Design of Enhanced Catalysts by Coupling of Noble Metals (Au,Ag) with Semiconductor SnO2 for Catalytic Reduction of 4‐Nitrophenol

The reduction of 4‐nitrophenol (Nip) into 4‐aminophenol (Amp) by NaBH₄, which is catalyzed by both binary and ternary yolk–shell noble‐metal/SnO₂ heterostructures, is reported. The binary heterostructures contain individual Au or Ag nanoparticles (NPs) and the ternary heterostructures contain both Au and Ag NPs. The Au@SnO₂ yolk–shell NPs are synthesized via a silica seeds‐mediated hydrothermal method. Subsequently, the Au@SnO₂@Ag and Au@SnO₂@Au yolk–shell–shell (YSS) NPs are synthesized, whereby SnO₂ is located between the Au and Ag NPs. The morphology, composition, and optical properties of the as‐prepared samples are analyzed. For the binary heterostructures, the rate of the reduction reaction increases with decreasing particle size. The catalytic results demonstrate the synergistic effect of Au and Ag in the ternary metal–semiconductor heterostructures, which is beneficial to the catalytic reduction of Nip into Amp. Both the binary and ternary heterostructures exhibit significantly better catalytic performances than the corresponding bare Au and Ag NPs. It is envisaged that the current synthesized strategy will promote further interest in the field of bimetal NP‐based catalysis.     

低温退火的X射线W/Si多层膜应力和结构性能

W/Si多层膜反射镜在硬X射线天文望远镜中有重要应用. 为减小其应力对反射镜面形和望远镜分辨率的影响, 同时保证较高的反射率, 采用150, 175和200 ℃ 的低温退火工艺对采用磁控溅射镀制的W/Si周期多层膜进行后处理. 利用掠入射X射线反射测试和样品表面面形测试对退火前后W/Si多层膜的应力和结构进行表征. 结果表明, 在150 ℃ 退火3 h 后, 多层膜1级峰反射率和膜层结构几乎没有发生变化, 应力减少约27%; 在175 ℃ 退火3 h后, 多层膜膜层结构开始发生变化, 应力减少约50%; 在200 ℃退火3 h 后, 多层膜应力减小超过60%, 但1级布拉格峰反射率相对下降17%, 且膜层结构发生了较大变化. W, Si界面层的增大和相互扩散加剧是应力和反射率下降的主要原因.     

ZnO/A1lN/Si(111)薄膜的外延生长和性能研究

用常压金属化学气相沉积法(MOCVD)在Si(111)衬底上制备了马赛克结构ZnO单晶薄膜.引入低温AlN缓冲层以阻止衬底氧化、缓解热失配和晶格失配.薄膜双晶X射线衍射2θ/ω联动扫描只出现了Si(111)、ZnO(000l)及AlN(000l)的衍射峰.ZnO/AlN/Si(111)薄膜C方向晶格常量为0.5195 nm,表明在面方向处于张应力状态;其对称(0002)面和斜对称(1012)面的双晶X射线衍ω摇摆曲线半峰全宽分别为460"和1105";干涉显微镜观察其表面有微裂纹,裂纹密度为20 cm-1;3 μm×3μm范围的原子力显微镜均方根粗糙度为1.5 nm激光实时监测曲线表明薄膜为准二维生长,生长速率4.3μm/h.低温10 K光致发光光谱观察到了薄膜的自由激子、束缚激子发射及它们的声子伴线.所有结果表明,采用金属化学气相沉积法并引入AlN为缓冲层能有效提高Si(111)衬底上ZnO薄膜的质量.     

掺杂对CH样品Rayleigh-Taylor不稳定性增长的影响

在神光II激光装置上进行了辐射驱动不同掺杂样品的单模Rayleigh-Taylor(RT)不稳定性实验.结果显示:与纯碳氢(CH)样品相比,掺Br的CH样品的扰动更早、更快地进入非线性区,产生二次谐波,并且掺Br比例越高,CH样品扰动进入非线性区的时间越早,相同时刻扰动的二次谐波的幅度越高.这是因为密度梯度效应抑制了二次谐波的产生,掺Br比例越高,密度梯度标长越小;同时密度梯度效应还抑制三次谐波对基模增长的负反馈,造成基模具有更大的线性增长,导致线性饱和幅值大于经典值0.1λ.     

Efficient generation of a photon pair in a bulk periodically poled potassium titanyl phosphate

In this report, we demonstrate the efficient generation of collinearly propagating photon pairs in a bulk periodically poled potassium titanyl phosphate pumped by a cw laser. The detected coincidence counts are more than 7400/s with 3.58 mW pump power in a Hanbury-Brown-Twiss-type experiment. The estimated photon pair production rate is about 0.73 MHz/mW. This is very promising for some applications, such as quantum key distribution, proof of the Bell-inequality, preparation of single photon states in broadband wave packets, Franson-type interference and so on.     

The effects of Si3N4 interlayer on the thermal stability and hardness of Ti/TiNx (x = 0.5-1) nanolayered coatings

The polycrystalline Ti/TiN_x multilayer films were deposited by magnetron sputtering, and the as-deposited multilayer coatings were annealed at 500-800 °C for 2-4 h in vacuum. We investigated the effects of annealing temperature and annealing time on the microstructural, interfacial, and mechanical properties of the polycrystalline Ti/TiN_x multilayer films. It was found that the hardness increased with annealing temperature. This hardness enhancement was probably caused by the preferred crystalline orientation TiN(1 1 1). The X-ray reflectivity measurements showed that the layer structure of the coatings could be maintained after annealing at 500 °C and the addition of the Si₃N₄ interlayer to Ti/TiN_x multilayer could improve the thermal stability to 800 °C.     

无光滤波六倍频微波信号产生的系统设计

基于两个级联偏振调制器,提出了一种高频谱纯度、稳定的六倍频微波信号产生方法。该方法通过适当调整偏振片的偏振方向、射频驱动信号电压和相位,实现无光滤波器条件下、任何波段六倍频微波信号的产生。利用Optisystem平台搭建的仿真系统,以S波段4 GHz信号为例,验证了该设计系统产生的六倍频信号质量,并分析了非理想射频驱动电压和相位对六倍频信号质量的影响,结果表明：该设计系统能产生最大光边带抑制比、射频无杂散抑制比分别为21.3,15.2 dB的六倍频微波信号;且非理想驱动电压和相位差的偏离应控制在理想值5%的范围之内。     

交流源作用下介观RLC电路系统量子态随时间的演化

根据量子不变量理论，同时考虑介观电容器极板间电子波函数的耦合作用和电路的耗散,研究介观RLC电路系统在交流电流源作用下动力学的演化过程，并且得到描述系统量子态随时间的演化算符.进一步的分析结果表明，介观RLC电路系统的波函数将由任意的初态演化到一般的压缩态. 关键词： 介观RLC电路 交变电源 不变量理论 时间演化算符     

半导体光放大器亚皮秒量级超快动态特性的研究

通过考虑脉冲频谱的增益色散，提出了一个分析亚皮秒光脉冲在半导体光放大器(SOA)中传输的新思路.分别对超快光脉冲在时域和频域内进行离散化，建立了一个更为合理的传输数值模型.基于该模型，观察到了脉冲频谱的明显漂移，并探讨了漂移量与脉冲载波波长、脉冲能量、脉冲宽度、SOA长度和注入电流等外部条件之间的关系，从理论上解释了文献没有证实的实验结果.同时，基于交叉增益调制原理，利用双光束结构，描述了载流子加热、光谱烧孔效应和双光子吸收等非线性效应引起的增益压缩.理论分析的结果为改善SOA的动态特性提供了指导. 关键词： 半导体光放大器 超快非线性效应 增益色散性     

垂直入射时无限长分层柱电磁散射的改进算法及应用

结合非均匀球粒子对平面波散射的散射场计算的改进算法,提出了平面波垂直入射无限长分层圆柱散射场快速稳定而有效的改进电磁散射算法。与已有算法相比,改进算法所能计算的无限长非均匀介质圆柱的尺寸参量突破10000,计算层数达到106,并且计算时间很短,最多仅为几秒。该算法可以用于不同的波段以及不同领域的任意无耗或吸收无限长圆柱体散射场的计算。最后将该算法应用于梯度折射率聚合物光纤(GI-POF)散射特性的研究,为非接触、在线测量聚合物光纤折射率分布提供了理论依据。