Dark Plasmons in Hot Spot Generation and Polarization in Interelectrode Nanoscale Junctions
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- 作者：Joseph B. Herzog ; Mark W. Knight ; Yajing Li ; Kenneth M. Evans ; Naomi J. Halas ; Douglas Natelson
- 刊名：Nano Letters
- 出版年：2013
- 出版时间：March 13, 2013
- 年：2013
- 卷：13
- 期：3
- 页码：1359-1364
- 全文大小：315K
- 年卷期：v.13,no.3(March 13, 2013)
- ISSN：1530-6992
文摘
Nanoscale gaps between adjacent metallic nanostructures give rise to extraordinarily large field enhancements, known as 鈥渉ot spots鈥? upon illumination. Incident light with the electric field polarized across the gap (along the interparticle axis) is generally known to induce the strongest surface enhanced Raman spectroscopy (SERS) enhancements. However, here we show that, for a nanogap located within a nanowire linking extended Au electrodes, the greatest enhancement and resulting SERS emission occurs when the electric field of the incident light is polarized along the gap (transverse to the interelectrode axis). This surprising and counterintuitive polarization dependence results from a strong dipolar plasmon mode that resonates transversely across the nanowire, coupling with dark multipolar modes arising from subtle intrinsic asymmetries in the nanogap. These modes give rise to highly reproducible SERS enhancements at least an order of magnitude larger than the longitudinal modes in these structures.