Comparative study of different properties of GaN films grown on(0001) sapphire using high and low temperature AlN interlayers

Comparative study of high and low temperature AlN interlayers and their roles in the properties of GaN epilayers prepared by means of metal organic chemical vapour deposition on (0001) plane sapphire substrates is carried out by high resolution x-ray diffraction, photoluminescence and Raman spectroscopy. It is found that the crystalline quality of GaN epilayers is improved significantly by using the high temperature AlN interlayers, which prevent the threading dislocations from extending, especially for the edge type dislocation. The analysis results based on photoluminescence and Raman measurements demonstrate that there exist more compressive stress in GaN epilayers with high temperature AlN interlayers. The band edge emission energy increases from 3.423~eV to 3.438~eV and the frequency of Raman shift of $E_{2 }$(TO) moves from 571.3~cm$^{ - 1}$ to 572.9~cm$^{ - 1}$ when the temperature of AlN interlayers increases from 700~$^{\circ}$C to 1050~$^{\circ}$C. It is believed that the temperature of AlN interlayers effectively determines the size, the density and the coalescence rate of the islands, and the high temperature AlN interlayers provide large size and low density islands for GaN epilayer growth and the threading dislocations are bent and interactive easily. Due to the threading dislocation reduction in GaN epilayers with high temperature AlN interlayers, the approaches of strain relaxation reduce drastically, and thus the compressive stress in GaN epilayers with high temperature AlN interlayers is high compared with that in GaN epilayers with low temperature AlN interlayers.     

光子晶体环形腔的四波长THz滤波器

提出一种基于光子晶体环形腔的四波长THz滤波器,该滤波器在光子晶体结构中引入两个环形腔,且环形腔内部各增加一个正方形介质柱,四周各引入一个散射介质柱。应用基于时域有限差分法(FDTD)的Rsoft软件进行仿真分析,结果表明通过对内部正方形介质柱的边长、散射介质柱半径以及耦合介质柱半径等结构参数的调节,可以滤出74.813,76.98,78.168和78.883 m四个太赫兹波长。该滤波器性能优良,透过率高、Q值高、信道隔离度大,对于THz技术应用具有重要意义。     

光纤布拉格光栅嵌入SMS光纤结构的湿度传感器

提出了一种基于光纤布拉格光栅嵌入单模-多模纤芯-单模(single-mode-multimode fiber core-single mode, SMS)光纤结构的湿度传感器。当环境湿度变化时,SMS光纤结构的干涉光谱会发生漂移,而光纤布拉格光栅对湿度不敏感,其纤芯基模保持不变。因此利用SMS光纤结构对环境湿度的敏感性去调制光纤布拉格光栅纤芯基模,通过检测光纤布拉格光栅纤芯基模的反射能量变化就可以实现湿度测量。数值模拟了SMS光纤结构的内部光场分布规律,理论计算了不同环境折射率时,多模纤芯的长度、直径对SMS光纤结构输出能量耦合系数的影响。理论模拟表明,随着环境折射率变化,SMS光纤结构中传输的纤芯基模的输出能量耦合系数会发生变化。同时制作了传感器样品并对其进行了传感实验研究,实验结果表明多模纤芯长35 mm、纤芯直径为85 μm的传感器在45%～95%RH湿度变化范围内,湿度灵敏度为0.06 dBm·(%RH)-1。在20～80 ℃温度范围内,传感器的温度灵敏度为0.008 nm·℃-1,温度所带来的湿度测量误差为0.047%RH·℃-1。传感器具有制作简单、灵敏度高、反射式能量检测等优点,在湿度测量领域有一定的应用价值。     

氢掺杂单层石墨体系的晶格动力学研究

采用密度泛函理论研究了氢掺杂单层石墨（graphene）体系,并采用密度泛函微扰理论方法计算了体系局域振动模（LVMs）.结果显示,高频位置的LVMs数目与缺陷中氢原子数相等,而不同掺杂类型的LVMs频谱位置各不相同.研究结果及分析表明,LVMs测量是评估质子辐射下石墨样品的替位氢掺杂类型及其含量的有效方法,该方法可推广应用于研究其他掺杂体系. 关键词： 石墨 局域模式 晶格动力学     

Collisional stability of fermionic Feshbach molecules

Using a Feshbach resonance, we create ultracold fermionic molecules starting from a Bose-Fermi atom gas mixture. The resulting mixture of atoms and weakly bound molecules provides a rich system for studying few-body collisions because of the variety of atomic collision partners for molecules; either bosonic, fermionic, or distinguishable atoms. Inelastic loss of the molecules near the Feshbach resonance is dramatically affected by the quantum statistics of the colliding particles and the scattering length. In particular, we observe a molecule lifetime as long as 100 ms near the Feshbach resonance.     

Tb3+掺杂硅酸盐玻璃发光性能的浓度依赖关系

 利用高温熔融法制备了不同浓度的Tb³⁺掺杂硅酸盐玻璃,并分别测量了紫外和X射线激发时的发射光谱。光谱结果表明,不同浓度Tb³⁺掺杂硅酸盐玻璃在紫外和X射线激发时发光行为具有相似的浓度依赖关系：低浓度Tb₄O₇掺杂时主要以蓝光(5D₃→⁷FJ)发射为主,而高浓度掺杂时以绿光(⁵D₄→⁷FJ)发射为主。Tb³⁺发光强度与掺杂浓度的关系分析表明,⁵D₃的浓度猝灭是电偶极-电偶极相互作用引起的, 而⁵D₄的浓度猝灭是交换相互作用引起的。     

双偏振结构保偏光纤偏振器的研制

提出了保偏光纤偏振器的一种串联结构,即双偏振结构,报道了研制的结果。并通过对单偏振结构和双偏振结构器件测试结果的比较,得出双偏振结构的保偏光纤偏振器可使器件达到高消光比,并且有稳定的温度特性。     

电流变液成链过程的一种序参量描述

A simple long-range-order parameterPis defined for describing the process of formation of chains in the electric field direction. The free energy of the system is taken to be the sum of the internal energy, the electrostatic interaction and configuration entropy as a function o P. Calculated results indicate that the critical parameter is a function of electric field, temperature, misfit dielectric coefficients and concentration of particles.