  Illuminated gapped-gold-nanorod dimers hold surface plasmon polaritons (SPPs)
that can be engineered, by an appropriate choice of geometrical parameters, to
enhance the electromagnetic field at the gap, allowing applications in
molecular detection via surface-enhanced Raman spectroscopy (SERS). Envisioning
hybrid devices in which the SERS spectroscopy of molecules in the gap is
complemented by electrical measurements, it arises the question of designing
efficient geometries to contact the nanorods without decreasing the enhancement
factor (EF) of the nanoantenna, i.e., the figure of merit for SERS
spectroscopy. Within this framework we theoretically study the feasibility to
fabricate designs based on covering with gold the far-from-the-gap areas of the
dimer. We show that by tuning the geometrical parameters of the designs these
systems can reach enhancement factors larger than the best achieved in the
uncovered dimer: this supremacy survives even in the presence of dimer
asymmetries and vacancies at the interfaces between the nanorods and the
covering layers. Our results show that geometrical modifications away from the
gap can improve the optical response at the gap, thus enabling the use of these
devices both for hybrid and optical applications.
