt-capacitor configuration

A novel Si-based metal-oxide-semiconductor (MOS) electrooptic phase modulator including two shunt oxide layer capacitors integrated on a silicon-on-insulator (SOI) waveguide is simulated and analyzed. The refractive index near the two gate oxide layers is modified by the free carrier dispersion effect induced by applying a positive bias on the electrodes. The theoretical calculation of free carrier distribution coupled with optical guided mode propagation characteristics has been carried out. The influence of the structure parameters such as the width and the doping level of the active region are analyzed. A half-wave voltage V-pi = 4 V is demonstrated with an 8-mm active region length and a 4-mu m width of an inner rib under an accumulation mode. When decreasing the inner rib width to 1 mu m, the phase modulation efficiency is even higher, and the rise and fall times reach 50 and 40 ps, respectively, with a 1.0 x 10(17) cm(-3) doping level in the active region.

Enhanced photocatalytic activity of TiO2 nano-structured thin film with a silver hierarchical configuration

TiO2 sol-gels with various Ag/TiO2 molar ratios from 0 to 0.9% were used to fabricate silver-modified nano-structured TiO2 thin films using a layer-by-layer dip-coating (LLDC) technique. This technique allows obtaining TiO2 nano-structured thin films with a silver hierarchical configuration. The coating of pure TiO2 sol-gel and Ag-modified sol-gel was marked as T and A, respectively. According to the coating order and the nature of the TiO2 sol-gel, four types of the TiO2 thin films were constructed, and marked as AT (bottom layer was Ag modified, surface layer was pure TiO,), TA (bottom layer was pure TiO,, surface layer was Ag modified), TT (pure TiO, thin film) and AA (TiO, thin film was uniformly Ag modified). These thin films were characterized by means of linear sweep voltammetry (LSV), X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy and transient photocurrent (I-ph). LSV confirmed the existence of Ago state in the TiO, thin film. SEM and XRD experiments indicated that the sizes of the TiO,, nanoparticles of the resulting films were in the order of TT > AT > TA > AA, suggesting the gradient Ag distribution in the films. The SEM and XRD results also confirmed that Ag had an inhibition effect on the size growth of anatase nanoparticles. Photocatalytic activities of the resulting thin films were also evaluated in the photocatalytic degradation process of methyl orange. The preliminary results demonstrated the sequence of the photocatalytic activity of the resulting films was AT > TA > AA > TT. This suggested that the silver hierarchical configuration can be used to improve the photocatalytic activity of TiO2 thin film.

Giant Goos-Hanchen displacement enhanced by dielectric film in frustrated total internal reflection configuration

It is predicted that the Goos-Hanchen displacement in the usual frustrated total internal reflection configuration can be resonantly enhanced greatly by coating a dielectric thin film onto the surface of the first prism when the angle of incidence is larger than the critical angle for total reflection at the prism-vacuum interface and is smaller than but close to the critical angle for total reflection at the prism-film interface. Theoretical analysis shows that the displacement of transmitted beam is about half the displacement of reflected beam in the thick limit of the vacuum gap between the two prisms. This is to be compared with the relation in the usual symmetric double-prism configuration that the displacement of transmitted beam is equal to the displacement of reflected beam. Numerical simulations for a Gaussian incident beam of waist width of 100 wavelengths reveal that when the dielectric thin film is of the order of wavelength in thickness, both the reflected and transmitted beams maintain well the shape of the incident beam in the thick limit of the vacuum gap. So largely enhanced displacements would lead to applications in optical devices and integrated optics. (c) 2007 American Institute of Physics.

Large positive and negative lateral displacements from total internal reflection configuration with a weakly absorbing dielectric film

It is theoretically shown that the simultaneously large positive and negative lateral displacements will appear when the resonant condition is satisfied for a TE-polarized light beam reflected from the total internal reflection configuration with a weakly absorbing dielectric film. Appearance of the enhanced negative lateral displacement is relative to the incidence angle, absorption of the thin Elm and its thickness. If we select an appropriate weakly absorbing dielectric film and its thickness, the simultaneously enhanced positive and negative lateral displacements will appear at different resonant angles. These phenomena may lead to convenient measurements and interesting applications in optical devices.

Large and negative lateral displacement in an active dielectric slab configuration

We investigate the large negative lateral displacements of TE polarized light beams reflected from or transmitted through an active slab surrounded by transparent medium. The large negative displacements can be achieved when the incidence angle of the beam is less than but close to the critical angle for total reflection. It is also shown that both the reflectivity and transmissivity of the beam that correspond to the large negative displacements can be enhanced by active medium. These phenomena may lead to convenient measurements and interesting applications in optical devices. (c) 2006 Elsevier B.V. All rights reserved.

Prediction of simultaneously large and opposite generalized Goos-Hanchen shifts for TE and TM light beams in an asymmetric double-prism configuration

It is predicted that large and opposite generalized Goos-Hanchen (GGH) shifts may occur simultaneously for TE and TM light beams upon reflection from an asymmetric double-prism configuration when the angle of incidence is below but near the critical angle for total reflection, which may lead to interesting applications in optical devices and integrated optics. Numerical simulations show that the magnitude of the GGH shift can be of the order of beam's width.

Magnetoexcitonic optical absorption in semiconductors under strong magnetic fields and intense terahertz radiation in the Voigt configuration

The magnetoexcitonic optical absorption of a GaAs bulk semiconductor driven by a terahertz (THz) field is investigated numerically. The method of the solution of the initial-value problem, in combination with the perfect matched layer technique, is used to calculate the optical susceptibility, with Coulomb interaction, Landau quantization, and THz fields involved nonperturbatively. It shows that there appear replicas and sidebands of magnetoexciton of different Landau levels, which greatly enrich the magneto-optical spectrum in the presence of a driving THz field. Copyright (C) EPLA, 2008.