Electric field driven quantum phase transition between band insulator and topological insulator

We demonstrate theoretically that electric field can drive a quantum phase transition between band insulator to topological insulator in CdTe/HgCdTe/CdTe quantum wells. The numerical results suggest that the electric field could be used as a switch to turn on or off the topological insulator phase, and temperature can affect significantly the phase diagram for different gate voltage and compositions. Our theoretical results provide us an efficient way to manipulate the quantum phase of HgTe quantum wells.

Photoinduced spin alignment of the magnetic ions in (Ga,Mn)As

Time-resolved Kerr rotation measurement in the (Ga,Mn)As diluted magnetic semiconductor allows direct observation of the dynamical properties of the spin system of the magnetic ions and the spin-polarized holes. Experimental results show that the magnetic ions can be aligned by the polarized holes, and the time scales of spin alignment and relaxation take place in tens and hundreds of picoseconds, respectively. The Larmor frequency and effective g factor obtained in the Voigt geometry show an unusual temperature dependence in the vicinity of the Curie temperature due to the exchange coupling between the photoexcited holes and magnetic ions. Such a spin coherent precession can be amplified or destructed by two sequential excitation pulses with circularly copolarized or oppositely polarized helicity, respectively. (c) 2006 American Institute of Physics.

Experimental measurement of microwave-induced electron spin-flip time

The electron spin resonance (ESR) is optically detected by monitoring the microwave-induced changes in the circular polarization of the neutral exciton (X) and the negatively charged exciton (X-) emission in CdTe quantum wells with low density of excess electrons. We find that the circular polarization of the X and X- emission is a mapping of the spin polarization of excess electrons. By analyzing the ESR-induced decrease in the circular polarization degree of the X emission, we deduce the microwave-induced electron spin-flip time >0.1 mus, which is much longer than the recombination time of X and X-. This demonstrates that the optically detected ESR in type I quantum wells with low density of excess electrons does not obey the prerequisite for the conventional optically detected magnetic resonance. (C) 2001 American Institute of Physics.

One-pot synthesis and self-assembly of colloidal copper(I) sulfide nanocrystals

A simple one-pot method is developed to prepare size-and shape-controlled copper(I) sulfide (Cu2S) nanocrystals by thermolysis of a mixed solution of copper acetylacetonate, dodecanethiol and oleylamine at a relatively high temperature. The crystal structure, chemical composition and morphology of the as-obtained products are characterized by powder x-ray diffraction (PXRD), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The morphology and size of the Cu2S nanocrystals can be easily controlled by adjusting the reaction parameters. The Cu2S nanocrystals evolve from spherical to disk-like with increasing reaction temperature. The spherical Cu2S nanocrystals have a high tendency to self-assemble into close-packed superlattice structures. The shape of the Cu2S nanodisks changes from cylinder to hexagonal prism with prolonged reaction time, accompanied by the diameter and thickness increasing. More interestingly, the nanodisks are inclined to self-assemble into face-to-face stacking chains with different lengths and orientations. This one-pot approach may extend to synthesis of other metal sulfide nanocrystals with different shapes and sizes.

金属纳米材料的合成，组装及电化学性质的研究

利用Brust的两相法制备了一系列Au纳米粒子，重点选择了三种代表性的硫醇配体：包括电活性的4-二茂铁苯硫酚配体，刚性的琉基一三苯基甲烷配体和树枝状硫醇配体。摸索了实验条件对Au纳米粒子粒径的影响。其中重点研究了电活性配体4-二茂铁苯硫酚包覆的Au纳米粒子的电化学性质，它受表面波控制。制备了梭酸配体包覆的水溶性的Au纳米粒子，讨论了梭酸配体在Au纳米粒子表面构向的不同对电解质诱导的Au纳米粒子聚沉的影响。利用双硫醇与4-二茂铁苯硫酚包覆的Au纳米粒子发生配体交换后，将这种电活性的Au纳米粒子组装在金电极表面。XPS结果证明了这个组装的过程，研究了这种电活性Au纳米粒子在电极表面的电化学行为，包括式量电位，峰峰电位差，覆盖度等等。重点讨论了这种组装在电极表面的Au纳米粒子的式量电位发生负移的原因。制备了水溶性的3一琉基甘油包覆的Au纳米粒子，利用微分脉冲伏安（DPv）技术发现了这种Au纳米粒子在水溶液中的量子化充放电现象。3一琉基甘油在Au纳米粒子表面的特殊结构，即大量存在的分子间氢键，避免了水分子渗入硫醇配体层带来的高介电常数的干扰，试验得到了这种Au纳米粒子的电容值，与经典的导电同心球模型计算的理论值接近。利用水溶性的Au纳米粒子为催化剂，催化一个经典的胶体催化的氧化还原反应：铁氰化钾与硫代硫酸钠之间的反应。其催化反应机理为：胶体金作为电子转移媒介体，铁氰根离子和硫代硫酸根离子在胶体金表面交换电子，促进氧化还原反应的进行．利用该氧化还原反应的速度，计算了电子在金纳米粒子表面的三维自组装膜中的电子转移速度。制备了一种空心CdTe＠Au核一壳结构的复合纳米材料。与传统方法制备的实心CdTe＠Au相比，这种空心的纳米材料仍然保留了cdTe的荧光性能．这种空心材料增加了CdTe导带电子和Au之间的电子传递距离，减弱了Au对CdTe发光的淬灭。这种可发光的空心的半导体一金属核一壳纳米材料，有望在光催化，太阳能电池，表面增强拉曼检测，生物标记等诸多领域获得应用．

几种硫属化合物半导体的电化学与光电化学研究

本文分别用恒电位电沉积和恒电位脉冲电沉积技术在ITO基底上成功地沉积出表面平滑均匀、与基底附着牢固、具有一定光活性的CdS多晶薄膜。系统地考察了CdS薄膜的电性质、光性质及光电化学行为。用电沉积技术在不同基底（Ni、Ti、ITO）上成功地实现了Hg_(1-X)Cd_xTe(MCT)的三元共沉积。初步组装了P-Hg_(1-X)Cd_xTe/n-CdS异质结PV池。研究了层状结构材料n-InSe的PEC行为并考察了多种单晶材料，诸如CdS、CdTe、CdSe、InSe等的光阳极特性和界面行为。

半导体中自旋轨道耦合及自旋霍尔效应

本文主要评述和介绍半导体微结构中自旋轨道耦合的研究和最近的研究进展.我们细致地讨论了半导体微结构中自旋轨道耦合的物理起源和窄带隙半导体量子阱中的自旋霍尔效应.我们发现目前国际上广泛采用的线性Rashba模型在较大的电子平面波矢处失效:即自旋轨道耦合导致的能带自旋劈裂不再随电子波矢的增加而增加,而是开始下降,即出现强烈的非线性行为.这种非线性的行为起源于导带和价带间耦合的减弱.这种非线性行为还会导致电子的D'yakonov-Perel'自旋弛豫速率在较高能量处下降,与线性模型的结果完全相反.在此基础上,我们构造统一描述电子和空穴自旋霍尔效应的理论框架.我们的方法可以非微扰地计入自旋轨道耦合对本征自旋霍尔效应的影响.我们将此方法应用于强自旋轨道耦合的情形,即窄带隙CdHgTe/CdTe半导体量子阱.我们发现调节外电场或量子阱的阱宽可以作为导致量子相变和本征自旋霍尔效应的开关.我们的工作可能会为区别和实验验证本征自旋霍尔效应提供物理基础.

MOCVD生长的II-VI族化合物固溶体组分的热力学分析.2.Hg（1-x）CdxTe体系

对MOCVD生长Hg_(1-x)Cd_xTe进行了热力学分析.所用的起始原材料为Hg、DM-Cd和R_2Te.计算结果一方面表明CdTe优先并入倾向使得在通常的DAG工艺中x值非常不易控制.另一方表明即使在Hg存在的情况下,也可以沉积几平纯的CdTe,这对实现IMP工艺非常有利,计算结果还表明II/VI比对HgCdTe的组分控制起着关键性的作用.在DAG工艺中,较低的II/VI比可以改善对x值的控制能力,LMP-DAG工艺是降低II/VI比的较好途径.还计算了生长温度和反应室压力对固相组分的影响以及LMP-DAG工艺中生长温度与HgCdTe组分对最低汞分压的影响.

Glutathione-Mediated Release of Functional Plasmid DNA from Positively Charged Quantum Dots

DNA was efficiently bound to water-soluble positively charged CdTe quantum dots (QDs) through complementary electrostatic interaction. These QDs-DNA complexes were disrupted and DNA was released by glutathione (GSH) at intracellular concentrations. Interestingly, there was almost no detectable DNA released by extracellular concentration of GSH. The formation of QDs-DNA complexes and GSH-mediated DNA release from the complexes were confirmed by dye displacement assay, electrophoretic mobility shift assay (EMSA), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) experiments.

Quantum dots-bienzyme hybrid system for the sensitive determination of glucose

In this paper, we attempt to develop a sensitive detection method for glucose with the combination of the unique optical property of quantum dots and the specificity of enzymatic reactions. With glucose and hydroquinone as substrates, benzoquinone that intensively quenches the photoluminescence of quantum dots can be produced via the catalysis of bienzyme (glucose oxidase and horseradish peroxidase) system. A relatively low detection limit of 1.0 x 10(-8) mol/L can be achieved. Two linear ranges from 1.0 x 10(-6) to 1.5 x 10(-4) M and from 1.5 x 10(-4) to 1.0 x 10(-3) M were obtained.

Nanoscale-enhanced Ru(bpy)(3)(2+) electrochemiluminescence labels and related aptamer-based biosensing system

A unique multilabeling at a single-site protocol of the Ru(bpy)(3)(2+) electrochemiluminescence (ECL) system is proposed. Nanoparticles (NPs) were used as assembly substrates to enrich ECL co-reactants of Ru(bpy)(3)(2+) to construct nanoscale-enhanced ECL labels. Two different kinds of NP substrates [including semiconductor NPs (CdTe) and noble metal NPs (gold)] capped with 2-(dimethylamino)ethanethiol (DMAET) [a tertiary amine derivative which is believed to be one of the most efficient of co-reactants of the Ru(bpy)(3)(2+) system] were synthesized through a simple one-pot synthesis method in aqueous media.

Investigation of some critical parameters of buffer conditions for the development of quantum dots-based optical sensors

The unique surface-sensitive properties make quantum dots (QDs) great potential in the development of sensors for various analytes. However, quantum dots are not only sensitive to a certain analyte, but also to the surrounding conditions. The controlled response to analyte may be the first step in the designing of functional quantum dots sensors. In this study, taking the quenching effect of benzoquinone (BQ) on CdTe QDs as model, several critical parameters of buffer solution conditions with potential effect on the sensors were investigated. The pH value and the concentration of sodium citrate in the buffer solution critically influenced the quenching effects of BQ.

Shape evolution of CdSe nanocrystals in vegetable oils: A synergistic effect of selenium precursor

In this contribution, common vegetable oils are used as coordination solvents for synthesis of high quality CdSe nanocrystals. Various shaped nanocrystals (quantum dots, quantum rods, multipods, arc structure, etc.) can be produced free of alkylphosphonic acids. Shape evolution can be induced by three types of selenium precursors: ODE-Se, VO-Se and TOP-Se (ODE, 1-octadecene; VO, vegetable oil; TOP, trio-n-octylphosphine). The quantum yields of NCs are 15-40%. The full width at half-maximum (fwhm) of the photoluminescence spectra are 27 +/- 1 nm for quantum clots and 23 +/- 1 nm for quantum rods/multipods.

Rapid fabrication of Au nanoparticle films with the aid of centrifugal force

In this work, rapid fabrication of Au nanoparticle (Au NP) films has been simply achieved by alternate adsorption of citrate-stabilized Au NPs and poly(diallyldimethylammonium chloride) with the aid of centrifugal force. In contrast to conventional electrostatic assembly, we carried out the assembly process in a centrifuge with a rotating speed of 4000 rpm, where centrifugal force can be imposed on Au NPs. Scanning electron microscopy and cyclic voltammetry were employed to characterize the assembly procedure and the thus-prepared thin solid films. Our results demonstrate that centrifugal force can promote the assembly of Au NPs and therefore enable the rapid fabrication of functional Au NP films.

Quantum dot electrochemiluminescence in aqueous solution at lower potential and its sensing application

The unique strategy for electrochemiluminescence (ECL) sensor based on the quantum dots (QDs) oxidation in aqueous solution to detect amines is proposed for the first time. Actually, there existed two QDs ECL peaks in anhydrous solution, one at high positive potential and another at high negative potential. However, here we introduced the QDs oxidation ECL in aqueous solution to fabricate a novel ECL sensor. Such sensor needed only lower positive potential to produce ECL, which could prevent the interferences resulted from high potential as that of QDs reduction ECL in aqueous solution. Therefore, the present work not only extended the QDs oxidation ECL application field from anhydrous to aqueous solution but also enriched the variety of ECL system in aqueous solution. Furthermore, we investigated the QDs oxidation ECL toward different kinds of amines, and found that both aliphatic alkyl and hydroxy groups could lead to the enhancement of ECL intensity. Among these amines, 2-(dibutylamino)ethanol (DBAE) is the most effective one, and accordingly, the first ECL sensing application of the QDs oxidation ECL toward DBAE is developed; the as-prepared ECL sensor shows wide linear range, high sensitivity, and good stability.