Physics Department, Technical University of Denmark, 2800 Kgs Lyngby, Denmark.
Beilstein J Nanotechnol. 2013 Dec 2;4:834-42. doi: 10.3762/bjnano.4.94. eCollection 2013.
Strongly enhanced and spatially confined near-fields in the vicinity of plasmonic nanostructures open up exciting new capabilities for photon-driven processes and particularly also for optical spectroscopy. Surface enhanced Raman signatures of single molecules can provide us with important information about the optical near-field. We discuss one- and two-photon excited surface enhanced Raman scattering at the level of single molecules as a tool for probing the plasmonic near-field of silver nanoaggregates. The experiments reveal enhancement factors of local fields in the hottest hot spots of the near-field and their dependence on the photon energy. Also, the number of the hottest spots and their approximate geometrical size are found. Near-field amplitudes in the hottest spots can be enhanced by three orders of magnitudes. Nanoaggregates of 100 nm dimensions provide one hot spot on this highest enhancement level where the enhancement is confined within less than 1nm dimension. The near-field enhancement in the hottest spots increases with decreasing photon energy.
在等离子体纳米结构附近，强增强和空间限制的近场为光子驱动过程，特别是光学光谱学开辟了令人兴奋的新功能。单分子的表面增强拉曼特征可以为我们提供有关光近场的重要信息。我们讨论了单分子水平上的单光子和双光子激发的表面增强拉曼散射，作为探测银纳米聚集体等离子体近场的一种工具。实验揭示了近场中最热热点的局部场的增强因子及其对光子能量的依赖性。此外，还发现了最热热点的数量及其近似几何尺寸。近场幅度在最热的热点可以增强三个数量级。在最高增强水平下，100nm 尺寸的纳米聚集体提供了一个热点，其中增强被限制在不到 1nm 的尺寸内。在最热的热点中的近场增强随着光子能量的降低而增加。
