投影边缘在硝基苯类化合物构效关系研究中的应用

在三维投影的基础上,对投影的边缘进行了描述,并以其进行了定量结构活性相关研究.实验结果表明,与Am指数、指示变量和量化参数相结合,可使其数学模型得到明显提高.通过人工神经网络对硝基苯类化合物的毒性进行预测,结果令人满意.     

Am指数的扩展与手性化合物的构效关系研究

构效关系研究中的分子拓扑指数(Am)通常仅代表一个化合物的拓扑特征,所以预测手性化合物活性的能力较差.我们对Am指数进行了扩展,得到eAm指数,并将其应用于手性分子的结构-活性相关研究.结果表明,由手性拓扑指数得到的QSAR模型比传统的拓扑指数有更好的统计和预测手性化合物活性的能力.     

气体标准物质的选择使用及期间核查试验方法探讨

标准物质是具有准确量值的计量标准,在分析化学、物理化学以及工程特性量的测量中,都使用标准物质传递量值,以实现测量结果的准确、一致。在分析仪器的检测／校准方面,人们根据被检仪器对标准物质的分析结果与其标准值的符合程度,或根据被检仪器的有关技术指标的计算结果是否满足规程或标准要求来判断仪器的计量性能。     

负载型铜基催化剂组分间相互作用及其催化性能

负载型铜基催化剂因其良好的催化性能和相对低廉的价格在诸多重要工业催化反应中得到广泛的应用.探讨负载型铜基催化剂中组分间的相互作用,有助于了解相关催化作用的本质,为现有催化剂的改进和新催化剂的设计提供科学依据.本文综述了近年来我们就CuO在不同载体上的分散、铜物种和载体的改性及其物理化学性质以及催化CO完全氧化、CO+NO和NH₃+NO+O₂反应性能等方面的研究进展.结果表明,CuO在多种氧化物载体表面的分散和所得负载型铜基催化剂的一些物理化学性质可参考“嵌入模型”得到解释,本文主要讨论了以CeO₂,Ce_xZr_1-xO₂和Mo₃-CeO₂为载体的一些铜基催化剂的组成-结构-性质间的关系.     

“嵌入模型”在γ-Al2O3负载单组分和双组分金属氧化物催化剂中的应用

探讨负载型金属氧化物催化剂的表面组分与载体之间的相互作用, 有助于理解相关催化剂的催化作用本质. 近年来, 我们对单组分CuO以及双组分CuO-Mn₂O₃, CuO-CoO等金属氧化物在γ-Al₂O₃载体表面的分散行为和存在状态, 及其物理化学性质和催化性能(CO+O₂和NO+CO模型反应)进行了研究. 结果表明, 这些金属氧化物在γ-Al₂O₃载体表面的分散行为和所得负载型催化剂样品的一些物理化学性质及其催化性能均可参照“嵌入模型”来解释. 在此基础上, 我们讨论了这些样品的“组成-结构-性质”间的关系, 并针对表面负载双组分金属氧化物样品提出了表面协同氧空位参与的NO+CO反应机理.     

负载型催化剂的表面相互作用及其在大气分子污染物NO和CO消除中的应用基础研究

负载型催化剂具有重要的应用背景,研究表面分散组分与载体之间的相互作用.对于了解催化过程的本质,进而设计开发高效实用的催化剂均有重要的指导意义.本课题组近年来在该领域中进行了一些探索研究,涉及的催化剂以负载型金属氧化物(如CuO/γ-Al_2O_3,CuO/Ce_xZr_(1-x)O_2和CuO/Ti_xSn_(1-x)O_2等)为主,涉及的反应包括CO完全氧化和NO+CO反应.通过改变活性组分的负载量、添加改性剂和改变样品制备条件等制得一系列样品,用多种固体催化剂表征手段考察各组分在催化剂中的作用以及在上述催化反应中的活性变化规律.研究表明:(1)金属氧化物和卤化物等离子化合物在氧化物载体表面的分散容量和分散后的一些性质均可从"嵌入模型"的考虑得到解释;(2)处于不同载体表面的活性物种或同一载体表面不同结构的活性物种,由于其存在状态的差异使得其氧化还原性质和催化性质不同;(3)在相关催化剂体系中进行的CO完全氧化和NO+CO反应的结果显示,通过探索催化剂的"组成-结构-性质"间的关系,有可能为实际催化剂的设计提供理论参考.     

固相浸渍法和湿浸渍法制备CuO/CeO2催化剂及其CO氧化性能的对比研究

采用固相浸渍法和常规湿浸渍法制备了一系列CuO/CeO₂催化剂,并结合X射线衍射（XRD）、氢气-程序升温还原（H₂-TPR）、激光拉曼光谱（LRS）、原位漫反射红外光谱（in situ DRIFTS）、X射线光电子能谱（XPS）等手段考察了制备方法对催化剂结构性质及其在CO氧化反应中性能的影响. XPS和H₂-TPR结果表明,固相浸渍法更有利于得到高分散的铜物种,并促进CuO物种的还原. LRS结果表明,相比于湿浸渍法,固相浸渍法能产生更多氧空位,而这些氧空位可以活化参与反应的O₂. CO氧化活性测试结果表明,当铜负载量相同时,固相浸渍法制备的催化剂相比于湿浸渍法表现出更好的催化性能. 结合多种表征结果发现,催化剂CO氧化性能与其表面氧空位和Cu⁺-CO浓度紧密相关,提出了CuO/CeO₂催化剂在CO氧化反应中可能的协同作用机制.     

High-performance 4H-SiC junction barrier Schottky diodes with double resistive termination extensions

4H-SiC junction barrier Schottky (JBS) diodes with a high-temperature annealed resistive termination extension (HARTE) are designed, fabricated and characterized in this work. The differential specific on-state resistance of the device is as low as 3.64 m ·cm2 with a total active area of 2.46×10-3 cm2 . Ti is the Schottky contact metal with a Schottky barrier height of 1.08 V and a low onset voltage of 0.7V. The ideality factor is calculated to be 1.06. Al implantation annealing is performed at 1250℃ in Ar, while good reverse characteristics are achieved. The maximum breakdown voltage is 1000 V with a leakage current of 9×10-5 A on chip level. These experimental results show good consistence with the simulation results and demonstrate that high-performance 4H-SiC JBS diodes can be obtained based on the double HARTE structure.     

Characterization of 4H-SiC substrates and epilayers by Fourier transform infrared reflectance spectroscopy

The infrared reflectance spectra of both 4H–SiC substrates and epilayers are measured in a wave number range from 400 cm 1 to 4000 cm 1 using a Fourier-transform spectrometer. The thicknesses of the 4H–SiC epilayers and the electrical properties, including the free-carrier concentrations and the mobilities of both the 4H–SiC substrates and the epilayers, are characterized through full line-shape fitting analyses. The correlations of the theoretical spectral profiles with the 4H–SiC electrical properties in the 30 cm 1 –4000 cm 1 and 400 cm 1 –4000 cm 1 spectral regions are established by introducing a parameter defined as error quadratic sum. It is indicated that their correlations become stronger at a higher carrier concentration and in a wider spectral region (30 cm 1 –4000 cm 1 ). These results suggest that the infrared reflectance technique can be used to accurately determine the thicknesses of the epilayers and the carrier concentrations, and the mobilities of both lightly and heavily doped 4H–SiC wafers.     

Determination of the transport properties in 4H-SiC wafers by Raman scattering measurement

The free carrier density and mobility in n-type 4H-SiC substrates and epilayers were determined by accurately analysing the frequency shift and the full-shape of the longitudinal optic phonon--plasmon coupled (LOPC) modes, and compared with those determined by Hall-effect measurement and that provided by the vendors. The transport properties of thick and thin 4H-SiC epilayers grown in both vertical and horizontal reactors were also studied. The free carrier density ranges between 2×10¹⁸ cm^-3 and 8×10¹⁸ cm^-3 with a carrier mobility of 30--55 cm²/(V·s) for n-type 4H-SiC substrates and 1×10¹⁶--3×10¹⁶ cm^-3 with mobility of 290--490 cm²/(V·s) for both thick and thin 4H-SiC epilayers grown in a horizontal reactor, while thick 4H-SiC epilayers grown in vertical reactor have a slightly higher carrier concentration of around 8.1×10¹⁶ cm^-3 with mobility of 380 cm²/(V·s). It was shown that Raman spectroscopy is a potential technique for determining the transport properties of 4H-SiC wafers with the advantage of being able to probe very small volumes and also being non-destructive. This is especially useful for future mass production of 4H-SiC epi-wafers.