## 3 Results
### Optical Properties of Nanostructured Glasses  
In order to characterize the optical performance of the nanostructured glass templates, we performed total integrated reflectance and haze measurements on the whole set of samples so far described (Samples 1, 1-T, 2, 2-T, 3, 3-T). In Figure 4a we study the differential variation of the total integrated reflectance in the Vis-NIR range (450-1000 nm) of the nanostructured glass substrates normalized to a flat reference borosilicate glass, according to the equation \(\mid\Delta R/R\mid\) = \(\mid(R_{\text{nano}}-R_{\text{flat}})/R_{\text{flat}}\mid\), where \(R_{\text{flat}}\approx 8\%\). All of the diffuse reflectance measurements were carried out by means of an integrating sphere setup. The \(\Delta R/R\) quantity describes the amount of anti-reflective effects present on nanostructured samples. Sample 2 and 2-T (blue squares and open triangles, respectively) reflect about 12% and 20% less light than a flat glass averaged on the whole Vis-NIR range of wavelengths. To summarize the information relative to all samples synthesized at different ion fluences, in Figure 4b (left scale) we plot the mean values of \(\Delta R/R\), integrated over the wavelength range \(\Delta\lambda\) = [450 nm; 1000 nm]. As the fluence is increased in the A-IPL process, the total reflectance raises towards the values of the flat glass and the antireflective effect vanishes. In particular, we observe an average reduction of reflectance from 23% (Sample 1-T) to 20% (Sample 2-T) to 6% (Sample 3-T-open red triangles). Correspondingly, for the samples without Ti, the average reduction of reflectance goes from 14% in Sample 1, to 5% for Sample 3 (blue squares). In other words, by modulating ion fluence one can control broadband anti-reflective effects, which are particularly enhanced in presence of the Ti layer. Such behavior is in qualitative agreement with the \"moth-eye\" effect observed in bio-mimetic systems [30]. In fact, high aspect ratio corrugations, whose amplitude is a significant fraction of the incident light wavelength and whose lateral size is below the diffraction limit, allow us to gradually match the refractive indexes of substrate and air, leading to a suppression of reflectance (index-grading effect [29; 31]). The morphological analysis carried out on the six samples (Figure 3b) confirms that the Ti layer leads to the formation of more ordered patterns endowed with smaller scale non-diffractive features for photons belonging to the Vis-NIR spectrum. The observed index-grading anti-reflective behavior is predominant in Sample 1-T, which has the smallest correlation length in the range of 105 nm. We stress that these features can be useful for all kinds of applications in which a decrease of surface reflectivity is an important issue, as in de-trapping schemes employed in LED/OLED applications [32]. At a higher ion fluence, the lateral correlation length of the spatial corrugations increases due to coarsening: the importance of the moth-eye antireflection effect decreases and large angle diffuse scattering becomes predominant [21; 33]. In view of light trapping applications employing the self-organized glass gratings, we stress that the scattering efficiency can be of predominant importance with respect to the anti-reflection behavior; enhanced light absorption in a PV device can in fact be achieved when scattered photons penetrate the absorber layer at the grazing angle and eventually are coupled to wave-guided modes by total internal reflection [34]. The scattering efficiency of the substrate, quantified as the ratio of diffuse reflectance to total reflectance (Haze), is determined experimentally by means of an integrating sphere. In Figure 4a, the haze signals measured on sample 2 (blue line) and 2-T (red-dashed line) are reported as a function of light wavelength.