Effects of annealing treatment on the formation of CO2 in ZnO thin films grown by metal-organic chemical vapor deposition

Post-growth annealing was carried out on ZnO thin films grown by metal-organic chemical vapor deposition (MOCVD). The grain size of ZnO thin film increases monotonically with annealing temperature. The ZnO thin films were preferential to c-axis oriented after annealing as confirmed by Xray diffraction (XRD) measurements. Fourier transformation infrared transmission measurements showed that ZnO films grown at low temperature contains CO2 molecules after post-growth annealing. A two-step reaction process has been proposed to explain the formation mechanism of CO2, which indicates the possible chemical reaction processes during the metal-organic chemical vapor deposition of ZnO films.

A study of indium incorporation in In-rich InGaN grown by MOVPE

InGaN/GaN heterostructures have been deposited onto (0 0 0 1) sapphire by our home-made low pressure MOVPE with different growth parameters. It has been noted that the indium incorporation depends by a complex way on a number of factors. In this work, the effect of substrate temperature, trimethylindium input flow and V/III ratio on the indium incorporation has been investigated. Finally, by optimizing the growth parameters, we made a series of single-phase InGaN samples with indium content from 10% up to 45%.

Valence band offset of ZnO/BaTiO3 heterojunction measured by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy has been used to measure the valence band offset of the ZnO/BaTiO3 heterojunction grown by metal-organic chemical vapor deposition. The valence band offset (VBO) is determined to be 0.48 +/- 0.09 eV, and the conduction band offset (CBO) is deduced to be about 0.75 eV using the band gap of 3.1 eV for bulk BaTiO3. It indicates that a type-II band alignment forms at the interface, in which the valence and conduction bands of ZnO are concomitantly higher than those of BaTiO3. The accurate determination of VBO and CBO is important for use of semiconductor/ferroelectric heterojunction multifunctional devices.

Measurement of GaN/Ge(001) Heterojunction Valence Band Offset by X-Ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy has been used to measure the valence band offset (VBO) at the GaN/Ge heterostructure interface. The VBO is directly determined to be 1.13 +/- 0.19 eV, according to the relationship between the conduction band offset Delta E-C and the valence band offset Delta E-V : Delta E-C = E-g(GaN) - E-g(Ge) - Delta E-V, and taking the room-temperature band-gaps as 3.4 and 0.67 eV for GaN and Ge, respectively. The conduction band offset is deduced to be 1.6 +/- 0.19 eV, which indicates a type-I band alignment for GaN/Ge. Accurate determination of the valence and conduction band offsets is important for the use of GaN/Ge based devices.

Valence band offset of MgO/TiO2 (rutile) heterojunction measured by X-ray photoelectron spectroscopy

The valence band offset (VBO) of MgO/TiO2 (rutile) heterojunction has been directly measured by Xray photoelectron spectroscopy. The VBO of the heterojunction is determined to be 1.6 +/- 0.3 eV and the conduction band offset (CBO) is deduced to be 3.2 +/- 0.3 eV, indicating that the heterojunction exhibits a type-I band alignment. These large values are sufficient for MgO to act as tunneling barriers in TiO2 based devices. The accurate determination of the valence and conduction band offsets is important for use of MgO as a buffer layer in TiO2 based field-effect transistors and dye-sensitized solar cells.

基于约束的主动规则终止性分析

终止性是主动规则所需的最重要的一个性质,但规则的终止性检查通常是不可判定的.已有的静态分析方法非常保守,SQL3标准也没有提供保证终止的机制,所以商业数据库限制规则级联触发的最大次数确保终止.由于规则可看成数据库状态转换器,而约束能够表示所有可能的数据库状态,基于约束表示的数据库状态及约束求解,模拟规则处理,可得到更精确的终止性结论.

生物油热解与燃烧特性的实验研究

生物质快速热解制油技术能以连续的工艺和工厂化的生产方式将木屑等生物质转化为易储存、易运输、能量密度高的生物油，是目前受到较多关注的一种转换技术。生物油既可以在锅炉中直接燃烧使用，也可用于热解气化制备合成气，再进一步合成为高品质的液体燃料。 为更好地处理生物油燃烧与热解过程中出现的问题，并为燃烧与热解反应装置的设计及优化提供必要数据，本文首先对由木屑在自热式生物质热解液化装置中热解得到的生物油进行了各种理化特性的分析，之后利用热重、热重-红外联用、管式炉等对生物油的热解与燃烧特性进行了实验研究。 生物油在氮气与氧气气氛下、不同升温速率的热重分析试验表明：生物油的热解分为两个阶段，第一阶段为生物油中低沸点有机物的挥发以及各组分间反应生成各类产物的过程，第二阶段为各种重组分的裂解过程。而生物油的燃烧则分为三个阶段，即前期的挥发与裂解和最后焦炭的燃烧过程。升温速率的升高使得氮气气氛中生物油样品的初始失重温度、失重峰值温度及对应的最大失重速率均有所增大，且在较高升温速率(20℃/min)下，较少含炭残余物形成。随升温速率升高，生物油着火温度提高，最终失重率无显著变化。采用热重-红外联用技术，对生物油热解过程中所释放气体进行了实时监测，在线分析结果表明，反应初始阶段主要析出物为自由水、低沸点的酸类、醇类、醛类、酮类等，随后主要释放物为水、CO2等，主要来自重组分的裂解。最后根据热重数据对热解与燃烧各段反应进行了动力学拟合。动力学分析结果表明：氮气气氛中生物油的热解过程可用两个一级反应来描述，对应其热解过程中的两个不同阶段，而生物油的燃烧过程可用三个一级反应来表示。 生物油的管式炉热解实验表明：随热解温度的升高，生物油产气率不断提高，在1100℃时达到最大值398ml/g。生物油热解气体产物中主要包含H2、CO、CO2及烃类如CH4、C2H4、C2H6等,产气热值在16.9～19.1MJ/Nm3间。在900℃下，生物油各种产物气体、残炭、焦油的比例约为30:6:64,残炭含量低于同温度下木粉热解结果，而焦油含量较高。

广东典型藻类特点及其能源利用可能性研究

大型海藻的生产力高，生产成本低，是一种理想的能源作物。广东省是我国海洋大省之一，约35万平方公里的海域，海藻物种丰富，为海藻养殖提供了有利的条件。我省是能源消耗大省，大部分依靠外省调入和进口，发展海藻能源技术是缓解能源问题的重要途径之一。目前，海藻作为生物质的利用技术还不成熟。在本论文中，选用我省常见的江蓠、马尾藻和麒麟菜三种的大型的海藻进行热解和发酵实验。 首先，对海藻在不同温度下（400℃～900℃）热解得到的各产物（气体、焦油和残渣）产率和热值以及气体组分进行了分析，研究了各热解产物产率、热值和气体组分随温度的变化规律，分析热解过程中的K、Ca、Na、Mg等元素的析出和迁移规律。用去离子水和稀盐酸对海藻进行洗滤预处理，研究其热解特性，进行热重分析，建立海藻热解的反应动力学模型，并计算海藻的动力学参数。分析结果表明：热解气体中的主要成分为H2、CO、CH4、C2H4、C2H6等，热解气低位热值介于5～15 MJ/m3之间。海藻本身具有灰分含量较高和热值较低的特点，水洗可以有效地脱除部分的碱金属，并可以减少灰分含量，改善海藻的热解特性。 其次，以江蓠和马尾藻为底物进行发酵。结果表明：海藻中含有大量金属阳离子，直接发酵容易溶解到料液中，抑制微生物生长，影响发酵效果。用淡水浸泡以后的海藻能容易进行发酵。江蓠的产气率要高于马尾藻。在发酵温度为35℃，简单破碎，料液浓度为5%的条件下，江蓠TS（总固体）产气率是390.6L/kg 。在55℃，颗粒大小0.6～0.9mm，料液浓度为5%的条件下，马尾藻TS产气率是173.1L/kg。 通过对比海藻热解和发酵过程及结果的比较可以发现，海藻热解产气率低，碱金属容易析出；海藻发酵可以直接利用湿原料，产气率高，但发酵时间较长，需要合适的菌种。在目前没有特殊专有技术的情况下，采用发酵比采用热解实现海藻的能源化利用可能性更大。 最后，对本论文的研究探讨进行总结，并对今后进一步完善该工作提出了建议。

Synthesis Gas Generation by Chemical-Looping Reforming Using Ce-Based Oxygen Carriers Modified with Fe, Cu, and Mn Oxides

Chemical-looping reforming (CLR) is a technology that can be used for partial oxidation and steam reforming of hydrocarbon fuels. It involves the use of a metal oxide as an oxygen carrier, which transfers oxygen from combustion air to the fuel. Composite oxygen carriers of cerium oxide added with Fe, Cu, and Mn oxides were prepared by co-precipitation and investigated in a thermogravimetric analyzer and a fixed-bed reactor using methane as fuel and air as oxidizing gas. It was revealed that the addition of transition-metal oxides into cerium oxide can improve the reactivity of the Ce-based oxygen carrier. The three kinds of mixed oxides showed high CO and H-2 selectivity at above 800 degrees C. As for the Ce-Fe-O oxygen carrier, methane was converted to synthesis gas at a H-2/CO molar ratio close to 2:1 at a temperature of 800-900 degrees C; however, the methane thermolysis reaction was found on Ce-Cu-O and Ce-Mn-O oxygen carriers at 850-900 degrees C. Among the three kinds of oxygen carriers, Ce-Fe-O presented the best performance for methane CLR. On Ce-Fe-O oxygen carriers, the CO and H-2 selectivity decreased as the Fe content increased in the carrier particles. An optimal range of the Ce/Fe molar ratio is Ce/Fe > 1 for Ce-Fe-O oxygen carriers. Scanning electron microscopy (SEM) analysis revealed that the microstructure of the Ce-Fe-O oxides was not dramatically changed before and after 20 cyclic reactions. A small amount of Fe3C was found in the reacted Ce-Fe-O oxides by X-ray diffraction (XRD) analysis.

Influence of 3A molecular sieve to tetrahydrofuran(THF) hydrate formation

Visual observation of the THF hydrate formation process in the presence of a 3A molecular sieve has been made at normal atmosphere and below a temperature of zero by microscopy. The results indicate that a 3A molecular sieve can induce the nucleation of the THF hydrate and promote the THF hydrate growth. With the existence of a 3A molecular sieve, the growth rate of THF hydrate is between 0.01 and 0.05 mu m/s. In comparison with the system without any 3A molecular sieve, the growth rate increases about 4 nm/s. After the THF hydrate grows into megacryst, the crystals will recombine and partially change under the same condition.

Synthesis of novel hexagon SnO2 nanosheets in ethanol/water solution by hydrothermal process

The novel hexagon SnO2 nanosheets are successfully synthesized in ethanol/water solution by hydrothermal process. The samples are characterized by X-ray diffraction (XRD), infrared ray (IR) and transmission electron microscopy (TEM). By changing the reaction conditions, the size and the morphology can be controlled. Comparison experiments show that when the temperature increased from 140 degrees C to 180 degrees C, the edge length of the hexagon nanoparticles increases from 300-450 nm to 700-900 nm. On the other hand, by adjusting the ratios of water to ethanol from 2 to 0.5, SnO2 nanoparticles with different morphologies of triangle and sphere are obtained. When the concentration of NaOH is increased from 0.15 M to 0.30 M, a hollow ring structure can be obtained. (c) 2006 Elsevier B.V. All rights reserved.