Low-frequency noise characteristics of InGaAs quantum-dot infrared photodetector structures grown by atomic layer molecular-beam epitaxy

Optical and electrical characteristics of n–i–n InGaAs/GaAs quantum-dot (QD) infrared photodetectors are reported. In particular, the low-frequency excess electrical noise is measured at room temperature and analyzed in conjunction with the optical properties of the structure. The three stackings of QD were formed by atomic layer molecular-beam epitaxy and highly Si-doped, and AlGaAs current-blocking layer was also included to reduce the dark current. The power-dependent photoluminescence (PL) spectra at 300 K indicates that there are at least three confined states in the QD. The photo-current was observed only at low temperatures (10 K) at wavelengths between 3 and 9 μm with three peaks. The dark current was relatively large and asymmetric at low temperatures. At room temperature the dark current was symmetric and ohmic. The 1/f-like low-frequency noise spectral density exhibited an almost quadratic current dependence giving a large value of the Hooge parameter of the order of unity. The relatively low-growth temperature for the AlGaAs current blocking layer and the high doping at the quantum dots seem to generate a considerable amount of defects and result in low-temperature photodetection and a large low-frequency noise density.     

丰中子Ru奇A核能级结构的进一步研究

通过对重核2?52?Cf自发裂变产生的瞬发γ谱的高精度测量数据的分析,扩展了丰中子奇A核10?9,111Ru的高自旋态,对不同延迟符合矩阵的数据分析,得到了10?7,10?9,111,113Ru低激发态多个能级的寿命,发现10?9Ru核中的96?.4keV的能级为一寿命约为130?0ns的同质异能态.对10?9,111Ru转动带的转动惯量随转动频率变化的分析表明,在相邻偶偶核110?Ru中观测到的集体回弯现象确实起源于一对h11/?2?中子的角动量顺排.用粒子?转子模型对10?7,10?9,111,113Ru的集体带的部分能级及跃迁几率进行了计算,得到与实验较为满意的符合,指出在这几个核中的中子h11/?2?闯入带尼尔逊轨道的起源.     

High electroluminescent properties of conjugated copolymers from poly[9,9‐dioctylfluorenyl‐2,7‐vinylene]‐co‐(2‐(3‐dimethyldodecylsilylphenyl)‐1,4‐phenylene vinylene)] for light‐emitting diode applications

A new series of copolymers with high brightness and luminance efficiency were synthesized using the Gilch polymerization method, and their electro‐optical properties were investigated. The weight‐average molecular weights (M_w) and polydispersities of the synthesized poly(9,9‐dioctylfluorenyl‐2,7‐vinylene) [poly(FV)], poly[2‐(3‐dimethyldodecylsilylphenyl)‐1,4‐phenylenevinylene] [poly(m‐SiPhPV)], and poly[9,9‐di‐n‐octylfluorenyl‐2,7‐vinylene]‐co‐(2‐(3‐dimethyldodecylsilylphenyl)‐1,4‐phenylene vinylene)] [poly(FV‐co‐m‐SiPhPV)] were found to be in the ranges of (8.7–32.6) × 10⁴ and 2.3–5.4, respectively. It was found that the electro‐optical properties of the copolymers could be adjusted by controlling the feed ratios of the comonomers. Thin films of poly(FV), poly(m‐SiPhPV), and poly(FV‐co‐m‐SiPhPV) were found to exhibit photoluminescence quantum yields between 21% and 42%, which are higher than those of MEH‐PPV. Light‐emitting diodes were fabricated in ITO/PEDOT/light‐emitting polymer/cathode configurations using either double layer (LiF/Al) or triple layer (Alq₃/LiF/Al) cathode structures. The performance of the polymer light‐emitting diodes (PLEDs) with triple layer cathodes was found to be better than that of the PLEDs with double layer cathodes in poly(FV) and poly(FV‐co‐m‐SiPhPV). The turn‐on voltages of the PLEDs were in the range of 4.5–6.0 V, with maximum brightness and luminance efficiency up to 9691 cd/m² at 16 V and 3.27 cd/A at 13 V, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5062–5071, 2005     

具有体膨胀和剪切效应的结构陶瓷相变塑性细观本构模型:Ⅰ.非比例加载历史

本文在对结构陶瓷的四方至单斜(t→m)马氏体相变进行细观力学、热力学和微观机制分析的基础上,导出了在非比例加载条件下考虑材料的体膨胀和剪切效应的相变塑性细观本构模型。作者首次采用 Mori-Tanaka 方法以自洽的方式导出了材料构元的 Helmho-ltz 自由能及余能函数的解析表达式,它是外加宏观应力(或应变)、温度、相变夹杂体积分数以及夹杂内平均相变应变的函数,其中夹杂体积分数和平均相变应变为描述材料构元微结构变化的内变量。最后按 Hill-Rice 本构理论框架导出相变塑性屈服面方程及增量本构关系。     

Catalytic formation of hydrogen peroxide from H2 and O2 over hydrogen transfer agent-anchored Pd°/beta zeolites

Hydrogen transfer agents (HTAs) have been successfully anchored on Pd°/H-beta zeolite and exhibit enhanced catalytic activity in the formation of H₂O₂ from H₂ and O₂ at atmospheric pressure compared with that of the Pd°/H-beta and the HTA included catalysts.     

93Nb knight shift and quadrupole coupling parameters in the orthorhombic β phase hydride and deuteride of niobium

The Knight shift tensor components and quadrupole coupling parameters of the ⁹³Nb NMR have been measured for the first time in the orthorhombic β phase hydride and deuteride of niobium. The isotropic component of the Knight shift tensor has the same value in the hydride phase as in the solid solution (α') phase at the same composition, indicating that no significant change in band structure details occurs as a consequence of the structural phase transition. Comparison of the measured asymmetry parameter of the quadrupole interaction with calculated values indicates that the probable Nb environment is that of the ordered NbH structure. Estimates of the activation energy for hydrogen (deuterium) diffusion are obtained from the temperature dependence of the linewidths of the spectrum features.     

Recoil corrections to magnetic moments of octet baryons in the MIT bag model

The presence of certain recoil corrections in the determination of baryon magnetic moments is described and taken into account for the octet members. Inclusion of these recoil corrections makes the MIT bag model, even in its zeroth-order version, very appealing, if the sum of many other corrections is not important by comparison.     

The temperature dependence of the elastic constants for highly oriented pyrolytic graphite determined by ultrasonic techniques

Sound velocities along the c-axis of highly oriented pyrolytic graphite between 4 and 325 K were measured with an ultrasonic pulse-echo phase-comparison method. The echo delay times were determined with an accuracy of 0.05 and 0.15%, respectively, for the longitudinal and transverse modes. The temperature dependence of the c-axis elastic constants C₃₃ and C₄₄ was deduced with the correction of thermal expansion. C₃₃ was found to decrease by 5.8% from 4 to 300 K and can be interpreted by a model based on the simple Lennard-Jones interlayer interaction. C₄₄ and its temperature variation are found to be strongly sample dependent.