# Self-Organized Conductive Gratings of Au Nanostripe Dimers Enable Tunable Plasmonic Activity
## 2 Results and Discussion  
### Plasmonic and Conductive Nanostripe Arrays  
Quasi-one dimensional (1D) nanopatterns are homogenously prepared at the glass surface by anisotropic nanoscale wrinkling. High-aspect-ratio subwavelength nanoripples extending over a large area (cm\({}^{2}\)) can be fabricated by a defocused ion beam irradiation performed near the glass transition temperature (see Supporting Information for experimental details). Periodic quasi-1D nanoripples as long as several micrometers and characterized by a mean height of about 80 nm are shown in Figure 1a,b (AFM topography and cross section profile). The rippling mechanism drives the peculiar growth of facets at the amorphous surface, which are asymmetrically tilted out of plane [30; 32], as sketched by the in-scale cross-section profiles of Figure 1d,e. In particular, the ridges directly exposed to the ion beam irradiation exhibit typical slopes of \(\alpha\) exceeding 50\({}^{\circ}\), while the opposite show highly defined orientation at about 30\({}^{\circ}\) (Supporting Information, Figure S1). This morphology enables the maskless and homogenous confinement of metallic nanostripes whose geometrical configuration can be tailored by changing the Au-illuminated ridges and/or the metal dose over large-area templates (several cm\({}^{2}\), as shown by the sample picture in Figure 1c and by the SEM images in Figure S2 of Supporting Information). Two representative examples are shown in the Scanning Electron Microscopy (SEM) images of Figure 1f,g, corresponding to Au growth on the wider facets (tilt of about 30\({}^{\circ}\)) and on the smaller ones (tilt of about 50\({}^{\circ}\)) [31]. Glancing angle Au evaporation has here been performed at \(\theta_{1}=50^{\circ}\) (Figure 1h,f) and at \(\theta_{2}=70^{\circ}\) (Figure 1e-g), respectively, enabling the growth of laterally disconnected Au nanostripes as long as several micrometers on the metal-illuminated facets. The local thickness of the nanostripes reading \(h=t_{0}\times cos\) (\(\theta\)-\(\alpha\)) has been here fixed at 22 nm, while their characteristic width \(w\) has been tailored from about 105 nm (Figure 1f) to about 85 nm (Figure 1g), as imposed by the underlying pattern and the metal deposition angle. The high-resolution SEM images highlight the subwavelength lateral disconnection of the nanostripes, while the longitudinal continuity is preserved even at the inter-ripples defect points. Under this condition, strongly anisotropic optical and electrical behavior is expected. The optical response of these arrays has been probed via far-field extinction spectroscopy across the near-UV, VIS and near-IR spectrum by using a broadband light source collimated over a macroscopic optical spot (diameter of about 3 mm), polarized either longitudinally or transversely, with respect to the major axis of the nanostripes. The optical transmission spectra of both wide nanostripes (Figure 2a) and narrow steeper stripes (Figure 2b) are strongly dichroic, showing the optical response typical of a continuous film under longitudinal polarization (TE-pol, continuous lines) and behaving as plasmonic nanoantennas under transversal polarization (TM-pol, dashed lines). In the first case (Figure 2a), the optical response has been modulated by confining Au nanostripes of thickness \(h\) = 22 nm (blue curves) and \(h\) = 30 nm (red curves) by evaporation at the incidence angle \(\theta_{1}\) = 50\({}^{\circ}\) (Figure 1f). For TE-polarization, the spectral response of these gratings is characterized by a maximum 530 nm wavelength due to the onset of Au inter-band transitions at higher energies, while the transmittance gradually decreases above 560 nm, corresponding to increasing reflectance at lower energies. Conversely, for transversal polarization with respect to the nanostripes (TM), a narrow-band transmission minimum is detected in the VIS spectrum (dashed blue and red curve) due to the excitation of a localized surface plasmon (LSP) resonance in the nanostripe antennas.