Dark plasmons in hot spot generation and polarization in interelectrode nanoscale junctions

Abstract

Nanoscale gaps between adjacent metallic nanostructures give rise to extraordinarily large field enhancements, known as "hot spots", 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.

20 pages, 4 figures

References in corpus (6)

• Optical Rectification and Field Enhancement in a Plasmonic Nanogap
• Electromigrated nanoscale gaps for surface-enhanced Raman spectroscopy
• Simultaneous measurements of electronic conduction and Raman response in molecular junctions
• Vibrational and electronic heating in nanoscale junctions
• Nanogaps with very large aspect ratios for electrical measurements
• Electronic and optical properties of electromigrated molecular junctions