Efficiency droop in InGaN/GaN-based LEDs with a gradually varying In composition in each InGaN well layer

Temperature-dependent and driving current-dependent electroluminescence spectra of two different InGaN/GaN multiple quantum well structures SA and SB are investigated,with the In composition in each well layer(WL)along the growth direction progressively increasing for SA and progressively decreasing for SB.The results show that SB exhibits an improved efficiency droop compared with SA.This phenomenon can be explained as follows:owing to the difference in growth pattern of the WL between these two samples,the terminal region of the WL in SB contains fewer In atoms than in SA,and therefore the former undergoes less In volatilization than the latter during the waiting period required for warming-up due to the difference in the growth temperature between well and barrier layers.This results in SB having a deeper triangular-shaped potential well in its WL than SA,which strongly confines the carriers to the initial region of the WL to prevent them from leaking to the p-GaN side,thus improving the efficiency droop.Moreover,the improvement in the efficiency droop for SB is also partly attributed to its stronger Coulomb screening effect and carrier localization effect.     

苯硝化反应机理及其溶剂效应的理论研究

在密度泛函理论(DFT)非限制B3LYP/6-311G^**水平上, 求得苯与硝酰阳离子(NO₂⁺ )硝化反应势能面上的π-过渡态、σ-过渡态, 以及由这两个过渡态通过内禀反应坐标(IRC)计算所得σ-反应络合物和σ-中间体(Wheland中间体)的全优化几何构型、电子结构、IR光谱和热力学性质, 确认了反应通道, 阐明了在亲电取代过程中无同位素效应的实验事实; 求得气相中反应的活化能为8.370 kJ/mol, 速率常数数量级为10¹⁰ mol^-1·s^-1. 从热力学和动力学两方面阐明了苯硝化的亲电取代机理优于单电子转移双自由基机理. 通过自洽反应场(SCRF)B3LYP/6-311G^**计算, 系统研究了相对介电常数分别为5.0, 25.0, 50.0和78.5的溶剂对苯与NO₂⁺反应过程中各驻点的结构和反应机理的影响, 发现溶剂效应使气相中形成σ-过渡态(速控步骤)的活化能下降, 并使该步骤在水溶液中成为无垒反应. 此外还揭示了实验与理论共同关心的Wheland中间体的电荷分布、偶极矩、前线轨道能级差与溶剂稳定化能之间存在的良好线性关系.     

亲水作用色谱-四极杆/静电场轨道阱高分辨率质谱快速测定水样中氨基脲

建立了亲水作用色谱-四极杆/静电场轨道阱高分辨质谱快速检测水中氨基脲的方法。水样中加入0.1 mol/ L NaOH 溶液后,以乙腈为提取剂,加入过量 Na2 SO4,使乙腈与水分层,乙腈提取液再经无水 Na2 SO4脱水后,采用亲水作用色谱柱 Amide 色谱柱分离,以0.1%甲酸水溶液及0.1%甲酸乙腈溶液为流动相进行梯度洗脱,四极杆/静电场轨道阱高分辨率质谱电喷雾正离子、选择离子监测模式检测,同位素内标法进行定量分析。在最优实验条件下,氨基脲在0.2~20μg/ L 浓度范围内线性相关系数为0.997,方法的检出限为0.09μg/ L,定量限为0.30μg/ L。以淡水和海水为空白样品,在添加浓度为0.5,1.0和5.0μg/ kg 水平下,氨基脲的加标回收率为82.3%~92.0%,相对标准偏差小于7.6%。本方法适用于环境水样中氨基脲的快速分析。     

手性(硫)脲衍生物在不对称有机催化反应中的应用

手性(硫)脲衍生物是各种亲核试剂对亚胺、醛、缺电子烯烃加成反应的非常有效的有机催化剂之一, 已成功应用于对映选择性催化Strecker反应、Michael加成反应、Mannich反应、Baylis-Hillman反应、Henry反应等一系列重要的有机合成反应. 手性(硫)脲衍生物具有催化活性高、对映选择性和功能基相容性好、易于制备和修饰、适用范围广等优点, 成为近年来研究较多的不对称反应有机催化剂. 对手性(硫)脲衍生物在有机催化不对称合成中的应用研究进展进行了评述.     

王水水浴消解-电感耦合等离子体质谱(ICP-MS)法测定土壤中10种重金属元素

为避免在土壤溶解过程中使用高氯酸、硫酸、氢氟酸和繁琐的赶酸步骤,减少污染、降低能耗,采用王水水浴法消解样品,以Rh为内标,优选测试同位素并消除质谱干扰,建立了电感耦合等离子体质谱(ICP-MS)法测定土壤中V、Cr、Mn、Co、Ni、Cu、Zn、Mo、Cd和Pb等10种重金属元素的方法。校准曲线的相关系数为0.999 5～0.999 9,各元素的检出限为0.01～0.96μg/g,测定的相对标准偏差(RSD,n=10)为0.60%～12.3%,加标回收率为95.0%～106%。通过测定30种农用地土壤成分标准物质,考察王水溶解法的提取能力。结果表明,提取率与元素种类有关,各元素的提取率中位数排列为V(51%)、Cr(51%)、Ni(82%)、Co(86%)、Mn(91%)、Mo(92%)、Cu(93%)、Pb(94%)、Zn(96%)和Cd(100%);提取率还与样品基体及重金属含量有关,不同土壤标准物质的提取率差别较大,元素含量越高,提取率有升高趋势,因此方法质控不宜使用全量分析标准物质。     

Band Structures of Ultrathin Bi(110) Films on Black Phosphorus Substrates Using Angle-Resolved Photoemission Spectroscopy

The band structures of two-monolayer Bi(110) films on black phosphorus substrates are studied using angleresolved photoemission spectroscopy. Within the band gap of bulk black phosphorus, the electronic states near the Fermi level are dominated by the Bi(110) film. The band dispersions revealed by our data suggest that the orientation of the Bi(110) film is aligned with the black phosphorus substrate. The electronic structures of the Bi(110) film strongly deviate from the band calculations of the free-standing Bi(110) film, suggesting that the substrate can significantly affect the electronic states in the Bi(110) film. Our data show that there are no non-trivial electronic states in Bi(110) films grown on black phosphorus substrates.     

四硝基并哌嗪（TNAD）与一些含能材料混合体系熔点的分子动力学模拟

利用分子动力学模拟方法预测了TNAD／HMX、TNAD／RDX、TNAD／DINA和TNAD／DNP四种混合体系的熔点,利用比容与温度的曲线拐点决定了四种混合体系的熔点．结果是TNAD／HMX、TNAD／RDX、TNAD／DINA的熔点分别为500、536、488K．而TNAD／DNP体系没有明显的熔点,表明此体系是不相容的．利用熔点进一步预测了四种体系的相容性,分析了它们的径向分布函数．TNAD与HMX、RDX、DINA和DNP之间的分子间相互作用是近距离相互作用,且相容性越好,分子间相互作用越强．同时还分析了不同温度下的力场能．     

卷弧翼气动特性研究进展

本文列举了卷弧翼在战术武器中的应用实例，介绍了卷弧翼的几何特性、气动特性、优缺点及布局设计，评述了对卷弧翼气动特性所做的理论与试验研究工作。最后指出了有待进一步研究的问题。     

甲基丙烯酸-4-羟基孔雀绿酯的合成及其共聚物的研究

合成了甲基丙烯酸－4－羟基孔雀绿酯并用傅立叶变换红外吸收光谱、核磁共振谱、元素分析以及TGA－DTA分析对该化合物进行了表征，证明了其结构，将该单体与丙烯酸乙酯共聚，并用UV－Vis证明了该单体与丙烯酸酯类进行自由基共聚的可能性。另外，将该单体与甲基丙烯酸甲酯共聚，成功地将该单体引入聚合物中，用TGA聚合物的稳定性进行了研究，用DSC对聚合物的热转变进行了分析，聚合物Tg由均聚物的96℃上升到4．1％CPMMA的108℃，对4．1％CPMMA的水解性能也进行了初步的研究，发现其水解反应发生得很慢。     

Shape co-existence and structural evolution of the Vi13/2 band in 157Yb

The high-spin states of 157Yb have been studied via the reaction of 144Sm(16O, 3n) at 16O energy of 90 MeV using techniques of in-beam γ-ray spectroscopy. Measurement of γ-γ-t coincidences was performed with 11 BGO(AC)HPGe detectors. Based on the γ-γ coincidence relationships and the measured results of γ-ray anisotropies and DCO ratios, the level scheme for 157Yb was established. The shape co-existence and structural evolution of the Vi13/2 band with increasing angular momentum in 157Yb have been discussed. The systematics of the Vi13/2 bands in the N = 87 odd-A isotones have been compared.