INTERFACIAL FORMATION PROCESS AND REACTIONS BETWEEN AU AND HYDROGENATED AMORPHOUS SI STUDIED BY XPS AND AES

Interfacial formation processes and reactions between Au and hydrogenated amorphous Si have been studied by photoemission spectroscopy and Auger electron spectroscopy. A three-dimensional growth of Au metal cluster occurs at initial formation of the Au/a-Si:H interface. When Au deposition exceeds a critical time, Au and Si begin interdiffusing and react to create an Au-Si alloy region. Annealing enhances interdiffusion and a Si-rich region exists on the topmost surface of Au films on a-Si:H.

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.

固氮酶钼铁蛋白金属原子簇的拆卸与组装的研究

将棕色固氮菌(Azotobacter vinelandii)固氮酶钼铁蛋白与邻菲罗啉和O2或邻非罗啉和尿素保温并经Sephadex G-25柱层析，可分别得到部分或高度缺失P—cluster和FcMoco的“不全蛋白”。其中，部分缺失金属原子簇的蛋白与含V、Mn、Cr的重组液重组后，所得相应的重组蛋白的底物还原活性及吸收光谱和圆二色(CD))谱虽均得到明显恢复，但与还原钼铁蛋白[MoFe (R)]相比又不尽相同：与含V重组液重组的蛋白的底物还原特性与VFe蛋白相似，波谱特性与MoFe (R)有所不同;分别与含Mn和Cr重组液重组的蛋白的底物还原特性与MoFe(R)相似，而波谱特性却与MoFe(R)有较大差异。高度缺失金属原子簇的蛋白分别与含Mo、Mn、Cr重组液重组后，所得相应的重组蛋白的乙炔还原活性虽都有明显的恢复，但与MoFe(R)相比仍相差较大;当与含钼重组液重组后，它的吸收光谱、可见CD谱及天然电泳图谱均可得到明显恢复，而紫外CD谱却与其乙炔还原活性一样，只能得到部分恢复。 根据上述实验结果，我们提出：(1)钼铁蛋白的金属原子簇与其构象密切相关;(2)部分或高度缺失金属原子簇的蛋白与重组液重组的机理——“零件组装”的基本内容;(3)钼原子在FeMoco中的可被取代性及不处于中心位置;(4)还原M oFe蛋白中Fe原子的价态不尽相同。

Oxidative activation of light alkanes on dense ionic oxygen conducting membranes

The oxidative dehydrogenation of ethane to ethylene (ODHE) has been studied in a catalytic membrane reactor (CMR) using a dense mixed ionic oxygen and electronic conducting perovskite membrane Ba0.5Sr0.5Co0.8Fe0.2O3-&. At 1080K, an ethylene yield of 66% was obtained with the bare membrane. After Pd cluster deposition, the ethylene yield reached 76% at 1050K. Ni cluster deposition led to a decrease of ethane conversion compared to the bare membrane without changing ethylene selectivity.

One step to detect the latent fingermarks with gold nanoparticles

A simple and environment friendly chemical route for detecting latent fingermarks by one-step single-metal nanoparticles deposition method (SND) was achieved successfully on several non-porous items. Gold nanoparticles (AuNPs) synthesized using sodium borohydride as reducing agent in the presence of glucose, were used as working solution for latent fingermarks detection. The SND technique just needs one step to obtain clear ridge details in a wide pH range (2.5-5.0), whereas the standard multi-metal deposition (MMD) technique requires six baths in a narrow pH range (2.5-2.8). The SND is very convenient to detect latent fingermarks in forensic scene or laboratory for forensic operators. The SND technique provided sharp and clear development of latent fingermarks, without background staining, dramatically diminished the bath steps.

Selective penetration of liquid-phase organic probe molecules into SAM of 2-mercapto-3-n-octylthiophene

An inherently disorganized self-assembled monolayer (SAM) of 2-mercapto-3-n-octylthiophene (MOT) has been formed on a gold bead electrode from its dilute ethanolic solution. The disorganization of the monolayer is attributed to the loose packing of the aliphatic chains of the MOT adsorbates, which results from a large difference in dimension/or cross-sectional area between the head (thiophene thiolate) and the tail (alkane chain) groups. Electrochemical measurements including ac impedance spectroscopy and metal underpotential deposition have shown that the monolayer is almost pinhole free. However, the MOT SAM can be penetrated by an organic probe molecule with affinity for the alkane chain part of the monolayer. Some typical probe molecules with different size and hydrophilicity have been employed to assess the permselectivity of the monolayer. Measurement results demonstrate that the ability of the employed probe molecules to penetrate into the monoalyer is mainly dominated by their hydrophilicity/or hydrophobicity. The results presented here suggest the potential application of MOT monoalyer to effectively modify the electrode surface for several research areas such as electrochemical sensors, electrocatalysis, electroanalysis, and supported hybrid bilayer membranes.

Catena-Poly[[[tetra-mu(2)-aqua-heptaaqua-(mu(2)-benzene-1,3,5-tricarboxylato)-mu(3)-hydroxido-trinickel(II)sodium]-mu(4)-benzene-1,3,5-tricarboxylato]sesqui-hydrate]

The title coordination polymer, {[Ni3Na(OH)(C9H3O6)(2)( H2O)(11)] center dot 1.5H(2)O}(n), is built up from three independent Ni-II ions and one Na-I cation bridged by benzene-2,4,6-tricarboxylate ( BTC) ligands and water molecules. Three Ni-II ions are bridged by three bidentate carboxylate groups of three BTC ligands, two aqua ligands and one OH- unit, to form a trinuclear metal cluster. The Na-I cation is bonded to the Ni-II cluster by two bridging water molecules. One of the three BTC ligands bridges neighbouring clusters into one-dimensional chains, which are further connected through a complex hydrogen-bonding scheme, forming a three-dimensional suprastructure. The title complex is isomorphous with the previously reported Co-II complex.

A micromechanical model of influence of particle fracture and particle cluster on mechanical properties of metal matrix composites

A general analytical model for a composite with an isotropic matrix and two populations of spherical inclusions is proposed. The method is based on the second order moment of stress for evaluating the homogenised effective stress in the matrix and on the secant moduli concept for the plastic deformation. With Webull's statistical law for the strength of SiCp particles, the model can quantitatively predict the influence of particle fracture on the mechanical properties of PMMCs. Application of the proposed model to the particle cluster shows that the particle cluster has neglected influence on the strain and stress curves of the composite. (C) 1998 Elsevier Science B.V.

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.

Characterization of m-plane ZnO thin film on gamma-LiAlO2 (100) substrate by metal-organic chemical vapor deposition

Non-polar (1 (1) over bar 00)m-plane ZnO thin film has been prepared on gamma-LiAlO2 (100)substrate via the low pressure metal organic chemical vapor deposition. Obvious intensity variation of the E-2 mode in the polarized Raman spectra and the absorption edge shift in the polarized optical transmission spectra indicate that the m-plane film exhibits optical anisotropy, which have applications in certain optical devices, such as the UV modulator and polarization-dependent beam switch. From the atomic force microscopy images, highly-oriented uniform-sized grains of rectangular shape were observed. (c) 2008 Elsevier B.V. All rights reserved.

Photoluminescence and lasing properties of InAs/GaAs quantum dots grown by metal-organic chemical vapour deposition

Photoluminescence (PL) and lasing properties of InAs/GaAs quantum dots (QDs) with direrent growth procedures prepared by metalorganic chemical vapour deposition are studied. PL measurements show that the low growth rate QD sample has a larger PL intensity and a narrower PL line width than the high growth rate sample. During rapid thermal annealing, however, the lowgrowth rate sample shows a greater blue shift of PL peak wave length. This is caused by the larger InAs layer thickness which results from the larger 2-3 dimensional transition critical layer thickness for the QDs in the low-growth-rate sample. A growth technique including growth interruption and in-situ annealing, named indium flush method, is used during the growth of GaAs cap layer, which can flatten the GaAs surface effectively. Though the method results in a blue shift of PL peak wavelength and a broadening of PL line width, it is essential for the fabrication of room temperature working QD lasers.

Characterization of ZnMgO hexagonal-nanotowers/films on m-plane sapphire synthesized by metal organic chemical vapour deposition

ZnMgO hexagonal-nanotowers/films grown on m-plane sapphire substrates were successfully synthesized using a vertical low-pressure metal organic chemical vapour deposition system. The structural and optical properties of the as-obtained products were characterized using various techniques. They were grown along the non-polar [1 0 (1) over bar 0] direction and possessed wurtzite structure. The ZnMgO hexagonal-nanotowers were about 200 nm in diameter at the bottom and 120 nm in length. Photoluminescence and Raman spectra show that the products have good crystal quality with few oxygen vacancies. With Mg incorporation, multiple-phonon scattering becomes weak and broad, and the intensities of all observed vibrational modes decrease. The ultraviolet near band edge emission shows a clear blueshift (as much as 100 meV) and broadening compared with that of pure ZnO products.

Photoluminescence properties of tensile-strained GaAsP/GaInP single quantum wells grown by metal organic chemical vapor deposition

Tensile-strained GaAsP/GaInP single quantum well (QW) laser diode (I-D) structures have been grown by low-pressure metal organic chemical vapor deposition (LP-MOCVD) and related photoluminescence (PL) properties have been investigated in detail. The samples have the same well thickness of 16 nm but different P compositions in a GaAsP QW. Two peaks in room temperature (RT) PL spectra are observed for samples with a composition larger than 0.10. Temperature and excitation-power-dependent PL spectra have been measured for a sample with it P composition of 0.15. It is found that the two peaks have a 35 meV energy separation independent of temperature and only the low-energy peak exists below 85 K. Additionally, both peak intensities exhibit a monotonous increase as excitation power increases. Analyses indicate that the two peaks arise from the intrinsic-exciton recombination mechanisms of electron-heavy hole (e-hh) and electron-light hole (e-hh). A theoretical calculation based oil model-solid theory, taking, into account the spin-orbit splitting energy, shows good agreement with our experimental results. The temperature dependence of PL intensity ratio is well explained using the spontaneous emission theory for e-hh and e-hh transitions. front which the ratio can be characterized mainly by the energy separation between the fill and Ill states.