Nanophotonic Tomography – Peering below plasmonic waves

表面等离子体激元波已经成为在纳米级操纵光的应用中，即在纳米光子应用中的关键成分。当光照射到金属表面时，它会导致电子振荡，在某些情况下会在金属表面的电荷密度中产生波纹或波动。这种波被称为表面等离子体激元（SPP），允许极端的光集中和高灵敏度的光学检测。虽然SPP波的存在是众所周知的，但研究其在金属表面以下的行为极具挑战性。为了应对这一挑战，该项目将通过测量位于表面以下不同深度的薄金属层的光发射来研究亚表面纳米光子效应。这种对纳米级光学响应的逐层分析被称为纳米光子断层扫描。这种薄膜的光发射的系统分析将用于深度分辨的研究SPP波在纳米光子系统，具有实际应用，包括热电子和热电子增强的photopolics。除了带来关键的纳米光子现象的基本理解，研究将被集成在纳米光子学课程材料。表面等离子体激元的深度剖析是一个极具挑战性的命题。拟议的工作利用了金光致发光（PL）的产生和检测的最新见解。基于对几nm厚的金膜上可检测到的Au PL的观察，将嵌入式薄金膜用作局部场增强的二维探针已经成为可行的。基于这一认识，逐层金PL分析将应用于对等离子体和纳米光子学领域具有重要意义的几何形状：（a）“镜面上的粒子”几何形状，其中纳米光子层析成像将用于绘制热电子和空穴对Au光致发光有贡献的深度，（B）具有嵌入纳米粒子的零模式波导（ZMW），其中周围ZMW的分层使得能够对间隙等离子体激元场幅度进行深度选择性定量分析，（c）超颖表面增强的拉曼散射，其中分层的金属超颖表面将允许来自2D材料和Au PL的拉曼散射增强的定量相关，以及（d）在Ag中的亚表面几nm Au膜，用于通过监测对Au PL谱的修改的激发能依赖性来研究热载流子再分布。从研究中获得的知识是非常重要的应用在生物传感器，电子探针，和热电子辅助光致发光。此外，拟议的工作将提供一个清晰和全面的身体的工作，使用金PL作为内部光场的一般探头。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Surface plasmon polariton waves have become a key ingredient in applications that manipulate light at the nanoscale, i.e. in nanophotonic applications. When light hits a metal surface it causes electrons to oscillate, in some cases generating ripples or waves in the charge density at the metal surface. Such waves, known as surface plasmon polaritons (SPPs), allow for extreme light concentration and highly sensitive optical detection. While the existence of SPP waves is well known, it is extremely challenging to investigate their behavior below the metal surface. To address this challenge, this project will study sub-surface nanophotonic effects by measuring light emission from thin metallic layers placed at different depths below the surface. This layer-by-layer analysis of the optical response at the nanoscale is referred to as nanophotonic tomography. The systematic analysis of such thin-film light emission will be used for depth-resolved studies of SPP waves in nanophotonic systems that have practical applications, including photocatalysis and hot electron enhanced photovoltaics. In addition to bringing fundamental understanding of key nanophotonic phenomena, the research will be integrated in Nanophotonics course materials.Depth profiling of surface plasmon polaritons is a highly challenging proposition. The proposed work leverages recent insights in the generation and detection of gold photoluminescence (PL). Based on the observation of detectable Au PL from few-nm thick gold layers, it has become feasible to use embedded thin gold films as 2D probes of local field enhancement. Based on this realization, layer-by-layer gold PL analysis will be applied to geometries that are of great current importance to the fields of plasmonics and nanophotonics: (a) the “particle on mirror” geometry, where nanophotonic tomography will be used to map the depth over which hot electrons and holes contribute to Au photoluminescence, (b) the zero-mode waveguide (ZMW) with an embedded nanoparticle, in which layering of the surrounding ZMW enables depth-selective quantitative analysis of gap plasmon field amplitudes, (c) Metasurface-enhanced Raman scattering, where layered metallic metasurfaces will allow for a quantitative correlation of Raman scattering enhancement from 2D materials and Au PL, and (d) sub-surface few-nm Au films in Ag for the investigation of hot carrier redistribution by monitoring the excitation-energy dependence of modifications to the Au PL spectrum. The knowledge gained from the research is of great importance to applications in biosensing, photocatalysis, and hot-electron assisted photovoltaics. In addition, the proposed work will provide a clear and comprehensive body of work on using gold PL as a general probe of internal optical fields. The results are anticipated to be of great value to the general field of nanophotonics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.