Nanophotonic Tomography – Peering below plasmonic waves

表面等离激元极化激子波已经成为在纳米尺度上操纵光的应用，即在纳米光子应用中的关键成分。当光线照射到金属表面时，它会引起电子振荡，在某些情况下，金属表面的电荷密度会产生涟漪或波动。这种波，被称为表面等离子激元（SPPs），允许极端的光浓度和高灵敏度的光学检测。虽然SPP波的存在是众所周知的，但研究它们在金属表面以下的行为是极具挑战性的。为了应对这一挑战，该项目将通过测量放置在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。这种在纳米尺度上对光学响应的逐层分析被称为纳米光子断层扫描。对这种薄膜光发射的系统分析将用于具有实际应用的纳米光子系统中SPP波的深度分辨研究，包括光催化和热电子增强光伏。除了带来对关键纳米光子现象的基本理解外，该研究还将整合到纳米光子学课程材料中。表面等离子激元的深度剖面是一个极具挑战性的命题。提出的工作利用了最近在金光致发光（PL）的产生和检测方面的见解。基于对几nm厚金层可探测到的Au PL的观察，利用嵌入的薄金膜作为局部场增强的二维探针是可行的。基于这一认识，逐层金PL分析将应用于当前对等离子体和纳米光子学领域非常重要的几何形状：(a)“镜面上的粒子”几何，其中纳米光子层析成像将用于绘制热电子和空穴对Au光致发光的深度，(b)嵌入纳米粒子的零模波导（ZMW），其中周围ZMW的分层可以对间隙等离子体场振幅进行深度选择定量分析，(c)超表面增强的拉曼散射，其中层状金属超表面将允许二维材料和Au PL的拉曼散射增强的定量关联，以及(d) Ag中的亚表面几纳米Au薄膜，通过监测Au PL光谱修改的激发能量依赖性来研究热载流子再分配。从研究中获得的知识对生物传感，光催化和热电子辅助光伏的应用具有重要意义。此外，所提出的工作将为使用金PL作为内部光场的一般探针提供一个清晰而全面的工作体。研究结果对纳米光子学领域具有重要的应用价值。该奖项反映了美国国家科学基金会的法定使命，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.