Ta2O5/MgF2异质结构三维光子晶体的偏振性

为了在可见及近红外波段得到具有良好带隙结构的三维光子晶体,利用传输矩阵法分析了MgF₂、Ta₂O₅ 以及Ta₂O₅/MgF₂异质结构三维光子晶体的带隙性质.结果表明：Ta₂O₅/MgF₂异质结构三维光子晶体在820~1 020 nm的近红外波段TM模式下具有不受入射光方向影响的全方位光子带隙.该结构有望用于制作近红外光波段的偏振器件.     

紫外线波段一维Ag/MgF_2光子特性的理论研究

利用传输矩阵方法对一维Ag/MgF2光子晶体的带隙特性进行了研究。构建了由Ag和MgF2组成的一维光子晶体结构模型,以此模型为基础详细讨论了填充比、周期层数、入射角等参数对光子晶体带隙结构的影响,并讨论了造成吸收的原因。研究结果表明,与其他金属光子晶体的研究结果相比,该结构的金属光子晶体在紫外线波段具有高反射率的光子带隙,属于不完全带隙的一维光子晶体,适用于制作紫外线波段的光学反射镜。     

一维Au/MgF2光子晶体的透射性质

理论上研究了一维金属/电介质光子晶体的透射率性质，用传输矩阵方法数值计算了Au/MgF2光子带隙晶体的透射率．发现周期性结构产生的透射共振会大幅度增加光通过层状金属的透射率．通过调节一维Au/MgF2光子晶体中金和氟化镁的厚度以及周期数，得到了可见波段的高透射允带，透射率在0.4以上，而对于可见波段以外的频率几乎是完全不能传输的．这种结构在保持了高透射率的前提下还具有金属的优点，这在传感器、护目装置、反射窗、液晶显示等诸多领域都有很大的实用价值．     

一维光子晶体光谱控制实验研究

光子晶体的禁带特性为伪装材料的光谱控制研究提供了一条新的技术途径。利用传输矩阵的方法建立了一维光子晶体光谱透射、反射的理论模型,针对伪装材料近红外高反射、中远红外低发射的要求,优选Ag,MgF2和ZnS等材料作为光子晶体的薄膜材料,采用真空蒸发镀膜的方法制备出Ag/MgF2,Ag/MgF2/ZnS 4种不同周期结构的一维光子晶体,并实验研究了一维光子晶体的光谱反射和透过特性。结果表明:材料和周期结构对一维光子晶体光谱特性有不同的影响,通过优化设计可以实现在伪装波段内的光谱特性要求。     

木堆结构三维光子晶体带隙特性

基于平面波展开法研究木堆结构三维光子晶体带隙特性.用硅材料构成木堆结构三维光子晶体,改变结构中木条的宽度和长度,得到当木堆条宽度为5μm,高度为7μm时形成的带隙结构较宽,在0.2899-0.3804Hz,带隙宽度为0.0905Hz.改变构成木堆结构三维光子晶体的材料,得到锗材料构成木堆结构三维光子晶体带隙结构在0.2585-0.3500Hz,带隙宽度为0.0915Hz,带隙相比硅材料和碳化硅材料较宽.研究结论为三维光子晶体的制备提供参考.     

可用于拓宽光波单向传输带宽的光子晶体异质结构界面

基于光波单向传输的全光二极管在集成光通信、全光网络和光信息处理中有重要应用.基于方向带隙失配设计的光子晶体异质结构可实现光波单向传输,但正向透射率较低,带宽较窄.基于对光子晶体异质界面倾斜角度的研究,根据界面全反射条件,利用可集成材料硅和二氧化硅设计了一种空气孔型二维光子晶体异质结构.异质结构界面两侧的光子晶体对1550 nm波长附近的TE模光波在Γ-X方向均呈导带,避免了方向带隙失配.研究发现当异质界面满足全反射条件时,由于光子晶体的自准直效应,较宽波段的正向光波得以高效传播,而反向光波在界面由于全反射而被禁止传播.光子晶体异质结构界面的全反射效应打破了方向带隙对光波单向传输的限制,使得反向光波在光子晶体中为导带时同样可实现近零透射率,从而拓宽了光波单向传输的波长范围.基于全反射界面的光子晶体异质结构经过优化后,其正向透射率达0.64,透射对比度为0.97,单向传输带宽可达553 nm.     

二氧化硅胶体球自组装光子晶体的研究

光子晶体由于具有光子带隙和光子局域等一系列优异的光学特性而受到了人们广泛的关注。由于采用胶体颗粒自组装法制备光子晶体制备工艺简单,所需要的费用也较低,因此已成为制备可见光至红外波段三维光子晶体的一种简便有效的方法。采用垂直沉积法制得了三维光子晶体薄膜,并用扫描电子显微镜和紫外-可见光-近红外分光光度计对其显微结构和光学特性进行了详细的研究。结果表明,自组装薄膜在三维方向上都具有有序结构,其密排面平行于载波片的表面。制备的光子晶体薄膜具有明显的光子带隙特性,带隙中心波长为956nm。研究了带隙中心波长同入射线与密排面法线夹角之间的变化关系,其结果与理论值吻合得很好。     

六角蜂窝结构光子晶体异质结带隙特性研究

利用蜂窝结构光子晶体具有两个范围较大绝对带隙的特性，设计新型六角蜂窝结构光子晶体异质结，采用平面波展开和超晶胞相结合的方法来研究异质结的能带结构特性.给出异质结的结构和相应的能带图，分析异质结界面传导模，研究两侧结构作横向拉开和侧向滑移时对传导模的影响，讨论这些结构的实际可行性.计算结果表明，没有任何晶格移动，此种结构异质结在绝对带隙中就有导模存在，两边晶格横向拉开对导模影响较大，而侧向滑移的影响则较小. 关键词： 光子晶体 异质结 光子带隙 超晶胞     

一维三元异质结构光子晶体反射特性

利用传输矩阵法对一维三元光子晶体异质结构的光学特性进行了研究,讨论了介质层厚无序度对三元结构光子禁带的影响.研究表明,将具有相互交叠光子禁带的一维光子晶体叠加构成异质结,可以有效地增大全角度反射的频率范围,当入射角从0°增大到89°,该结构均可实现从0.410 w/w0到0.654 w/w0宽频波段的全反射;相对于二元结构,三元结构可以减小在实际制作过程中随机误差引起的介质层厚无序对光子带隙的影响.该研究结果可为实现可见光及红外光波段大角度反射器的制备及应用提供理论支持.     

准完全带隙胶体非晶光子晶体

三维面心立方结构的固有的高对称性使其只具备非完全光子带隙,而非晶结构可降低对称性导致准完全光子带隙的出现.实验结果表明非晶胶状晶体具有准完全光子带隙.非晶胶状光子晶体中的光子带隙的禁带宽度与波长均不随光入射到样品池的角度的变化而明显变化.其禁带宽度比SiO₂小球面心单晶的禁带宽度宽得多 关键词： 光子带隙 非晶 光谱     

Magnetic ordering in HoRu2Si2, HoRh2Si2, TbRh2Si2 and TbIr2Si2 by neutron diffraction

Neutron diffraction study of polycrystalline HoRu₂Si₂, HoRh₂Si₂, TbRh₂Si₂, and TbIr₂Si₂ was performed in the temperature range between 4.2 and 300 K. For HoRu₂Si₂ the magnetic spin alignment of a linear transverse wave mode below the Néel temperature 19 K is observed. This static moment wave is propagating along the b-axis with k=(0, 0.2, 0) and is polarized in the c-axis. The root-mean-square and maximum saturation moments per Ho atom are 9.26 and 13.09μ_B, respectively. HoRh₂Si₂, TbRh₂Si₂ an TbIr₂Si₂ are simple collinear antiferromagnets of +-+- type with Néel temperatures of (27±1), (98±2) and (72±3) K, respectively. For TbRh₂Si₂ and TbIr₂Si₂ magnetic moments are localized on RE ions only and are aligned along the tetragonal axis, while for HoRh₂Si₂ they form an angle ø = (28±3)°.     

μ+SR study of LaNi2As2, URh2Si2 and CeRh2Si2

Muon spin relaxation experiments have been carried out in the paramagnetic and magnetically ordered states of URh₂Si₂ and CeRh₂Si₂. As the magnetic structure of these compounds is well known, these measurements can help to characterise their magnetic properties probed by μSR and to understand the μSR results of the heavy fermion compounds of the same crystallographic family. Our measurements show that the muons occupy two different crystallographic sites. The spectra of URh₂Si₂ and CeRh₂Si₂ in the magnetically ordered states are very different, probably reflecting their different magnetic structures. The spectra obtained on CeRh₂Si₂ are similar to the published spectra of the heavy fermion compound CeCu_2.1 Si₂. Muon spin rotation measurements on LaNi₂As₂ indicate that the muon is diffusing at 150 K.     

13C-selective IRMPD of CBr2F2/Cl2 and CCl2F2/Br2 systems

The CO₂ TEA laser irradiation of CBr₂F₂ in the presence of Cl₂ yielded ¹³C-enriched CBrClF₂ and ¹³C-enriched CCl₂F₂ under selected experimental conditions. As the photolysis proceeded, the ¹³C concentration of CBrClF₂ decreased gradually and that of CCl₂F₂ increased up to 90% or higher. These results can be explained by the mechanism involving the secondary ¹³C-selective IRMPD of the primary product CBrClF₂. On the other hand, the carbon-containing product for a CCl₂F₂/Br₂ system was only CBrClF₂; the further IRMPD of which probably regenerated CBrClF₂ in the presence of Br₂. The decomposition probabilities of ¹²C- and ¹³C-containing molecules in both systems were measured as functions of laser line, laser fluence, and reactant pressures.     

Magnetostriction of SmMn2Ge2 and GdMn2Ge2 intermetallic compounds

Longitudinal and transverse magnetostrictions of polycrystalline samples of intermetallic compounds RMn₂Ge₂ (R=Sm or Gd) are measured in pulsed magnetic fields up to 250 kOe. It is found that linear magnetostrictive strains of about 10^?3 arise in a temperature range in which the magnetic field causes a change in the magnetic state of a manganese magnetic subsystem. The results obtained are described within the model of a two-sublattice ferrimagnet with a negative exchange interaction in the manganese subsystem in terms of a strong dependence of this interaction on interatomic distances.     

Polar optic phonons in Hg2Cl2 and Hg2Br2

Far infrared (30–430 cm^?1) reflectivity measurements of Hg₂Cl₂ and Hg₂Br₂ single crystals have been performed in polarized light. The spectra, which are in agreement with group-theoretical predictions, were analyzed by the oscillator fitting procedure and Kramers-Kronig method. The results are compared with the existing data from other measurements and the large anisotropy of polar modes is briefly discussed. The polarization vectors of all long-wavelength symmetry modes were determined group-theoretically.     

Superconductivity in LaPd_2Bi_2 with CaBe_2Ge_2-type structure

正Since the discovery of superconductivity in LaFeAsO_(1-x)F_x,the high-T_c iron-based superconductors have been extensively studied from both experimental and theoretical viewpoints [1-8]. However, the mechanism of the unconventional superconductivity is still to be resolved. To     

Structural,magnetic and neutron diffraction studies on TbFe2-TbAl2, TbCo2-TbAl2 and HoCo2-HoAl2

Both pseudobinary systems exhibit large homogeneous regions of cubic and hexagonal Laves phases. Ordering tendencies on crystallographic sites between Al and the transition metals are observed in the hexagonal type.Electron transfer to the transition metals quenches their moments so that they become nonmagnetic at high Al concentrations. The peculiarities in the mechanism of magnetization which appear in rare earth dialuminides when Al is replaced by a transition metal have been studied in detail at cryogenic temperatures.The first replacement of Al results in a decrease in saturation moment. Neutron diffraction verifies the low ordered rare earth sublattice moments and reveals the ‘lost part’ as a disordered component. Considerable magnetic hardness develops in certain regions of concentration often connected with spontaneous increases in magnetization with field. All available evidence suggests the presence of unusual domain wall effects to be responsible for this effect. High remanences develop in both the hexagonal and in the cubic structures in the intermediate region. The development of disordered magnetic components is connected either with the disorder on crystallographic sites or changes in the free electron concentration.