纳米球刻印法制备的金属纳米颗粒阵列的结构、等离激元共振模式与SERS性能研究

发布时间：2018-03-31 03:31

本文选题：表面增强拉曼散射　切入点：金属纳米颗粒阵列　出处：《南京大学》2017年博士论文

【摘要】：近些年来,利用各种新型纳米材料制备工艺与控制技术,人们设计并制造出众多形貌与功能各异的金属纳米结构。这些金属纳米结构由于支持表面等离激元(surfaceplasmon,SP)共振而表现出极为丰富的光学性能。伴随着表面等离基元共振激发,金属微纳结构中的局部电场得到大幅提高,从而提高对场强敏感的各种光学非线性过程的转换效率,表面增强拉曼散射(Surface-Enhanced Raman Scattering,SERS)就是最具有代表性的应用。作为一种高度灵敏且无损的检测技术,SERS被广泛应用于化学、生物、材料科学以及医学检测等诸多领域,成为当前国际国内学术界的研究热点之一。本文围绕新颖金属纳米结构的光学性质研究,用纳米球刻印法发展和制备不同种类的金属纳米颗粒阵列。我们从实验上对金属纳米结构的几何参数对结构表面等离激元特性、以及作为SERS芯片性能的影响进行了研究,并深入研究了金属纳米结构SP模式与SERS性能之间的关系。论文具体包括以下几个方面:1、系统研究了贵金属半球壳阵列的透射、反射、吸收光谱特性,以及其作为SERS基底对R6G分子的拉曼增强效果,并找到了基底的SERS强度与吸收特性之间普遍存在的相关规律。在实验上采用Langmuir-Blodgett方法制备了具有不同周期的单层六角密堆的聚苯乙烯(Polystyrene,PS)微球阵列;通过在这些PS微球阵列上沉积了不同厚度的贵金属薄层,形成一系列的SERS基底;通过测量这些贵金属半球壳阵列的透射、反射光谱与结构的周期、沉积金属厚度之间的关系,总结出线性光学性质的标度关系。实验进一步以金属半球壳阵列为衬底,测量其对R6G分子的拉曼增强效果,发现SERS增强效果明显依赖于金属半球壳阵列的高光学吸收特性,并且找出了最佳SERS基底。研究表明,在偶极共振的模式下基底的SERS强度与基底在激发光波长、拉曼散射光波长处的吸收系数乘积成正比。2、详细研究了热点驱动的准三维金属网的线性光学性质及其在表面增强拉曼上的应用,发现结构中大量分布的～10nm超小间隙可以大大提高基底的SERS性能。该准三维金属网是在纳米球刻印技术的基础上,结合氧等离子体刻蚀技术,真空溅射等工艺制备而成的。通过优化氧等离子体刻蚀时间、金属沉积厚度,在依然保持对激发光和斯托克斯光的高吸收的同时,结构中的纳米间隙被调整至～10nm。在514nm激光的激发下,最佳SERS基底的拉曼增强因子高达1.5×108,对R6G溶液探测浓度的极限低至1nM。进一步的分析表明,当金属颗粒间距降至～10nm时,颗粒间强烈的近场耦合使得超小间隙附近的局域电场被极大地增强,超强局域电场进一步增强了结构表面吸附分子的拉曼散射,从而大大提高了基底的SERS性能,这个结论也被数值模拟计算所证实。3、研究了金属三角MIM(Metal/Insulator/Metal)结构的几何参数对其吸收特性及其SERS性能的影响,并分析了其背后的物理机制。在实验上,通过纳米球刻印法制备了由金属三角纳米颗粒、二氧化硅薄膜、金属组成的MIM结构。发现改变结构中的二氧化硅介质层厚度可以调节光吸收程度,将结构优化为宽带和偏振不敏感的完美吸收器;通过改变结构的周期,可以使结构所支持的宽带吸收波段从可见光扩展到近红外。进一步的实验发现拉曼增强因子依赖于在激发光波长和拉曼散射光波长处的吸收系数,而结构对激发光的高吸收性能有助于实现SERS信号的增强。最佳基底拉曼增强因子值达到4.9×106,这个数值是单纯石英衬底上的相同金属三角纳米颗粒的22倍。从数值模拟计算分析可知,该MIM结构的宽带完美吸收是由于该结构中多个等离激元共振模式所形成的,这些共振导致了结构表面局域电磁场的增强。利用氧等离子体刻蚀技术,将MIM结构中金属三角纳米颗粒的间距减小到亚10纳米的尺度,金属颗粒间的局域场耦合使得颗粒间的电场被极大地增强,从而进一步提高了金属三角纳米颗粒/Si02薄膜/金属三层结构的SERS性能,使基底拉曼增强因子进一步提高到3.1×107。上述这些纳米结构的制备过程具有低成本,大面积,技术工艺要求低等特点,它们在SERS以及太阳能电池等商用领域有着极大的潜力。
[Abstract]:In recent years, the use of a variety of new nano material preparation technology and control technology, people design and manufacture of metal nano structure morphology and outstanding different functions. These metal nanostructures support due to surface plasmon resonance (surfaceplasmon, SP) and exhibit extremely rich optical properties with surface plasmon based. Element resonance excitation, metal micro nano structure in the local electric field has been greatly improved, so as to improve the conversion of various nonlinear optical processes field sensitive efficiency, surface enhanced Raman scattering (Surface-Enhanced Raman, Scattering, SERS) is the most representative. With the application as a highly sensitive and nondestructive detection technology, SERS is widely used in chemistry, biology, materials science, medical testing and many other fields, has become a hot research topic in the current international and domestic academic circles. Based on novel metal nanostructures The optical properties of the prepared metal nanoparticles of different arrays of nanosphere lithography and development system. We experimentally on the geometrical parameters of the metal nano structure on the structure of the surface plasmon properties, as well as the influence of the performance of SERS chip is studied. To study the relationship between SP model and metal nano structure the performance of SERS and depth. The paper includes the following aspects: 1, the reflection transmission system research, precious metal hemispherical array, absorption spectra, as well as its SERS Raman enhancement effect of R6G molecules, and find the relevant rules commonly exists between and absorption properties of SERS substrates. With strength different period of six angle close packed polystyrene monolayer was fabricated by Langmuir-Blodgett method in experiment (Polystyrene, PS) microspheres by PS microspheres array; in these arrays of different deposition The noble metal layer thickness, the formation of a series of SERS substrate; measured by transmission of these precious metals hemispherical array, periodic reflection spectrum and structure, the relationship between the thickness of the metal deposition, summed up the linear optical properties of scale. Further experiments using metal hemisphere shell array substrate, the measurement of R6G molecule the Raman enhancement effect, high optical absorption properties of SERS significantly enhance the effect depends on the metal hemispherical array, and find out the best SERS substrate. The results show that the substrate in the dipole resonance mode of SERS intensity and the substrate in the excitation wavelength, the absorption coefficient is proportional to the product of the.2 Raman scattering light wavelength, a detailed study of the hot spots drive the quasi three dimensional metal mesh of the linear optical properties and its application in surface enhanced Raman of the structure found a large number of distributed to 10nm ultra small gap can greatly improve the efficiency of Gao Jidi The performance of SERS. The quasi-3D metal mesh is based on lithography nanospheres, combined with oxygen plasma etching technology, vacuum sputtering process was prepared. By optimizing the oxygen plasma etching time, metal deposition thickness, the remains on the excitation light and Stokes light high absorption at the same time, nano gap structure in be adjusted to ~ 10nm. excited by 514nm laser Raman, best SERS substrate enhancement factor of up to 1.5 x 108, the limit of detection of low concentration R6G solution to 1nM. further analysis shows that when the metal particle spacing to ~ 10nm, inter particle strong near-field coupling makes the local electric field near the ultra small the gap is greatly enhanced, strong local electric field to further enhance the Raman scattering of molecular adsorbent surface structure, which greatly improves the performance of the SERS substrate, the conclusion was also calculated by the numerical simulation of .3, the metal triangle MIM (Metal/Insulator/Metal) SERS performance characteristics and effects of structure parameters on the uptake, and analyzed the physical mechanism behind it. In the experiment, the nanoparticles were prepared by metal engraving triangular nanoparticles, silica film, MIM metal structure consisting of changing the thickness of silica. The dielectric layer structure can adjust the light absorption degree, the structure optimization for the perfect broadband and polarization insensitive absorber; by changing the structure of the cycle, can make the broadband support structure absorption band extended from visible to near infrared. Further experiments found that the Raman enhancement factor depends on the excitation wavelength and Raman absorption coefficient the scattering light wavelength, and the structure will help to enhance the realization of SERS signal of high excitation light absorption properties. The best Raman enhancement factor values up to 4.9 x 10 6, this value is 22 times the same triangle metal nanoparticles alone on the quartz substrate. The analysis from the numerical simulation, the MIM structure of the perfect broadband absorption is due to the structure of a plurality of plasmon resonance modes formed by these resonance leads to enhanced surface structure of electromagnetic field. The use of oxygen administration plasma etching technology, metal nanoparticles will decrease the spacing triangle in the MIM structure to 10 sub nanometer scale, local field coupling between metal particles in the electric field between the particles can be greatly enhanced, so as to further improve the performance of SERS nano meter particle metal triangle /Si02 film / metal three layer structure, the Raman enhancement factor to further improve the preparation process of 3.1 * 107. of these nano structure has the advantages of low cost, large area, low technical requirements, they are in SERS and solar battery business There is a great potential.

【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.1;O657.37

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