High‐Quality Photonic Crystals Infiltrated with Quantum Dots

We report a method for producing colloidal crystals heavily loaded with PbS quantum dots (QDs). The approach employed uses capillary forces to load the QDs in the interstitial voids of the colloid crystals and yields highly ordered structures with a high loading of QDs. The infiltration process is qualitatively monitored using confocal fluorescence microscopy and scanning electron microscopy. The optical properties of the resulting composite structure are examined using optical spectroscopy. The shift in the stopband resulting from the infiltration of the colloid crystal shows that the PbS QDs occupy nearly 100 % of the volume of the interstitial space.     

Magnetic Memory Effect of Nanocomposites

The magnetic memory effect (MME) is the ability of magneto‐sensitive materials to remember the magnetic field strength (H_def), at which they were deformed recently. They respond close to H_def either by recovering their initial shape at a switching magnetic field strength H_sw under stress‐free conditions or by building up stress with a peak maximum at H_σ,max under constant strain conditions. This paper explores whether such a MME can be created for polymer‐based nanocomposites. The concept is based on temperature‐memory polymers (TMP) as matrix, in which silica coated iron(III)oxide nanoparticles (mNP) are dispersed. The MME was explored in a cyclic magneto‐mechanical test, in which the nanocomposite sample was elongated to ?_m while being exposed to an alternating magnetic field at H_def. The magnetic memory was read out by determining H_σ,max or H_sw. A linear correlation between H_σ,max (or H_sw) and H_def in a range from 15 to 23 kA m^?1 at a fixed frequency of f = 258 kHz is observed and demonstrates the excellent magnetic memory properties of the investigated nanocomposites containing either crystallizable or amorphous, vitrifiable domains as controlling units. The deformation ?m at H_def can be fixed with an accuracy of more than 72% and the initial shape can be recovered almost completely by more than 86%. The MME allows the design of magnetically programmable devices such as switches or mechanical manipulators.     

Sub‐20 nm Magnetic Dots with Perpendicular Magnetic Anisotropy

A new and simple method for the preparation of magnetic dot arrays is introduced. Diblock copolymer micelles with a silica core are used as template for the generation of nanostructure arrays. The silica cores are utilized as mask for ion milling preparation. The morphology and size of the silica and magnetic dot arrays are discussed. The magnetic dots are made from Co/Pt multilayer films. Ferromagnetic dots with a diameter well below 20 nm and perpendicular easy axis of magnetization are created. The switching behavior changes from domain wall motion, dominant in the film, to single domain particle switching in the dots. The magneto‐optic saturation signals and the evolution of magnetic anisotropy are discussed.     

Superparamagnetic Nanostructures for Off‐Resonance Magnetic Resonance Spectroscopic Imaging

This study proposes a new method to generate positive contrast in magnetic resonance imaging (MRI) using superparamagnetic contrast agents. Superparamagnetic nanostructures consisting of octahedron manganese ferrite nanoparticles embedded in spherical nanogels are fabricated using a bottom‐up approach. The composite nanoparticles are strongly magnetized in an external magnetic field and produce a unique NMR frequency shift in water protons, which can be demonstrated in MR spectroscopy and imaging to be different from the bulk pool. Moreover, the particles exhibit excellent colloidal stability in aqueous media and good cell biocompatibility. Hence, these particles are potentially useful as biomarkers by taking advantage of the positive contrast effects produced in MRI.     

Photosensitization of TiO2 Nanostructures with CdS Quantum Dots: Particulate versus Tubular Support Architectures

TiO₂ nanotube arrays and particulate films are modified with CdS quantum dots with an aim to tune the response of the photoelectrochemical cell in the visible region. The method of successive ionic layer adsorption and reaction facilitates size control of CdS quantum dots. These CdS nanocrystals, upon excitation with visible light, inject electrons into the TiO₂ nanotubes and particles and thus enable their use as photosensitive electrodes. Maximum incident photon to charge carrier efficiency (IPCE) values of 55% and 26% are observed for CdS sensitized TiO₂ nanotube and nanoparticulate architectures respectively. The nearly doubling of IPCE observed with the TiO₂ nanotube architecture is attributed to the increased efficiency of charge separation and transport of electrons.     

磁场内双声子作用对量子点中极化子的影响

为突出双声子相互作用对磁场内量子点中极化子的影响,简化了理论模型,把库仑势对电子质量的影响用电子在能带中的质量来代替。使用线性组合算符和么正变换对系统进行理论计算,导出了半导体量子点中磁极化子的基态和各部分能量。当考虑电子在反冲效应中反射和吸收不同波矢的声子之间相互作用时,讨论了这种作用对半导体量子点中磁极化子基态能量的影响。通过数值计算表明,半导体量子点中磁极化子的基态能量随量子点的有效受限长度的减小而迅速增大,随磁场的增加而增加。当磁场较弱时,声子之间的相互作用对极化子性质的影响是不能忽略的。     

II-VI族半导体量子点的发光特性及其应用研究进展

半导体量子点由于具有独特的发光特性而具有极高的应用价值。结合本实验室的工作介绍了半导体量子点的发光原理和发光特性，在实验中发现核壳结构的CdSe／CdS半导体量子点比没有包覆的CdSe半导体量子点的发光稳定性提高．吸收光谱和发射光谱均发生红移，而且粒径不同．半导体量子点所呈现的颜色也不同，随着粒径的增加吸收光谱和发射光谱向长波方向红移。介绍了半导体量子点在光电子器件和生物医学方面的应用．并对其发展前景进行了展望。     

Doxorubicin Nanocarriers Based on Magnetic Colloids with a Bio‐polyelectrolyte Corona and High Non‐linear Optical Response: Synthesis,Characterization, and Properties

Magnetic drug nanocarriers are synthesized following an arrested mineralization of magnetic spinel iron oxides in the presence of the biopolymer of sodium carboxymethylcellulose. Based on the experimental results, the polyelectrolyte corona probably attains a brushlike configuration around the magnetic particles. The inner core of these colloids may be constituted of polymer‐associated nanocrystallites, forming nanogel colloids. The hybrid colloids are endowed with a high loading capacity for the anticancer agent doxorubicin and pronounced pH responsiveness. They also display a dramatic increase in non‐linear optical response as compared to previous studies of similar materials. Furthermore, as cell studies indicate, the blank nanocarriers are cytocompatible and the drug retains its activity after loading in the nanocarriers.     

Hybrids of Magnetic Nanoparticles with Double‐Hydrophilic Core/Shell Cylindrical Polymer Brushes and Their Alignment in a Magnetic Field

The synthesis of double‐hydrophilic core/shell cylindrical polymer brushes (CPBs), their hybrids with magnetite nanoparticles, and the directed alignment of these magnetic hybrid cylinders by a magnetic field are demonstrated. Consecutive grafting from a polyinitiator poly(2‐(2‐bromoisobutyryloxy)ethyl methacrylate) (PBIEM) of tert‐butyl methacrylate (tBMA) and oligo(ethylene glycol) methacrylate (OEGMA) using atom‐transfer radical polymerization (ATRP) and further de‐protection yields core/shell CPBs with poly(methacrylic acid) (PMAA) as the core and POEGMA as the shell, which is evidenced by ¹H NMR, gel permeation chromatography (GPC), and dynamic and static light scattering (DLS and SLS). The resulting core/shell brush is well soluble in water and shows a pH responsiveness because of its weak polyelectrolyte core. Pearl‐necklace structures are observed by cryogenic transmission electron microscopy (cryo‐TEM) at pH 4, while at pH 7, these structures disappear owing to the ionization of the core. A similar morphology is also found for the polychelate of the core/shell CPBs with Fe³⁺ ions. Superparamagnetic magnetite nanoparticles have also been prepared and introduced into the core of the brushes. The hybrid material retains the superparamagnetic property of the magnetite nanoparticles, which is verified by superconducting quantum interference device (SQUID) magnetization measurements. Large‐scale alignment of the hybrid cylinders in relatively low magnetic fields (40–300 mT) can easily be performed when deposited on a surface. which is clearly revealed by the atomic force microscopy (AFM) and TEM measurements.     

胶体硒化镉量子点的荧光时间分辨谱研究

使用化学胶体法合成了12个高质量、不同尺寸的胶体硒化镉量子点.测量了样品的时间分辨光致发光谱、TEM谱,同时测量并计算了样品的光致发光量子产率以及光致发光寿命.研究结果表明:硒化镉量子点的光辐射强度与表面相关的光辐射强度均由量子点的表面缺陷形式决定,并且也决定了光致发光量子产率、光致发光寿命.量子点的表面缺陷形式决定于尺寸,在量子点的生长过程中存在的表面的优化/重构也依赖于尺寸.     

半导体量子点中强耦合激子的性质

研究了抛物型半导体量子点中强耦合激子的性质.在有效质量近似下,采用线性组合算符和幺正变换的方法,导出了半导体量子点中重空穴激子的基态能量.在强耦合情况下讨论了量子点半径和受限强度对半导体量子点中激子基态能量的影响.以氯化铊(TlCl)半导体为例进行了数值计算.结果表明:在强耦合情况下,重空穴激子的基态能量随量子点半径的增大而减小,随量子点受限强度的增大而增大.     

半导体量子点中极化子的有效质量

研究了半导体量子点中极化子的有效质量.采用改进的线性组合算符方法,导出在电子-体纵光学声子(LO)强耦合时抛物量子点中极化子的振动频率、相互作用能和有效质量随受限强度和电子-声子耦合强度的变化.对RbCl晶体量子点进行了数值计算,结果表明,量子点受限越强,半导体量子点中强耦合极化子的振动频率和有效质量就越大;极化子的相互作用能随受限强度的增加先急剧增加,当达到极值后,随受限强度的增加而急剧减少     

Mussel‐Inspired Electrospun Smart Magnetic Nanofibers for Hyperthermic Chemotherapy

A method for the versatile synthesis of novel, mussel‐inspired, electrospun nanofibers with catechol moieties is reported. These mussel‐inspired nanofibers are used to bind iron oxide nanoparticles (IONPs) and the borate‐containing anticancer drug Bortezomib (BTZ) through a catechol metal binding mechanism adapted from nature. These smart nanofibers exhibit a unique conjugation of Bortezomib to their 1, 2‐benzenediol (catechol) moieties for enabling a pH‐dependent drug delivery towards the cancer cells and the IONPs via strong coordination bonds for exploiting the repeated application of hyperthermia. Thus the synergistic anticancer effect of these mussel‐inspired magnetic nanofibers were tested in vitro for the repeated application of hyperthermia along with the chemotherapy and found that the drug‐bound catecholic magnetic nanofibers exhibited excellent therapeutic efficacy for potential anticancer treatment.     

InAs/InP Self‐Assembled Quantum Dots: Wavelength Tuning and Optical Nonlinearities

Quantum dots (QDs, i.e., semiconductor nanocrystals) can be formed by spontaneous self‐assembly during epitaxial growth of lattice‐mismatched semiconductor systems. InAs QDs embedded in GaInAsP on InP are introduced, which can be continuously wavelength‐tuned over the 1.55 μm region by inserting ultrathin GaAs or GaP interlayers below them. We subsequently introduce a state‐filling optical nonlinearity, which only requires two electron–hole pairs per QD. We employ this nonlinearity for all‐optical switching using a Mach–Zehnder interferometric switch. We find a switching energy as low as 6 fJ.     

Pharmacokinetics of Nanoscale Quantum Dots: In Vivo Distribution,Sequestration, and Clearance in the Rat

Advances in nanotechnology research on quantum dots (QDs)—water soluble ZnS‐capped, CdSe fluorescent semiconductor nanocrystals—for in vivo biomedical applications have prompted a close scrutiny of the behavior of nanostructures in vivo. Data pertaining to pharmacokinetics and toxicity will undoubtedly assist in designing better in vivo nanostructure contrast agents or therapies. In vivo kinetics, clearance, and metabolism of semiconductor QDs are characterized following their intravenous dosing in Sprague–Dawley rats. The QDs coated with the organic molecule mercaptoundecanoic acid and crosslinked with lysine (denoted as QD‐LM) are cleared from plasma with a clearance of 0.59 ± 0.16 mL min^–1 kg^–1. A higher clearance (1.23 ± 0.22 mL min^–1 kg^–1) exists when the QDs are conjugated to bovine serum albumin (denoted as QD‐BSA, P < .05 (P = statistical significance). The biodistribution between these two QDs is also different. The liver takes up 40 % of the QD‐LM dose and 99 % of QD‐BSA dose after 90 min. Small amounts of both QDs appear in the spleen, kidney, and bone marrow. However, QDs are not detected in feces or urine for up to ten days after intravenous dosing.     

渐逝波耦合半导体量子点光纤放大器

基于半导体量子点的特性,结合光纤渐逝波耦合器,提出了一种新型的光纤放大器件,它将以溶液形式的硫化铅(PbS)半导体量子点材料沉积于耦合器熔锥区,信号光和抽运光通过渐逝波共同与半导体量子点材料相互作用,实现光的放大作用。PbS量子点材料是采用工艺容易控制的反胶束法制备的,通过透射电镜(TEM)测量得到其粒子尺寸小于10 nm。利用工作波长为980 nm,功率为30 mW的半导体激光器抽运光源对该光纤放大器抽运,在1310 nm波段得到了大于4 dB的增益,这是半导体量子点尺寸效应引起的光谱蓝移现象的体现。因此,这种有源区短、器件结构紧凑的光纤放大器在高速、宽带光纤接入等领域具有重要的实际意义和应用价值。     

Magnetic/Silica Nanocomposites as Dual‐Mode Contrast Agents for Combined Magnetic Resonance Imaging and Ultrasonography

A simple and efficient method for synthesizing a range of hybrid nanocomposites based on a core of silica nanospheres (160, 330, and 660 nm in diameter) covered by an outer shell of superparamagnetic nanoparticles, either iron oxide or heterodimeric FePt‐iron oxide nanocrystals, is presented. The magnetic and ultrasound characterization of the resulting nanocomposites shows that they have great potential as contrast agents for dual‐mode imaging purposes, combining magnetic resonance imaging (MRI) and ultrasonography (US).     

扫描近场光学显微镜测量量子点团簇超辐射

用扫描近场光学显微镜的针尖照明模式对ZnSe量子点团簇进行精确定位测量,研究了量子点团簇的超辐射效应。在理论上根据Wannier激子超辐射模型阐述了量子点系统的超辐射发光机制;实验上用荧光光谱表征ZnSe量子点溶液的荧光性质,用扫描近场光学显微镜(SNOM)表征单个量子点团簇的超辐射光谱。结果表明,在Wannier激子超辐射模型中,量子点团簇辐射衰变率受到量子点团簇的大小和辐射光谱的共同影响,在实验上得出团簇的辐射衰变率随团簇尺寸的增加而增大,同时,不同尺寸的量子点团簇产生的辐射光谱也会对其产生影响,理论和实验的结合验证了激子超辐射的适用性。此研究结果可广泛用于生物传感器和光子器件等领域。     

自组装半导体量子点在纳米电子器件中的应用

随着微电子工艺逐渐逼近其物理极限,具有量子特性的纳米电子器件的研制被提上日程.自组装半导体量子点由于缺陷少、生长技术成熟和具有δ函数形式的能态密度等优点而被广泛用于纳米电子器件制备中.本文按纵向输运器件、横向输运器件的分类扼要评述了该领域的最新进展,并对待解决的问题和发展前景作了分析.     

Single‐Electron Tunneling through Molecular Quantum Dots in a Metal‐Insulator‐Semiconductor Structure

A sigle‐electron tunneling (SET) in a metal‐insulator‐semiconductor (MIS) structure is demonstrated, in which C₆₀ and copper phthalocyanine (CuPc) molecules are embedded as quantum dots in the insulator layer. The SET is found to originate from resonant tunneling via the energy levels of the embedded molecules, (e.g., the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)). These findings show that the threshold voltages for SET are tunable according to the energy levels of the molecules. Furthermore, SET is observable even near room temperature. The results suggest, together with the fact that these properties are demonstrated in a practical device configuration, that the integration of molecular dots into the Si‐MIS structure has considerable potential for achieving novel SET devices. Moreover, the attempt allows large‐scale integration of individual molecular functionalities.