半导体量子点中磁极化子基态能修正的温度效应

采用Larsen方法研究了半导体量子点中磁极化子基态能量的温度效应．在有限温度下导出了磁场内半导体量子点中电子—体纵光学(LO)声子相互作用系统的基态能量及二级微扰能量修正．讨论了磁场、量子点尺寸以及温度对半导体量子点中电子—体纵光学(LO)声子相互耦合磁极化子的基态能量影响．为了更清楚、直观地说明半导体量子点中磁极化子的性质，以GaAs半导体为例进行了数值计算，得到在强磁场的作用下半导体量子点中电子—体纵光学(LO)声子耦合系统的基态能量修正与磁场强度、量子点厚度及温度的关系曲线．结果表明：强磁场中电子—体纵光学(LO)声子相互耦合磁极化子的基态能量修正随磁场强度的增加而增大，随量子点厚度的增加而减少，随温度的升高而增大。     

Assembly of hybrid photonic architectures from nanophotonic constituents

The assembly of hybrid nanophotonic devices from different fundamental photonic entities--such as single molecules, nanocrystals, semiconductor quantum dots, nanowires and metal nanoparticles--can yield functionalities that exceed those of the individual subunits. Combining these photonic elements requires nanometre-scale fabrication precision and potentially involves a material diversity that is incompatible with standard nanotechnological processes. Although merging these different systems on a single hybrid platform is at present challenging, it promises improved performance and novel devices. Particularly rapid progress is seen in the combination of plasmonic-dielectric constituents with quantum emitters that can be assembled on demand into fundamental model systems for future optical elements.     

Ag纳米粒子增强CdS白光量子点器件的研制

在十八烯体系中合成Cd S量子点,用光诱导法制备银纳米粒子,并将两者复合,制备成4种复合样品,分析复合样品的荧光谱,在银纳米颗粒的表面等离子体共振峰分别对应于富含缺陷的硫化镉量子点的带边荧光峰和表面态荧光峰时,发生了带边荧光淬灭而表面态荧光增强的现象.结果表明,通过控制金属和量子点之间的距离,能够控制带边荧光辐射和缺陷带荧光辐射的比例,从而控制白光量子点的色温.采用395 nm紫光LED作为激发光源,将涂有荧光样品的玻片与激发光源组装成银纳米颗粒/量子点复合结构白光照明器件原型,银纳米粒子能够改变Cd S量子点样品发光颜色,荧光效应的增强程度随着量子点样品的厚度减小而加强.该研究为认识荧光物质和金属之间的相互作用提供了新途径,同时探讨了该器件在变色发光材料方向的应用前景.     

n-type colloidal semiconductor nanocrystals

Colloidal semiconductor nanocrystals combine the physical and chemical properties of molecules with the optoelectronic properties of semiconductors. Their colour is highly controllable, a direct consequence of quantum confinement on the electronic states. Such nanocrystals are a form of 'artificial atoms' (ref. 4) that may find applications in optoelectronic systems such as light-emitting diodes and photovoltaic cells, or as components of future nanoelectronic devices. The ability to control the electron occupation (especially in n-type or p-type nanocrystals) is important for tailoring the electrical and optical properties, and should lead to a wider range of practical devices. But conventional doping by introducing impurity atoms has been unsuccessful so far: impurities tend to be expelled from the small crystalline cores (as observed for magnetic impurities), and thermal ionization of the impurities (which provides free carriers) is hindered by strong confinement. Here we report the fabrication of n-type nanocrystals using an electron transfer approach commonly employed in the field of conducting organic polymers. We find that semiconductor nanocrystals prepared as colloids can be made n-type, with electrons in quantum confined states.     

Shape control of CdSe nanocrystals

Nanometre-size inorganic dots, tubes and wires exhibit a wide range of electrical and optical properties that depend sensitively on both size and shape, and are of both fundamental and technological interest. In contrast to the syntheses of zero-dimensional systems, existing preparations of one-dimensional systems often yield networks of tubes or rods which are difficult to separate. And, in the case of optically active II-VI and III-V semiconductors, the resulting rod diameters are too large to exhibit quantum confinement effects. Thus, except for some metal nanocrystals, there are no methods of preparation that yield soluble and monodisperse particles that are quantum-confined in two of their dimensions. For semiconductors, a benchmark preparation is the growth of nearly spherical II-VI and III-V nanocrystals by injection of precursor molecules into a hot surfactant. Here we demonstrate that control of the growth kinetics of the II-VI semiconductor cadmium selenide can be used to vary the shapes of the resulting particles from a nearly spherical morphology to a rod-like one, with aspect ratios as large as ten to one. This method should be useful, not only for testing theories of quantum confinement, but also for obtaining particles with spectroscopic properties that could prove advantageous in biological labelling experiments and as chromophores in light-emitting diodes.     

半导体量子点光谱特性标准样品及高分辨透射电子显微镜粒径定值研究

半导体量子点纳米晶体是一类典型的纳米材料,具有独特的光学特性,已在生物医学、光电转换等领域得到应用.量子点纳米晶体的标准样品对其质量控制和产业应用都有重要的意义,但需要对其光学特性和尺寸特性进行准确测量研究.我们研制了以硒化镉量子点为代表的半导体量子点纳米晶体标准样品,并对其光学特性进行定值.针对目前制约量子点粒子尺寸准确测量的透射电子显微镜样品基底问题进行改进,用碳管-氧化石墨烯微栅代替常用的超薄碳膜微栅.通过高分辨透射电子显微镜表征得到晶格清晰的小尺寸半导体量子点纳米晶体的形貌像.这些结果有助于建立硒化镉量子点半导体纳米晶体的特征带边吸收峰值与粒子粒径的准确定量对应关系,从而推动量子点的应用.     

Optically programmable electron spin memory using semiconductor quantum dots

The spin of a single electron subject to a static magnetic field provides a natural two-level system that is suitable for use as a quantum bit, the fundamental logical unit in a quantum computer. Semiconductor quantum dots fabricated by strain driven self-assembly are particularly attractive for the realization of spin quantum bits, as they can be controllably positioned, electronically coupled and embedded into active devices. It has been predicted that the atomic-like electronic structure of such quantum dots suppresses coupling of the spin to the solid-state quantum dot environment, thus protecting the 'spin' quantum information against decoherence. Here we demonstrate a single electron spin memory device in which the electron spin can be programmed by frequency selective optical excitation. We use the device to prepare single electron spins in semiconductor quantum dots with a well defined orientation, and directly measure the intrinsic spin flip time and its dependence on magnetic field. A very long spin lifetime is obtained, with a lower limit of about 20 milliseconds at a magnetic field of 4 tesla and at 1 kelvin.     

CdSe量子点修饰物DSPE-PAA对其荧光增强效应的研究

采用有机热溶剂法制备出荧光量子效率高、单分散性良好的油溶性CdSe半导体量子点,将其用水溶性低分子量两性聚合物DSPE-PAA[poly（acylicacid）-1,2-distearoyl-sn-glycero-3-phosphoethanolamine,聚丙烯酸-1,2-二硬脂酰-sn-丙三醇-3-磷脂酰乙醇胺]进行修饰,得到水溶性和生物相容性良好的量子点。用透射电子显微镜（TEM）和荧光光谱等方法对CdSe纳米微粒的结构、形貌和光学特性分别进行了表征。并探讨和研究了在修饰过程中发生的DSPE-PAA对量子点由于荧光共振能量转移（FRET）作用产生的量子点荧光增强的现象。     

Ge量子点材料的制备工艺研究

采用射频磁控技术,用Ge、SiO_2的复合靶制备锗纳米晶镶嵌在二氧化硅中的复合薄膜.作为量子点的Ge纳米晶粒的尺寸是决定这类材料物性的关键,因而研究对镶嵌在SiO_2中的Ge晶粒尺寸调制的工艺十分重要.本文研究了制备过程中各种工艺参数与薄膜中Ge晶粒尺寸的关系.结果表明通过溅射时控制基片温度能有效地对锗晶粒尺寸进行调制.     

量子点光跃迁性质的研究

针对半导体量子点中电子的光跃迁性质进行了研究 ,建立起盘形量子点模型 ,具体分析了该模型的电子结构和电子态 .讨论了光场作用下 ,量子点中电子的跃迁几率、跃迁频率、选择定则和能级结构 ,并给出了吸收系数α的解析表达式和相应的吸收曲线 .最后 ,还讨论了量子点光跃迁性质对尺寸的依赖性以及此模型的一维、二维过渡 .结果表明 ,当束缚增强 ,能级随半径变小而增高 ,能级差变大 ;而且 ,吸收峰随尺寸减小向短波方向移动 ,即发生蓝移     

Ge纳米结构的制备技术与发光特性研究进展

Si基纳米发光材料与器件的研究是目前半导体光电子技术领域中的一个活跃前沿.除了Si纳米晶粒、Si量子点和Si/SiO2超晶格等Si纳米结构之外,属于同族元素的Ge纳米结构也因其所具有的优异特性,而呈现出良好的发光性能.评述了Ge纳米结构的制备方法与发光特性在近年内取得的研究进展.     

高荧光CdSe／ZnTeⅡ型核壳量子点的水相合成与表征

以巯基丙酸（MPA）为稳定剂,CdSe量子点为核,在水相中合成了具有较高荧光量子效率和化学稳定性的Ⅱ型核壳半导体量子点．通过荧光光谱、紫外-可见光吸收光谱和X-射线衍射方法对该CdSe／ZnTeⅡ型核壳量子点的光谱性质和结构进行了表征,证明：CdSe／ZnTeⅡ型核壳量子点的荧光发射光谱在500—573nm连续可调,半峰宽为40～50nm,荧光量子产率高达6．8％;粒型为球形,粒径约3．2nm,且粒径分布均匀;晶体结构为立方晶型．     

Energy-transfer pumping of semiconductor nanocrystals using an epitaxial quantum well

As a result of quantum-confinement effects, the emission colour of semiconductor nanocrystals can be modified dramatically by simply changing their size. Such spectral tunability, together with large photoluminescence quantum yields and high photostability, make nanocrystals attractive for use in a variety of light-emitting technologies--for example, displays, fluorescence tagging, solid-state lighting and lasers. An important limitation for such applications, however, is the difficulty of achieving electrical pumping, largely due to the presence of an insulating organic capping layer on the nanocrystals. Here, we describe an approach for indirect injection of electron-hole pairs (the electron-hole radiative recombination gives rise to light emission) into nanocrystals by non-contact, non-radiative energy transfer from a proximal quantum well that can in principle be pumped either electrically or optically. Our theoretical and experimental results indicate that this transfer is fast enough to compete with electron-hole recombination in the quantum well, and results in greater than 50 per cent energy-transfer efficiencies in the tested structures. Furthermore, the measured energy-transfer rates are sufficiently large to provide pumping in the stimulated emission regime, indicating the feasibility of nanocrystal-based optical amplifiers and lasers based on this approach.     

Optical gain in silicon nanocrystals

Adding optical functionality to a silicon microelectronic chip is one of the most challenging problems of materials research. Silicon is an indirect-bandgap semiconductor and so is an inefficient emitter of light. For this reason, integration of optically functional elements with silicon microelectronic circuitry has largely been achieved through the use of direct-bandgap compound semiconductors. For optoelectronic applications, the key device is the light source--a laser. Compound semiconductor lasers exploit low-dimensional electronic systems, such as quantum wells and quantum dots, as the active optical amplifying medium. Here we demonstrate that light amplification is possible using silicon itself, in the form of quantum dots dispersed in a silicon dioxide matrix. Net optical gain is seen in both waveguide and transmission configurations, with the material gain being of the same order as that of direct-bandgap quantum dots. We explain the observations using a model based on population inversion of radiative states associated with the Si/SiO2 interface. These findings open a route to the fabrication of a silicon laser.     

Colloidal nanocrystal heterostructures with linear and branched topology

The development of colloidal quantum dots has led to practical applications of quantum confinement, such as in solution-processed solar cells, lasers and as biological labels. Further scientific and technological advances should be achievable if these colloidal quantum systems could be electronically coupled in a general way. For example, this was the case when it became possible to couple solid-state embedded quantum dots into quantum dot molecules. Similarly, the preparation of nanowires with linear alternating compositions--another form of coupled quantum dots--has led to the rapid development of single-nanowire light-emitting diodes and single-electron transistors. Current strategies to connect colloidal quantum dots use organic coupling agents, which suffer from limited control over coupling parameters and over the geometry and complexity of assemblies. Here we demonstrate a general approach for fabricating inorganically coupled colloidal quantum dots and rods, connected epitaxially at branched and linear junctions within single nanocrystals. We achieve control over branching and composition throughout the growth of nanocrystal heterostructures to independently tune the properties of each component and the nature of their interactions. Distinct dots and rods are coupled through potential barriers of tuneable height and width, and arranged in three-dimensional space at well-defined angles and distances. Such control allows investigation of potential applications ranging from quantum information processing to artificial photosynthesis.     

CdTe量子点荧光量子产率及生物标记

采用巯基乙酸为稳定剂,在水相中直接合成CdTe量子点,实现半导体纳米晶体的水溶性.利用巯基乙酸包覆的CdTe量子点外端的羧基与牛血清白蛋白的氨基,通过偶联剂的作用形成酰胺键,从而达到标记蛋白质的作用.利用荧光和紫外可见分光光度计,研究标记前后体系的发射光谱和吸收光谱的变化以及荧光量子产率,通过透析膜对标记后的牛血清白蛋白进行纯化,进一步用琼脂糖电泳证明牛血清白蛋白与CdTe量子点的结合.     

Optical emission from a charge-tunable quantum ring

Quantum dots or rings are artificial nanometre-sized clusters that confine electrons in all three directions. They can be fabricated in a semiconductor system by embedding an island of low-bandgap material in a sea of material with a higher bandgap. Quantum dots are often referred to as artificial atoms because, when filled sequentially with electrons, the charging energies are pronounced for particular electron numbers; this is analogous to Hund's rules in atomic physics. But semiconductors also have a valence band with strong optical transitions to the conduction band. These transitions are the basis for the application of quantum dots as laser emitters, storage devices and fluorescence markers. Here we report how the optical emission (photoluminescence) of a single quantum ring changes as electrons are added one-by-one. We find that the emission energy changes abruptly whenever an electron is added to the artificial atom, and that the sizes of the jumps reveal a shell structure.     

半导体量子点中磁极化子的性质

采用Larsen方法研究了半导体量子点中磁极化子的基态能量，对GaAs半导体材料进行了数值计算结果表明，量子点中磁极化子的基态能量随磁场的增加而增加，随量子点的厚度增大而减小．     

拓扑绝缘体量子点中的磁交换相互作用

从理论上研究了拓扑绝缘体量子点中的磁交换相互作用.在拓扑绝缘体量子点中,边缘态电子数可以通过量子点的尺寸和外加电场进行调控.当量子点中掺入单个磁离子并且边缘态填充奇数电子时,电子与单个磁离子之间的交换相互作用达到最大值;而边缘态填充偶数电子时,电子与单个磁离子之间的交换相互作用消失.当量子点中掺入2个磁离子时,电子与Mn离子的sp-d相互作用会出现奇偶振荡行为,Mn离子间的相互作用取决于Mn离子间距和量子点壳层中的电子数,表现出典型的Ruderman-Kittel-Kasuya-Yosida型间接交换机制.工作澄清了拓扑绝缘体量子点壳层结构对其磁性的影响,有助于人们设计基于拓扑绝缘体量子点的自旋电子学或量子信息器件.     

半导体发光Ag_2S量子点合成及应用

近年来窄带隙溶胶半导体纳米晶引起人们极大关注,该类纳米晶在光学、电学、生物医疗、材料科学等其他领域有着非常重要的应用.大量研究证实了Ag_2S量子点具有许多优异性能,比如:近红外荧光发射、低毒性、荧光量子效率高、稳定性好、成本低和合成设备简单.与传统的量子点(含有重金属Cd,Hg,Pb元素)相比,近红外发光的Ag_2S量子点避免了重金属离子本身固有的毒性,并且因其具有低毒性被用在生物医疗中.在本文中详细讨论了半导体发光Ag_2S量子点的性质、晶体结构和合成方法,并对Ag_2S量子点的生物相容性评价方法以及在生命科学领域的应用进行了阐述.