高Q值THz类EIT超材料及传感特性研究

设计了一种具有类电磁诱导透明(EIT)效应的高Q值太赫兹超材料。该结构单元由上下平行的双金属线及中间垂直的单金属线组成。分别对单金属线、双金属线及组合结构进行仿真,分析了组合结构中金属线的位置和尺寸对透射率及品质因数Q的影响。结果表明,随着单金属线的水平移动产生了类EIT效应,透射率和Q值随着偏移距离的增大而发生变化,通过调整结构和尺寸可以实现不同Q值。通过优化,当偏移距离为8 μm时,在0.73 THz附近得到一个3 dB带宽约为11.56 GHz的透明窗,相应的Q值为63.09,其透射率为0.50。最后,对谐振器的传感特性进行了测量,其折射率灵敏度为60.69 GHz/RIU,FOM值为5.25/RIU,具有优异的传感特性。     

一种旋转可调的太赫兹超材料及其传感特性

本文设计了一种具有电磁诱导透明(EIT)效应的太赫兹超材料,其单元结构由水平放置的单金属线以及垂直放置的双金属线组成。仿真结果表明,通过单金属线绕其自身中心旋转,可以激发出电磁诱导透明效应。金属线的旋转角度逐渐变大,透明峰的幅度也随之增大,当旋转角度为60°时达到最大值;旋转角度进一步增大,透明峰的幅度逐渐降低;旋转角度为90°时,透明峰消失。仿真说明该结构可以通过单金属线的旋转调控透明峰的出现。最后,对旋转角度为60°时结构的传感特性进行了分析。该结构设计简单,具有可调性、较高的Q值以及良好的传感特性。     

基于硫属化物相变材料的可重构太赫兹超表面器件的研究进展

超表面在控制电磁波的强度、相位、偏振和复杂波前等方面发挥了重要的作用,通过与各种主动调控手段结合可实现动态可调谐器件。本文分析总结了近期基于Ge₂Sb₂Te₅ (GST)的太赫兹超表面器件的研究进展,介绍了GST在太赫兹波段的光谱特性和可逆相变条件,重点回顾了GST与超表面设计相结合用于实现对太赫兹波的振幅、偏振以及波前的非易失、可重构、和多级操纵的前沿研究工作,并讨论展望了未来的发展前景和需要解决的问题。     

基于超材料的光学太阳反射镜的研究

研究了一种基于超材料的光学太阳反射镜(optical solar reflector, OSR),其由掺铝氧化锌(AZO)超表面、MgF₂介质层和Ag金属反射层三层结构组成。在热红外AZO超表面激发表面等离激元共振增强电磁吸收,MgF₂介质层介电常数的稳定性减少了吸收振荡带来的反射,在可见光照射下AZO超表面和MgF₂介质层的透明特性可降低太阳辐射损耗,Ag金属反射层可有效抑制透射。仿真结果表明,优化后的OSR在0.3~2.5 µm内有17.6%的低太阳吸收率,在2.5~30.0 µm内有86.5%的高红外发射率。此外,偏振和入射角度对其性能影响较小。该结构在红外波段实现了较好的吸收,在红外热成像、辐射制冷等领域也具有潜在应用价值。

     

超快激光制造表面增强拉曼散射传感器

表面增强拉曼散射(SERS)传感器在诸多领域拥有重要的应用潜力。为实现高精度SERS检测,增加热点密度和热点区域中分析物分子数量成为当前研究的重点。超快激光可快速在材料表面构筑大面积的微纳米结构,对于高性能SERS基底的商业化制备具有重要的意义。本文从热点密度和检测区域中分析物分子浓度两个方面,总结了近年来超快激光制造高性能SERS基底的工艺方法。超快激光既能“自下而上”,也能“自上而下”加工出具有局域场增强效应的微纳米结构。其中,超快激光制备的超疏水表面是目前实现待测分子富集的有效方法之一。最后展望了激光制备SERS基底的应用前景。     

基于光频双曲超材料的无标记远场超分辨显微成像

超分辨光学显微成像技术具有非接触、无损伤等优点。现有超分辨成像手段大多依赖荧光染料,限制其应用场合。近年来基于频谱平移原理的无标记远场显微成像手段被提出,但其分辨率受限于波导材料折射率。利用双曲超材料(hyperbolic metamaterials,HMM)的空间频率带通滤波特性,结合亚波长光栅,激发大面积均匀高频体等离激元(bulk plasmon polariton,BPP)照明场,得益于照明的高波矢量,物体的高频信息可以转移到传统成像系统的通带,为远场图像提供亚波长空间信息。基于该方法,采用0.85数值孔径标准物镜,532 nm波长下2.66k₀横向波矢的BPP照明中心距为100 nm双缝结构成像,横向分辨力提高至λ/5.32。进一步提高BPP的横向波矢可使分辨力提升至λ/7.82。该方法无需标记,便于与传统显微镜集成,为生物医学、芯片工业、材料科学等领域的应用提供了一种可视化的超分辨手段。     

基于高阻硅超表面结构的太赫兹聚焦透镜设计

本文利用亚波长硅圆柱组成的超表面设计了用于太赫兹探测器的聚焦透镜,通过改变硅柱的直径,实现对太赫兹波传输相位0～2π的调控。在1 THz频率下,所设计的单面超表面透镜,太赫兹波电场能量密度提升到入射平面波的32倍。基于工艺制备可行性和抗反射考虑,提出了一种双面超表面透镜,将电场能量密度提升到入射平面波的44倍。对比于传统超半球太赫兹硅透镜,超表面透镜具有厚度薄,体积小的优点,有利于太赫兹探测器组件的小型化,为实现与太赫兹探测器的集成提供了可能性。     

SiC和Si_3N_4粉体的太赫兹时域光谱研究

采用太赫兹时域光谱装置测试SiC和Si3N4粉体在0.4～2.4 THz的透射光谱,研究SiC和Si3N4粉体对太赫兹波的吸收性能与其电导率的关系,分析SiC和Si3N4粉体对太赫兹波的散射特性。结果表明,SiC是一种半导体材料,其内部含有较多可以自由移动的载流子,对太赫兹波的吸收较强;Si3N4是绝缘性很好的材料,对太赫兹波的吸收很小;SiC和Si3N4粉体对太赫兹波的散射作用属于瑞利散射,但是测试波长比粉体粒径大得多,散射效果不明显。     

基于石墨烯超表面的效率可调太赫兹聚焦透镜

本文提出了一种基于石墨烯超表面的效率可调太赫兹聚焦透镜.该超表面单元结构由两层对称的圆形镂空石墨烯和中间介质层组成,其中镂空圆形中间由长方形石墨烯片连接.该结构可实现偏振转换,入射到超表面的圆偏振波将以其正交的形式出射,如左旋圆到右旋圆偏振转换.利用几何相位原理,通过旋转长方形条的方向,透射波会携带额外的附加相位并能满...     

太赫兹超表面计算全息

全息术是一种三维成像技术,它已经被应用于多种实际场景。随着计算机科学与技术的迅猛发展,计算全息由于其方便和灵活的特性,已经成为一种广泛应用的全息成像方法。本文回顾了我们近期基于超表面的太赫兹计算全息研究进展。其中,作为全息板的超表面展示出了超越传统光学器件的独特性能。首先,利用超表面实现了对于全息板每个像素的相位振幅同时且独立的调控,进而实现了高质量全息成像。这种新的电磁波操控能力也带来了新的全息成像效果,如利用介质超表面实现了全息像沿传播方向上的连续变化。其次,对超表面在不同偏振态下的响应进行设计,分别实现了线偏振态与频率复用、圆偏振态复用、以及基于表面波的偏振复用超表面全息术。此外,本文提出了依赖于温度变化而主动可控的超表面全息术,为今后计算全息术的设计与实现提供了新的方案,也推动了超表面在实际应用方面的发展。     

Effect of silane flow rate on structural,electrical and optical properties of silicon thin films grown by VHF PECVD technique

Hydrogenated silicon thin films deposited by VHF PECVD process for various silane flow rates have been investigated. The silane flow rate was varied from 5 sccm to 30 sccm, maintaining all other parameters constant. The electrical, structural and optical properties of these films were systematically studied as a function of silane flow rate. These films were characterized by Raman spectroscopy, Scanning Electron Microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy and UV–visible (UV–Vis) spectroscopy. Different crystalline volume fraction (22%–60%) and band gap (∼1.58 eV–∼1.96 eV) were achieved for silicon thin films by varying the silane concentration. A transition from amorphous to nanocrystalline silicon has been confirmed by Raman and FTIR analysis. The film grown at this transition region shows the high conductivity in the order of 10⁻⁴ Ω⁻¹ cm⁻¹.     

Synthesis and optical properties of cubic gold nanoframes

This paper describes a facile method of preparing cubic Au nanoframes with open structures via the galvanic replacement reaction between Ag nanocubes and AuCl₂ ⁻. A mechanistic study of the reaction revealed that the formation of Au nanoframes relies on the diffusion of both Au and Ag atoms. The effect of the edge length and ridge thickness of the nanoframes on the localized surface plasmon resonance peak was explored by a combination of discrete dipole approximation calculations and single nanoparticle spectroscopy. With their hollow and open structures, the Au nanoframes represent a novel class of substrates for applications including surface plasmonics and surface-enhanced Raman scattering.      

纳米银SERS的应用研究进展

文章对表面增强拉曼散射效应进行了简要介绍,同时对近几年来国内对于纳米银表面增强拉曼散射在生物分子、染料、医学及分析检测等方面的应用研究进行了简要的概括和展望。     

高拉曼散射信号增强衬底材料:银分形网络

基于扩散限制聚集过程机制合成的大型银分形网络被用作表面增强拉曼散射活性衬底材料.此衬底材料具有很好的拉曼增强特性以及很宽的动态响应范围.其较大的增强因子可归结为高度局域化的等离激元共振.     

Mesoflowers: A new class of highly efficient surface-enhanced Raman active and infrared-absorbing materials

A method for the synthesis of a new class of anisotropic mesostructured gold material, which we call “mesoflowers”, is demonstrated. The mesoflowers, unsymmetrical at the single particle level, resemble several natural objects and are made up of a large number of stems with unusual pentagonal symmetry. The mesostructured material has a high degree of structural purity with star-shaped, nano-structured stems. The mesoflowers were obtained in high yield, without any contaminating structures and their size could be tuned from nano- to meso-dimensions. The dependence of various properties of the mesoflowers on their conditions of formation was studied. The near-infrared-infrared (NIR-IR) absorption exhibited by the mesoflowers has been used for the development of infrared filters. Using a prototypical device, we demonstrated the utility of the gold mesoflowers in reducing the temperature rise in an enclosure exposed to daylight in peak summer. These structures showed a high degree of surface-enhanced Raman scattering (SERS) activity compared to spherical analogues. SERS-based imaging of a single mesoflower is demonstrated. The high SERS activity and NIR-IR absorption property open up a number of exciting applications in diverse areas. Electronic Supplementary Material  Supplementary material is available in the online version of this article at http://dx.doi.org/ and is accessible free of charge.     

Implantation effect of diamond-like carbon films by 110 keV nitrogen ions

Diamond-like carbon films, grown on microscope slides by a dual-ion beam sputtering system, were implanted by 110 keV N⁺ under the doses of 1 × 10¹⁵, 1 × 10¹⁶ and 1 × 10¹⁷ions cm⁻² respectively. The implantation induced changes in electrical resistivity of the films and in infrared (IR) transmittance of the specimens were investigated as a function of implantation dose. The structural changes of the films were also studied using IR spectroscopy and Raman spectroscopy. It was observed that, with the increase of implantation dose, the diamond-like carbon films display two different stages in electrical and optical behaviours. The first is the increase of both the film resistivity and the IR transmittance of specimen at the dose of 1 × 10¹⁵ ions cm⁻² which, we consider, is attributed to the implantation-induced increase sp³ C---H bonds. However, when the doses are higher than 1 × 10¹⁵ ions cm⁻², the film resistivity and the IR transmittance of specimen decrea significantly and the decrease rates at dose range of 1×10¹⁶ to 1×10¹⁷ ions cm⁻² are smaller than those between 1×10¹⁵ and 1 × 10¹⁶ ions cm⁻². We conclude that the significant reductions of the two parameters at high doses are caused by the decreases of bond-angle disorder and of sp³ C---H bonds, the increases of sp² C---C bonds dominated the crystallite size and/or number and also the sp² C---H bonds. The smaller decrease rates at a dose range of 1 × 10¹⁶ to 1 × 10¹⁷ ions cm⁻² may be caused by further recombination of some retained hydrogen atoms to carbon atoms.