Preparation of crystalline beta barium borate thin films on Sr2+-doped alpha barium borate substrates by liquid phase epitaxy

Thin films of beta barium borate have been prepared by liquid phase epitaxy on Si2+-doped alpha-BaB2O4 (alpha-BBO, the high temperature phase of barium berate) (001) and (110) substrates. The results of X-ray diffraction indicate that the films show highly (001) preferred orientation on (001)-oriented substrates while the films grown on (110) substrates are textured with (140) orientation. The crystallinity of these films was found to depend on growth temperature, rotation rate, dip time and orientation of substrate. Growth conditions were optimized to grow films with (001) orientation on (001) substrates reproducibly. The films show second harmonic generation of 400 nm light upon irradiation with 800 nm Ti: Sapphire femtosecond laser light. (c) 2005 Elsevier B.V. All rights reserved.

Deposition of ZnO thin films on (100) γ-LiAlO2 substrate

Optical properties for ZnO thin films grown on (100) γ-LiAlO2 (LAO) substrate by pulsed laser deposition method were investigated. The c-axis oriented ZnO films were grown on (100) γ-LiAlO2 substrates at the substrate temperature of 550 Celsius degrees. The transmittance of the films was over 85%. Peaks attributed to excitons were shown in absorption spectra, which indicated that thin films had high crystallinity. Photoluminescence spectra with the maximum peak at 540 nm were observed at room temperature, which seemed to be ascribed to oxygen vacancy in the ZnO films caused by diffusion of Li from the substrates into the films during the deposition.

Defects in LPE-grown beta-barium borate (beta-BaB2O4) thin films

Morphological defects in beta-barium borate (beta-BBO) thin films grown on Sr2+ -doped alpha-BBO substrates by liquid phase epitaxy (LPE) technique were studied by scanning electron micrograph (SEM), atomic force microscopy (AFM) and optical spectroscopy. The present results indicate that the main defects exit in beta-BBO thin films are microcracks and hollow structure. The formation of microcrack is due to the lattice mismatch and the difference of thermal expansion coefficients between substrate and film. The hollow structure might be caused during the combination of islands, which formed in the initial stage. (C) 2006 Elsevier GmbH. All rights reserved.

Structural and optical properties of a-plane ZnO thin films synthesized on γ-LiAlO2 (302) substrates by low pressure metal-organic chemical vapor deposition

Nonpolar a-plane (1120) ZnO thin films have been fabricated on gamma-LiAlO2 (302) substrates via the low-pressure metal-organic chemical vapor deposition. An obvious intensity variation of the E-2 mode in the Raman spectra indicates that there exhibits in-plane optical anisotropy in the a-plane ZnO thin films. Highly-oriented uniform grains of rectangular shape can be seen from the atomic force microscopy images, which mean that the lateral growth rate of the thin films is also anisotropic. It is demonstrated experimentally that a buffer layer deposited at a low temperature (200 degrees C) can improve the structural and optical properties of the epilayer to a large extent. (c) 2007 Elsevier B.V. All rights reserved.

Enhancement of near-band edge photoluminescence of ZnO thin films by employing MgF2 buffer layer

ZnO/MgF2/ZnO sandwich structure films were fabricated. The effects of a buffer layer on structure and optical properties of ZnO films were investigated by X-ray diffraction, photoluminescence, optical transmittance and absorption measurements. Measurement results showed that the buffer layer had the effects of improving the quality of ZnO films and releasing the residual stresses in the films. The near-band edge emissions of ZnO films deposited on the MgF2 buffer layer were significantly enhanced compared with those deposited on bare substrate due to the smaller lattice mismatch between MgF2 and ZnO than that between fused silica and ZnO. (c) 2006 Elsevier B.V. All rights reserved.

The study on the interface adhesion comparison of the MgF2, Al2O3, SiO2 and Ag thin films

Adhesion between the interface of pure silver thin film and three kinds of low refractive index coatings MgF2, Al2O3, SiO2 were compared in this article. The results indicated that the adhesion of Al2O3 and Ag was evidently superior to that of MgF2 and Ag, and the adhesion of MgF2 and Ag was evidently superior to that Of SiO2 and Ag. Reasons were analyzed accordingly. On the other hand, we compared the effect on the optical characteristic of Ag film when these three kinds of films were used as protective coatings and enhanced coatings. Considering the difference of the adhesion between Ag and MgF2, Al2O3, SiO2, suited uses are given for each other. © 2004 Elsevier B.V. All rights reserved.

Influence of buffer layer thickness on the structure and optical properties of ZnO thin films

A series of ZnO thin films were deposited on ZnO buffer layers by DC reactive magnetron sputtering. The buffer layer thickness determination of microstructure and optical properties of ZnO films was investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. XRD results revealed that the stress of ZnO thin films varied with the buffer layer thickness. With the increase of buffer layer thickness, the band gap edge shifted toward longer wavelength. The near-band-edge (NBE) emission intensity of ZnO films deposited on ZnO buffer layer also varied with the increase of thickness due to the spatial confinement increasing the Coulomb interaction between electrons and holes. The PL measurement showed that the optimum thickness of the ZnO buffer layer was around 12 nm. (c) 2005 Elsevier B.V. All rights reserved.

Influence of LiB3O5 structure on microstructure and optical properties of ZrO2, thin films prepared by electron beam evaporation

ZrO2 thin films were deposited bill using an electron beam evaporation technique on three kinds of lithium triborate (LiB3O5 or LBO) substrates with the surfaces at specified crystalline orientations. The influences of the LBO structure on the structural and optical properties of ZrO2 thin films are studied by spectrophotometer and x-ray diffraction. The results indicate that the substrate structure has obvious effects on the structural end optical properties of the film: namely. the ZrO2 thin film deposited on the X-LBO, Y-LBO and Z-LBO orients to m(-212), m(021) and o(130) directions. It is also found that the ZrO2 thin film with m(021) has the highest refractive index and the least lattice misfit.

Effective medium model for refractive indices of thin films with oblique columnar structure

The refractive indices of thin films, containing dielectric and voids in an oblique columnar structure, are, modelled in the quasi-static limit. The dielectric function is shown to be strongly dependent on the angle of incidence and on the columnar orientation for p-polarized light. This model is applied to model ZnS thin films with oblique columnar structures and the computed results have been given.

Extended effective medium model for refractive indices of thin films with oblique columnar structure

The refractive indices of thin films, containing dielectric and voids in an oblique columnar structure, are modeled by extended effective medium in the quasi-static limit. The dielectric function is shown to be strongly dependent on the angle of incidence and on the columnar orientation for p-polarized light. This model is applied to model ZrO2 thin films with oblique columnar structures and the computed results, with the Maxwell Garnett, the Bragg-Pippard, and the Bruggeman formalisms, have been given. (c) 2004 Elsevier B.V. All rights reserved.

Design of anisotropic reflector with birefringent thin films

A novel design for dielectric anisotropic mirrors with birefringent thin films for normal incidence is presented. This mirror consists of a stack of quarter-wave biaxial layers. The biaxial anisotropic layers can be fabricated by oblique deposition. The reflectance is different for two linear polarizations of light incidence on the mirrors. As a numerical example, the design is carried out on glass with TiO2 and ZrO2. These thin films could be applied to anisotropic reflective devices for lasers.

Optical, structural and laser-induced damage threshold properties of HfO2 thin films prepared by electron beam evaporation

We prepare HfO2 thin films by electron beam evaporation technology. The samples are annealed in air after deposition. With increasing annealing temperature, it is found that the absorption of the samples decreases firstly and then increases. Also, the laser-induced damage threshold (LIDT) increases firstly and then decreases. When annealing temperature is 473K, the sample has the highest LIDT of 2.17J/cm(2), and the lowest absorption of 18 ppm. By investigating the optical and structural characteristics and their relations to LIDT, it is shown that the principal factor dominating the LIDT is absorption.

Influence of different post-treatments on the structure and optical properties of zinc oxide thin films

Zinc oxide (ZnO) films with c-oriented were grown on fused quartz glass substrates at room temperature using dc reactive magnetron sputtering. The as-grown films were annealed at 700 degrees C in air and bombarded by ion beam, respectively. The effects of post-treatments on the structural and optical properties of the ZnO films were investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. The XRD spectra indicate that the crystal quality of ZnO films has been improved by both the post-treatments. Compared with the as-grown sample, both annealed and bombarded samples exhibited blueshift in the UV emission peaks, and a strong green emission was found in the annealed ZnO film. In both optical transmittance and absorption spectra, a blueshift of the band-gap edge was observed in the bombarded film, while a redshift was observed in the annealed film. (c) 2004 Elsevier B.V. All rights reserved.

Influences of CO2 laser irradiation on the structure and photoluminescence of zinc oxide thin films

CO2 laser irradiation experiments on ZnO thin films are reported. The structural, optical, luminescent and vibrational properties of the samples were investigated by X-ray diffraction (XRD), transmittance, photoluminescence (PL) and Raman measurements. XRD results show that the crystalline of the irradiated films was improved. The (002) peaks of irradiated ZnO films shift to. higher 20 angles due to the stress relaxation in the case of laser beam irradiation. From optical transmittance spectra, all films exhibit high transmittance in the visible range, the optical band edge of irradiated films showed a redshift compared with that of as-grown films. Compared with the as-grown films, the photoluminescence emission (in particular the relative intensities of visible emissions) intensities of irradiated samples enhanced. In the Raman scattering spectral both the A I. and E modes exhibited slight Raman blueshift. (c) 2005 Elsevier B.V. All rights reserved.