Silicon nanowires as efficient thermoelectric materials

Thermoelectric materials interconvert thermal gradients and electric fields for power generation or for refrigeration. Thermoelectrics currently find only niche applications because of their limited efficiency, which is measured by the dimensionless parameter ZT-a function of the Seebeck coefficient or thermoelectric power, and of the electrical and thermal conductivities. Maximizing ZT is challenging because optimizing one physical parameter often adversely affects another. Several groups have achieved significant improvements in ZT through multi-component nanostructured thermoelectrics, such as Bi(2)Te(3)/Sb(2)Te(3) thin-film superlattices, or embedded PbSeTe quantum dot superlattices. Here we report efficient thermoelectric performance from the single-component system of silicon nanowires for cross-sectional areas of 10 nm x 20 nm and 20 nm x 20 nm. By varying the nanowire size and impurity doping levels, ZT values representing an approximately 100-fold improvement over bulk Si are achieved over a broad temperature range, including ZT approximately 1 at 200 K. Independent measurements of the Seebeck coefficient, the electrical conductivity and the thermal conductivity, combined with theory, indicate that the improved efficiency originates from phonon effects. These results are expected to apply to other classes of semiconductor nanomaterials.     

双弯曲对称石墨烯纳米带的热电性质

运用非平衡格林函数方法,研究了双弯曲对称石墨烯纳米带结构中的电子和声子输运规律．研究结果表明：两种双弯曲对称石墨纳米带对应的ZT值可以远大于相应理想石墨纳米带对应的值;同时发现,两种双弯曲对称石墨纳米带对应ZT的最大值非常敏感地依赖于其散射区的长度和宽度的变化．     

声波在声子晶体中的Zener共振遂穿效应

应用转移矩阵方法,研究了由两个全同声子晶体构成的可调谐声学谐振腔中声波的共振遂穿效应,其遂穿过程类似于量子力学中的Zener共振遂穿效应.通过改变声波谐振腔的长度,研究了声子晶体的带隙中声波遂穿的动力学过程.结果表明:不同带隙具有不同的遂穿特征,遂穿频率随着谐振腔的增加呈周期性振荡变化的规律.     

亚波长十字型MIM等离子波导滤波器

运用时域有限差分方法(FDTD)方法数值研究了一种亚波长十字型金属—绝缘体—金属(MIM)等离子波导结构的透射属性.结果表明该结构的透射极小值与十字型切口的长度密切相关,表现出良好的滤波性质.十字型切口被直MIM等离子波导分为上下两段,每一段独立构成一个驻波谐振腔.当各段长度独立满足驻波谐振条件时,该结构均会产生透射极小值.     

Wave-vector-dependent Tunneling Transmission Characteristics in Periodic and Quasiperiodic Semiconductor Superlattices

Introduction　　Thepropositionofsemiconductorsuper-lattices[1],thediscoveryofquasicrystalsandtherealizationofGaAs/AlAsFibonaccisuperlatticeshavemotivatedalargebodyofcurrentresearchworkonthephysicalpropertiesofperiodicandquasiperiodicsuperlattices.Manyelectronicandoptoelectroniceffectshavebeendiscovered.Thequasiperiodicstructuresareintermediatebetweencompletelyperiodicperfectcrystalsandrandomordisorderedamorphoussolids.Becauseoftheaperiodicityandself-similarity,competitionbetweenlocalizationa…     

复杂周期磁超晶格的电导共振劈裂

利用转移矩阵方法,研究了在非均匀垂直磁场作用下的二维电子气中弹道电导的共振劈裂.这一非均匀磁场可以通过在异质结上沉积铁磁条来实现.结果显示:对于n个周期且每个周期含有m个构筑块的复杂的磁超晶格结构,弹道电导的共振区将劈裂为m个子能窗,并且在每个子能窗中,弹道电导具有n-1重的劈裂峰.本质上,弹道电导的劈裂规则仍然是隧穿几率劈裂的反应.     

Single scattering particles based analytical techniques

Single scattering particles,especially noble metal(plasmonic) nanoparticles,based analytical techniques are attractive recently and becoming the research focus of the light scattering analytical techniques.In this mini review,we summarize the single scattering particles based analytical techniques in the past decade including single scattering particles counting,single plasmonic nanoparticles sensing,and single plasmonic nanoparticles tracking/imaging.We emphasize the discussion on the single plasmonic nanoparticles sensing that combines with dark-field microscopy and resonant Rayleigh scattering spectroscopy.     

压力波传递速度的测量方法

为准确地确定水管路系统管道内的压力波传递速度，在研究谐振频率测量法和时差域测量法的基础上，对水管路系统中的压力波传递速度进行实验测量。实验结果证明，测得的管路系统的压力波传递速度总是略小于自由场中的声速，且两种方法的测量结果相近、测量精度较高。     

表面等离子体激元增强荧光辐射的机理研究

荧光光谱技术在研究物质分子结构及物质相互作用动力学过程中具有重要应用,基于荧光的化学或生物传感器得到人们广泛研究,如何提高基于荧光传感器的灵敏度是一个重要研究课题,表面等离子体激元可有效增强荧光分子的发光强度,因而从物理机制上研究表面等离子体激元增强荧光的内函具有重要意义。本文在讨论荧光辐射基本原理的基础上,论述了基于金属的表面等离子体激元增强荧光的物理机制,主要有荧光共振能量转移、表面等离子体激元共振增强荧光辐射理论和RP模型等三种理论模型。     

多层半导体结构的共振隧穿性质

应用转移矩阵方法，计算了多层半导体结构的电子透射系数，研究了三元准周期超晶格的电子共振隧穿性质，讨论了不同结构对隧穿性质的影响。结果表明：准周期超晶格结构的自相似性导致了电子透射率谱的自相似性；随着代数的增加，高透射率的区域越来越集中于某一小的能量范围；对应不同的排列结构，电子透射率随能量的分布也不相同，透射率较大的能量位置与系统中占多数的那种势阱的能级相对应。     

一种新型的多层共振结构

我们提出一种新型的多层共振结构,即带尾巴的共振结构,它是由尾巴层和共振层两部分构成.这种共振结构能够在阻抗不匹配的介质间实现声波能量的有效耦合,这种功能是传统的单层共振结构不可能具备的.我们讨论了两类带尾巴的共振结构的特性和解释了产生这些特性的原因.在这种新型的共振结构中,一般而言尾巴层起振幅放大作用,而共振层起频率选择作用.     

Au纳米耦合结构表面等离激元的EELS分析

应用透射电子显微镜中电子能量损失谱仪(TEM-EELS),对电子束激发的单晶Au纳米线耦合结构及单晶/多晶纳米薄膜的表面等离激元(SPs)特征进行分析.结果表明:直径约为10 nm的两单晶Au纳米线平行耦合时,单根纳米线和耦合结构中均存在位于2.4 eV 的SPs共振,耦合结构中SPs的纵模数增加;单晶及多晶Au纳米薄膜在1.4 eV附近存在SPs模式,相较于单晶薄膜,多晶Au纳米薄膜的SPs共振峰位出现明显红移.     

Thin-film thermoelectric devices with high room-temperature figures of merit

Thermoelectric materials are of interest for applications as heat pumps and power generators. The performance of thermoelectric devices is quantified by a figure of merit, ZT, where Z is a measure of a material's thermoelectric properties and T is the absolute temperature. A material with a figure of merit of around unity was first reported over four decades ago, but since then-despite investigation of various approaches-there has been only modest progress in finding materials with enhanced ZT values at room temperature. Here we report thin-film thermoelectric materials that demonstrate a significant enhancement in ZT at 300 K, compared to state-of-the-art bulk Bi2Te3 alloys. This amounts to a maximum observed factor of approximately 2.4 for our p-type Bi2Te3/Sb2Te3 superlattice devices. The enhancement is achieved by controlling the transport of phonons and electrons in the superlattices. Preliminary devices exhibit significant cooling (32 K at around room temperature) and the potential to pump a heat flux of up to 700 W cm-2; the localized cooling and heating occurs some 23,000 times faster than in bulk devices. We anticipate that the combination of performance, power density and speed achieved in these materials will lead to diverse technological applications: for example, in thermochemistry-on-a-chip, DNA microarrays, fibre-optic switches and microelectrothermal systems.     

纵向多矩形腔表面等离子体滤波器研究

 提出一种新型的纵向有多个矩形腔的表面等离子体滤波器,采用时域有限差分方法(FDTD)分别研究了单个腔、2个腔和3个腔的透射性质,发现单个腔中F-P共振导致了透射峰;在单个腔中间增加一层金属薄膜构成2个腔,原来单腔的透射峰出现劈裂或者消失,劈裂间距受结构参数变化影响;结合近场分布和理论分析,认为长短表面等离子体共振导致了劈裂.     

荸荠茎尖培养体系的研究

以荸荠茎尖为材料,对茎尖诱导、分化、增殖的激素和激素浓度及培养方式进行了研究。试验结果表明:激素6-BA对茎尖有显著促进分蘖增殖芽的作用,KT和ZT无或少。6-BA 1.0～2.0 mg/L芽苗增殖数高于其它组合,叶状茎健壮。芽增殖培养方式以液体静态培养效果好,平均增殖系数2.6倍,周期短(25 d),叶状茎生长旺盛,有利于快繁体系的建立及工厂化生产应用。     

电除尘器电场数值计算与性能预测的实验研究

通过实验测量了大型电除尘器常用的12种放电极与C480和ZT24板匹配时极板表面电流密度大小及分布。采用实验和数值计算相结合的方法,以极板表面平均电流密度、电流密度相对标准差为指标对电场性能进行了评价和预测,给出了几种电场性能较好的电极配置形式和几何参数调整范围。用有限元法求出V型线与ZT24板匹配时的电位与场强的空间分布,结合实验与数值计算结果分析了场强对电晕电流的影响。对电除尘器的设计选型有一定的参考价值。     

不对称纳米环/椭球二聚体的高阶表面等离激元共振特性

基于三维有限元法,研究了不对称纳米环/椭球二聚体的表面等离激元共振和局域场增强光学特性。结果可得可调的高阶表面等离激元共振,这样的高阶共振源于纳米环和纳米椭球之间的等离激元耦合。同时,在两个纳米结构耦合下,在纳米椭球上可以观察到环形电流,其产生了增强的局域电磁场。数值模拟结果表明,纳米环/椭球二聚体的偏心方向和偏心率对表面等离激元共振有着重要的影响。此结果在表面增强光谱学和生物传感方面都有着潜在的应用。     

用具有空间分布的驱动光控制慢光

从慢光的运动方程出发，沿着探测光的运动方向引入两种特殊空间分布的驱动光：“U-型”和“V-型”分布，研究在电磁感应透明介质中，慢光的运动性质，并分别与量子力学中单粒子在方阱中的共振透射和光学黑洞进行类比．     

涂覆石墨烯的电介质纳米盘的表面等离激元回音壁模特性

提出涂覆单层石墨烯的电介质纳米盘结构,并利用有限元方法数值解析这种纳米结构的表面等离子激元回音壁模的电磁场特性.计算并分析品质因子(Q值)、模式体积随着电介质纳米盘半径大小、石墨烯化学势和谐振频率的变化规律.结果表明:当纳米盘的半径为5 nm,石墨烯化学势为0.9 eV时,其品质因子高达195,对应模式体积小于2×10^-7(λ₀/2n)³.     

Manipulation of light in MIM plasmonic waveguide systems

Plasmonic waveguides that allow deeply subwavelength confinement of light provide an effective platform for the design of ultracompact photonic devices.As an important plasmonic waveguide,metal-insulator-metal(MIM)structure supports the propagation of light in the nanoscale regime at the visible and near-infrared ranges.Here,we focus on our work in MIM plasmonic waveguide devices for manipulating light,and review some of the recent development of this topic.We introduce MIM plasmonic wavelength filtering and demultiplexing devices,and present the electromagnetic induced transparency(EIT)-like and Fano resonance effects in MIM waveguide systems.The slow-light and rainbow trapping effects are demonstrated theoretically.These results pave a way toward dynamic control of the special and useful optical responses,which actualize some new plasmonic waveguide-integrated devices such as nanoscale filters,demultiplexers,sensors,slow light waveguides,and buffers.