【作者】 龚理；

【导师】 张晓萍；

【作者基本信息】 兰州大学 ， 无线电物理， 2013， 硕士

【摘要】 贵金属,特别是金(Au)和银(Ag),在可见光波段其介电常数为负值,对光线呈现负折射率的特性,可以作为负折射率材料,也称为超材料(Metamaterials)。由金和银构成的金属纳米颗粒由于存在表面等离子体共振(Surface Plasmon Resonance)具有独特和可调的光学特性,在分子成像和光谱分析,化学和生物传感,生物医学,纳米光子学器件有潜在的应用。特别是介质核-金属覆层纳米颗粒,相比于实心的金属纳米颗粒,其等离子体光学特性更加容易调节。并且,金属覆层纳米颗粒的等离子体共振波长高度地依赖金属覆层和介质核的相对尺寸。通过减小金属覆层的厚度,等离子体共振波长可以从可见光区域红移到近红外区域。在近红外波段的可调性使得金属覆层纳米颗粒非常适用于光学生物医学成像和传感。利用金属覆层纳米颗粒对光频电磁场的局域特性,可以将其排布为链式结构从而在亚波长空间内传输光波。本文章研究了金属纳米覆层颗粒链的结构共振特性和能量传输特性。利用有限元数值仿真软件COMSOL Multiphysics详细分析了金属覆层厚度、颗粒间距、介质核折射率、周围介质折射率和颗粒数对金属纳米覆层颗粒链结构共振波长和能量传输衰减常数的影响规律。发现当减小金属纳米覆层的厚度时,颗粒链的偶极等离子体结构共振波长发生红移,而在该共振波长激发下能量传输损耗随着金属纳米覆层厚度的减小而急剧增加。同样,当颗粒间距减小时,颗粒链的偶极等离子体结构共振波长也发生红移,而在该共振波长激发下传输损耗也在减小。当介质核的折射率增加时,颗粒链的偶极等离子体结构共振波长同样发生红移现象,而在该共振波长激发下,能量传输损耗也相应地增加。当周围介质折射率增加时,颗粒链的偶极等离子体结构共振波长也发生红移现象,而在该共振波长激发下,当周围介质折射率与介质核折射率相等时能量传输损耗最小,其他情况下能量传输损耗都大于该值。最后,当颗粒数增加时,颗粒链的偶极等离子体结构共振波长继续发生红移现象,而能量传输损耗也随之增大。综上所述,金属纳米覆层颗粒链中金属覆层厚度、颗粒间距、介质核折射率、周围介质折射率和颗粒数均会对金属纳米覆层颗粒链结构共振波长和能量传输损耗产生有规律的影响。对这些规律的认识将对金属纳米覆层颗粒链在光学等离子体相关应用领域中的应用提供理论支持。更多还原

【Abstract】 Precious metals, especially gold (Au) and silver (Ag), is negative, its dielectric constant in the visible band of light rendering the characteristics of negative refractive index, can be used as a negative refractive index material, also referred to as a meta-material (Metamaterials). Metal nanoparticles of gold and silver has a unique and tunable optical properties due to the presence of surface plasmon resonance (Surface Plasmon Resonance), molecular imaging and spectral analysis, chemical and biological sensing, biomedical, nano-photonics devices potential applications. Especially dielectric core-metal cladding nano-particles, compared to the solid metal nano nanoparticles, the plasma optical characteristics more easily adjustable. Further, the wavelength of the plasmon resonance of the nano-particles of the metal coating layer is highly dependent on the relative dimensions of the metal cladding layer and a dielectric core. By reducing the thickness of the layer of metal cladding, the plasmon resonance wavelength can be moved from the visible light region of red to near-infrared region. The near infrared band tunability makes the metal cladding nanoparticles is ideal for optical biomedical imaging and sensing.The metal coating nanoparticles local characteristics of optical frequency electromagnetic field can be arranged as a chain structure which transmit light in the subwavelength space. This article studies the cladding of metal nano-particles chain the structure resonance characteristics and energy transfer characteristics. A detailed analysis of the influence of the resonance wavelength and energy transmission attenuation constant metal cladding thickness, particle spacing, medium refractive index of the core, the refractive index of the surrounding medium and the number of particles of metal nano-the cladding particle chain structure using finite element numerical simulation software COMSOL Multiphysics. Found that reducing the metal nano-coating thickness, particle chain structure of the dipole plasma resonance wavelength red shift in the resonance wavelength of the excitation energy transmission loss increased dramatically decreasing the coating thickness of the metal nano. Similarly, when the particle spacing decreases, the the dipole plasma structure of the particle chain resonance wavelength red shift in the resonance wavelength excitation under the transmission loss is also reduced. When the increase in the refractive index of the dielectric core, the by particle chains dipole plasma structure resonance wavelength also occurs the redshift phenomenon which, at the resonant wavelength excitation, energy transmission loss is also a corresponding increase in. Resonance wavelength redshift phenomenon occurs when increased refractive index of the surrounding medium, the the dipole plasma structure of the particle chain, and in the resonance wavelength excitation the energy minimum transmission loss when the refractive index of the surrounding medium, the medium is equal to the refractive index of the core, other case the energy transmission loss is greater than this value. Finally, when the increase in the number of particles, the particle chains dipole plasma structures resonance wavelength redshift continue to occur, and the energy transmission loss also increases.To sum up, the thickness of the metal coating layer in the cladding layer of the metal nano-particles in the chain, the distance between particles, the medium of refractive index of the core, the refractive index of the surrounding medium, and the number of particles are interested in a metal nano-particle chain structures of the cladding layer to the resonant wavelength and energy transmission loss generatedthe impact of the law. The understanding of these laws will cladding of metal nano-particles chain in the the optical plasmon application field in theoretical support.更多还原