GROWTH MODE AND SURFACE RECONSTRUCTION OF GaN(0001) THIN FILMS ON 6H-SiC(0001)

Two-dimensional growth of GaN thin films on an atomically flat C-face 6H-SiC(0001) surface prepared by ultra-high vacuum Si-etching is observed when using an AlN buffer layer in N plasma-assisted molecular beam epitaxy. Scanning tunneling microscopy and reflection high energy electron diffraction observations reveal a series of Ga-stabilized reconstructions which are consistent with those reported for an N-polar GaN(0001) film. The result, including the effect observed previously for GaN thin film on Si-terminated 6H-SiC(0001), agrees with the polarity assignment of heteroepitaxial wurtzite GaN films on polar 6H-SiC substrates, i.e., GaN film grown on SiC(0001) is <0001> oriented (N-face) while that on SiC(0001) is <0001> oriented (Ga-face).     

STUDY OF THE Al/GRAPHITE INTERFACE

Thin Al films with a thickness of 20－30nm were prepared by ultra-high vacuum deposition of Al onto a graphite surface parallel to a (0001) basal plane. The samples were annealed up to 1070K. X-ray photoelectron spectroscopy analysis has shown that for temperatures just higher than 770K, a little carbide occurs in the Al film and only an Al－C phase is present at the Al/graphite interface. After annealing at 970K, the Al₄C₃ phase can be observed, and the binding energy of the Al2p electrons increases continuously from 72.7 to 74.2eV with increasing temperature up to 1070K. Auger electron spectroscopy depth profiles are measured to investigate the phases existing in the Al film as well as at the Al/graphite interface. It is found that the Al₄C₃ phase at the interface is the final product of a series of Al carbides from the interfacial reaction between Al and graphite.     

具有二阶消失矩的多进制对称Coiflet小波基

本文研究了具有二阶消失矩的多进制对称Coiflet小波的构造方法,分析了它们的特征,并给出了算例。     

不同含能取代基和桥基对碳桥联四唑-2-氮氧化物的性能影响密度泛函理论研究

Based on the parent tetrazole 2N-oxide, six series of novel carbon-linked ditetrazole 2N-oxides with different energetic substituent groups (-NH₂, -N₃, -NO₂, NF₂, -NHNO₂) and energetic bridge groups (-CH₂-, -CH₂-CH₂-, -NH-, -N=N-, -NH-NH-) were designed. The overall performance and the effects of different energetic substituent groups and energetic bridge groups on the performance were investigated by density functional theory and electrostatic potential methods. The results showed that most of designed compounds have oxygen balance around zero, high heats of formation, high density, high energy, and acceptable sensitivity, indicating that tetrazole N-oxide is a useful parent energetic compound employed for obtaining high energy compounds, even only combined with some very common energetic substituent groups and bridge groups. Comprehensively considering the effects on energy and sensitivity, the -NO₂, -NF₂, -NH-and -NH-NH-are appropriate substituent groups for combining tetrozale N-oxide to design new energetic compounds, while -NH₂, -N₃, -CH₂-CH₂-, and -N=N-are inappropriate.     

基于超材料结构的小型化可调滤波器

为了提高频谱资源的利用率,解决传统滤波器组体积大的问题,利用开口环结构的超材料具有高集成度的特性,设计了一款整体尺寸仅为15mm×20mm的滤波器.基于时域有限积分法分析了开口环结构滤波器的反射系数曲线与电磁参数之间的响应特性,通过在开口环缝隙处加载可调谐的二极管器件,实现了超材料滤波器在X波段(10.9~12GHz)的连续可调,扩展了滤波器的工作频带.该可调谐超材料滤波器的工作带宽达11.0%,通带内回波损耗最小值为32dB,插入损耗最大值为0.38dB,具有高集成度、宽频带、通带内选频特性良好的特点.     

固态van der Waals C60膜晶格的Coulomb膨胀

利用扫描隧道显微镜观测到生长在GaAs(001)2×4表面上的固态van der Waals C60膜在室温下较之C60晶体具有13%的晶格膨胀.这种膨胀是由从GaAs衬底饱和的As悬挂键上转移到C60分子上的电荷之间的Coulomb作用引起的.理论计算表明,平均约有1.76个电子转移到每个C60分子上.有趣的是,该固态C60膜为(110)取向,这明显不同于生长于其他半导体或金属表面上的具有(111)取向的六角密排C60膜.这种反常取向的薄膜是由GaAs衬底的各向异性产生的一维限制作用导致的.通过选择不同的衬底,可以控制C60薄膜的晶体生长.     

气体在不同离子液体中电化学响应灵敏度的研究

不同气体在不同离子液体中的电化学响应存在差异。本文以氢气、氧气作为目标研究气体,采用循环伏安法和计时安培电流法研究对比了基于两种不同离子液体[Bmpy][NTf₂]和[Bmim][NTf₂]的电化学传感器中气体的电化学行为,并就气体电化学信号的响应时间及灵敏度等电化学行为进行了讨论分析。结果表明:在[Bmpy][NTf₂]和[Bmim][NTf₂]中检测氢气的灵敏度分别为4.93μA/%和0.03μA/%,且其电化学信号值与浓度均呈线性正比关系;在[Bmpy][NTf₂]和[Bmim][NTf₂]中检测氧气的灵敏度分别为-0.055 mA/%和-0.002 mA/%,且其电化学信号值与浓度均呈线性正比关系。研究发现:相比于离子液体[Bmim][NTf₂],[Bmpy][NTf₂]中气体的灵敏度更高,响应性能更好,且对于氢气和氧气的混合气体同样适用。通过研究优选出更适用于检测氢气氧气的离子液体电解质溶液,为后续电化学气体传感器的开发研究提供了理论依据与技术支持。     

过渡金属催化的环丙烯聚合反应研究

环丙烯是一类最小的不饱和环状化合物,其在有机化学中是十分重要的合成中间体,同时在高分子聚合中也是一类独特的单体.尽管环丙烯的研究大部分集中于有机化学领域,近年来有关过渡金属催化的环丙烯聚合反应也逐渐引起了人们的兴趣.综述了环丙烯聚合反应的研究进展,主要包括加成聚合和开环复分解聚合(ROMP)两类聚合反应,并从聚合物合成...     

微波辐射下纳米水滑石的合成

在微波辐射下用变速滴加共沉淀法合成了粒径为10 nm~40 nm的Mg-A l纳米水滑石(nano-HT),其结构经XRD,TEM,TG和元素分析表征。以nano-HT为载体,制备了Cu/nano-HT和CuN i/nano-HT催化剂,通过苯酚羟基化反应考察了它们的催化活性,实验结果表明,双氧水有效利用率和产物的选择性均比以常规水滑石为载体的催化剂高。     

过渡金属卡宾配合物 VI:单、双核锰和双核铼的铁硫原子簇卡宾配合物-π-C5H5(CO)2MnC(C6H5)(μ-S)(μ-C6H5S)Fe2(CO)6和[π-C5H5(CO)2MC(C6H5)]2(μ-S)2Fe2(CO)6(M=Mn,Re)的合成和波谱

本文报道了锰和铼的阳离子卡拜配合物[π-C5H5(CO)2MCC6H5]BRr4(M=Mn, Re)分别与(μ-苯硫)六羰基二铁和双(μ-锂硫)六羰基二铁阴离子反应生成标题化合物. 产物的组成和结构由元素分析, IR, ^1H NMR和MS分析, 以及7的单晶X射线结构分析确定的. 文中还对合成和波谱研究结果进行了讨论.