Structural and electrical properties of single crystalline and bi-crystalline ZnO thin films grown by molecular beam epitaxy

C-oriented ZnO epitaxial thin films are grown separately on the a-plane and c-plane sapphire substrates by using a molecular-beam epitaxy technique. In contrast to single crystalline ZnO films grown on a-plane sapphire, the films grown on c-plane sapphire are found to be bi-crystalline; some domains have a 30o rotation to reduce the large mismatch between the film and the substrate. The presence of these rotation domains in the bi-crystalline ZnO thin film causes much more carrier scatterings at the boundaries, leading to much lower mobility and smaller mean free path of the mobile carriers than those of the single crystalline one. In addition, the complex impedance spectra are also studied to identify relaxation mechanisms due to the domains and/or domain boundaries in both the single crystalline and bi-crystalline ZnO thin films.     

具有四配位铁中心的微孔磷酸铁晶体的溶剂热合成与表征

在有机溶剂乙二醇中合成了具有三维骨架结构的磷酸铁晶体 ,对其进行了单晶结构解析 ,热重分析 ,穆斯堡尔谱以及红外光谱测试 ,证实晶体组成为 [NH3CH2 CH2 NH3]0 .5[FePO4 ],晶体结构属正交晶系 ,空间群Pc cn ,晶胞参数a =10 .36 1(6 ) ,b =10 .390 (5) ,c=9.135(7) ,V =983.3(11) 3,Z =8,Dc=2 .4 57Mg·m- 3,F(0 0 0 ) =72 8,R =0 .0 52 8,wR =0 .1194。在其结构中 ,磷氧四面体和铁氧四面体严格交替共用顶点在 [0 0 1]方向上形成八员环 ,双质子化的乙二胺分子占据八员环空隙。该晶体结构最为显著的特征是具有在磷酸盐中非常少见的四配位铁中心     

Cu修饰的MCM—41的合成,表征及对芳烃羟化反应催化作？…

利用ＭＣＭ－４１形成过程中协同自组装特点,在合成过程中引入Ｃｕ（ＮＨ３）４＾２＋,制备出过渡金属表面修饰的纯硅介孔分子筛Ｃｕ－ＭＣＭ－４１,采用ＸＲＤ,ＩＣＰ,ＥＳＲ,Ｎ２吸附等手段确定Ｃｕ处于ＭＣＭ－４１的表面,取代了端羟基中氢的位置,与骨架桥氧和硅羟基中的氧配位,利用苯酚羟化反应为探针,考察了Ｃｕ－ＭＣＭ－４１的催化活性。结果表明,Ｃｕ－ＭＣＭ－４１具有很高的苯酚羟化活性,与ＴＳ－１分子筛的催     

二杂芳基乙烯光二聚反应与二聚体的晶体结构

通过反-1,2-双(2-苯并唑基)乙烯(BBE)和反-1-(2-苯并咪唑基)-2-(2-苯并唑基)乙烯(BME)的光二聚反应合成了r-1,c-2,t-3,t-4-四(2-苯并唑基)环丁烷(BBC)和r-1,c-2,t-3,t-4-1,3-双(2-苯并咪唑基)-2,4-双(2-苯并唑基)环丁烷(BMC).用元素分析、红外、紫外、核磁共振谱、质谱及X射线衍射表征了二聚体的结构.BBC晶体属三斜晶系,空间群为P1.晶胞参数:a=0.64684(13)nm,b=1.3242(3)nm,c=1.6245(3)nm;α=74.66(3)°,β=78.77(3)°,γ=76.06(3)°,Z=2.BBC晶胞中分子有两种取向,两种取向不同分子的苯并唑平面间存在着π-堆积现象.π-堆积面间的距离在0.330～0.376nm之间,与石墨晶体中分子平面片层间的距离非常接近.BBC和BMC都具有中心对称性,光二聚反应的高度立体选择性以及BBE和BME的光二聚反应不受空气中氧的影响的事实表明它们是经激发单线态历程以面对面的方式进行二聚反应的,本文检测到了BBE和BME在高浓度溶液中的激基缔合物荧光.     

AlPO4-5分子筛模板剂的量子化学计算

以23种有机分子作为模板剂用于AlPO₄-5分子筛的合成,利用分子图形技术研究这些有机分子的形状和尺寸,采用量子化学PM3方法研究这些有机分子的电子性质,计算它们与AlPO₄-5分子筛骨架模型簇之间的相互作用能。结果表明,量子化学计算数据可以作为寻找合成AlPO₄-5分子筛新型模板剂时的重要参考依据。     

One-dimensional Coordination Polymers of rctt-1,3-Diphenyl-2,4-bis[2-(5-phenyl)-oxazolyl]cyclobutane with CuCl2 and CoCl2

The Cu(Ⅱ) and Co(Ⅱ) supramolecular coordination polymers,[CuCl2(DPO)-(CH3CN)0.5(CH2Cl2)0.5]n(CuDPO,DPO=rctt-1,3-diphenyl-2,4-bis[2-(5-phenyl)oxazolyl]cyclo-butane) and [CoCl2(DPO)]n(CoDPO),were synthesized and characterized by single-crystal X-ray diffraction method.CuDPO crystallizes in monoclinic,space group P21/n,with a=11.243(5),b=16.070(8),c=19.872(9) ,β=95.678(10)°,Z=4,V=3573(3) 3,C35.50H28.50Cl3CuN2.50O2,Mr=692.00,Dc=1.287 g/cm3,μ=0.868 mm-1,F(000)=1420,S=1.089,(△/σ)max=0.069,the final R=0.0682 and wR=0.1749.CoDPO is of monoclinic,space group P21/n,with a=11.396(4),b=15.151(5),c=17.673(6) ,β=90.528(6)°,Z=4,V=3051.4(17) 3,C34H26Cl2CoN2O2,Mr=624.40,Dc=1.359 g/cm3,μ=0.770 mm-1,F(000)=1284,S=0.981,(△/σ)max=0.001,the final R=0.0471 and wR=0.0961.In each case,the metal cation is coordinated by two Cl anions and two N atoms from oxazole ring of the ligands,which leads to the formation of a one-dimensional polymeric structure.It is found that the cyclobutane ring of coordinated DPO adopts a distorted conformation in the crystal,which is attributed to the increased steric effect between adjacent aryl substituents for the coordination of oxazole ring to metal cation.Thermal gravimetric analysis of the two complexes was also observed.     

Directional Modulation Using Frequency Diverse Array For Secure Communications

Wireless Personal Communications - In this paper, to obtain a better physical layer security for wireless communications, a directional modulation (DM) using frequency diverse array (FDA) is...     

MIMO radar OFDM chirp waveform diversity design with sparse modeling and joint optimization

In multiple-input multiple-output radar systems, the employed waveforms should have a large time-bandwidth product, good correlation property and satisfactory ambiguity function performance. This paper proposes a orthogonal frequency division multiplexing (OFDM) chirp waveform diversity design scheme with sparse modeling and joint optimization of the waveform code matrix and amplitude matrix. First, we formulate the waveform diversity design as a mathematical optimization problem with sparse modeling and optimally design a code matrix to select the hopping frequencies for each waveform. Thereafter, the waveform amplitudes are adaptively designed by minimizing the cross-correlation peaks with genetic algorithm. The proposed method can easily generate multiple pseudo-orthogonal waveforms with satisfactory correlation and ambiguity function performance. Additionally, the impacts of waveform number, hopping frequency interval and selectable frequency index are discussed. The superiority of the proposed OFDM chirp waveform design over existing methods is verified by extensive simulation results.     

BaZrO3基质固体电解质的水热合成与表征

利用水热晶化法制备了BaZrO₃纯相和BaZr_1-xM_xO_3-α(M=Al,Ga,In;x≤0.20)体系固体电解质,通过XRD、SEM、IR、²⁷AlMASNMR和化学分析,对产物的物相、粒度和掺杂质进入晶格的数量进行了表征。结果表明,产物为立方钙钛矿结构,粒度为3～5μm,在0≤x≤0.20范围内,产物的金属离子比与投料比基本一致。     

中孔分子筛MCM-41的合成与表征

以白炭黑和正硅酸乙酯为硅源,十二、十六烷基三甲基铵为模板剂,用水热法和室温直接法合成出中孔分子筛MCM-41,考察了对合成的影响因素,用红外光谱、吸附、孔分布、热分析等手段对这两种产物进行了表征。结果表明:这种分子筛可以在很宽的配比范围内获得,但较高水硅比更有利于合成;在水硅比较低的体系中得到了一种类MCM-41中孔相(亦应属于MCM-41),其XRD衍射峰较宽,2θ角度偏低,具有类似于无定形硅铝酸盐的骨架结构。