负载型Heck反应催化剂的研究进展

Heck反应是一类重要的C-C偶联反应,传统的均相Heck反应催化剂存在分离和回收困难等问题;近年来负载型Heck反应催化剂的研究引起了人们的广泛关注.本文综述了钯基和非钯基负载型Heck反应催化剂的研究进展,评述了不同载体上催化活性组分对Heck反应的特点,并展望了其发展趋势.     

中子辐照硅中一个新的EPR缺陷及氢对它的影响

在中子辐照区熔硅中,观测到一个具有C_2v对称性、有效自旋为1的新的顺磁性缺陷,按惯例称为Si-PK3,其g和D的主值为g₁=2.0048,g₂=2.0118,g₃=2.0085;D₃=35.9×10^-4cm^-1,D₂=-17.1×10^-4cm^-1,D₃=-18.8×10^-4cm^-1.可能的微观结构是沿〈110〉晶向、在中间空位上俘获一个氧原子的平面三空位链.氢的存在可使它的退火消失温度由500℃降为350℃左右.     

高效毛细管柱气相色谱法快速测定樟脑丸中萘

应用并试验了高效毛细管柱气相色谱法分离和测定樟脑丸中萘含量。选择二硫化碳作为试样溶剂,因它具有溶样速度快和提供良好的色谱分离的介质条件。色谱分析中采用了DB-17毛细管柱(30 m×0.25 mm,0.25μm)和FID检测器,方法的检出限为5×10-4μg,RSD在0.92%~3.37%之间;加标回收率为96.2%~104.8%,回归方程的相关系数为0.999 9(进样量为1μL)。     

Coupling length variation and multi-wavelength demultiplexing in photonic crystal waveguides

In this Letter, the effects of material/structure parameters of photonic crystal(Ph C) parallel waveguides on the coupling length are investigated. The results show that, increasing the effective relative permittivity of the Ph C leads to a downward shift of the photonic bandgap and a variation of the coupling length. A compact Ph C 1.31/1.55 μm wavelength division multiplexer(WDM)/demultiplexer with simple structure is proposed,where the output power ratios are more than 24 d B. This WDM can multiplex/demultiplex other light waves efficiently.     

Characteristics of stable L-band SFS using dual-forward synchronous pumping technique

We investigate the characteristics of the dual-forward synchronously pumped L-band erbium-doped su- perfiuorescent fiber source （SFS）. The effects of pump ratio and fiber length arrangements on the output characteristics of the L-band SFS in terms of mean wavelength, spectral linewidth, and output power are analyzed. It is shown that the optimized pump ratio and fiber length arrangements provide broadening spectral linewidth and enhanced pumping efficiency, while the synchronous pump ensures stable mean wavelength operation. A new single-forward pumping scheme with a section of unpumped fiber is pro- posed to achieve a mean wavelength stable L-band SFS with a broadening linewidth of 50.4 nm and a pumping efficiency of 33.5%.     

Passively Q-switched green laser operation using CdTe/CdS quantum dots

The direct generation of passively Q-switched lasers at a green wavelength has rarely been investigated in the past. In this Letter, we demonstrate a passively Q-switched praseodymium-doped yttrium lithium fluoride green laser at 522 nm using CdTe/CdS quantum dots as a saturable absorber. A maximum average output power of 33.6 m W is achieved with the shortest pulse width of 840 ns. The corresponding pulse energy and peak power reached 0.18 μJ and 0.21 W, respectively. To the best of our knowledge, this is the first demonstration in regard to a quantum dots saturable absorber operating in the green spectral region.     

中子辐照高掺硅砷化镓的光致发光研究

研究了高掺硅的n型GaAs在中子辐照前后和150℃-500℃等时热退火以后的光致发光光谱。观察到在中子辐照后积分发光强度降低为辐照前的1/36。在退火温度超过250℃时,积分发光强度显著增长,当退火温度达400℃以上时,在带边峰的低能侧出现能量为1.35eV、1.30eV和1.26eV的发光峰。假设250℃退火阶段对应于较大的空位团分解为较小的空位团,400℃退火阶段对应于较小的空位团分解出VGa,可以较好地解释实验现象。     

镁卟啉与氮、氧杂环化合物的相互作用

以镁卟啉为主体化合物,模拟了生物体内常见的氮、氧杂环客体与主体化合物之间的相互作用.研究结果表明:镁卟啉与氮、氧杂环化合物的相互作用引起了镁卟啉中的镁原子与卟吩环不共面,且二面角越小不共面程度越大.自然键轨道(NBO)理论分析表明氮、氧孤对电子和金属镁的空孤对轨道的相互作用对复合物的稳定性贡献很大.使用约化密度梯度(RDG)函数等值面图和散点图可视化分析了配位相互作用和周边氢键作用的位置及强度.概念密度泛函(DFT)理论参数表明所形成的复合物比主体化合物的热力学稳定性小而反应活性高.芳香性计算表明含氧杂环客体与主体的相互作用使复合物中的卟吩环具有反芳香性,而含氮杂环客体与主体的相互作用使复合物中卟吩环呈现区域性芳香性.     

在p型硅MOS结构Si/SiO2界面区中与金有关的界面态和深能级

用深能级瞬态谱(DLTS)技术详细研究了金在p型<111>晶向硅MOS结构Si/SiO₂界面区中的行为。结果表明,金与Si/SiO₂界面缺陷H_it(0.494)相互作用形成新的缺陷Au-H_it(0.445),和金在硅的禁带中产生一个能量分布很广的连续界面态,利用这些界面态可以合理地解释金使硅MOS结构平带电压向正方向移动的物理机制。结果还表明,在Si/SiO₂界面附近的半导体中,金施主中心的剖面分 关键词：     

Investigation of the Substituent Effects on π-Type Pnicogen Bond Interaction

Intermolecular interactions between PH_2Cl and Ar–R(R = H,OH,NH_2,CH_3,Br,Cl,F,CN,NO_2) were calculated by using MP2/aug-cc-p VDZ quantum chemical method.It has been shown from our calculations that the aromatic rings with electron-withdrawing groups represent much weaker binding affinities than those with electron-donating groups.The charge-transfer interaction between PH_2Cl and Ar–R plays an important role in the formation of pnicogen bond complexes,as revealed by NBO analysis.Nevertheless,AIM analysis shows that the nature of the interactions between PH_2Cl and Ar–R is electrostatic,and the interaction energies of the complexes are correlated positively with the electron densities in the bond critical points(BCPs).RDG/ELF graphical analyses were performed to visualize the positions and strengths of the pnicogen bonding,as well as the spatial change of the electron localization upon the formation of complexes.The π-type halogen bond was also calculated,and it has been revealed that the π-type pnicogen bond systems are more stable than the halogen bond ones.