The influence of 1D, meso- and crystal structures on charge transport and recombination in solid-state dye-sensitized solar cells

We have prepared single crystalline SnO2 and ZnO nanowires and polycrystalline TiO2 nanotubes (1D networks) as well as nanoparticle-based films (3D networks) from the same materials to be used as photoanodes for solid-state dye-sensitized solar cells. In general, superior photovoltaic performance can be achieved from devices based on 3-dimensional networks, mostly due to their higher short circuit currents. To further characterize the fabricated devices, the electronic properties of the different networks were measured via the transient photocurrent and photovoltage decay techniques. Nanowire-based devices exhibit extremely high, light independent electron transport rates while recombination dynamics remain unchanged. This indicates, contrary to expectations, a decoupling of transport and recombination dynamics. For typical nanoparticle-based photoanodes, the devices are usually considered electron-limited due to the poor electron transport through nanocrystalline titania networks. In the case of the nanowire-based devices, the system becomes limited by the organic hole transporter used. In the case of polycrystalline TiO2 nanotube-based devices, we observe lower transport rates and higher recombination dynamics than their nanoparticle-based counterparts, suggesting that in order to improve the electron transport properties of solid-state dye-sensitized solar cells, single crystalline structures should be used. These findings should aid future design of photoanodes based on nanowires or porous semiconductors with extended crystallinity to be used in dye-sensitized solar cells. © 2013 The Royal Society of Chemistry.

Growth kinetics and uniform scaling-up of graphene synthesis

Chemical vapor deposition on copper is the most widely used method to synthesize graphene at large scale. However, the clear understanding of the fundamental mechanisms that govern this synthesis is lacking. Using a vertical-flow, cold-wall reactor with short gas residence time we observe the early growths to study the kinetics of chemical vapor deposition of graphene on copper foils and demonstrate uniform synthesis at wafer scale. Our results indicate that the growth is limited by the catalytic dissociative dehydrogenation on the surface and copper sublimation hinders the graphene growth. We report an activation energy of 3.1 eV for ethylene-based graphene synthesis. © The Electrochemical Society.

Polychromatic single-shot spectroscopy on SOI-FET trapped electrons

The behavior of trapped electrons, in a dielectric close to the channel of a silicon SOI-FET, is studied by cryogenic microwave spectroscopy. On-resonance microwave excitation causes one of these trapped electrons to undergo spatial Rabi oscillations between widely separated trap sites. This charge displacement causes a change in the drain current of the transistor, resulting in high quality factor resonances in continuous wave spectroscopy. The potential of this effect for non-classical information processing is investigated through polychromatic single-shot spectroscopy, using on-resonance and difference frequencies. Interaction between different trapped electrons is seen in the post excitation behavior and the possibilities of quantum gate operations are discussed. © The Electrochemical Society.

Electrical detection of trapped charge displacements using an ultra-thin SOI percolation transistor

Electrical detection of solid-state charge qubits requires ultrasensitive charge measurement, typically using a quantum point contact or single-electron-transistor, which imposes strict limits on operating temperature, voltage and current. A conventional FET offers relaxed operating conditions, but the back-action of the channel charge is a problem for such small quantum systems. Here, we discuss the use of a percolation transistor as a measurement device, with regard to charge sensing and backaction. The transistor is based on a 10nm thick SOI channel layer and is designed to measure the displacement of trapped charges in a nearby dielectric. At cryogenic temperatures, the trapped charges result in strong disorder in the channel layer, so that current is constrained to a percolation pathway in sub-threshold conditions. A microwave driven spatial Rabi oscillation of the trapped charge causes a change in the percolation pathway, which results in a measurable change in channel current. © The Electrochemical Society.

水利工程与鱼类资源的利用和保护

<正> 兴修水利,控制和改造江河湖泊,必然会使水体的某些环境因子发生变化,对鱼类资源产生一定的影响。解放以来,我国相继修建了86,000多座水库,水面近3,000万亩,占我国淡水可养鱼水面的40%左右。利用水库发展渔业,存在着巨大的潜力。另一方面,兴修水利工程对天然捕捞鱼类产量也带来不利影响。水利工程对于江河内鱼类的生活有何影响,对于一些必须通过枢纽上溯繁殖的洄游性鱼类如何救护,都是需要研究解决的问题。

Highly efficient photoluminescence of Er2SiO5 films grown by reactive magnetron sputtering method

E2SiO5 thin films were fabricated on Si substrate by reactive magnetron sputtering method with subsequent annealing treatment. The morphology properties of as-deposited films have been studied by scanning electron microscope. The fraction of erbium is estimated to be 23.5 at% based on Rutherford backscattering measurement in as-deposited Er-Si-O film. X-ray diffraction measurement revealed that Er2SiO5 crystalline structure was formed as sample treated at 1100 degrees C for 1 h in O-2 atmosphere. Through proper thermal treatment, the 1.53 mu m Er3+-related emission intensity can be enhanced by a factor of 50 with respect to the sample annealed at 800 degrees C. Analysis of pump-power dependence of Er3+ PL intensity indicated that the upconversion phenomenon could be neglected even under a high photon flux of 10(21) (photons/cm(2)/sec). Temperature-dependent photoluminescence (PL) of Er2SiO5 was studied and showed a weak thermal quenching factor of 2. Highly efficienct photoluminescence of Er2SiO5 films has been demonstrated with Er3+ concentration of 10(22)/cm(3), and it opens a promising way towards future Si-based light source for Si photonics. (C) 2009 Elsevier B.V. All rights reserved.

光学自旋注入方法

于AD批量导入至AEzhangdi

GaAs基InAs/GaSb超晶格红外光电探测器及其制作方法

于AD批量导入至AEzhangdi

一种可用于直下式LCD背光源的LED的透镜

于AD批量导入至AEzhangdi

一种抗振动与噪声干扰的光纤传感波长解调系统

于AD批量导入至AEzhangdi

Electrical properties and electroluminescence of 4H-SiC p-n junction diodes

Homoepitaxial growth of 4H-SiC on off-oriented Si-face(0001) substrates was performed by using the step-controlled epitaxy technique in a newly developed low-pressure hot-wall CVD (LP-HWCVD) system with a horizontal air-cooled quartz tube at around 1500 degreesC and 1.33 x 10(4) Pa by employing SiH4 + C2H4 + H-2. In-situ doping during growth was carried out by adding NH3 gas into the precursor gases. It was shown that the maximum Hall mobility of the undoped 4H-SiC epilayers at room temperature is about 430 cm(2) (.) V-1 (.) s(-1) with a carrier concentration of similar to 10(16) cm(-3) and the highest carrier concentration of the N-doped 4H-SiC epilayer obtained at NH3 flow rate of 3 sccm is about 2.7 x 10(21) cm(-3) with a mobility of 0.75 cm(2) (.) V-1 (.) s(-1). SiC p-n junctions were obtained by epitaxially growing N-doped 4H-SiC epilayers on Al-doped 4H-SiC substrates. The C - V characteristics of the diodes were linear in the 1/C-3 - V coordinates indicating that the obtained p-n junctions were graded with a built-in voltage of 2.7 eV. The room temperature electroluminescence spectra of 4H-SiC p-n junctions are studied as a function of forward current. The D-A pair recombination due to nitrogen donors and the unintentional, deep boron center is dominant at low forward bias, while the D-A pair recombination due to nitrogen donors and aluminum acceptors are dominant at higher forward biases. The p-n junctions could operate at temperature of up to 400 degreesC, which provides a potential for high-temperature applications.

Room-temperature ferromagnetic semiconductor MnxGa1-xSb

Ferromagnetic semiconductor MnxGa1-xSb single crystals were fabricated by Mn-ions implantation, deposition, and the post annealing. Magnetic hysteresis-loops in the MnxGa1-xSb single crystals were obtained at room temperature (300 K). The structure of the ferromagnetic semiconductor MnxGa1-xSb single crystal was analyzed by Xray diffraction. The distribution of carrier concentrations in MnxGa1-xSb was investigated by electrochemical capacitance-voltage profiler. The content of Mn in MnxGa1-xSb varied gradually from x = 0.09 near the surface to x = 0 in the wafer inner analyzed by X-ray diffraction. Electrochemical capacitance-voltage profiler reveals that the concentration of p-type carriers in MnxGa1-xSb is as high as 1 X 10(21) cm(-3), indicating that most of the Mn atoms in MnxGa1-xSb take the site of Ga, and play a role of acceptors.

High-concentration hydrogen in unintentionally doped GaN

We use nuclear reaction analysis to study hydrogen in unintentionally doped GaN, and high-concentration hydrogen, nearly 10(21) cm(-3), is detected. Accordingly, a broad but intense infrared absorption zone with a peak at 2962 cm(-1) is reported, which is tentatively assigned to the stretch mode of NH: Ga complex. The complex is assumed to be one candidate answering for background electrons in unintentionally doped GaN. (C) 1998 Elsevier Science B.V. All rights reserved.

太阳能利用技术现状及展望

本文系统地论述了目前世界上利用太阳能技术的最新进展，并展示了其诱人的前景。未来10年，太阳能的研究与利用会“火热”一阵，以后会更热，直到聚变核能实现商业化。预计，太阳能将成为21世纪的主要能源，到2030年世界电力的50%将依靠太阳能。

贾第虫的核仁基因组与真核细胞核仁的起源进化

核仁是真核细胞核中最明显的结构，是rRNA转录、加工和核糖体亚基组装的场所。核仁的起源进化无疑是真核细胞起源进化问题的一个极为重要的方面。但迄今为止，这方面的研究很少。本文首先对"不具核仁"的低等单细胞真核生物贾第虫的"核仁"基因及核糖体合成系统的基因群进行了研究，进而对已知的核仁蛋白质组的生物进行了比较基因组研究，从而从基因和基因组的角度对核仁的起源进化问题进行了较为深入的研究。获得了如下结，和结论：1）在"不具核仁"的贾第虫中分离鉴定出了典型真核细胞参与pre-rRNA加工的krr］基因；表明贾第虫中的pre-rRNA加工机制与典型真核细胞的是一致的。在具有核仁结构的典型真核细胞中，krr1基因所编码的KRRIP蛋白是参与Pre一rRNA加工的核仁定位蛋白之一。我们在一度被认为是极为原始的"不具核仁结构"的真核生物－贾弟虫的基因组中分离鉴定出了该基因，并证明该基因在贾第虫中是活跃转录的。同时，还调查发现与KRRIP形成蛋白复合体从而发挥功能的众场，其基因在贾第虫中也是存在的，这提示贾第虫的pre寸RNA加工机制与具有核仁结构的典型真核细胞是一致的。2）对贾第虫核糖体合成系统的基因群／亚基因组进行了全面调查，发现在典型真核生物中所共有的参与核搪体合成的129条保守蛋白基因中有89条在贾第虫基因组具有相应的直系同源基因，包括编码参与rRNA申基化和假尿嗜陡化的蛋白复合体成员以及存在于905、405和605复合体中的蛋白等诸多重要基因。这表明贾第虫的核糖体合成系统与典型的真核生物相似，只是参与的成分相对简单些。以上1）、2）的结果表明贾第虫虽然没有核仁结构，但其核糖体合成机制却与具核仁结构的典型真核细胞一致。这可能意味着真核细胞核仁的核糖体合成功能的起源形成是在核仁结构形成之前，那么核仁结构的形成可能是在此功能之外另有"新意"；另外也可能是由于贾第虫因适应寄生生活而导致核仁"退化"之故，虽然这种可能性偏少，但若果真如此也是生物适应性进化中的一个重要现象，值得深入研究。3）对已知核仁蛋白质组的人、酵母和拟南芥进行了比较基因组学研究。通过搜索KOG直系同源蛋白簇数据库，发现约74％的人的核仁蛋白，约75％的酵母的核仁蛋白以及约84％的拟南芥的核仁蛋白在动物、真菌和植物中都保守。这表明这些高等真核生物的核仁蛋白大都在它们分化之前就已起源形成。进一步的调查发现：共同定位于人和酵母核仁中的同源蛋白中，人有154条蛋白对应于酵母的134条蛋白，其中人的核仁蛋白相对于酵母的有10条蛋白发生了基因重复；同样的分析发现，人的核仁蛋自相对于拟南芥的有21条蛋白发生了基因重复。这些事实表明：随着真核生物的进化，至少在高等真核生物中基因重复是核仁成分复杂化和核仁进化的重要途径。4）用人的442条核仁蛋白（它们在植物和真菌中也都存在同源蛋白，但不一定是核仁蛋白）对原核生物基因组进行了搜索。结果表明，在真细菌和原（古）细菌中都能找到好多同源物，但发现下列重要现象：只在原（古）细菌有同源物的核仁蛋白要比只在真细菌中有同源物的核仁蛋白多得多，包括了RNA修饰蛋白、核糖体蛋自以及参与翻译的相关蛋白等；而只在真细菌中有同源物的核仁蛋白只是RNA螺旋酶和WD重复蛋白。因此，我们认为核仁可能是由真细菌和原细菌复合起源的，但其主体起源于原细菌。