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题名:
金属纳米结构的表面增强拉曼散射研究
作者: 杨兰英
学位类别: 博士
答辩日期: 2009-02-18
授予单位: 中国科学院光电技术研究所
授予地点: 光电技术研究所
导师: 罗先刚
关键词: 表面等离子体 ; 表面增强拉曼散射 ; 离散偶极子近似 ; 时域有限差分 ; 纳米球光刻 ; bowtie ; crescent
学位专业: 光学工程
中文摘要: 表面增强拉曼散射(surface enhanced Raman scattering,SERS)是将激光拉曼光谱应用于表面科学研究的探索中所发现的异常表面光学现象。表面增强拉曼散射光谱具有高特异性和高灵敏度,已广泛应用于分析化学等领域,但作为SERS效应的主要载体和实现SERS放大效应的关键,金属纳米结构的SERS增强能力和加工工艺成为目前制约推广SERS应用的技术瓶颈。研究易于阵列化、高拉曼增强能力的单体或双聚体纳米结构;以及发展低成本且容易实现批量生产的纳米加工工艺,从而发展低成本且具有普适性的SERS基底,成为SERS领域的一个重要而又必要的课题。 论文介绍了SERS技术的增强机理、应用及发展趋势,特别是SERS基底的发展以及SERS技术在生化传感中的应用。SERS效应的电磁增强机制表明金属的表面等离子体共振(surface Plasmon resonance,SPR)在很大程度上决定了金属纳米结构的SERS活性,因此论文研究了新型金属纳米结构的SPR光学特性,在此基础上探索了结构的SERS增强能力,重点研究了金属纳米bowtie结构和新月(crescent)结构的SERS性能,提出了三明治bowtie和crescent自相似链两种易于阵列化且分别具有SPR波长易调、高拉曼增强能力特点的新型纳米结构;本着发展低成本且具有普适性的SERS基底这一目标,研究了金属覆盖纳米球(metal film over nanosphere, MFON)结构的制作工艺以及应用前景。对MFON、三明治bowtie和自相似crescent链三种结构的提出和研究,丰富了现有的SERS活性基底,为推广SERS技术应用提供了坚实的基础。论文的具体研究内容如下: 纳米球光刻技术(Nanoshpere Lithography,NSL)成本低、方法简单,适合大面积纳米结构制作。采用NSL技术和自组装单层表面活化技术制作出了对葡萄糖分子具有亲和力、性能稳定的AgFON结构,形成粗糙度在纳米量级、均匀分布的SERS活性表面,采用共聚焦光路提高信噪比,成功地在10秒内探测到了浓度100 mmol/L葡萄糖溶液的九个主要特征峰。该实验表明这种AgFON金属纳米结构制作简单、性能稳定、具有中等拉曼增强能力和普适性,是一种比较经济和成熟的SERS活性基底,同时该结构在葡萄糖的探测实例中所表现的灵敏度表明SERS技术对实现生理浓度的葡萄糖的快速探测进而实现血糖监测具有潜在的意义。 离散偶极子近似(discrete dipole approximation,DDA)方法,可用于计算复杂介质环境中任意形状及尺寸的纳米颗粒的光学特性,其计算结果与实验结果吻合较好,已发展成为计算纳米颗粒的光学性质的重要手段之一。采用DDA方法探讨了纳米bowtie结构的光学特性,重点探讨了bowtie结构的等离子体光学特性和电场增强能力这两个与SERS基底增强能力相关的重要性能:(I)从实验中可能出现的加工误差出发,讨论了间隙、顶尖错位、尺寸对bowtie 光学特性的影响;(II)在单层bowtie结构的基础上,提出了LSPR易调的Ag/SiO2/Ag三明治bowtie结构,讨论了该三明治bowtie结构随介质层厚、金属层厚进行调节的光学特性,探讨了其相对于单层bowtie结构的光学特性差异。发现随着介质层或金属层厚度的增加,LSPR峰红移,但相对于单层bowtie始终是蓝移的,其拉曼增强因子超过6×109。得到三明治bowtie可通过介质层或金属层的厚度很容易地实现LSPR的波长调节,又具有局部电场增强很大的优点,非常适合作为SERS活性基底的结论。 时域有限差分(finite difference time-domain,FDTD)法,对周期结构的电磁场计算具有独到的优势。联合FDTD方法和DDA方法研究了新月单体、新月周期链的消光谱和电场分布,在此基础上提出了易于阵列化且拉曼增强能力超过1010的新月自相似链结构。研究结果表明,对新月单体来说,最大电场增强因子(EFmax)发生在d/2R=0.4附近。对一维周期新月阵列来说,通过优化周期和阵列大小,一维新月阵列可以获得比较窄的消光峰,这种特性非常适合应用于LSPR和SERS传感领域。对新月自相似链来说,其光学特性和链轴线与新月尖端连线的排布相关,最大电场增强因子比对应月牙单体最高可高达9.3倍,比对应自相似球体链最高可高达655倍,充分展现了这种结构在局部电场放大方面的优异性能和成为高性能SERS基底的潜力。 总之,在现有工艺技术基础上,制作出了能在10秒内快速探测浓度低达100 mmol/L的葡萄糖溶液的具有AgFON结构的SERS传感芯片;提出了兼具LSPR易调和拉曼增强能力超过6×109的三明治bowtie结构,提出了拉曼增强能力超过2.8×1010的Crescent自相似链结构;而且研究了间隙、错位、尺寸大小等加工误差对bowtie光学特性的影响,探索了获得陡窄等离子体共振峰的结构。这些新结构的提出和研究拓展了现有的SERS活性基底范围,为促进SERS技术走出实验室进入工业现场提供了基础。
英文摘要: Surface enhanced Raman scattering (SERS) is an extraordinary optics phenomena found when laser Raman spectroscopy was applied in research of surface science. SERS spectroscopy is characteristic of high specificity and sensitivity and so it has been used in many fields such as analytical chemistry. The main bottlenecks to expand the application of SERS spectroscopy are the Raman enhancement performance and the fabrication of the SERS active substrates, which are the main carriers and the keys to embody the enlargement effect of SERS. Therefore, it is very important and necessary to study metallic monomer or dimmer nanostructures with high Raman enhancement factor, and to develop cost-effective and batch-production nanofabrication. The status of SERS technology, including the enhancement mechanisms, application and tendency, especially the development of the SERS substrate and the application of SERS in bio-chemical sensors, was presented. Beacause the electromagnetic enhancement mechanism of SERS shows that the surface plasmons resonance (SPR) of metallic nanostructures dominates their optical properties and SERS activity, nanostructures’ SERS performance were explored based on studying their SPR. Two metallic nanostructures for SERS were studied: nanobowtie and nanocrescent. A sandwich nanobowtie and self-similar chain of crescents were presented, which hold simply-tunable surface Plasmons resonance (SPR) wavelengths and high Raman enhancement respectively. The two structures are both easily formed into array. In order to develop low-cost and universally applicable substrates, silver film over the nanosphere (AgFON) was studied, including its fabrication and application. The presentation and study of these three nanostructures (i.e. MFON, sandwich bowtie, and self-similar chain of crescents) enrich the SERS substrates. Nanosphere lithography (NSL) is a low-cost and easy method for large-area fabrication of nanostructures. In this thesis, silver film over the nanosphere (AgFON) was fabricated by NSL and modified by a self-assembled monolayer (SAM), with improved stability and affinity to glucose. The modified AgFON with uniform nanostructures was used as a SERS-active surface to detect the glucose solution with low concentration of 100mmol/L and nine feature peaks were successfully obtain as fast as in ten seconds, with the confocal optical configuration applied to improve signal to noise ratio (SNR). Our experimental results demonstrated that this approach can fast detect glucose solution with low concentration by using easily fabricated and stable nanostructures, thus hold promise in fast detection of glucose solution with physiological concentration. A discrete dipole approximation (DDA) method can be used to calculate absorption, scattering and extinction of nanoparticles with arbitrary shapes in complex surroundings. The calculation results of DDA are in accordance with the experimental results, thus DDA has been an important method to calculate optical properties of nanoparticles. Here DDA is used to study optical properties of the silver nanobowtie, especially its surface plasmons and E-field enhancement. (I) the influences of the possible manufacturing error such as gap, topology and size on the optical properties are discussed. (II) A novel structure of Ag/SiO2/Ag sandwich nanobowties is presented and its optical properties tuned by the thickness of metallic layers or medium layer are investigated. The differences between sandwich bowtie and single layer bowtie are also studied. A Raman EF of over 6×109 is demonstrated by this structure. The LSPR red shifts with the increase of the layers, thickness but all along blue shifts relative to that of the single layer bowtie. The results show that the sandwich bowtie has characteristics of simply-tunable surface Plasmons resonance (SPR) wavelengths and high localized E-field enhancement, thereby this structure has a great potential application in surface-enhanced Raman scattering (SERS). FDTD method holds a unique superiority for calculation of period nanostructures. In this thesis FDTD and DDA method are employed to investigate the extinction spectra and E-field distribution of the monomer and periodic chain of nanocrescents. A novel structure of self-similar chain of crescents is presented, which is easily formed in array and with Raman enhancement factor of over 1010. The results show that for the crescent monomer, the maximum EF appears when its width is near half of its outer diameter (d/2R=0.4). For the periodic chain of crescent, the sharp extinction spectrum is obtained by optimizing its period and the size of the chain. So this periodic chain of crescent holds promise in application of LSPR and SERS sensing.For the self-similar chain of crescents, the maximum EF is over 9 and 650 times higher than that of corresponding crescent monomer and self-similar chain of spheres, respectively. So it can be considered as a good candidate for a novel SERS substrate due to its good performance in localized E-field enhancement. In conclusion, based on the state-of-art nanofabrication, the AgFON structure as a SERS substrate is fabricated and successfully used for detection of 100 mmol/L aqueous glucose solution as fast as in ten seconds. A novel structure of sandwich nanobowtie with easily-tunable LSPR and EFSERS of over 6×109, and a novel structure of self-similar chain of crescents with EFSERS of over 1010 are proposed. The influences of manufacturing errors on the optical properties of nanobowties are studied, and the structure with sharp LSPR peak is explored. Our researches extend SERS substrates and open a way towards field application of SERS technology.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.ioe.ac.cn/handle/181551/276
Appears in Collections:光电技术研究所博硕士论文_学位论文

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杨兰英. 金属纳米结构的表面增强拉曼散射研究[D]. 光电技术研究所. 中国科学院光电技术研究所. 2009.
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