## 3 Results
### Self-Organized Nanopatterning
The vertical scale of projected nanostructures is enhanced since Au adatoms evaporated on the heated surface can diffuse for longer distances until they reach the top of ripples, where they enrich the stencil mask and prolong its lifetime during ion irradiation. At the end of the process, the samples were further exposed to the ion beam until complete removal of the gold stencil mask was achieved. Further details on the A-IPL process can be found in reference [18]. In order to get high aspect ratio and tunable nanostructures capable of optical functionalization of the glass templates in terms of antireflection and light scattering effects [28; 29], the A-IPL process has been applied to different stencil masks endowed with engineered morphologies presented in Figure 1. To this purpose, different substrates were prepared by A-IPL at \(T\) = 700 K and performed on the borosilicate glass with three different ion fluences: \(F_{1}\) = 1.63 \(\times\) 10\({}^{19}\) ions\(\cdot\)cm\({}^{-2}\), \(F_{2}\) = 2.08 \(\times\) 10\({}^{19}\) ions\(\cdot\)cm\({}^{-2}\), and \(F_{3}\) = 2.97 \(\times\) 10\({}^{19}\) ions cm\({}^{-2}\), corresponding to Sample 1, Sample 2, and Sample 3, respectively. For the sake of simplicity, the samples synthesized at the same fluences, but with a Ti layer interposed between the glass and Au film, are named Sample 1-T, Sample 2-T, and Sample 3-T, respectively. In Figure 2a,b the morphology of representative samples prepared respectively in the absence and in presence of titanium, for a given ion fluence (\(F_{2}\)), are compared. Significantly, we can notice that in both cases the pattern transferred from the Au NWs mask into the glass exhibits an almost ten-fold vertical amplification. RMS roughness goes from \(\sigma\) = 17 \(\pm\) 2 nm (11 \(\pm\) 2 nm) to an average \(\sigma\) = 136 \(\pm\) 9 nm (\(\sigma\) = 94 \(\pm\) 8 nm) respectively without (with) Ti. Moreover, nanostructures synthesized in presence of Ti adhesion layer appear more elongated in the longitudinal direction and present a narrower lateral size, as shown by the comparison of line profiles in Figure 2c. In a more quantitative way, the lateral correlation length \(\xi\), reads 220 \(\pm\) 11 nm for Sample 2, while we measure \(\xi\) = 160 \(\pm\) 11 nm in presence of Ti (Sample 2-T). In addition to the morphological tunability favored by Ti adhesion layer, we stress the broadband nature of the pattern presented in Figure 2a,b ensured by the presence of multiscale nanostructures organized in a pseudo-periodic array. Since diffractive properties are dependent on the Fourier spectra  
Figure 2: **(a,b)** AFM topographies (10 \(\upmu\)m \(\times\) 20 \(\upmu\)m) of glasses nanostructured by assisted-ion projection lithography (A-IPL) at 700 K respectively without and with Ti layer with fluence F\({}_{2}\). Vertical scales are 780 nm and 405 nm; **(c)** Selected topographic line profiles from (**a**-green and **b**-red); The root mean square roughness of the surfaces are (**a**) \(\sigma\) = 143 nm, (**b**) \(\sigma\) = 88 nm; **(d)** Sketch of A-IPL process used to synthesize nanostructured glasses sketched in (**e**). Yellow arrow –Au atom from source, Red arrow-Ar ions, Black arrow-Au adatom diffusion from glass to Au nanowires  
of the spatial frequencies, we calculated one dimensional power spectral densities (1D-PSD plotted in Figure 3a) from AFM data acquired on Sample 2 and 2-T, in similar manner to what was done for the \(H_{\text{cf}}(r)\) calculation. Firstly, we highlight the broadband nature of the roughness distribution for both samples: a characteristic of paramount importance in view of optical broadband functionality required in PV applications; secondly, we also emphasize the peculiar behavior of Sample 2-T, which shows higher vertical amplification of surface features with large wavenumbers (small spatial wavelengths), while Sample 2 displays a strongly amplified roughness associated with small wavenumbers (large spatial wavelengths).