Electromagnetic enhancement of one-dimensional plasmonic hotspots along silver nanowire dimer examined by ultrafast surface enhanced fluorescence

TL;DR

This study explores electromagnetic enhancement in one-dimensional hotspots between silver nanowire dimers using ultrafast surface-enhanced fluorescence, revealing non-superradiant plasmon contributions and the influence of nanowire morphology.

Contribution

It provides experimental and numerical insights into the spectral properties and mechanisms of EM enhancement in silver nanowire dimers, highlighting the role of subradiant modes.

Findings

EM enhancement spectra can deviate from plasmon resonance Rayleigh scattering spectra.

Dipole-quadrupole coupled plasmons mainly generate EM enhancement in larger nanowires.

Numerical calculations reproduce the observed spectral deviations based on nanowire diameter.

Abstract

We investigated the spectral properties of electromagnetic (EM) enhancement of one-dimensional hotspots (1D HSs) generated between silver nanowire (NW) dimers. The EM enhancement spectra were directly derived by dividing the spectra of ultrafast surface-enhanced fluorescence (UFSEF) from single NW dimers with UFSEF obtained from large nanoparticle aggregates, which aggregate-by-aggregate variations in the UFSEF spectra were averaged out. Some NW dimers were found to exhibit EM enhancement spectra that deviated from the plasmon resonance Rayleigh scattering spectra, indicating that their EM enhancement was not generated by superradiant plasmons. These experimental results were examined by numerical calculation based on the EM mechanism by varying the morphology of the NW dimers. The calculations reproduced the spectral deviations as the NW diameter dependence of EM enhancement. Phase analysis of the enhanced EM near fields along the 1D HSs revealed that the dipole-quadrupole coupled plasmon, which is a subradiant mode, mainly generates EM enhancement for dimers with NW diameters larger than ~80 nm, which was consistent with scanning electron microscopic measurements.