Robust operation of mesoporous antireflective coatings under variable ambient conditions

Abstract

Antireflective coatings (ARCs) are important components in optical applications due to their ability to reduce reflection and maximize transmission of light across interfaces. Generating mesoporous films with adequate film thickness and refractive index is a common method to achieve amplitude and phase matching in low-cost single- layer interference-based ARCs. For high surface energy materials, pores on the 2 - 50 nm, i.e. the sub-wavelength scale, are subject to capillary condensation, and pore filling by surrounding gas phase water molecules at size-characteristic humidity values hampers their functioning. In this work, we examine the effect of relative humidity on mesoporous ARCs and present a simple method for the preparation of ARCs with robust operation under variable conditions. The materials route is based on the generation of well-defined porous aluminosilicate networks by block copolymer co- assembly with poly(isobutylene)block-poly(ethylene oxide) and post-synthesis grafting of trichloro(octyl)silane molecules to the pore walls. The functionalized films exhibited a maximum transmittance value of 99.8% with an average transmittance of 99.1% in the visible wavelength range from 400 nm to 700 nm. Crucially, the AR performance was maintained at high humidity values with an average transmittance decrease of only 0.2% and maximum values maintained at 99.7 %, which compared to maximum and average losses of 3.6% and 2.7 %, respectively, for non-functionalized reference samples. The ARCs were shown to withstand at least 50 humidity cycles, indicating long-term stability against fluctuating environmental conditions.

Tuning Pore Dimensions of Mesoporous Inorganic Films by Homopolymer Swelling

“…36,38,65 Calculation of individual and overall pore volume Alongside expanded pore sizes were expected with increasing HP content, concurrent rises in sample porosity and film thickness were also observed with higher contents of HP (Figure 1d,e & Table S1, Supplementary Information) It is well established that, when preparing mesoporous films from BCP SDAs, the sample porosity is directly related to the BCP to inorganic ratio. 2,3 While all samples were prepared with a constant BCP to inorganic ratio (Table 1), the porosity increased from ≈50% in BCP ref to as high as ≈60% in BCP/PIB1500 0.8 as a consequence of the HP addition. Similarly, thickness values were found to gradually rise in BCP/HP samples with higher HP content.…”

“…57 Application of the Lorentz-Lorentz effective medium approximation allowed accurate determination of the overall porosity of each sample based on the change in refractive index as a consequence of capillary conden-sation inside the mesopores. 3 The incremental onset of capillary condensation was related to the pore diameter of the material via the Kelvin Equation. 57,58 Pore size and pore volume measurements were derived from the adsorption branches of the EP porosity isotherm and adjusted based on the assumption of an ellipsoidal pore shape which evolves with film contraction during template removal.…”

“…This correlates with previously reported results using similar materials. 2,3,17 Figure 5: AFM images of all HP swollen samples. (a) BCP/PIB800 0.3 , (b)BCP/PIB800 0.5 , (c)BCP/PIB800 0.8 , (d) BCP/PIB1500 0.3 , (e)BCP/PIB1500 0.5 , (f)BCP/PIB1500 0.8 .…”

“…Mesoporous inorganic film architectures are important components in applications such as photovoltaics, 1 protective optical coatings, 2,3 nanophotonics, 4 superconductors 5 and varied sensing applications. [6][7][8] A number of bottom-up self assembly methods offer control over the mesoscale material arrangement, including colloidal self-assembly, 9 polymeric porogens, 8,10 and sacrificial "structure-directing agents" (SDAs) such as small molecule surfactants 11,12 or block copolymers (BCPs) [13][14][15] These SDAs interact with inorganic precursors (typically sol-gel derived) in solution and produce ordered hybrid films via evaporation induced coassembly before being removed to reveal the porous network.…”

Tuning Pore Dimensions of Mesoporous Inorganic Films by Homopolymer Swelling

“…Mesoporous inorganic film architectures are important components in applications such as photovoltaics, 1 protective optical coatings, 2,3 nanophotonics, 4 superconductors 5 and varied sensing applications. [6][7][8] A number of bottom-up self assembly methods offer control over the mesoscale material arrangement, including colloidal self-assembly, 9 polymeric porogens, 8,10 and sacrificial "structure-directing agents" (SDAs) such as small molecule surfactants 11,12 or block copolymers (BCPs) [13][14][15] These SDAs interact with inorganic precursors (typically sol-gel derived) in solution and produce ordered hybrid films via evaporation induced coassembly before being removed to reveal the porous network.…”