Nonlinear response and optical limiting in SrBi2Ta2O9 thin films

SrBi2Ta2O9 (SBT) thin films on quartz substrates were prepared by use of the pulsed-laser deposition technique. The nonlinear refractive indices, n(2), Of the SBT films were measured by use of z-scan techniques with picosecond pulses. Large negative nonlinear refractive indices of 3.84 and 3.58 cm(2)/GW were obtained for the wavelengths 532 nm and 1.064 mum, respectively. The two-photon absorption coefficient was determined to be 7.3 cm/GW for 532 nm. The limiting behavior of SBT thin film on a quartz substrate was investigated in an f/5 defocusing geometry by use of 38-ps-duration, 532-nm, 1.064-mum. laser excitation. (C) 2001 Optical Society of America.

Growth of beta barium borate (beta-BaB2O4) thin films on alpha barium borate (alpha-BaB2O4) substrates

Crystalline beta-BBO thin films have been successfully prepared on (001)-oriented Sr2+-doped alpha-BBO substrates using liquid phase epitaxy and pulsed laser deposition techniques. The films were characterized by X-ray diffraction and X-ray rocking curve (XRC). The present results manifest that the beta-BBO thin films grown on Sr2+-doped alpha-BBO substrates have larger degree of orientation f-value and smaller XRC FWHM than the ones grown on other reported substrates. Compared with other substrates, alpha-BBO has the same UV cutoff and the similar structure to beta-BBO. These results reveal that alpha-BBO single crystal may be a promising substrate proper to the growth of beta-BBO films. (c) 2005 Elsevier B.V. All rights reserved.

在Sr～2+α_BBO单晶衬底上生长β_BBO薄膜的研究

Crystalline beta-BBO thin films were successfully prepared on (001)-oriented Sr2+-doped alpha-BBO substrates by using liquid phase epitaxy, pulsed laser deposition and vapor transport equilibration techniques. The films were characterized by X-ray diffraction and X-ray rocking curve. The present results manifest that the beta-BBO thin films grown on Sr2+-doped alpha-BBO substrates have larger degree of orientation f value and smaller X-ray rocking curve FWHM than the ones grown on other reported substrates. Compared with other substrates, alpha-BBO has the similar structure, the same UV cutoff and the same chemical properties to beta-BBO. These results reveal that Sr2+-doped alpha-BBO single crystal may be a promising substrate proper to the growth of beta-BBO films.

在钛酸锶衬底上外延生长ZnO薄膜及其性能研究

用脉冲激光淀积法（PLD）在（111）面SrTiO3衬底上外延生长ZnO单晶薄膜。样品分别在衬底温度为350℃、500℃、600℃下外延生长。X射线衍射（XRD）的结果表明,所得的ZnO单晶薄膜结晶性能好,只出现（002）和（004）两个衍射峰,（002）峰的半高宽度（FWHM）为0.23°。在荧光光谱中我们只观察到来源于带边激子跃迁的强UV发射,并且随着生长温度的升高,紫外峰的强度逐渐增强。样品的SEM图像表明所得ZnO薄膜表面平整,晶粒均匀。衬底温度为600℃时,所得到的ZnO薄膜结构完整,晶粒尺寸最

γ-LiAIO2上非极性ZnO薄膜制备及其光谱性质研究

利用激光脉冲沉积（PLD）技术在（302）γ-LiAIO2衬底上成功生长了非极性的a面（112^-0）γZnO薄膜．衬底温度为350℃时，薄膜是混合取向（a向和C向），以c面ZnO为主，且晶粒尺寸分布很宽；提高温度达500℃，薄膜变为单一的（1120）取向，摇摆曲线半高宽O.65^o，晶粒尺寸分布趋窄，利用偏振透射谱可以明显看出其面内的各向异性．衬底温度650℃下制备的样品晶粒继续长大，虽然摇摆曲线半高宽变大，但光致发光谱（PL）带边发射峰半高宽仅为105meV，比在350℃，500℃下制备的样品小1／5

γ-LiAlO_2上a面ZnO薄膜的光谱特性研究

利用激光脉冲沉积(PLD)技术在(302)γ-LiAlO2衬底上成功生长了非极性的a面(1120)ZnO薄膜,光致发光谱(PL)带边发射峰半峰宽仅为115meV.研究了非极性ZnO薄膜光谱特性的面内各向异性,发现随着入射光偏振方向改变,在偏振透射光谱上,吸收边移动了20meV,这与A、B激子和C激子的能量差一致;而在拉曼光谱上,激发光偏振方向的改变导致E2模式的强度发生明显改变.

Benefits of current percolation in superconducting coated conductors

The critical currents of coated conductors fabricated by metal-organic deposition (MOD) on rolling-assisted biaxially textured substrates (RABiTS) and by pulsed laser deposition (PLD) on ion-beam assisted deposition (IBAD) templates have been measured as a function of magnetic field orientation and compared to films grown on single crystal substrates. By varying the orientation of magnetic field applied in the plane of the film, we are able to determine the extent to which current flow in each type of conductor is percolative. Standard MOD/RABiTS conductors have also been compared to samples whose grain boundaries have been doped by diffusing Ca from an overlayer. We find that undoped MOD/RABiTS tapes have a less anisotropic in-plane field dependence than PLD/IBAD tapes and that the uniformity of critical current as a function of in-plane field angle is greater for MOD/RABiTS samples doped with Ca. (C) 2005 American Institute of Physics.

Active glass-polymer superlattice structure for photonic integration.

We propose an all-laser processing approach allowing controlled growth of organic-inorganic superlattice structures of rare-earth ion doped tellurium-oxide-based glass and optically transparent polydimethyl siloxane (PDMS) polymer; the purpose of which is to illustrate the structural and thermal compatibility of chemically dissimilar materials at the nanometer scale. Superlattice films with interlayer thicknesses as low as 2 nm were grown using pulsed laser deposition (PLD) at low temperatures (100 °C). Planar waveguides were successfully patterned by femtosecond-laser micro-machining for light propagation and efficient Er(3+)-ion amplified spontaneous emission (ASE). The proposed approach to achieve polymer-glass integration will allow the fabrication of efficient and durable polymer optical amplifiers and lossless photonic devices. The all-laser processing approach, discussed further in this paper, permits the growth of films of a multitude of chemically complex and dissimilar materials for a range of optical, thermal, mechanical and biological functions, which otherwise are impossible to integrate via conventional materials processing techniques.

Glass-polymer superlattice for integrated optics

Glass and polymer interstacked superlattice like nanolayers were fabricated by nanosecond-pulsed laser deposition with a 193-nm-ultraviolet laser. The individual layer thickness of this highly transparent thin film could be scaled down to 2 nm, proving a near atomic scale deposition of complex multilayered optical and electronic materials. The layers were selectively doped with Er3\+ and Eu3\+ ions, making it optically active and targeted for integrated sensor application. © The Authors.

Structural and electrical properties of (110) ZnO epitaxial thin films on (001) SrTiO3 substrates

(110) oriented ZnO thin films were epitaxially prepared on (001) SrTiO3 single crystal substrates by a pulsed laser deposition method. The evolution of structure, surface morphology, and electrical conductivity of ZnO films was investigated on changing the growth temperature. Two domain configurations with 90 degrees rotation to each other in the film plane were found to exist to reduce the lattice mismatch between the films and substrates. In the measured temperature range between 80 K and 300 K, the electrical conductivity can be perfectly fitted by a formula of a (T) = sigma(0) + aT(b/2). implying that the electron-phonon scattering might have a significant contribution to the conductivity. (C) 2008 Elsevier Ltd. All rights reserved.

First-principles study of defects in CuGaO2

Using the first-principles methods, we study the electronic structure, intrinsic and extrinsic defects doping in transparent conducting oxides CuGaO2. Intrinsic defects, acceptor-type and donor-type extrinsic defects in their relevant charge state are considered. The calculation result show that copper vacancy and oxygen interstitial are the relevant defects in CuGaO2. In addition, copper vacancy is the most efficient acceptor. Substituting Be for Ga is the prominent acceptor, and substituting Ca for Cu is the prominent donors in CuGaO2. Our calculation results are expected to be a guide for preparing n-type and p-type materials in CuGaO2.

Effect of silver growth temperature on the contacts between Ag and ZnO thin films

Highly c-axis oriented ZnO thin films were deposited on Si substrates by the pulsed laser deposition (PLD) method. At different growth temperatures, 200 nm silver films as the contact metal were deposited on the ZnO thin films. The growth temperatures have great influence on the crystal quality of Ag films. Current-voltage characteristics were measured at room temperature. The Schottky contacts between Ag and ZnO thin films were successfully obtained when silver electrodes were deposited at 150A degrees C and 200A degrees C. Ohmic contacts were formed while the growth temperatures were lower than 150A degrees C or higher than 200A degrees C. After analysis, the forming of Ag/ZnO Schottky contacts was shown to be dependent on the appearance of the p-type inversion layer at the interface between Ag and ZnO layers.

Optical properties of aluminum-, gallium-, and indium-doped Bi4Ti3O12 thin films

Undoped and Al-, Ga-, and In-doped Bi4Ti3O12 thin films were prepared on fused quartz substrates by chemical solution deposition. Their microstructures and optical properties were investigated by x-ray diffraction and UV-visible-NIR spectrophotometer, respectively. The optical band-gap energies, Urbach energies, and linear refractive indices of all the films are derived from the transmittance spectrum. Following the single oscillator model, the dispersion parameters such as the average oscillator energy (E-0) and dispersion energy (E-d) are achieved. The energy band gap and refractive indices are found to decrease with introducing the dopants of Al, Ga, and In, which is useful for the band-gap engineering and optical waveguide devices. The refractive index dispersion parameter (E-0/S-0) increases and the chemical bonding quantity (beta) decreases in all the films compared with those of bulk. It is supposed to be caused by the nanosize grains in films. (c) 2009 American Institute of Physics. [DOI 10.1063/1.3138813]

Structural and optical properties of ZnO films on SrTiO3 substrates by MOCVD

ZnO films have been fabricated on (0 0 1), (0 1 1) and (1 1 1) SrTiO3 (STO) substrates by metal-organic chemical vapour deposition (MOCVD). It is interesting that the ZnO films on (0 0 1) and (0 1 1) STO substrates show polar and semipolar orientations, which are different from previous reports, while the same growing direction of polar ZnO with previous results is found on (1 1 1) STO. For the atomic arrangements, two orthogonal domains and a single domain are observed on (0 0 1) and (1 1 1) STO, respectively. Photoluminescence spectra show that every sample has a sharp near-band-edge emission peak at about 3.28 eV without any deep-level emission band between 1.5 and 2.8 eV, implying a high optical quality. A violet emission around 3.0 eV is observed only in ZnO films on (0 0 1) and (0 1 1) STO substrates grown at 600 degrees C, which is discussed briefly. Additionally, the semipolar ZnO does not weaken the emission efficiency along with the reduction in the polarization effect compared with polar ZnO. These results show that high-quality polar and semipolar ZnO films can be grown on STO substrates by MOCVD.

Effect of the variation of temperature on the structural and optical properties of ZnO thin films prepared on Si (111) substrates using PLD

ZnO thin films were prepared on Si (1 11) substrates at various temperatures from 250 to 700 degrees C using pulsed laser deposition (PLD) technique in order to investigate the structural and optical properties of the films. The structural and morphological properties of the films were investigated by XRD and SEM measurements, respectively. The quality of the films was improved with the increase of the temperature. By XRD patterns the FWHMs of the (0 0 2) peaks of the ZnO films became narrower when the temperatures were above 500 degrees C. The FWHMs of the peaks of (0 0 2) of the films were as narrow as about 0. 19 degrees when films were grown at 650 and 700 degrees C. This indicates the superior crystallinity of the films. The optical properties of the films were studied by photoluminescence spectra using a 325 nm He-Cd laser. The two strongest UV peaks were found at 377.9 nm from ZnO films grown at 650 and 700 degrees C. This result is consistent with that of the XRD investigation. Broad bands in visible region from 450 to 550 nm were also observed. Our works suggest that UV emissions have close relations with not only the crystallinity but also the stoichiometry of the ZnO films. (c) 2005 Elsevier Ltd. All rights reserved.