表面等离激元光热效应研究进展

表面等离激元微纳结构能够将光场束缚在亚波长尺度,实现突破光学衍射极限的光操控,并显著增强光与物质的相互作用.在基于表面等离激元机理的光电器件研究中,微纳结构的自身光吸收通常被认为是损耗,而通过光热效应,光吸收则可有效利用并转换成热能,其中的物理过程研究和应用是当前等离激元学领域的热点方向.本文回顾了近年来表面等离激元微纳结构光热效应的相关工作,聚焦于表面等离激元热效应的物理过程、热产生和热传导调控方式的研究进展.在此基础上,介绍了表面等离激元微纳结构在微纳加工、宽谱光热转换等方面的应用.     

微纳结构光纤光谱学

微纳结构光纤光谱学是指以空芯微结构或微纳光纤为样品池,光和物质在纤芯内部或表面进行相互作用的光谱学技术。本文回顾空芯和微纳光纤导光的基本原理,介绍气体、液体样品池构建的理论和方法,综述基于光谱吸收、光热、光声、荧光、拉曼等效应的微纳结构光纤光谱学的最新进展及今后可能的发展方向。微纳结构光纤对光场的束缚能力强、模场能量在空气中的比例高,可实现光和物质在其中的高效、长距离相互作用。微纳结构光纤样品池的采用,可提升传统光谱学系统的性能或构建新型的光谱学系统;应用传输光纤与其他光学元器件进行柔性连接,可促进光谱学仪器和传感器的小型化和实用化。     

超快激光的光电应用

超快激光一般是指脉冲宽度短于10ps的脉冲激光,主要指短皮秒和飞秒(10-15s)激光。这个时间尺度短于激发态电子向晶格弛豫能量的所需时长,使光与物质相互作用呈现了与通常光激发显著不同的特性,也促成了其崭新的光电应用。围绕飞秒激光与物质相互作用快(作用时间短)、强(瞬态功率高)、精(非线性使作用区体积小,用作加工分辨率高)的特点,开展了系列研究,包括飞秒激光超快光谱用于光/电-电/光转换动力学探索,激光诱导气体成丝用于近程遥感探测,及飞秒激光微纳加工用于新原理、新材料微纳集成器件的制备。介绍了相关研究的进展。     

离子束刻蚀辅助飞秒激光加工制备碳化硅微光学元件

为了解决飞秒激光加工硬质材料所带来的表面质量差的问题,提出了离子束刻蚀与飞秒激光复合加工技术.利用飞秒激光加工技术在碳化硅表面制备微纳结构图形,然后通过离子束刻蚀技术对碳化硅微纳结构进行刻蚀,以调控结构的线宽和深度,使结构表面粗糙度由约106nm降低到11.8nm.研究表明,利用该技术制备的碳化硅菲涅尔波带片展现出良好的聚焦和成像效果.     

仿生异质结全太阳光谱催化CO2还原特性研究

为了突破光热催化CO₂还原中太阳能吸收、光热转化以及载流子传输受限的瓶颈，本文受蝴蝶翅膀的启发，将原子薄纳米片Bi₂MoO₆垂直生长在柚子皮衍生碳(CPP)表面形成具有波导效应的脊阵列，利用多重散射强化太阳光吸收，实现光催化与光捕获中心的有机集成；受植物对光选择性吸收的启发，利用分形结构诱导太阳光的多级吸收，实现全太阳光谱的梯级利用。通过UV-Vis DRS、XPS、瞬态光电流以及DFT研究表明，CPP@Bi₂MoO₆的脊阵列和分形结构导致禁带宽度降低至2.43 e V并且催化表面温度迅速升高至117.2?C,M-O-C电子桥实现电子跨界面传输并形成“电子–热能–CO₂”富集中心，光热效应导致富集在CPP表面的电子向CO₂吸附位点迁移，使得CO₂被大量电子活化并沿CO₂→CO₂*→CO₂-→COOH*→CO*→CO的反应机理转化。     

聚光光伏与温差联合发电装置的研究

针对太阳能量利用率较低的现状,设计了基于砷化镓多结太阳能电池、半导体温差发电片的聚光光伏与温差联合发电装置.通过测量得出单独聚光光伏发电模块在几何聚光比为75时光电转换效率最大,达31.87%;而在加了半导体温差发电模块之后在几何聚光比为112时系统光电转换效率达32.81%,提高了整体光能量转化电能效率.     

飞秒激光直写偏振转换器件和几何相位器件(特邀)

光学器件的微型化和集成化是当前研究的热点,其中利用微纳结构实现局域电磁改性的超构光学更是引人关注。本文从微纳结构的制备出发,总结了利用超衍射精密加工的飞秒激光直写技术,制备偏振转换器件和几何相位器件的工作。介绍了微纳结构改性的物理机制,飞秒激光直写光刻胶、飞秒激光烧蚀金属薄膜、飞秒激光诱导纳米光栅等手段在偏振转换器件和几何相位器件制备方面的进展,展望了飞秒激光微纳加工技术在超构光学器件制备方面的挑战。     

飞秒激光湿法刻蚀微纳制造

飞秒激光微加工作为一种新型微纳制造技术,在复杂三维构型制作方面具有其独特的优势,但激光加工效率问题严重制约了飞秒激光微加工技术走向实际工程应用,提出一种飞秒激光湿法刻蚀微纳制造方法,以提高飞秒激光微加工的效率为突破口,通过调控激光与物质相互作用获得材料的目标靶向改性,进而结合化学湿法刻蚀实现硬质材料上的高效和高精度三维微加工,采用这一方法制作出的微透镜尺寸为80 m,球冠高6.7 m,表面粗糙度小于10 nm。利用这种方法,实现了不同结构与特性的高质量微透镜阵列的超精密制备,在石英内部也实现了螺旋微通道的复杂三维结构,螺旋通道直径为20 m,长径比超过100。     

金纳米颗粒溶液的光热转换效率测量

激光照射金属材料表面会引起材料内部性质的变化,金属材料会对光产生吸收并可以将其转化为热能,导致材料表面温度的变化.金属材料的不同形貌、尺寸对光的能量转换效应是不同的,光热转换效率是材料吸收光能转换成热能的重要参数.在材料尺寸相同条件下光热转换效率大小与入射波长、激光器的功率密度、溶液浓度等因素有关.本文选取金纳米棒材料作为研究对象,通过改变入射波长、激光功率等条件研究金纳米棒光热转化效率,借此建立一种微观物质的能量转换的测量研究方法.     

GaAs薄膜电池光电转换特性研究

微纳减反层结构及微纳金属等离激元结构能有效提高砷化镓(GaAs)薄膜光伏器件在可见到近红外波段的吸收效率。本文采用有限元法(FEM)分析了微纳减反层对GaAs光伏器件的光谱吸收率的影响,并获得相应结构的光电转换特性。进一步探究了在器件内部布置金纳米线对相应结构的光电特性的影响。对应的计算结果显示,微纳减反层结构及金属纳米线结构能有效增强器件的电学输出特性,并提高器件光电转换能力到19.6%。掌握微结构对光伏器件内部光电特性的影响规律可为器件设计和制备提供有益指导。     

基于梯度翅片换热器的热电发电系统性能研究

本文建立了热电发电系统(TEG)多物理场数值模型,并充分考虑换热器流体影响,综合研究了具有不同热侧换热器翅片结构的TEG系统性能。在雷诺数为1000~10000范围内,分析了流体沿程温度分布特征、泵功及热电发电模块的能量转换特性.所研究的三种翅片结构包括:全流道等高度直翅片(Fin-1)、下游强化梯度翅片(Fin-2)以及上游强化梯度翅片(Fin-3).研究表明,通道长高比及热电材料覆盖率一定,热电发电功率及转换效率随流量呈二次曲线变化关系,存在最匹配流量使得系统发电性能最佳。等高度直翅片对流量的变化敏感,随流量增大,则压损增大,导致系统净输出功率及发电效率无收益.而梯度翅片可以在更大范围内产生正收益;下游强化梯度翅片具有最佳的流体沿程温度均匀性,但沿程局部热阻却最大.综合考虑沿程局部热阻分布及泵功消耗,上游强化梯度翅片TEG系统净转换效率最高,因此局部热阻分布及泵功综合因素应为TEG内的换热器合理设计的关键。     

Performance of thermoelectric generator with graphene nanofluid cooling

Improvement of the heat transfer of the cold side is one of the approaches to enhance the performance of TEG systems.As a new type of heat transfer media, nanofluids can enhance the heat transfer performance of working liquid significantly.Based on a three-dimensional and steady-state numerical model,the heat transfer and thermoelectric conversion properties of TEG systems were studied. Graphene anoplatelet aqueous nanofluids were used as the coolants for the cold side of the TEG system to improve the heat transfer capacity of the cold side. The results showed that the heat absorbed by the hot side, voltage, output power, and conversion efficiency of the TEG system were increased greatly by the nanofluid coolants.The output power and the conversion efficiency using 0.1-wt% graphene nanoplatelet aqueous nanofluid as the coolant are enhanced by 26.39% and 14.74%, respectively.     

Study of the performance of a thermoelectric generator transformation of the thermal energy conveyed by a heat transfer fluid into electrical energy

A mathematical model to predict the maximum energy conversion efficiency of the thermoelectric generator is developed to improve the performance and maximize the energy conversion efficiency of the thermoelectric power generator. The studied device corresponds to an original configuration of thermoelectric modules mounted on the peripheral surfaces of two channels, one of the channels is crossed by hot fluid and the other by a cold fluid. First, the effect of the flow rate was studied to choose the flow rate adapted to our study for three different configurations of the thermopile, the co-current configuration, the counter-current configuration, and the sandwich configuration. Then a comparison was made to choose the best configuration between these three studied configurations by addressing their thermoelectric performances. The results revealed that the sandwich configuration is much better than the co-current and counter-current configurations and reduces the surface area occupied by the TEG by half while generating more power than a solar panel.     

半导体温差发电过程的模型分析与数值仿真

本文提出一种新型的半导体温差发电模型,在温差发电过程的数值模拟中考虑了热电单元之间封闭腔体内空气传热的影响.同时进一步运用有限元的数值计算方法对不同电臂对数和不同型号温差发电模型的温度场、电压场进行了数值仿真计算,并对仿真结果进行分析.结果表明:采用127对热电单元模型计算的能量转换效率随冷热端温差增大而迅速提高,与采用1对热电单元模型计算的能量转换效率之差从冷热端温差为20℃的0.39%提高到冷热端温差为220℃时的5.16%,能量转换效率比1对热电单元平均高出3.02%.冷端温度恒定在30℃时,温差发电芯片的输出电压、功率以及能量转换效率均随着电偶臂的横截面积的增大而提高,且电偶臂冷热两端的温差越大提高幅度也越大,而温差发电芯片内阻则与电偶臂横截面积成反比关系,当温差为220℃时对应的输出功率最高达28.9 W.     

A New Insight of the Photothermal Effect on the Highly Efficient Visible‐Light‐Driven Photocatalytic Performance of Novel‐Designed TiO2 Rambutan‐Like Microspheres Decorated by Au Nanorods

Photocatalyst‐assisted degradation of organic pollutants, which exhibits a novel strategy for solar‐energy utilization, possesses enormous potential in various applications. Extending the light‐absorption range in the spectrum of sunlight and improving light‐conversion efficiency are always primary issues to enhance the catalytic performance of these photocatalysts. Herein, a new structure of gold‐nanorod‐decorated TiO₂ rambutan‐like microspheres is designed, which exhibits superior photocatalytic ability toward Rhodamine B in the range of visible light due to the 3D distribution of the TiO₂ branches on the surface of the microspheres, which prompts the multireflection of photons. The absorption rate of photons is thereby tremendously enhanced. This is beneficial for the generation of hot electrons originating from the localized surface plasmonic resonance of Au nanorods, which can be used to both initiate the reaction and produce the photothermal effect. Hot electrons generated by a single Au nanorod in microspheres to initiate the degradation reaction can be as high as 2.5 times of those in the nanowires' counterpart. Moreover, the heating power of a single Au nanorod in microspheres reaches up to 4.4 times higher than that in nanowires, which further accelerates the degradation rate. The reaction pathway of visible‐light‐assisted RhB degradation catalyzed by Au/TiO₂ microspheres goes through an initial N‐deethylation process instead of the complete cycloreversion catalyzed by pure TiO₂ microspheres under UV irradiation. This strategy of structure design for improved photon absorption, which achieves high degradation rate and photothermal effect, is promising for the development of novel photocatalysts.     

飞秒平顶光束经微透镜阵列在熔融石英中的成丝及其超连续辐射

实验研究了平顶激光光束经微透镜阵列在熔融石英中成丝的演化以及超连续辐射的产生,并进一步与高斯光束的成丝和超连续辐射进行了对比研究.分别对这两种光束的多丝传输进行了横向和纵向成像.结果表明,使用平顶光束可以获得更为均匀的多丝分布,成丝的起点也更为一致;尤其重要的是,相对于高斯光束,平顶光束可以使用更高的入射激光脉冲能量而不会造成介质的损伤,从而可以获得更高脉冲能量和更高转换效率的超连续辐射.     

Graphene for Thermoelectric Applications: Prospects and Challenges

Thermoelectric power generators require high-efficiency thermoelectric materials to transform waste heat into usable electrical energy. An efficient thermoelectric material should have high Seebeck coefficient and excellent electrical conductivity as well as low thermal conductivity. Graphene, the first truly 2D nanomaterial, exhibits unique properties which suit it for use in thermoelectric power generators, but its application in thermoelectrics is limited by the high thermal conductivity and low Seebeck coefficient resulting from its gapless spectrum. However, with the possibility of modification of graphene's band structure to enhance Seebeck coefficient and the reduction of its thermal conductivity, it is an exciting prospect for application in thermoelectric power generation. This article examines the electronic, optical, thermal, and thermoelectric properties of graphene systems. The factors that contribute to these material properties in graphene systems like charge carriers scattering mechanisms are discussed. A salient aspect of this article is a synergistic perspective on the reduction of thermal conductivity and improvement of Seebeck coefficient of graphene for a higher thermoelectric energy conversion efficiency. In this regard, the effect of graphene nanostructuring and doping, forming of structural defects, as well as graphene integration into a polymer matrix on its thermal conductivity and Seebeck coefficient is elucidated.     

Optimization and fabrication of a planar thermoelectric generator for a high-performance solar thermoelectric generator

A planar thermoelectric generator (TEG) could be used as an energy harvester for wireless sensor networks (WSNs). Its planar configuration offers the advantages of miniaturization and low-cost fabrication. Herein, we report the fabrication of a device based on a co-evaporated thick film of Bi–Te. Before fabrication we studied quantitative optimization dimensions for the planar TEG via finite element method (FEM) simulations. The planar TEG was also used in a high-performance solar thermoelectric generator (STEG) that concentrated heat from solar radiation via a solar absorber to generate a temperature difference (ΔT) between two thermoelectric and electrode junctions. When exposed to a solar simulator, the STEG produced a ΔT of about 6 °C and generated 2.3 μW of power. The demonstrated high flexibility and mechanical stability of this device suggests applications in wearable electronics.     

Geometry Optimization of Thermoelectric Modules: Deviation of Optimum Power Output and Conversion Efficiency

Besides the material research in the field of thermoelectrics, the way from a material to a functional thermoelectric (TE) module comes alongside additional challenges. Thus, comprehension and optimization of the properties and the design of a TE module are important tasks. In this work, different geometry optimization strategies to reach maximum power output or maximum conversion efficiency are applied and the resulting performances of various modules and respective materials are analyzed. A Bi₂Te₃-based module, a half-Heusler-based module, and an oxide-based module are characterized via FEM simulations. By this, a deviation of optimum power output and optimum conversion efficiency in dependence of the diversity of thermoelectric materials is found. Additionally, for all modules, the respective fluxes of entropy and charge as well as the corresponding fluxes of thermal and electrical energy within the thermolegs are shown. The full understanding and enhancement of the performance of a TE module may be further improved.     

Performance analysis of near-field thermophotovoltaic devices considering absorption distribution

This paper elucidates the energy transfer and conversion processes in near-field thermophotovoltaic (TPV) systems, considering local radiation absorption and photocurrent generation in the TPV cell. Radiation heat transfer in a multilayered structure is modeled using the fluctuation-dissipation theorem, and the electric current generation is evaluated based on the photogeneration and recombination of electron-hole pairs in different regions of the TPV cell. The effects of near-field radiation on the photon penetration depth, photocurrent generation, and quantum efficiency are examined in the spectral region of interest. The detailed analysis performed in the present work demonstrates that, while the near-field operation can enhance the power throughput, the conversion efficiency is not much improved and may even be reduced. Subsequently, a modified design of near-field TPV systems is proposed to improve the efficiency.