Influence of growth parameters of frequency-radio plasma nitrogen source on extending emission wavelengths from 1.31 mu m to 1.55 mu m GaInNAs/GaAs quantum wells grown by molecular-beam epitaxy

High (42.5%) indium content GaInNAs/GaAs quantum wells with room temperature emission wavelength from 1.3 mu m to 1.5 mu m range were successfully grown by Radio Frequency Plasma Nitrogen source assisted Molecular Beam Epitaxy. The growth parameters of plasma power and N-2 How rate were optimized systematically to improve the material quality. Photoluminescence and transmission electron microscopy measurements showed that the optical and crystal quality of the 1.54 mu m GaInNAs/GaAs QWs was kept as comparable as that in 1.31 mu m.

Microstructure and photoluminescence of a-SiOx : H

Two strong photoluminescence (PL) bands in the spectral range of 550-900 nm have been observed at room temperature from a series of a-SiOx:H films fabricated by plasma-enhanced chemical vapor deposition (PECVD) technique. One is composed of a main band in the red-light region and a shoulder; the other is located at about 850 nm, only found after 1170 degrees C annealing in N-2 atmosphere. In conjunction with infrared (IR) and micro-Raman spectra, it is thought that the two PL bands are associated with a-Si clusters in the SiOx network and nanocrystalline silicon in SiO2, respectively.

Pool boiling heat transfer of ultra-light copper foam with open cells

High speed visualizations and thermal performance studies of pool boiling heat transfer on copper foam covers were performed at atmospheric pressure, with the heating surface area of 12.0 mm by 12.0 mm, using acetone as the working fluid. The foam covers have ppi (pores per inch) from 30 to 90, cover thickness from 2.0 to 5.0 mm, and porosity of 0.88 and 0.95. The surface superheats are from -20 to 190 K, and the heat fluxes reach 140 W/cm(2). The 30 and 60 ppi foam covers show the periodic single bubble generation and departure pattern at low surface superheats. With continuous increases in surface superheats, they show the periodic bubble coalescence and/or re-coalescence pattern. Cage bubbles were observed to be those with liquid filled inside and vented to the pool liquid. For the 90 ppi foam covers, the bubble coalescence takes place at low surface superheats. At moderate or large surface superheats, vapor fragments continuously escape to the pool liquid. Boiling curves of copper foams show three distinct regions. Region I and II are those of natural convection heat transfer, and nucleate boiling heat transfer for all the foam covers. Region III is that of either a resistance to vapor release for the 30 and 60 ppi foam covers, or a capillary-assist liquid flow towards foam cells for the 90 ppi foam covers. The value of ppi has an important effect on the thermal performance. Boiling curves are crossed between the high and low ppi foam covers. Low ppi foams have better thermal performance at low surface superheats, but high ppi foams have better one at moderate or large surface superheats and extend the operation range of surface superheats. The effects of other factors such as pool liquid temperature, foam cover thickness on the thermal performance are also discussed.

三甲硅基丙炔的合成、聚合及聚合物膜的透气性能和改性

在现有的聚合物材料中，聚（1-三甲硅基丙炔）（PTMSP）具有最高的气体透过性能，这种非常有趣的玻璃态聚合物在混合气体的选择透过分离（包括渗透蒸发混合液体分离）例如空气中的氧氮分离、水中溶解氧的富集、醇水分离等方面具有广阔的发展前途。本工作对1-三甲硅基丙炔（TMSP）的合成和聚合、聚合物的制膜及膜的透气性能和改性等方面作了初步探索。1 参考文献中的格氏反应合成法，通过增加对反应产物的氨气后处理这一关键性的改进，有效地避免了严重影响催化聚合反应的杂质M_2的生成，高质量地合成出纯度大于99.8%的TMSP单体。2 采用两步格氏反应合成法，首先合成TMSA，然后合成TMSP，巧妙地避开了TMSP与M_2的分馏分离，开创了一条更适合制备TMSP单体的新路线。3 详细研究了环境对PTMSP膜透气性能的影响，发现透气不稳定的原因除了结构松驰的影响外，主要是由于环境的影响，尤其是存在有机气氛的环境影响非常大。4 热处理对膜的结构松驰有加速作用，使膜的透气性能快速向PDMS的水平靠近。5 PTMSP分子中存在交替双键和丙二烯结构的构型转化，这种构型转化受热力学控制。6 PTMSP膜经过氢氟酸表面处理以后，选择透气性能明显变好。7 PTMSP膜经过表面溴化以后，氧气透过系数有所下降（>10~3 barrer）氧氮选择分离系数可提高到2甚至3以上，透气稳定性提高。8 PTMSP膜经过CF_4等离子体表面处理以后，表面硅含量大幅度减少，氟含量可达50%，膜的氧气透过系数保持在～10~3 barrer，氧氮选择分离系数提高到4甚至5以上，而且透气稳定性良好。9 PTMSP膜表面等离子体聚合一层六氟丙烯形成复合膜。氧气透过系数下降幅度不大，氧氮选择分离系数提高到3以上。

808 nm high-power laser grown by MBE through the control of Be diffusion and use of superlattice

808 nm high-power laser diodes are gown by MBE. In the laser structure, the combination of Si-doped GRIN (graded-index) region adjacent to n-AlGaAs cladding layer with reduced Be doping concentration near the active region has been used to diminish Be diffusion and oxygen incorporation. As compared with the laser structure which has undoped GRIN region and uniform doping concentration for Si and Be, respectively, in the cladding layers, the slope efficiency has increased by about 8%. Typical threshold current density of 300 A/cm(2) and the minimum threshold current density of 220 A/cm(2) for lasers with 500 mu m cavity length are obtained. A high slope efficiency of 1.3 W/A for coated lasers with 1000 mu m cavity length is also demonstrated, Recorded CW output power at room temperature has reached 2.3 W.

Structures of an asymmetrically coupled double-well superlattice by double-crystal X-ray diffraction

An asymmetrically coupled (GaAs/AlAs/GaAs/AlAs)/GaAs (001) double-well supperlattice is studied by HRDCD (high resolution double-crystal X-ray diffractometry). The intensity of satellite peaks is modulated by wave packet of different sublayers. In the course of simulation, the satellite peaks in the vicinity of the node points of wave packet are very informative for precise determination of sublayer thickness and for improving accuracy.

GaN基蓝光激光器光场特性模拟

采用有限差分法对GaN基多量子阱(MQWs)脊形激光器进行二维光场模拟.InGaN和AlGaN材料的折射率分别由修正的Brunner以及Bergmann方法得到.分析了激光器单模特性和远场发散角同器件的脊形刻蚀深度和脊形条宽的关系.研究了在脊形上用Si/SiO2膜取代传统SiO2介质膜这种新的脊形设计对激光器结构参数的影响.模拟结果发现,脊形条宽越窄,脊形刻蚀深度越深,平行结平面方向的发散角越大,但由此会引起单模特性不稳定,两者之间有一个折衷值.通过引入新的脊形设计,可以降低对器件刻蚀深度精度的要求,同时有很好的单模稳定性.

非局部理论新框架和基于新框架的塑性应变梯度理论

<正>纳米材料和器件的蓬勃发展,微机电系统和微电子元件微型化趋势,先进材料微结构设计以及精细薄膜涂层,促使材料科学家和力学家关注微米尺度和纳米尺度范围内材料的力学行为。大量实验表明,当非均匀塑性变形的特征长度在微米量级时,金属材料材料呈现很强的尺度效应。典型的实验包括:细铜丝扭转;纯镍薄膜弯曲;不同金属材料的微纳米压痕;炭化硅粒子增强的铝-镁基

用反应窗理论研究离子与原子碰撞的态选择微分截面

基于描述低能离子与原子碰撞的分子库仑过垒模型,详细阐述了与入射离子速度相关的反应窗理论,并对影响势垒变化的平均径向速度做了修正.根据该理论,计算了C5+-He和He2+-He碰撞体系单电子俘获过程的态选择微分截面,并分别与Kamber等人和Mergel等人的实验结果进行了比较.

中国西北地区季节间干湿变化的时空分布――基于pdsi数据

IEECAS SKLLQG

Study of n=2, Delta n=0 transition of Be-, B-, C-, N- and O-like sequence in the beam-foil spectrum of titanium

The foil-excited the spectrum of highly stripped titanium ions between 12-40 nm has been studied. Titanium ions of 80 and 120 MeV were provided by the HI-13 tandem accelerator at the China Institute of Atomic Energy. GIM-957 XUV-VUV monochromator was refocused to get highly-resolved spectra. Our experimental results and the published spectral data of laser-produced plasma show agreement in nearly all cases within +/- 0.03 nm. The spectra contained some weak or strong lines previously unclassified. These spectral lines mainly belong to 2s2p(2) for TiXVIII, 2p(3) for TiXVIII, 2s2p(3) for TiXVII, 2p(6)4p for Ti XII and 2p(6)3d for Ti XII transitions.