Enhancement in broadband and quasi-omnidirectional antireflection of nanopillar arrays by ion milling

Abstract

A new technique is developed to fabricate biomimetic antireflection coatings (ARCs). This technique combines a bottom-up fabrication approach (glancing angle deposition, or GLAD) with a top-down engineering process (ion milling). The GLAD technique is first utilized to produce nanopillar arrays (NPAs) with broadened structures, which are subsequently transformed into biomimetic tapered geometries by means of post-deposition ion milling. This structure transformation, due to milling-induced mass redistribution, remarkably decreases reflection over a wide wavelength range (300-1700 nm) and field of view (angle of incidence < 60° with respect to the substrate normal). The milling-induced antireflection enhancement has been demonstrated in the NPAs made of Si, SiO(x) and TiO(2), illustrating that this integrated technique is readily adapted to a wide variety of materials. Good agreement between simulation and experiment indicates that the enhanced antireflection performance is ascribed to a smoother refractive index transition from the substrate to the air, which improves the impedance match and reduces reflection losses. Additionally, ion bombardment tends to alter the stoichiometry and diminish the crystallographic structure of the NPA materials. The broadband and quasi-omnidirectional antireflection observed establishes the strong competitiveness of this technique with the methods previously reported.

Wafer-scale, three-dimensional helical porous thin films deposited at a glancing angle

“…In principle, the ARC is located at the air/substrate interface and has a refractive index (n r ) between that of air and the substrate. 66 For example, on glass SiO 2 CHPTFs were deposited at r r of 0.07 rpm, as function of a in the range of 0-85 . 67 n r of SiO 2 CHPTFs decreases with a, owing to the a-induced porosication in the CHPTFs.…”

Monolithic graded-refractive-index glass-based antireflective coatings: broadband/omnidirectional light harvesting and self-cleaning characteristics

“…14,15 However, commercially such graded-index-coatings presently are very challenging, being mainly based on either expensive, elaborate and limited resolution top-down lithography techniques (e.g., photolithography, e-beam lithography, nanoimprint lithography, interference lithography) [16][17][18][19][20] or on bottom-up approaches (e.g., colloidal self-assembly, anodic alumina films, carbon nanotubes), 21,22 or a combination of both. 23 While the latter methods can be relatively cost-effective, they are mostly pertinent to laboratory-scale fabrication. Moreover, coatings based on both general approaches have a propensity to exhibit poor mechanical and thermal stability, impeding the integration into large-scale development and production.…”

Titanium Nanopillar Arrays Functioning as Electron Transporting Layers for Efficient, Anti‐Aging Perovskite Solar Cells

“…Ti columns generally appear to broaden in diameter along with their growth, i.e., the structural broadening (Figure 1c ‐II,d ‐II, and inset in Figure 1e) due to the GLAD‐caused competition effect. [ 18 ] The closely packed arrays have an intercolumn spacing varying in the range of 50–150 nm. The as‐deposited Ti nanostructures generally have rough surfaces (Figure 1e), and are polycrystalline (Figure 1f) with dominant crystal orientation direction along 〈110〉 (Figure 1g).…”