Impact of the Nanoscale Gap Morphology on the Plasmon Coupling in Asymmetric Nanoparticle Dimer Antennas. Issue 12 (5th February 2016) - Popp, Paul S.
Abstract : Coupling of plasmon resonances in metallic gap antennas is of interest for a wide range of applications due to the highly localized strong electric fields supported by these structures, and their high sensitivity to alterations of their structure, geometry, and environment. Morphological alterations of asymmetric nanoparticle dimer antennas with (sub)‐nanometer size gaps are assigned to changes of their optical response in correlative dark‐field spectroscopy and high‐resolution transmission electron microscopy (HR‐TEM) investigations. This multimodal approach to investigate individual dimer structures clearly demonstrates that the coupling of the plasmon modes, in addition to well‐known parameters such as the particle geometry and the gap size, is also affected by the relative alignment of both nanoparticles. The investigations corroborate that the alignment of the gap forming facets, and with that the gap area, is crucial for their scattering properties. The impact of a flat versus a rounded gap structure on the optical properties of equivalent dimers becomes stronger with decreasing gap size. These results hint at a higher confinement of the electric field in the gap and possibly a different onset of quantum transport effects for flat and rounded gap antennas in corresponding structures for very narrow gaps. Abstract : Correlative high‐resolution transmission electron microscopy (HR‐TEM) investigations and dark‐field spectroscopy of individual asymmetric dimers composed of spherical AuNPs (nanoparticles) address the impact of nanoscale gap morphology on their plasmon resonance. The mode splitting of the gap plasmon for dimers with comparable (sub)‐nanometric gap size is shown to clearly depend on the particular alignment of the gap forming facets, and thus, the gap capacitor properties.