Department of Electrical and Computer Engineering, University of Victoria , Victoria, British Columbia V8P5C2, Canada.
Nano Lett. 2014 Nov 12;14(11):6651-4. doi: 10.1021/nl503324g. Epub 2014 Oct 20.
Metal nanostructures provide extreme focusing of optical energy that is limited fundamentally by quantum tunneling. We directly probe the onset of the quantum tunneling regime observed by a sharp reduction in the local field intensity in subnanometer self-assembled monolayer gaps using third harmonic generation. Unlike past works that have inferred local limits from far-field spectra, this nonlinear measurement is sensitive to the near-field intensity as the third power. We calculate the local field intensity using a quantum corrected model and find good quantitative agreement with the measured third harmonic. The onset of the quantum regime occurs for double the gap size of past studies because of the reduced barrier height of the self-assembled monolayer, which will be critical for many applications of plasmonics, including nonlinear optics and surface enhanced Raman spectroscopy.
金属纳米结构提供了光能量的极限聚焦，这种聚焦受到量子隧穿的根本限制。我们使用三次谐波产生直接探测到了局域场强急剧降低所观察到的量子隧穿区域的开始，这种降低发生在亚纳米自组装单层间隙中。与过去从远场光谱推断局域极限的工作不同，这种非线性测量对近场强度的灵敏度为三次方。我们使用量子修正模型计算了局域场强，并发现与测量的三次谐波有很好的定量一致性。由于自组装单层的势垒高度降低，量子区域的开始发生在过去研究的两倍间隙尺寸处，这对于等离子体学的许多应用（包括非线性光学和表面增强拉曼光谱学）将是至关重要的。
