School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, Massachusetts 02138, USA.
1] School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, Massachusetts 02138, USA [2] School of Physics, University of Melbourne, Victoria 3010, Australia [3] Department of Electrical and Electronic Engineering, University of Melbourne, Victoria 3010, Australia.
Nat Commun. 2014 Oct 14;5:5228. doi: 10.1038/ncomms6228.
Plasmonic nanostructures enable light to be concentrated into nanoscale 'hotspots', wherein the intensity of light can be enhanced by orders of magnitude. This plasmonic enhancement significantly boosts the efficiency of nanoscale light-matter interactions, enabling unique linear and nonlinear optical applications. Large enhancements are often observed within narrow gaps or at sharp tips, as predicted by the classical electromagnetic theory. Only recently has it become appreciated that quantum mechanical effects could emerge as the feature size approaches atomic length-scale. Here we experimentally demonstrate, through observations of surface-enhanced Raman scattering, that the emergence of electron tunnelling at optical frequencies limits the maximum achievable plasmonic enhancement. Such quantum mechanical effects are revealed for metallic nanostructures with gap-widths in the single-digit angstrom range by correlating each structure with its optical properties. This work furthers our understanding of quantum mechanical effects in plasmonic systems and could enable future applications of quantum plasmonics.
等离子体纳米结构可以将光集中到纳米级的“热点”中，在这些热点中，光的强度可以增强几个数量级。这种等离子体增强极大地提高了纳米尺度光物质相互作用的效率，实现了独特的线性和非线性光学应用。正如经典电磁理论所预测的那样，在狭窄的间隙内或在尖锐的尖端处经常观察到较大的增强。直到最近，人们才开始认识到，当特征尺寸接近原子长度尺度时，可能会出现量子力学效应。在这里，我们通过观察表面增强拉曼散射实验证明，在光学频率下电子隧穿的出现限制了可实现的最大等离子体增强。通过将每个结构与其光学特性相关联，我们揭示了具有个位数埃宽度间隙的金属纳米结构中的这种量子力学效应。这项工作增进了我们对等离子体系统中量子力学效应的理解，并可能为量子等离子体学的未来应用铺平道路。
