## 3 Results
### Optical Properties of Nanostructured Glasses
Haze values decrease from 60% to 45% (43% to 28%) in the wavelength range 450-1000 nm; a comparison with conventional Asahi-U reference substrates, measured in the same experimental condition, which exhibit haze values in the range 30%-2% [35] demonstrates the remarkable scattering efficiency of the novel substrates. The broadband scattering efficiency is high across the whole Vis-NIR spectrum and can be ascribed to the multiscale and pseudo-periodic nature of the self-organized structures highlighted in the reciprocal space spectral analysis (1D-PSD in Figure 3a and AFM data shown in Figure 2). The possibility to engineer the roughness spectrum of the nanostructured patterns, either by varying ion fluence or by adding a Ti adhesion layer, allows us to selectively enhance the scattering efficiency or the antireflective properties of the self-organized surfaces. The high haze of Sample 2 can be attributed to the presence of large scale spatial modulations which contribute to the 1D-PSD (Figure 3a blue trace) in the small wavenumber region below 1.5 \(\times\) 10\({}^{-3}\) nm\({}^{-1}\). On the contrary, the moth-eye antireflective effect measured on Sample 2-T can be attributed to the presence of small scale structures, as witnessed by the cross-over of the 1D-PSD (Figure 3a red trace) observed in the large wavenumber region above 1.5 \(\times\) 10\({}^{-3}\) nm\({}^{-1}\). Figure 4: **(a)** Left scale: differential variation of the optical reflectance \(\Delta R/R\) with respect to the flat reference glass measured on nanostructured Sample 2 (squares) and 2-T (open triangles), integrated in angle. Right scale: solid and dashed lines refer to optical haze in reflection measured on Sample 2 and 2-T, respectively; **(b)** Spectrally averaged values of haze and \(\Delta R/R\) are reported as function of ion fluence; **(c,d)** Picture of light scattered in transmission configuration across flat and patterned glass as sketched in **(e)**. Light is waveguided and scattered orthogonal to the ripples which run horizontally. For what concerns the light scattering performance of the substrates prepared with different ion fluences, in Figure 4b (right scale) we summarize the average values of haze integrated over the whole spectral range (full and open circles refer to samples with and without Ti, respectively). One can notice that (i) higher haze values are observed for samples exposed to larger ion fluences; (ii) at fixed ion dose, haze is higher on the sample prepared without Ti adhesion layer. These observations can be rationalized in terms of the morphological evolution of the substrates with ion fluence summarized in Figure 3b. The RMS roughness and the lateral correlation length of the structures become larger (coarsening) as a consequence of dewetting of Au NWs mask, especially in absence of Ti. Due to coarsening, the dominant lateral size of the surface features grows at a point that scattering (haze) increases while index grading (mod-eye anti-reflective effect) decreases, as observed in the \(\Delta R/R\) trace of Figure 4b. A further aspect, of paramount importance for light trapping amplification in opto-electronic devices, is represented by the possibility to couple incoming light to wave-guided modes which confine propagation in the high refractive index layers formed by the substrate and absorber film [36; 37]. In Figure 4d (see also sketch in Figure 4e), we directly visualize the presence of waveguided light which propagates laterally via internal reflection through the slab after being scattered at the textured glass interface. A light beam is propagated through the nanostructured glass slab in transmission geometry (pattern analogous to Sample 2), while the directly transmitted component is blocked by a beam stopper. Red dashed lines indicate the glass borders, while white dashed lines highlight the limits of the patterned area. Pictures have been taken from the top side in absence of ambient light, excluding the direct beam in order to avoid saturation of the camera.