The response of porous Al2O3 probed to nanoindentation

The response of porous Al2O3 to nanoindentation was investigated at microscopic scales (nm-mu m) and under ultra-low loads from 5 to 90 mN with special attention paid to the dependence of the load-depth behaviour to sample porosity. It was found that the load-depth curves manifest local responses typical of the various porous structures investigated. This is particularly clear for the residual deformation after load removal. Similarly, the limited mean pressure of the sample containing small grains and interconnected pores is consistent with its porous structure. By comparison, the samples with larger grain size and various porous structures exhibit higher pressures and smaller residual deformations that can be attributed to the mechanical response of the solid phase. (C) 2007 Elsevier B.V. All rights reserved.

Plastic Deformation Of Nanocrystalline Nickel

A high-resolution electron microscopy study has uncovered the plastic behavior of accommodating large strains in nanocrystalline (NC) Ni subject to cold rolling at liquid nitrogen temperature. The activation of grain-boundary-mediated-plasticity is evidenced in NC-Ni, including twinning and formation of stacking fault via partial dislocation slips from the grain boundary. The formation and storage of 60A degrees full dislocations are observed inside NC-grains. The grain/twin boundaries act as the barriers of dislocation slips, leading to dislocation pile-up, severe lattice distortion, and formation of sub-grain boundary. The vicinity of grain/twin boundary is where defects preferentially accumulate and likely the favorable place for onset of plastic deformation. The present results indicate the heterogeneous and multiple natures of accommodating plastic strains in NC-grains.

Effect of humidity on microstructure and properties of YBCO film prepared by TFA-MOD method

Epitaxial YBCO superconducting films were deposited on the single crystal LaAlO3 (001) substrate by metal organic deposition method. All YBCO films were fired at 820 degrees C in humidity range of 2.6%-19.7% atmosphere. Microstructure of YBCO thin films was analyzed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Superconducting properties of YBCO films were measured by four-probe method. XRD results showed that the second phase (such as BaF2)and a-axis-oriented grains existed in the films prepared at 2.6% humidity condition; a-axis-oriented grains increased in the film prepared at higher than 4.2% humidity condition; almost pure c-axias-oriented grains existed in the films fired at 4.2% humidity condition. Morphologies of the YBCO films showed that all films had a smooth and crack-free surface. YBCO film prepared at 4.2% humidity condition showed J(c) value of 3.3 MA/cm(2) at 77 K in self-field.

强散射体产生的像面散斑对比度与随机表面及成像系统关系的研究

We study the statistical properties of the image speckles produced by strong-scattering objects in the 4f optical imaging system. Using the generic expression of the complex amplitude of speckles and the approximation of the double-exponential function, we first obtain the ensemble average of the speckle intensity. Then we derive the variance of the speckle intensity based on the rotational transformation of the real and imaginary parts of the complex amplitude of speckles. We finally obtain the expression for the contrast of the. speckles, which is explicitly related to the statistical parameters of random surface and to the parameters of the imaging system. Our results are an obvious improvement compared with those reported in the literature, where the relations including such implicit quantities as the average size of the scattering grains of the random surface and the number of scattering grains are usually used. The results of this paper would be helpful for the characterization of random surface by speckle contrast.

Crystallization of amorphous Ge2Sb2Te5 films induced by a single femtosecond laser pulse

Crystallization is achieved in amorphous Ge2Sb2Te5 films upon irradiation with a single femtosecond laser pulse. Transmission electron microscopy images evidence the morphology of the crystallized spot which depends on the fluence of the ferntosecond laser pulse. Fine crystalline grains are induced at low fluence, and the coarse crystalline grains are obtained at high fluence. At the damage fluence, ablation of the films occurs. (C) 2004 Elsevier Ltd. All rights reserved.

河南南阳独山玉的岩相结构和无损分析(英文)

河南南阳独山玉的开采历史可以追溯到新石器时代,在我国玉文化中占有重要地位。鉴于当前对独山玉进行无损鉴别的方法较少,利用质子激发X荧光技术(proton induced X-ray emission,PIXE)、X射线衍射(X-ray diffraction,XRD)、激光Raman光谱(laser Raman spectroscopy,LRS)和扫描电子显微镜(scanning electron microscope,SEM)等技术对河南南阳独山玉料进行岩石矿物学分析。结果表明:独山玉主要由钙长石矿物构成,晶粒细小且结合紧密的显微结构与独山玉具有极高的稳定性有较大关系。PIXE,XRD和Raman技术作为无损分析方法为鉴定独山玉提供了准确有效的方法,为研究贵重的古玉样品提供了技术支持。

MOCVD growth and properties of ZnO thin films on LiNbO3 substrates

ZnO thin films were grown on (0001)LiNbO3 substrates by the MOCVD technique. The substrate temperatures during growth were changed from 400 to 600 degrees C. The X-ray diffraction (XRD) pattern of the ZnO film showed a strong [002] reflection peak, and the peak intensity was dependent on substrate temperature. The ZnO columnar grains were highly oriented along the (002) direction when the film processing temperature was 600 degrees C. The optical transmission and PL results also indicated that highest crystalline quality of the ZnO films could be obtained at elevated temperatures. (c) 2005 Elsevier B.V. All rights reserved.

Effect of La2O3 on microstructure and transmittance of transparent alumina ceramics

Optically transparent alumina ceramics were fabricated by conventional process and sintered without pressure in H-2 atmosphere. The results indicate that relative densities of alumina specimens increase to theoretical densities (T. D.) with increasing content of La2O3. With increasing holding time during sintering, much less pores and larger grains were found in the sintered alumina samples. Higher transmittance was achieved in alumina codoped with MgO and La2O3 as compared with that doped with MgO only. The total-transmittance of alumina sample is up to 86% at a wavelength range of 300 - 800 nm.

Diode-pumped Yb : YAG ceramic laser

Transparent polycrystalline Yb:YAG ceramics were fabricated by solid-state reactive sintering a mixture of commercial Al2O3, Y2O3, and Yb2O3 powders. The powders were mixed in ethanol and doped with 0.5 wt% tetraethoxysilane, dried, and pressed. Pressed samples were sintered at 1730 degrees C in vacuum. Transparent fully dense samples with grain sizes of several micrometers were obtained. The phase from 1500 degrees to 1700 degrees C was important for the grain growth, in which the grains grew quickly and a mass of pores were eliminated from the body of the sample. Annealing was an important step to remove the vacancies of oxygen and transform Yb2+ to Yb3+. The 1 at.% Yb:YAG ceramic sample was pumped by a diode laser to study the laser properties. The maximum output power of 1.02 W was obtained with a slope efficiency of 25% at 1030 nm. The size of the lasering sample was 4 mm x 4 mm x 3 mm.

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.

Synthesis of CaCu3Ti4O12 ceramic via a sol-gel method

The novel nano-ultrafine powders for the preparation of CaCu3Ti4O12 ceramic were prepared by the sol-gel method and citrate auto-ignition method. The obtained precursor powders were pressed, sintered at 1000 degrees C to fabricate microcrystal CaCu3Ti4O12 ceramic. The microcrystalline phase of CaCu3Ti4O12 was confirmed by X-ray powder diffraction (XRD). The morphology and size of the grains of the powders and ceramics under different heat treatments were observed using scanning electron microscopy (SEM). The relative dielectric constant of the ceramic sintered at 1000 degrees C was measured with a magnitude of more than 10(4) at room temperature, which was approaching to those of Pb-containing complex perovskite ceramics, and the loss tangent was less than 0.20 in a broad frequency region. The relative dielectric constant and loss tangent were also compared with that of CaCu3Ti4O12 ceramic prepared by other reported methods. (c) 2006 Elsevier B.V. All rights reserved.

Yb：YAG透明陶瓷的制备和激光输出

制备了高质量的Yb：YAG透明陶瓷．Yb：YAG透明陶瓷的晶粒尺寸为10μm左右且分布均匀，晶界处和晶粒中没有杂质、气孔的存在．Yb：YAG样品中所有元素分布均匀，不同的晶粒间，晶粒和晶界间成分是一致的，没有出现成分的偏析．4mm厚样品的透过率为80％．LD泵浦获得了波长为1030nm，最大功率为268mW的连续激光输出．

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

Fabrication and spectral properties of Nd3+-doped yttrium lanthanum oxide transparent ceramics

Transparent 1 at% Nd3+:Y1.9La0.1O3 ceramics were fabricated with nanopowders prepared by carbonate coprecipitation method. The powder compacts were sintered in H-2 atmosphere at 1550 degrees C for 30 h. The Nd3+:Y1.9La0.1O3 ceramics display uniform grains of about 50 mu m and high transparency. The highest transmittance of the ceramics reaches 67%. The strongest absorption peak is in the wavelength of 820 nm with absorption cross section of 2.48 x 10(-20) cm(2). The absorption is still high at LD wavelength 806 nm with absorption cross section of 1.78 x 10(-20) cm(2) and broad full width at half maximum (FWHM) of about 6.3 nm. The strongest emission peak was centered at 1078 nm with large stimulated emission cross section of 9.63 x 10(-20) cm(2) and broad FWHM of about 7.8 nm. The broad absorption and emission bandwidth of Nd3+:y(1.9)La(0.1)O(3) transparent ceramics are favorable to achieve the miniaturized LD pumping apparatus and ultrashort modelocked pulse laser output, respectively. (c) 2007 Elsevier B.V. All rights reserved.

Growth and characterization of ZnO films on (0 0 1), (1 0 0) and (0 1 0) LiGaO2 substrates

ZnO films were fabricated on LiGaO2 (0 0 1), (10 0) and (0 10) planes by RF magnetron sputtering. The structural, morphological and optical properties of as-grown ZnO films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectra and photoluminescence (PL) spectra. It is found that the orientation of ZnO films is strongly dependent on the substrate plane. [0 0 0 11, [1 (1) over bar 00] and [11 (2) over bar0] oriented ZnO films are deposited on LiGaO2 (001), (100) and (010), respectively. AFM shows the (0001) ZnO film consists of well-aligned regular hexagonal grains. Raman spectra reveal a tensile stress in the (0 0 0 1) ZnO film and a compressive stress in (110 0) and (112 0) ZnO films. PL spectra of all ZnO films exhibit only a near-band-edge UV emission peak. (C) 2008 Elsevier B.V. All rights reserved.