Rh in the gap: maximizing E-field enhancement within nanorod heterodimers

Bimetallic AuRh_Au nanorod (NR) dimers, composed of AuRh and Au NRs separated by nanoscale distances, are synthesized via on-wire lithography (OWL). The influence of a thin lossy Rh segment inserted within the gap region is studied using electron energy loss spectroscopy (EELS), electromagnetic simulations and surface-enhanced Raman spectroscopy (SERS). We provide experimental evidence of strong E-field enhancement at the Rh segment due to the formation of plasmonic hot spots within the gap. The similarity of the plasmonic modes measured on the Au_Au and AuRh_Au NR dimers demonstrates a strong coupling between the Au NR antennas regardless of the presence of Rh. The effect of NR length, gap size, Rh location, and NR dimer asymmetry is investigated to provide simple design rules for maximizing the E-field at a given wavelength within and on the Rh. Such bimetallic NR dimers, which can be synthesized via OWL, are versatile platforms for studying strong plasmonic coupling within heterostructures, with potential uses in plasmonic catalysis.