High responsivity resonant-cavity-enhanced InGaAs/GaAs quantum-dot photodetector for wavelength of similar to 1 mu m at room temperature

The characteristics of a resonant cavity-enhanced InGaAs/GaAs quantum-dot n-i-n photodiode with only a bottom distributed Bragg reflector used as the cavity mirror, are reported. To suppress the dark current, an AlAs layer is inserted into the device structure as the blocking layer. It turns out that the structure still possesses the resonant coupling nature, and makes Rabi splitting discernible in the photoluminescence spectra. The measured responsivity spectrum of the photocurrent shows a peak at lambda = 1030 nm, and increases rapidly as the bias voltage increases. A peak responsivity of 0.75 A/W, or equivalently an external quantum efficiency of 90.3%, is obtained at V-bias = -1.4 V.

Magneto - Transport of electron symmetric and antisymmrtric states in highly doped InGaAs/InAlAs single quantum well

Beating patterns in longitudinal resistance caused by the symmetric and antisymmetric states were observed in a heavily doped InGaAs/InAlAs quantum well by using variable temperature Hall measurement. The energy gap of symmetric and antisymmetric states is estimated to be 4meV from the analysis of beating node positions. In addition, the temperature dependences of the subband electron mobility and concentration were also studied from the mobility spectrum and multicarrier fitting procedure.

Growth of Ge quantum dot mediated by boron on Ge wetting layer

We, report on the influence of boron on the formation of Ge quantum dots. The investigated structure consists of a Ge wetting layer, on which a sub-monolayer boron is deposited and subsequently a Ge top layer. For sufficiently thin Ge top layers, the strain field induced by boron on Ge wetting layer destabilizes the Ge top layer and causes the formation of small Ge quantum dots. However, for thicker Ge top layers, boron on the Ge wetting layer diffuses into Ge layers, compensates partly the strain and delays the evolution of Ge quantum dots. By this method, small Ge quantum dots with high density as well as size uniformity can be formed by optimizing the growth condition. (c) 2005 Elsevier B.V. All rights reserved.

Effects of phase-breaking on long-range charge transfer in DNA: Partially-coherent-tunneling model study

The mechanism of hole charge transfer in DNA of various lengths and sequences is investigated based on a partially coherent tunneling theory (Zhang et al., J Chem Phys 117:4578, 2002), where the effects of phase-breaking in adenine-thymine and guanine-cytosine base pairs are treated on equal foot. This work aims at providing a self-consistent microscopic interpretation for rate experiments on various DNA systems. We will also clarify the condition under which the simple superexchange-mediated-hopping picture is valid, and make some comments on the further development of present theory.

Cathodoluminescence on GaN hexagonal pyramids on submicron dot-patterns via selective MOVPE

Three-dimensional GaN pyramids have been successfully obtained on submicron dot-patterned (0001) sapphire substrates by using the selective metalorganic vapor phase epitaxy (MOVPE) technique. The dot-pattern is a hexagon arranged with a 0.5-mu m width and 1.0-mu m spacing. The GaN structure comprises a hexagonal pyramid covered with six {1 (1) over bar 01} pyramidal facets on the side of a hexagonal pyramid having a (0001) facet on the top. Cathodoluminescence (CL) measurement was carried our. on the hexagonal pyramid at low temperature. Two distinct spectra were observed to occur at about 359 and 329 nm. The higher energy is thought to be related to GaN dot, and the lower one is due to GaN dot band edge emission. The intensities of the two spectra were investigated as a function of temperature in the range of 135-150 K. (C) 2000 Published by Elsevier Science B.V.

“中介逻辑”与Woodruff三值逻辑系统

在《“中介逻辑”的特征问题》一文里,我们对近来朱梧梗、肖奚安等同志发表的称为“中介逻辑”的命题系统MP的三个联接词(对立否定),～(模糊否定)与→(蕴含)建立了如下的三值真值表:

多线程程序数据竞争的静态检测

多线程并发程序的广泛使用带来了更多的数据竞争错误．传统的数据竞争静态检测由于对并发语义和别名信息的保守分析会导致很多假错误．因此，提出了一个精确有效的静态检测框架：分析应用了精确的别名分析并静态模拟了访问事件发生序；为提高分析效率，检测算法提出了一个以对象为中心，结合Escape分析缩小检测范围的检测算法并配合设计了压缩的别名等价类表示．检测框架在一个静态Java编译器JTool上做了实现，对于测试程序取得了很好的分析结果．

本氏针茅与柳枝稷光合生理生态特征比较研究

采用美国LI—COR公司生产的Li-6400便携式光合测定系统,选择在干旱季节里,在田间自然条件下,测定并比较研究了引种牧草柳枝稷和天然牧草本氏针茅两种禾本科植物的光合生理生态特征的日变化。结果表明,柳枝稷属于高光合、低蒸腾和高水分利用效率的植物,具有较强的气孔调节能力。柳枝稷之所以具有较高的光合速率,主要是因为它具有较强的叶肉细胞羧化能力,较低的气孔导度降低了蒸腾速率,从而提高了水分利用效率;本氏针茅属于较低光合,较高蒸腾和低水分利用效率的植物,但二者均能在黄土高原保持良好的生长。

镍-金属氢化物电池新型负极材料研究

贮氢合金是镍一金属氢化物电池的核心材料，其综合性能的改善是提高镍一金属氢化物电池性能的关键。本研究以探索镍一金属氢化物电池新型负极材料为目的，以非ABS型贮氢合金为研究对象，采用X射线衍射、Rietveld分析、恒电流充／放电、P-C-T曲线及线性微极化等方法，从基础和潜在应用等方面详细研究了非ABS型合金的结构与电化学性能。对La-Ni体系中非ABS型二元合金的结构和电化学性能的研究表明，LaNi_(228)具有最优异的高倍率充电性能；La_2Ni_7合金电极的高倍率放电性能最佳；La_7Ni_3在低温条件下表现出较好的放电性能。然而，所有得到的La-Ni合金电极容量远低于其理论容量。因此，必须通过进一步研究，如元素取代、热处理、表面处理等来提高其电化学容量。对RENi_3（RE＝La，Ce，Pr，Nd，Sm，Gd，Th，Dy，Ho，Er，Y）研究表明：YNi_3合金因其具有最大的晶胞体积，最小的密度，而表现出最好的高倍率充／放电性能及低温放电性能，但其高温放电性能需要进一步提高，以满足实际应用的要求。用Al、Mn、Ti、Fe、Sn、Si、Cr、M。、Cu和Co十种元素取代Ni进行了大量的配方筛选工作。得到了大量的实验数据，并发现LaNi_(3.7)Al_(0.3)合金电极电化学放电容量最高，达290.8mAh／g；LaNi_(3.7)Mo_(0.3)合金电极的高倍率放电性能最好，在以4200mA/g的电流密度下进行放电时，其放电容量仍达到145.8mA/g；而I镍一金属氢化物电池新型负极材料研究镍一金属氢化物电池新型负极材料的研究Al的取代会使合金电极性能对温度不敏感。以我们的实验为基础，进一步进行合金配方的微调，具有可能开发出具有实用价值的贮氢合金的潜力。在Ar保护下用真空电弧炉熔炼合成了四种Lal一xMg：（NICoAI）3．6体系贮氢合金，制成姐卜Ni电池负极，通过恒电流充／放电方法研究了其电化学性能。结果表明：Lal一xMg：（NiCoAI）3．6体系金属氢化物电极较容易活化，室温下具有优异的高倍率放电性能，在以4200mA／g电流放电时，La卜汉gx（NICoAI）36合金电极的放电容量是ABS型合金电极的3倍，达152hah／g，显示出良好的动力学特性。R，入1兮Ni（R：raree田劝，Ca，Y）型合金因能吸引／释放1．8一1．87％质量的HZ而被认为是种很有希望的贮氢合金。但其吸／放氢平台过高，循环寿命短。如何提高Rh厦g剑19循环稳定性是这类合金能否成功商业化的关键。研究发现，Co能够显著提高ABS型合金电极的循环寿命，但其价格太贵。人们发现Al在提高电极寿命方面与C。有类似的作用，但Al元素的添加因其在碱性电解质的作用下在电极表面易生成致密的氧化膜而不利于氢的扩散，进而对高倍率放电性能不利。入物在提高电极表面活性，改善其高倍率放电性方面作用明显。本工作在前面的基础上用Al和MO联合取代Ni，以期待同时改善La一Mg一Ni一Co合金的循环稳定性和高倍率放电性能。详细研究了La07Mg03Ni切一（A105Mo05）x（x：o，0．2，0．4，0．6，0．8）系列贮氢合金的晶体结构和电化学性能。X射线衍射及Rietveld分析发现：所有La07Mg03Ni4D一x（A105Mo05）x合金均为包含PuNi3结构的六方LaZMgNig相、CaCus结构的LaNis主相及L匆Ni7，LaN儿和LaNi杂相的多相结构。合金中La（La，Mg）剑19相及LaNis相的晶格参数及晶胞体积均随合金中Al和Mo含量的增加而增大。用电化学方法测得的RC一T曲线显示：Al和'fo部分取代Ni降低了氢的平台压力。随合金中Al和Mo含量的增加，电极的电化学容量从329．7（x＝0）、徽橇毓孺鑫盆一11瀚加至365．物A吨（＝0．6）后又降低到351．3毗吨（x＝0．8）。当以1200m刀g的电流密度进行放电时，其I｛RD从62．0％沁0）增加到82．1％沁0．8）。线性微极化结果显示：Al和Mo的添加增大了合金表面的交换电流密度，因而也改善了合金电极的高倍率放电性能。另外，Al和M。取代合金中的Ni增大了氢在电极合金中的扩散系数（D），改善了La07Mgo3Ni4。一x（Alo5M。。5）x（X＝o，0．2，0．4，0．6，0．8）合金电极的低温放电性能（LTD）。