Structural, morphological and optical properties of ZnO thin films grown on gamma-LiAlO2 substrate by pulsed laser deposition

ZnO thin films were deposited on the substrates of (100) gamma-LiAlO2 at 400, 550 and 700 degrees C using pulsed laser deposition (PLD) with the fixed oxygen pressure of 20 Pa, respectively. When the substrate temperature is 400 degrees C, the grain size of the film is less than 1 mu m observed by Leitz microscope and measured by X-ray diffraction (XRD). As the substrate temperature increases to 550 degrees C, highly-preferred c-orientation and high-quality ZnO film can be attained. While the substrate temperature rises to 700 degrees C, more defects appears on the surface of film and the ZnO films become polycrystalline again possibly because more Li of the substrate diffused into the ZnO film at high substrate temperature. The photoluminescence (PL) spectra of ZnO films at room temperature show the blue emission peaks centered at 430 nm. We suggest that the blue emission corresponds to the electron transition from the level of interstitial Zn to the valence band. Meanwhile, the films grown on gamma-LiAlO2 (LAO) exhibit green emission centered at 540 nm, which seemed to be ascribed to excess zinc and/or oxygen vacancy in the ZnO films caused by diffusion of Li. from the substrates into the films during the deposition.

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.

用PLD法在MgO（100）衬底十生长ZnO薄膜的结构和光学特性

用脉冲激光沉积法在MgO（100）衬底上沉积了ZnO薄膜．衬底温度分别为400℃、550℃和700℃．利用X射线衍射（XRD）和光致发光谱（PL）对薄膜的结构和光学性能进行研究．x射线衍射的结果表明，在400℃和550℃下生长的ZnO薄膜具有高度c一轴择优取向．仉足当衬底温度升高到700℃时，薄膜由单一的择优取向变为有两个较强的择优取向．通过光致发光谱可以发现，在550℃下生长的ZnO薄膜具有强的紫外发射和窄的FWHM，并且紫外发光峰的强度与ZnO薄膜的结晶质量密切相关．

La crisis actual: una visión desde la transparencia y las medidas al respecto

[ES]Este trabajo tiene como objetivo fundamental, valorar si podría haber sido distinto el transcurso de la crisis actual de haber existido mayor transparencia. Al mismo tiempo, también se tratan de observar tanto las medidas actuales como futuras tomadas al respecto. Para ello, se plantean una serie de objetivos secundarios con la finalidad de conseguir de esta manera guiar el desarrollo ordenado de los acontecimientos. Uno de estos objetivos es ver cuál ha sido el origen y desarrollo de la crisis. Para ello, se ha planteado el surgimiento de las hipotecas subprime, base de un sistema que empezó a fallar cuando muchas de estas fueron insolventes. Además, la globalización del sistema financiero contribuyó a que el número de afectados por la titulización de estas hipotecas, un procedimiento muy habitual entonces, fuese mayor. De esta manera, la crisis que surgió originariamente en Estados Unidos pasó a afectar prácticamente a todos los demás países. Otros de los objetivos, están centrados alrededor de la falta de transparencia, sus consecuencias y las medidas paliativas tomadas tanto presentes como futuras. Todo esto se ha planteado acerca de varios aspectos, pero quizás los más importante son los que tratan acerca de la transparencia de los procedimientos bancarios, los cuales debido a su opacidad contribuyeron a generar desconfianza en el sistema interbancario, derivando en un colapso del mismo y en crisis de liquidez.

退火处理对ZnO薄膜发光特性的影响

用脉冲激光沉积法(PLD)在MgO(100)、a-Al2O3(0001)和MgAl2O4(111)衬底上沉积了ZnO薄膜，测量了它们的发射光谱，观察到430nm的蓝光发射，并研究了退火、衬底和激发波长对ZnO薄膜这一蓝光发射的影响。指出ZnO薄膜中430nm的蓝光发射是由锌填隙原子缺陷能级到价带顶能级间的跃迁以及电子从氧空位浅施主能级到价带顶能级间的跃迁两种机理共同作用的结果。在MgO衬底上沉积的ZnO薄膜在350nm光激发下蓝光发射峰最强。

Si（111）衬底上ZnO薄膜的磁控溅射法制备及表征

采用磁控溅射法在(111)单晶硅衬底上沉积了ZnO薄膜，并研究了退火温度对ZnO薄膜晶体质量、晶粒度大小、应力和光致发光谱的影响。X射线衍射(XRD)表明薄膜为高度c轴择优取向。不同退火温度下的ZnO薄膜应力有明显变化。应力分布最为均匀的退火温度为500℃。室温下对ZnO薄膜进行了光谱分析，可观测到明显的紫光发射(波长为380nm左右)。实验结果表明，用磁控溅射法在单晶硅衬底上能获得高质量的ZnO薄膜。

水热法ZnO晶体特征研究

ZnO具有优良的综合性能使其成为极有前途的下一代光电材料，水热法是一种重要的生长ZnO晶体的方法。本文对水热法生长的面积约150mm^2的ZnO晶体进行了报道，研究了晶体不同方向的生长速度、形貌特征和光学性能。X射线摇摆曲线表明晶体的质量较好。对于光学性质的分析表明晶体生长时加入H2O2能显著提高晶体的质量。494nm附近的发光带可能与氧空位有关。520nm的发光可能与Na或者Si所形成的杂质能级跃迁有关。

Al2O3衬底上生长ZnO薄膜的结构和光学特性

用脉冲激光沉积法在Al2O3（0001）衬底上沉积了ZnO薄膜。衬底温度分别为300℃、400℃、500℃、600℃和700℃。利用X射线衍射（XRD）和光致发光谱（PL）对薄膜的结构和光学性能进行研究。X射线衍射的结果表明在不同温度下生长的ZnO薄膜均具有高度c轴择优取向，衬底温度400℃时，膜的应力较小质量较高。ZnO薄膜有很强的紫外发光峰，紫外发光峰的强度与衬底温度密切相关，并发现当衬底温度从300℃增到400℃时，紫外发射峰出现6nm的蓝移。

退火对Si（111）衬底上ZnO薄膜的结构和发光特性的影响

采用磁控溅射法在硅（111）衬底上制备了C轴高度取向的ZnO薄膜，并研究了退火温度和氧气气氛对ZnO薄膜晶体质量、晶粒度大小和光致发光谱的影响。X射线衍射表明，所有薄膜均为高度C轴择优取向，当退火温度低于900℃时，随着退火温度的升高，薄膜的取向性和结晶度都明显提高。室温下对ZnO薄膜进行了光谱分析，退火后的样品均可观测到明显的紫光发射。在一定的退火温度范围内，还可以观测到明显的紫外双峰。空气中退火的样品，当退火温度达到或高于600℃还可观测到绿光发射。实验结果表明，发光峰强度随退火温度和氧气气氛不同而不

Annealing effects of sapphire substrate on properties of ZnO films grown by magnetron sputtering

The annealing effects of sapphire substrates on the quality of epitaxial ZnO films grown by dc reactive magnetron sputtering were studied. The atomic steps formed on (0001) sapphire (alpha-Al2O3) substrates surface by annealing at high temperature were analyzed by atomic force microscopy. Their influence on the growth of ZnO films was examined by X-ray diffraction and photoluminescence measurements. Experimental results indicate that the film quality is strongly affected by annealing treatment of the sapphire substrate surface. The optimum annealing temperature of sapphire substrates for ZnO grown by magnetron sputtering is 1400 degrees C for 1 h in air.

Nonpolar a-plane ZnO films fabricated on (302)gamma-LiAlO2 by pulsed laser deposition

Nonpolar a-plane (1 1 2 0) ZnO films are fabricated on (3 0 2)gamma-LiAlO2 substrate by pulsed laser deposition. When substrate temperature is low, c-plane ZnO is dominant. As growth temperature increases to similar to 500 degrees C, pure (1 1 2 0)-oriented ZnO film can be obtained. The X-ray rocking curve of a-plane ZnO film broadens sharply when growth temperature is up to similar to 650 degrees C; such a broadening may be related to the anisotropic lateral growth rate of (1 12 0)-oriented ZnO grains. Atomic force microscopy reveals the surface morphology changes of ZnO films deposited at different temperatures. Raman spectra reveal that a compressive stress exists in the a-plane ZnO film. (C) 2007 Published by Elsevier B.V.

Low-temperature hydrothermal growth of oriented [0001] ZnO film

Well-aligned ZnO films have been successfully prepared by using low-temperature hydrothermal approach on (0001) sapphire substrates that were pre-coated with a ZnO nano-layer by dip-coating. The characterizations of scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicate that the ZnO films consist of hexagonal rods that grow along the c axis based on the sapphire substrates. It is found that the size of ZnO rods can be adjusted by an aqueous solution with some methenamine. (c) 2006 Elsevier B.V. All rights reserved.

Homoepitaxial growth of ZnO films via low-temperature liquid-phase epitaxy

Homoepitaxial ZnO films have been grown via liquid-phase epitaxy (LPE) on (000 1) oriented ZnO substrates. X-ray rocking curve revealed the high quality of the ZnO films with a FWHM of 40 arc sec. Films of thickness about 20 gm were gown in the temperature range 700-720 degrees C. The growth rate of ZnO films was estimated to be 0.3 mu m h(-1). Atomic force microscope analysis showed that the surface roughness of ZnO films was very low, which further confirmed the high crystallinity of ZnO films. (c) 2006 Elsevier B.V. All rights reserved.

Spectroscopic properties of Nd3+:(La,Sr)(Al,Ta)O-3 crystal

A new laser crystal Nd3+:(La, Sr)(Al, Ta)O-3 (abbreviated as Nd3+:LSAT) has been grown by the conventional Czochralski method. The absorption and luminescence spectra of trivalent neodymium in Nd3+:LSAT crystal were measured at room temperature. The value of absorption and emission cross-section was calculated. The Judd-Ofelt analysis was applied to the crystal to get the phenomenological parameters (Omega(i), i = 2,4,6), the line strengths, the radiative transition rates, the branching ratios and the radiative lifetime. (C) 2006 Elsevier B.V. All rights reserved.

Yb∶Y3Al5O12晶体晶格振动光谱的研究

采用提拉法生长Y3Al5O12(YAG)晶体和Yb3+掺杂原子数分数分别为5%, 10%, 15%, 20%, 25%, 50%和100%的Yb∶Y3Al5O12(Yb∶YAG)晶体。系统表征和分析了Yb3+掺杂浓度对拉曼光谱的影响。随着Yb3+掺杂浓度的增加,晶体的振动模式没有明显的变化,晶体结构没有改变;在370 cm-1和785 cm-1附近,振动吸收峰的半峰全宽逐渐增大。分析得出,Yb3+掺杂浓度对晶体的晶格、对称性、荧光寿命均有影响,从而可能影响到晶体的光谱和激光性能。