Mechanism of Enhanced Dielectric Properties of SiC/Ni Nanocomposites

Dielectric properties of SiC/Ni nanocomposites prepared by a simple and facile electroless plating approach at X band are investigated. Compared to the original SiC nanopartieles （SiCp）, the real part of the permittivity, ε＇, and the dielectric loss tangent tang δe of SiC/Ni nanocomposites are clearly enhanced by about 31% and 33%, respectively. The effective equations for complex permittivity of SiC/Ni nanoeomposites are proposed. We also calculate ε＇ and tan δe of SiC/Ni nanoeomposites and the calculated results are well consistent with the measured data.     

High-Temperature Dielectric Response and Multiscale Mechanism of SiO2/Si3N4 Nanocomposites

The high-temperature dielectric properties of SiO₂/Si₃N₄ nanocomposites are investigated theoretically and experimentally. Its permittivities and loss tangents at the temperature ranging from room temperature to 1300°C at 9.0GHz are measured by the resonant cavity method. The SiO_2/Si₃N₄ nanocomposites show complex dielectric behaviour at elevated temperature, and a multi-scale model is proposed to describe the dependence of the dielectric properties in the SiO₂/Si₃N₄ on its compositional variations. Such a theory is needed so that the available property measurements could be extrapolated to other operating frequencies and temperatures.     

Transforming a Two-Dimensional Layered Insulator into a Semiconductor or a Highly Conductive Metal through Transition Metal Ion Intercalation

Atomically thin two-dimensional(2D) materials are the building bricks for next-generation electronics and optoelectronics, which demand plentiful functional properties in mechanics, transport, magnetism and photoresponse.For electronic devices, not only metals and high-performance semiconductors but also insulators and dielectric materials are highly desirable. Layered structures composed of 2D materials of different properties can be delicately designed as various useful heterojunction or homojunction devices, in which the designs on the same material(namely homojunction) are of special interest because preparation techniques can be greatly simplified and atomically seamless interfaces can be achieved. We demonstrate that the insulating pristine ZnPS_3, a ternary transition-metal phosphorus trichalcogenide, can be transformed into a highly conductive metal and an n-type semiconductor by intercalating Co and Cu atoms, respectively. The field-effect-transistor(FET) devices are prepared via an ultraviolet exposure lithography technique. The Co-ZnPS_3 device exhibits an electrical conductivity of 8 × 10~4 S/m, which is comparable to the conductivity of graphene. The Cu-ZnPS_3 FET reveals a current ON/OFF ratio of 1~05 and a mobility of 3 × 10~(-2 )cm~2·V~(-1)·s~(-1). The realization of an insulator, a typical semiconductor and a metallic state in the same 2D material provides an opportunity to fabricate n-metal homojunctions and other in-plane electronic functional devices.     

光电导开关产生太赫兹电磁波双极特性分析

利用光电导体产生太赫兹电磁波(THz波)，THz远场辐射波形与光电导体材料的载流子寿命、偏置电场以及触发光有直接关系.用不同方法对低温GaAs(LT-GaAs)和半绝缘GaAs(SI-GaAs)光电导开关辐射的THz电磁波所呈现的双极特性进行了模拟计算.结果表明，LT-GaAs光电导开关辐射THz波呈现双极性的主要原因是光生载流子寿命小于一个THz波产生时间；而光生载流子寿命大于100ps的SI-GaAs光电导开关，在不同的实验条件（不同偏置电场、不同光脉冲能量）下，产生的THz波呈现双极特性的主要原因分别是载流子发生了谷间散射和空间电荷电场屏蔽. 关键词： 光电导开关 THz电磁波 载流子寿命 空间电荷屏蔽     

BBOⅠ类相位匹配非共线参量产生中的群速自匹配

利用重复频率为1kHz的钛宝石激光的倍频蓝光抽运Ⅰ类相位匹配的偏硼酸钡(BBO)晶体，获得了可见光区的非共线参量超荧光.给出了最强光强处参量超荧光的非共线角，波长随相位匹配角的变化.理论计算了在参量超荧光中三波的群速失配随非共线角和相位匹配角的变化规律.结果表明，Ⅰ类非共线相位匹配的参量超荧光关于抽运光中心对称.并且沿光强最强的参量超荧光方向三波的群速失配最小，有效互作用长度最大，即参量超荧光的强度角分布是三波的相速和群速自匹配的结果.该理论和实验研究为减小飞秒光参量放大中三波的群速失配提供了一个理想的几何模型，为获得高增益、窄脉冲宽度的参量光输出提供了理论依据和实验验证. 关键词： 群速自匹配 参量超荧光 非共线相位匹配 飞秒光参量放大     

飞秒激光在双折射微结构光纤中模式控制的四波混频效应的实验研究

利用飞秒激光脉冲在长度为10cm，包层具有大空气比的双折射微结构光纤中通过高阶模相位 匹配的四波混频获得了波长可调谐的反斯托克斯波.实验中脉冲宽度为35fs，中心波长820nm ，单脉冲能量4nJ的飞秒激光脉冲耦合到长轴直径为5μm，短轴为46μm的双折射微结构光 纤中.在高阶模传输情况下，通过调制耦合光的偏振方向，获得了具有不同中心波长的反斯 托克斯波.通过对比分析，讨论了输入光的偏振态对双折射微结构光纤中高阶模式下四波混 频效应的影响情况.理论计算分析很好的解释了实验结果. 关键词： 微结构光纤 飞秒脉冲激光 四波混频     

高能电子–正电子碰撞产生的喷注内部分形性质的蒙特–卡洛研究

用蒙特–卡洛方法研究了91.2GeV e⁺e^－碰撞产生的喷注内部的分形性质.采用一个新变量r得到了很好的反常标度性.研究了不同阶标度指数之间的关系,得到了喷注内部强子系统的Lévy指数,并和电子–正电子碰撞及强子–强子碰撞的相应指数作了对比.讨论了结果的意义.     

Synthesis and mesomorphic properties of n-alkyl 4-[4-(4-n-octyloxybenzyloxy-2,3,5,6-tetrafluorophenyl)ethynyl]benzoates

A new series of n-alkyl 4-[4-(4-n-octyloxybenzyloxy-2,3,5,6-tetrafluorophenyl)ethynyl)benzoates have been prepared. Polarizing microscopic textural observation shows that they are liquid crystals with nematic phase.     

吡咯取代的杂环俘精酸酐的合成及溶剂对其吸收光谱的影响

合成了五个新的3-乙酰基吡咯衍生物,以它们为原料,进一步合成了五个新的吡咯取代的俘精酸酐。研究了五个俘精酸酐化合物在不同溶剂中的光致变色性能,考察了溶剂极性对俘精酸酐及其光致变色反应产物(7,7a-二氢吲哚衍生物)吸收光谱的影响,结果表明,随溶剂极性的增加吸收光谱发生红移。对7,7a-二氢吲哚衍生物的影响远比对俘精酸酐本身的影响显著的多。     

Sb有序单晶纳米线阵列的制备

采用直流电沉积的方法在氧化铝模板（AAM）中成功地制备了Sb单晶纳米线阵列. X射线衍射（XRD）证明所制得的纳米线阵列为(110)取向的六方相Sb.透射电镜（TEM）显示Sb纳米线平滑而均匀,直径40～50 nm,长径比大于1000.选区电子衍射（SAED）结果表明,所制得的纳米丝为Sb单晶丝.场发射扫描电镜（FE-SEM）显示Sb纳米线阵列规则,填充率接近100％.