Nanophotonic Tomography – Peering below plasmonic waves

表面等离子体激元波已经成为在纳米尺度上操纵光的应用的关键成分，即在纳米光子学应用中。当光线照射到金属表面时，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上产生涟漪或波动。这种波被称为表面等离子激元(SPP)，允许极端的光集中和高灵敏度的光学探测。虽然SPP波的存在是众所周知的，但要研究它们在金属表面下的行为是非常具有挑战性的。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。这种对纳米尺度的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纳米光子系统中SPP波的深度分辨研究，这些系统具有实际应用，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了解外，这项研究还将被整合到纳米光子学课程材料中。表面等离子激元的深度剖析是一个极具挑战性的命题。这项拟议的工作利用了在金光致发光(PL)的产生和检测方面的最新见解。基于从几nm厚的金层中观察到的可探测到的Au PL，将嵌入的金薄膜用作局部场增强的2D探针是可行的。基于这一认识，逐层金发光分析将被应用于对等离子体和纳米光子学领域具有重大当前重要性的几何形状：(A)“镜面粒子”几何结构，其中将使用纳米光子断层成像来绘制热电子和空穴对Au光致发光的贡献深度；(B)具有嵌入纳米粒子的零模波导(ZMW)，其中周围ZMW的分层使得能够对带隙等离子体场幅进行深度选择性的定量分析；(C)亚表面增强拉曼散射，其中分层的金属亚表面将允许来自2D材料的拉曼散射增强和Au光的定量关联，以及(D)银中亚表面的几nm金膜，用于通过监测Au光致发光光谱的修正对激发能量的依赖关系来研究热载流子再分布。这些研究成果对生物传感、光催化、热电子辅助光伏等领域的应用具有重要意义。此外，拟议的工作将为使用金发光作为内部光场的一般探测器提供明确和全面的工作。这一奖项反映了NSF的法定使命，通过使用基金会的学术价值和更广泛的影响审查标准进行评估，被认为是值得支持的。

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.