【作者】 李海波；

【导师】 徐蔚青； 徐抒平；

【作者基本信息】 吉林大学 ， 物理化学， 2014， 博士

【摘要】 表面等离子体光子学（plasmonics）由于其在亚波长尺度内对光波有卓越的调控能力而引起了人们极大地研究兴趣，近年来发展迅速。表面等离子体（SPs）可以作为一个连接宏观的光场与微纳尺度的局域光场（或者说远场与近场）的媒介，可将光限域在亚波长尺度范围内，因此实现对衍射极限尺寸下光场的控制。SPs不仅广泛用于制备纳米光学器件，在增强光谱领域也有广泛的应用，如表面增强拉曼（SERS），表面等离子控制的荧光等。通过SPs的共振和限域作用，分子所在的局域电磁场强度会得到极大地提高，因此分子的拉曼信号等光谱信号会得到几个数量级的提高。由SPs与光的耦合机理可知，SPs尤其是传播型SPs的激发与发射具有方向性，因此借助SPs还可实现对光发射方向性的控制。对SPs增强光谱的方向性进行研究可以实现高效的激发，增强信号强度，更为重要的是可实现定向的光谱信号发射，从而提高收集效率。此外，借助SPs我们还可以对光束方向（如荧光，透射光束等）进行调控，可实现在微纳尺度下光束控制等问题，这在微纳光学和光电领域都有很大的研究价值。在本文中，我们围绕SPs调控光谱学中与方向相关的问题，利用自行搭建的角度分辨的光谱检测平台，研究了以下一些问题：1.研究了SERS的定向发射问题。基于电磁场增强的原理，SERS的增强因子最高可达109-1010，然而却无法达到单分子检测所需要的1014左右，因此SERS要达到更高灵敏度只能借助其他增强途径，如共振增强，电荷转移等，而化学增强对分子种类依赖性很强，并不是一种普适的增强方法。因而任何有助于额外增强SERS的途径都受到了人们的重视。最近研究者们注意到，由于SERS的发射方向一般是分散的而导致SERS在的收集效率很低，如果能实现将SERS定向发射，则可以极大地提高收集效率，进而提高SERS的检测灵敏度。我们研究了在kretschmann棱镜结构和周期纳米井阵列结构下的传播型SPs的定向的耦合发射。用传播型SPs耦合SERS，可以实现SERS的定向发射，引入纳米粒子的局域SPs共振现象可提高局域电磁场强度，我们将两种SPs组合在一起可以实现高增强倍数的SERS的定向发射。我们通过基地优化结构参数，如光栅周期等，使发射方向与基片法线方向垂直，从而有助于提高SERS的收集效率，详细内容见第二章。2.开发了一些面向特殊检测需求的拉曼光谱检测平台。商品化的设备无法满足一些特殊的检测对象的测量要求，借助自行研制的新型检测仪器可以率先在新的研究领域展开研究，因而研发新型检测平台对提高团队科研水平有重大意义。为满足特殊测量需求及特殊样品的光谱检测，结合本课题的研究成果，我们开发了多种新型拉曼检测仪器和检测平台：针对SERS的基底制备和检测过程复杂、重现性低的问题，结合上述的SERS定向发射现象，我们开发了便携式SERS检测仪，具有较高灵敏度和使用方便性，是一种很有应用潜力的拉曼检测仪器；针对拉曼光谱仪在微流控芯片领域应用的困难和局限性，开发了便于在微流控芯片上使用的小型微流控拉曼分析仪，对在微流控芯片上的拉曼光谱研究提供了便利；针对普通拉曼无法观察和定位透明生物组织和亚波长尺寸的样品，将拉曼检测与荧光成像和暗场成像技术联用，可以方便的在透明生物组织及纳米结构下的用成像方法找到感兴趣的位置，然后用拉曼光谱进行分析，是一种非常灵活、功能强大的综合光谱检测平台。这些自行开发的仪器和检测平台，为课题组开展更加具有挑战性的科研项目提供了必要的硬件基础。详细内容见第三章。3.利用电信号实现对光发射方向的调控。用电信号来调控光信号一直以来都是光电研究领域的一个热点和难点，尤其是在微纳尺度上的器件上。由于SPs在微纳尺度下对光有卓越的调控能力，而且由于SPs对环境折射率变化十分敏感，可利用该性质在微纳器件上实现对光的调控。液晶材料是一种具有电光效应的典型的超分子材料，其折射率随外界电场改变，因此可以用液晶材料实现用电信号实现对SPs的调控，进而实现在微纳器件上对光的调控。基于以上想法，我们分别在kretschmann棱镜结构和周期纳米井阵列结构下的荧光发射的方向和波长进行了用电信号的调控，证明该方法是一种非常实用的调制手段，具有可连续地、可逆的、快速地（响应速度为毫秒量级）调控光谱的优点。详细内容见第四章。我们又基于SPs引起的光的异常透过现象，用电信号实现了光束透射方向的控制，该方案具有器件结构简单、光束强度较高、光束方向性好、透射方向可控等优点，该研究成果可以用于三维立体显示领域。详细见第五章。更多还原

【Abstract】 Plasmonics have been received much attentions due to their excellent ability tocontrol light in subwavelength range. Surface plasmons (SPs), which could be as thebridge to link the far field and near filed of light, could control light beyond thediffraction limit. Therefore SPs have wide applications in the development andpreparation of the nano-sized optical elements. SPs are also important to surfaceenhanced spectroscopy, such as surface enhanced Raman (SERS) and surfacePlasmon controlled fluorescence. Due to the SPs resonance effect, the localelectric-magnetic fields could be effectively enhanced, thus the spectrum signals (e.g.Raman scattering) could be improved for several orders. Besides, the coupling of SPsand light wave is usually directional, thus the emission direction of light could betuned by SPs. In this work, we studied some issues about the directional spectroscopyby means the self-built angle-resolved spectrometer:1.We studied the directional emission of SERS. The SERS enhancement factorcould reach109-1010according the electric-magnetic (EM) enhancement mechanismof SERS. It is not strong enough to detect the SERS signal of single molecule (>1014).To achieve the single molecule SERS, other enhance approach should be employedsuch as the resonance enhancement and charge transfer effect. However thesechemical enhancement methods which strongly depend on the species of themolecules are not universial methods. Thus any way to provide extra enhancement issignificant to SERS. The collection efficiency of SERS is usually very low due to theemanative nature of scattering. The SERS sensitivity could be efficiently improved ifthe SERS collection efficiency is improved. We studied the propagating SPs couplingemission on kretschmann configuration and periodical nano-well array. The directional SERS was achieved. Even the emission direction of SERS could along thenormal line of substrate after optimizing the parameters of the structure. We believe itis beneficial to improve the collection efficiency of SERS. The details could be foundin chapter2.2.We developed some Raman detection platform to match some special detectionrequirements. The commercial device could match the most detection requirements,however some special samples could not be detected, therefore the development ofnew detection devices is very important to improve the quality of the scientificresearch.1. We developed several novel Raman spectrometers based our previousresearch results: we developed a portable SERS spectrometer based on the directionalSERS phenomenon. The SERS spectrometer has a high sensitivity and accessibility;2.We built a compact microfluidics Raman spectrometer which is convenient to detectRaman on chips to solve the problem that the traditional Raman spectrometer is notsuitable to detect Raman spectra on microfluidic chips,;3. We integrated fluorescenceimage and dark field image with Raman spectrometer. We can fast locate theinterested samples of transparent biological samples or nanoparticles usingfluorescence image and dark field image, and then analyzed the components of thesample by Raman spectra. These self-built detection platforms has more flexiblefunctions comparing the commercial instruments, which is the hardware basics toresearch the challenging projects in our research group. The details could be found inchapter3.3.The control of light emission directions using electric signals. Since SPs is verysensitivity to the refractive index (RI) of surrounding, and the RI of liquid crystalscould be tuned by electric signals, we could tune the plasmonic devices by voltagesignals based on this. We achieved the electric control of the wavelength and emissiondirections of fluorescence on kretschmann configuration and nanograting structure. Itwas proved that the modulation method using liquid crystals was very efficiently. Thedetails could be found in chapter4. In additions, we tuned the light beam transmissiondirections based on SPs induced extraordinary optical emission. A liquid crystals layerwas added on the thick Ag film with nanograting pattern, and the beam transmissiondirections could be tuned. It is a very simple, but very efficiently method to modulate the beam directions. This research achievement could be using in three-dimensionaldisplay fields. The details could be found in chapter5.更多还原