非局域效应下金属亚纳米结构表面等离激元近场增强特性的研究

More recently, the excitation and applications of surface plasmon polaritons (SPPs) at sub-nanoscale has been one of the most attractive research field attributed to the rapid development of fabrication techniques for metallic nanostructures. At this scale, the nonlocal model and quantum-corrected model can produces great prediction of the properties of scattering spectra than that would be achieved from classical treatment. However, in the existing literatures of experimentally studying of near-field limitation properties, researchers mainly focused on the resonance shift of scattering, whereas a little experimental works of the suppressed near-field enhancement are limited associated with disadvantages on the aspect of non-continuous adjustable gap size of the nanostructures and non-effective utilization of near-field enhancement. Meanwhile, the dominant spatial scale of the nonlocal model is still unclear..This project proposes to adopt a tip-enhanced Raman spectroscopy (TERS) system composed of Raman spectroscopy system with feedback control and a coupled structure consisting of a nanoscale metallic probe tip and thin metal film coated by polyelectrolytes with monolayers, in between with an adjustable gap size. This system can be utilized to theoretically and experimentally investigate the mechanism of excitation of SPPs and properties of near-field distribution within a sub-nanometer gap between the three-dimensional metallic probe tip-film structures with continuous adjustability. Through the realization of detecting the effect of gap size of the metallic nanostructure on scattering spectroscopy and near-field enhancement, the dominant spatial scales of nonlocal model and quantum-corrected model can be distinguished. The nonlocal effect of other metal materials will also be studied in this project. It is expected that this project can provide basis and help for the applications of SPPs in sub-nanoscale region.

近年来，随着金属纳米结构制备技术的发展，表面等激元在间隙结构中的激发与应用已经成为研究热点之一。在亚纳米尺度下时，基于自由电子响应的传统局域模型失效，而非局域模型和量子修正模型能对散射光谱做出预测。然而，亚纳米尺度表面等离激元近场增强受限特性的实验探测在尺寸连续可调性和场强增益的有效利用方面受到了限制，且非局域模型的主导空间范围尚未明确。.对此本项目将采用金属探针与覆盖单分子层有机材料的金属薄膜制备耦合纳米结构，与拉曼光谱系统共同构成纳米间隙尺寸可调的尖端增强拉曼光谱系统，从理论和实验上研究三维金属亚纳米间隙结构表面等离激元的激发行为和近场增强受限特性。通过将属亚纳米结构间隙尺寸对散射光谱和近场分布的影响规律的实验结果与理论结果进行比较，希望对两种模型的主导空间范围进行探索，并对表面等离激元应用中常见金属材料的非局域效应进行研究。该项目能够为亚纳米尺度下表面等离激元近场增强的应用提供帮助。

贵金属纳米结构中产生的表面等离激元现象近年来引起了广泛的关注，在理论计算和实验表证上对贵金属表面等离激元谐振频率和近场增强特性的精确描述也成为了近年来的研究热点。项目以具有亚纳米间隙的纳米线、纳米线-薄膜耦合结构、纳米间隙阵列结构为主要理论模型，研究了亚纳米尺度下由表面等离激元所激发的近场增强特性，以及空间非局域效应对近场增强因子的影响。本项目已经按照原计划开展了相关内容的研究，完成了计划中的要点内容，基本达到了预期目标，取得了一些研究成果。项目负责人以第一作者或通讯作者身份发表SCI期刊论文1篇，合作发表SCI期刊论文2篇，中文核心期刊1篇。本项目取得的主要研究成果如下：1、研究了截面为月牙形结构和壳层结构的纳米线结构中非局域效应对其吸收光谱和散射光谱的影响，研究发现月牙结构和壳层结构中非局域效应的引入使谐振峰的位置向短波方向移动，同时降低了尖端部位电场增强的倍数，为纳米线光伏器件的设计提供了理论基础。2、研究了金属纳米线-金属薄膜耦合结构的非局域效应，对该结构消光谱进行了计算，发现在这种结构中相比于铂材料，金材料制备的纳米线-薄膜结构对于非局域效应有更明显的响应。3、研究了紧密排列的半圆柱或半椭圆柱形成的含有尖锐角一维阵列结构，结果表明在局域效应和非局域效应下，一维阵列结构的共振波长是不同的，非局域效应下的共振波长向短波方向移动。在半椭圆结构中，尖锐角的大小与长短轴的比例有关，因此可以形成的不同大小和形貌的纳米间隙，进而影响阵列结构的共振波长位置和光吸收能力。这一项目的开展为金属亚纳米结构在光电转换和光伏器件的设计方面提供了一定得理论指导。