Ultraviolet electroluminescence from ZnO-based light-emitting diode with p-ZnO:N/n-GaN:Si heterojunction structure

A p-ZnO:N/n-GaN:Si structure heterojunction light-emitting diode (LED) is fabricated on c-plane sapphire by full metal organic chemical vapor deposition (MOCVD) technique. The p-type layer with hole concentration of 8.94×10¹⁶ cm⁻³ is composed of nitrogen-doped ZnO using NH₃ as the doping source with subsequent annealing in N₂O plasma ambient. Silicon-doped GaN film with electron concentration of 1.15×10¹⁸ cm⁻³ is used as the n-type layer. Desirable rectifying behavior is observed from the current-voltage (I-V) curve of the device. The forward turn on voltage is about 4 V and the reverse breakdown voltage is more than 7 V. A distinct ultraviolet (UV) electroluminescence (EL) with a dominant emission peak centered at 390 nm is detected at room temperature from the heterojunction structure under forward bias conditions. The origins of the EL emissions are discussed in comparison with the photoluminescence (PL) spectra.     

Microgravity experiments of two-phase flow patterns aboard MIR space station

A first experimental study on two-phase flow patterns at a long-term, steady microgravity condition was conducted on board the Russian Space Station “MIR” in August 1999. Carbogal and air are used as the liquid and the gas phase, respectively. Bubble, slug, slug-annular transitional, and annular flows are observed. A new region of annular flow with lower liquid superficial velocity is discovered, and the region of the slug-annular transitional flow is wider than that observed by experiments on board the parabolic aircraft. The main patterns are bubble, slug-annular transitional and annular flows based on the experiments on board MIR space station. Some influences on the two-phase flow patterns in the present experiments are discussed. The project supported by the National Natural Science Foundation of China (19789201), the Ministry of Science and Technology of China (95-Yu-34), and the Post-doctoral Science Foundation of China     

Relationship between the density of supercritical CO_2 + ethanol binary system and its critical properties

The solvent strength and selectivity of supercritical fluids (SCF) can be greatly enhanced by addition of one or two entrainers into the system. The amount of entrainer added is usually less than 5% (mole fraction). However, even with such slight amount, solubility of organic solutes has been observed to increase by several orders magnitude[1]. Therefore, critical pressure and tem-perature data of these supercritical fluid + cosolvent systems are imperative for the reasonable design of effici…     

碳化铁超微粒子催化剂的表征及催化机理研究

用激光热解法制备了非晶态Fe/C超微粉,经有机溶剂洗涤及高温处理获得了碳化铁催化剂。用XRD、TEM及电子衍射测试结果表明,其粒度大都在1～4nm之间,为多晶态的α-Fe、Fe_3C。经测试表明,在常压下反应温度为380℃时,碳化铁超微粒子催化剂具有较高的活性和对低碳烯烃的高选择性。通过测试催化剂在使用过程中的物相变化,进一步证明了F-T合成催化活性物种为α-Fe、Fe_xC_y的碳化物机理。     

The synthesis and photoelectric study of 6,13-bis(4-propylphenyl)pentacene, and its TiO2 nano-sized composite films

The synthesized 6,13-bis(4-propylphenyl)pentacene(BPP) is much more soluble and stable than pentacene. The introduction of 4-propylphenyl group leads the solubility to 7.33 mg/mL in CHCl₃. In cyclic voltammetry (CV) test, it was found that its forbidden band gap is 1.88 eV. Moreover, a series of BPP-TiO₂ composites were constructed. Characterizations proved that an interaction between BPP and TiO₂ has probably occurred, leading to the generation of some novel properties. The most interesting result is that the forbidden band gaps of the composite materials are much smaller than that of BPP and TiO₂.     

激光气相法研制硅系超微粉

激光气相法是制备超微粉末的新方法之一,目前还存在超微粉末粒径太小难于收集,原料SiH_4价格较昂贵等困难。我们以SiH_4为主要原料,成功地合成出超微Si、Si_3N_4、SiC粉末,研究了反应条件对超微粉性能的影响,探索了用廉价原料代替SiH_4的可能性,并且在超微粉的收集方面做了若干探索,取得了一些有意义的结果。     

双核双配体稀土配合物Tb1-xEux(TTA)3Phen的合成及光学性能研究

合成了系列铕铽双核稀土有机稀土配合物Tb1-xEux（TTA）3Phen，通过差热．热重分析、XRD、红外光谱、紫外光谱和荧光光谱等测试手段研究了配合物的组成、结构和发光性质。由紫外可见光谱可以看出，稀土有机配合物的吸收峰主要来自有机配体HTrA和1，10-Phen；差热-热重分析证明，稀土有机配合物热稳定性较好。荧光光谱和电致发光表明，铽对铕配合物的发光有协同作用。在该系列配合物中，不仅有机配体可以将吸收的能量传递给发光的铕离子使其发光，而且铽离子也可将其吸收的能量通过分子内能量传递给铕离子，增强铕的发光强度。同时就双核稀土有机配合物光致发光和电致发光的特性及掺杂体系的能量传递过程进行了讨论。     

粘性涡方法在多圆柱绕流数值模拟中的应用

用粘性涡方法求解了涡量速度形式的二维不可压缩Navier—Stokes方程．利用分步方法分别求解无粘的对流运动和粘性扩散，粘性扩散用随机走步方法来处理，利用涡量交换技术来满足无滑移边界条件，同时为进一步减少计算量，在求解对流速度时，采用了多极子展开法加速技术使得计算量由N2的量级减少到NlogN的量级．数值模拟了单圆柱和双圆柱纵向排列的绕流流场．     

超临界流体技术在催化反应和金属有机反应中的应用

本文详细地介绍了超临界流体技术在催化反应和金属有机反应中近10年来国内外发展的最新成果及动向,表明将超临界流体技术应用于催化反应中,将提高催化剂活性,选择性及寿命,并可提高反应速率,改变反应历程,特别是在开展控制化学及环境友好的绿化学反应方面的研究具有很大的潜在优势。