Thermodynamic properties of 3C-SiC

In the present paper, we report on the results of various thermodynamic properties of 3C-SiC at high pressure and temperature using first principles calculations. We use the plane-wave pseudopotential density functional theory as im- plemented in Quantum ESPRESSO code for calculating various cohesive properties in ambient condition. Further, ionic motion at a finite temperature is taken into account using the quasiharmonic Debye model. The calculated thermody- namic properties, phonon dispersion curves, and phonon densities of states at different temperatures and structural phase transitions at high pressures are found to be in good agreement with experimental and other theoretical results.     

功能层厚度对叠层有机电致发光器件出光性能影响的数值研究

功能层厚度是影响有机电致发光器件出光效率的主要因素之一,故获得不同功能层厚度对器件出光特性的影响规律是制备高性能器件的重要基础. 本文基于薄膜光学原理、电偶极子辐射理论及Fabry-Pérot微腔原理,建立了结构为glass/ITO/N,N0-bis（naphthalen-1-yl）-N,N0-bis（phenyl）-benzidine（NPB）/tris（8-hydroxyquinoline）aluminum（Alq₃）/molybdenum trioxide（MoO₃）/NPB/Alq₃/Al的叠层有机电致发光器件的光学模型,系统地研究了各个功能层厚度对叠层有机电致发光器件出光强度的影响,得到了功能层厚度对器件出光强度影响的规律. 该模型的建立与所获得的结果可对深入了解叠层有机电致发光器件的工作机理以及制备高性能的器件提供一定的帮助. 关键词： 叠层有机发光器件 出光特性 厚度 数值研究     

空富勒烯C36和嵌入Mg原子的C36分子的电子学特性研究

采用基于密度泛涵理论的第一性原理和非平衡格林函数方法研究了富勒烯C36分子和以金原子面为电极的Au-S-C36-S-Au电子传输系统的电子结构和传输特性.然后将镁原子嵌入C36笼腔内得到了一个新的分子器件Mg@C36,接金电极后建立了它的电子传输系统Au-S-Mg@C36-S-Au,并且得出了这一系统的电子能级、分子轨道分布、传输概率、态密度、伏安特性和电导曲线.结果显示C36和Mg@C36的电子传导主要集中在分子壳上,且系统Au-S-C36-S-Au中的电子传输主要分布在分子壳的外侧,而系统Au-S-Mg@C36-S-Au中的电子传输在分子壳外侧和内侧的近似相同,二个系统都有着非线性的Ⅰ-Ⅴ特性和电导曲线.     

一类具有Markov性质的混沌系统的构造

本文构造了一类具有Markov性质的分段扩张线性映射, 计算表明其具有正的李雅普诺夫指数. 通过理论分析, 证明了其极限分布是均匀分布, 并给出了其最小周期的计算公式. 通过分析符号熵测度应用于此系统时的具体涵义, 指出该系统的复杂度与系统的最小周期之间存在着矛盾关系, 说明了此系统具有可控的复杂度并给出了其复杂度随系统参数变化时的理论极限公式. 通过统计测试和复杂度测试表明, 此系统产生的混沌序列服从均匀分布, 而通过参数的调整该系统的符号熵可以接近其理论极限, 而与Logistic映射和斜帐篷映射的基于近似熵和符号熵的对比实验可知, 本文所提系统具有更高的复杂度, 并有更长的最小周期. 这表明此系统比较适合用于构造保密通信系统. 关键词： 混沌 Markov性质 复杂度 均匀分布     

Surface-modified antibacterial TiO2/Ag nanoparticles: Preparation and properties

Studies were performed on surface modification of antibacterial TiO₂/Ag⁺ nanoparticles by grafting γ-aminopropyltriethoxysilane (APS). The interfacial structure of the modified particles was characterized by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric analysis. The thickness of the surface layer was determined by using Auger electron spectroscopy (AES). The results show that APS is chemically bonded to the surface of antibacterial TiO₂/Ag⁺ nanoparticles. Furthermore, the modified particles were mixed in PVC to prepare composites whose antibacterial property was investigated. The results suggest that surface modification has no negative effect on antibacterial activity of TiO₂/Ag⁺ nanoparticles and PVC-TiO₂/Ag⁺ composites exhibits good antibacterial property.     

密度泛函理论研究簇合物(HFGaN3)n (n=1-6)：尺寸效应

用密度泛函理论DFT方法,计算研究不对称簇合物(HFGaN3)n (n=1-6)的几何构型、稳定性、IR谱和热力学性质。结果表明,簇合物(HFGaN3)n (n=2-6)的优化构型拥有一个Ga和α−N原子交替的2n元环状结构。通过计算研究(HFGaN3)n (n=1-6)的平均结合能、二阶能量差分和能隙与团簇尺寸关系,发现后两者表现出明显的“奇－偶”振荡现象。对计算获得的IR谱进行归属,获得四个特征区。讨论了团簇尺寸和温度对(HFGaN3)n (n=1-6)热力学函数的影响。由焓变和吉布斯自由能可知,200-800 K温度范围内由单体形成稳定的多聚体(HFGaN3)n (n=2-6)在热力学上有利。     

Investigation the effects of the excess Pb content and annealing conditions on the microstructure and ferroelectric properties of PZT (52-48) films prepared by sol-gel method

The effects of the PbO volatilization, excess Pb content of PbZr_0.52Ti_0.48 (PZT) precursor, PbTiO₃ (PT) seeding layers and annealing condition on the microstructures, surface morphologies, preferred orientation and ferroelectric properties of PbZr_0.52Ti_0.48 films were systematically investigated. PZT films with a variety of excess Pb (0-20%) were spin-deposited on Si(1 0 0) and Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by sol-gel technique. The films composition, Pb/Zr/Ti/O atom rate and Pb loss were semiquantitative analyzed by X-ray photoelectron spectrometer (XPS). When the excess Pb of PZT precursor was 10%, the Pb/Zr/Ti/O atomic rate of the fabricated films was very close to the designed rate of 1:0.52:0.48:3. The XRD and AFM investigations confirmed that PT seeding layer promoted the PZT films perovskite phase transformation and grains growth with (1 1 0) plane preferred orientation, accordingly lowered perovskite phase crystallization temperature and reduced Pb loss. The PZT films annealed in O₂ flow demonstrated better microstructure and ferroelectric properties comparing with films annealed in air by double remnant polarization increase and 8% coercive field increase. The underlying mechanism was also investigated.     

Chemical synthesis of p-type nanocrystalline copper selenide thin films for heterojunction solar cells

Nanocrystalline thin films of copper selenide have been grown on glass and tin doped-indium oxide substrates using chemical method. At ambient temperature, golden films have been synthesized and annealed at 200 °C for 1 h and were examined for their structural, surface morphological and optical properties by means of X-ray diffraction (XRD), scanning electron microscopy and UV-vis spectrophotometry techniques, respectively. Cu_2−xSe phase was confirmed by XRD pattern and spherical grains of 30 ± 4 - 40 ± 4 nm in size aggregated over about 130 ± 10 nm islands were seen by SEM images. Effect of annealing on crystallinity improvement, band edge shift and photoelectrochemical performance (under 80 mW/cm² light intensity and in lithium iodide electrolyte) has been studied and reported. Observed p-type electrical conductivity in copper selenide thin films make it a suitable candidate for heterojunction solar cells.     

Mn和Co线性单原子链填充Cu纳米管的稳定性和磁性

基于密度泛函理论框架下的第一性原理计算,系统地研究了过渡金属(TM)Mn和Co线性单原子链填充Cu纳米管所形成复合结构的稳定性和磁性.相对于孤立单原子链,复合结构的结合能大大增加,表明Cu纳米管的包裹使得Mn和Co单原子链的稳定性显著增强.随着管内TM原子间距的增加,Mn@CuNT复合结构表现出由反铁磁向铁磁的磁相变,而Co@CuNT复合结构则表现出由铁磁向反铁磁的磁相变.相对于自由单原子链,复合结构的磁晶各向异性能显著增强,且Cu纳米管的包裹使得Mn原子链的易磁化方向发生了改变.     

反射式光纤传感器光纤参量对调制系数的影响

介绍了反射式强度型光纤传感器的光强调制原理,并以最简单的光纤对为基础,仿真研究了光纤参量对光强调制特性的影响规律.给出了这类传感器设计的指导原则.