997 resultados para 164-997B
Resumo:
婴恒河猴是国家珍稀野生动物,随着自然环境遭 到破坏和非法捕猎,猕猴在自然界中的数量已经骤 减。昆明动物研究所经过30 多年的人工驯养实践, 恒河猴的人工驯养技术已比较成熟,以前刚出生母猴 因不照顾新生婴猴,致使全人工饲养成活率较低,经 过多年来对全人工哺育婴猴方法的不断改进、探索, 最近3 年通过使用婴儿培养箱哺育新生婴猴,取得有 效进展,新生婴猴的成活率明显提高
Resumo:
Using a home-made gas-source molecular beam epitaxy system, high quality InGaAs quantum wells with different well widths lattice-matched to a (001) InP substrate have been obtained. Sharp and intense peaks for each well can be well resolved in the PL spectra for the sample. For well widths larger than similar to 60 Angstrom, the exciton energies are in good agreement with those of calculation. For wells narrower than 40 Angstrom, our line widths are below the theoretical values of line width broadening due to one monolayer interface fluctuation, showing that the interface fluctuation of our sample is within one monolayer.
Resumo:
比较研究了InGaAs/GaAs量子链和量子点的稳态和瞬态光学特性.实验发现,量子链的荧光寿命有很强的探测能量依赖关系,而量子点的荧光寿命随能量变化较小;量子链的荧光寿命随着激发功率迅速增加,高功率时趋于饱和,而量子点的荧光寿命随激发功率变化缓慢;此外,量子链样品的荧光上升时间也比量子点的小得多.这些结果清楚表明,在量子链结构中,参与发光的载流子之间存在很强的耦合和输运.进一步分析表明,这种耦合作用主要发生在量子链方向.荧光的偏振特性进一步证实了这一点.
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研究了原子氢辅助分子束外延(MBE)中,原子氢对不同晶面GaAs外延层表面形貌特征的诱导作用。原子力显微镜(AFM)测试表明,在GaAs的(311)A和(331)A面,原子氢导致了台阶状形貌的形成。提出了一种简单模型,解释了台阶面形貌形成的物理机制。为最终有序低维纳米表面结构提供了一种实验参考。
Resumo:
采用金属有机物化学气相外延方法在(0001)面蓝宝石上生长了高质量、高阻的未掺杂(0001)面GaN薄膜。为精确测量GaN薄膜材料的声表面波特性,在GaN薄膜表面上沉积了金属叉指换能器,叉指换能器采用等叉指结构,叉指的数目为40对,叉指间距为15μm。采用脉冲法测量了声表面波在自由表面和金属表面上的速度,并通过计算得到了机电耦合系数(κ^2)。所测量的声表面波速度(ν)为5667m/s,机电耦合系数(κ^2)为1.9%。
Resumo:
利用MOCVD生长技术在GaAs(100)衬底上生长了高质量的立方相AlGaN薄膜。通过光致发光(PL)、扫描电镜(SEM)分析了不同NH_3流量、不同生长温度对AlGaN外延层的结晶质量和表面形貌的影响。发现相对高的NH_3流量和相对高的生长温度可以提高AlGaN外延层的结晶质量。
Resumo:
In this paper, we investigated the self-assembled quantum dots formed on (100) and (N11)B (N = 2, 3, 4, 5) InP substrates by molecular beam epitaxy (MBE). Two kinds of ternary QDs (In0.9Ga0.1As and In0.9Al0.1As QDs) are grown on the above substrates; Transmission electron microscopy (TEM) and photoluminescence (PL) results confirm QDs formation for all samples. The PL spectra reveal obvious differences in integral luminescence, peak position, full-width at half-maximum and peak shape between different oriented surfaces. Highest PL integral intensity is observed from QDs on (411)B surfaces, which shows a potential for improving the optical properties of QDs by using high-index surface. (C) 2000 Elsevier Science B.V. All rights reserved.