# Self-Organized Conductive Gratings of Au Nanostripe Dimers Enable Tunable Plasmonic Activity
## 2 Results and Discussion
### Plasmon Hybridization in Nanostripe Dimer Arrays
The simulations of Figure 4a clearly show a strong red-shift of the MD mode from about 600 nm to 1300 nm wavelength, as the aspect ratio _h/w_ decreases from 0.35 (violet curve) to 0.12 (black curve), while the spectral position of the ED mode is here weakly dependent on the morphology. In parallel, both the ED and the MD mode are characterized by a pronounced spectral broadening as _h/w_ decreases, with a subsequent reduction of efficiency in terms of field enhancement. Note that this trend in broadening is precisely in line with the hybridization mechanism, according to which the plasmonic resonances of  
Figure 3: (**a**) Cross-section sketch of the Au-SiO\({}_{2}\)-Au nanostripe dimers; (**b,c**) cross-section and top-view SEM image of the nanostripe dimer arrays, respectively. The scale bars correspond to 500 nm and 1 μm, respectively; (**d**) extinction optical spectra for the TM-polarized excitation of Au nanostripe (black curve), Au-silica (blue curve) and Au-silica-Au nanostripe dimer arrays (red curve). The nanostripes’ width was fixed at about 105 nm, while the local thickness of the Au-silica-Au layers was set at 30-44-30 nm respectively; and (**e,f**) FEM simulation of the near field distribution for nanostripe dimer excited in resonance with the plasmonic electric- and magnetic-dipole mode (550 nm and 700 nm wavelength), respectively. the hybridized system (nanostripe dimer) basically inherit the broadening of the plasmonic resonance of the individual monomers, which for a nanostripe increases with decreasing values of _lhw_[37; 38]. The experimental proof of this behavior is provided by the extinction spectra (Figure 4b), where the tuning of the MD mode is demonstrated by tailoring the shape of the nanostripe dimers. In particular, the width \(w\) was fixed at about 105 nm, while the local thickness of the Au or of the silica layer was changed. If the dielectric spacer is kept constant at 44 nm and the Au thickness is reduced from 30 nm (red spectrum) to 22 nm (green spectrum), a softening and red shift of the hybridized plasmonic resonances is detected, as expected based on the theoretical calculations and in line with the theoretical predictions reported in References [37; 38]. Indeed, retardation effects determined by thickness-dependent propagation phase shifts strongly affect the longitudinal resonances of single stripe and dimer stripe nanoresonators. In parallel, a strong red shift in the NIR spectrum is observed when the silica thickness decreases to 22 nm (black spectrum in Figure 4b), due to the increase in the coupling strength of the antibonding hybridized nanostripe resonances, which is also in quantitative agreement with the calculated spectra of Figure 4a. An unexpected red shift of the ED mode from 550 nm to 580 nm wavelength is also observed when the thickness of the silica is reduced to 22 nm, which is not in accordance with the pure hybridization model. We attribute this small spectral shift to a change (reduction) of the refractive index of the silica layer in the case of a thinner film, due to a slight difference in the stoichiometry obtained by RF sputtering deposition.