Bilayer SiO₂ Nanorod Arrays as Omnidirectional and Thermally Stable Antireflective Coating

Abstract

Nature instigates researchers significantly in imitating to engender comparable properties using artificial methods, which unlocks developing trend in material science and engineering progress. Fabricating graded‐index nanostructures is an effective approach to tune and generate similar properties artificially such as the moth's eye antireflectance (AR) or lotus like superhydrophobicity. Herein, Bilayer AR coatings with periodically arranged SiO2 hierarchical nanostructures resembling moth eyes are fabricated on dense SiO2 matrix base layer using the versatile route of glancing angle deposition technique (GLAD). The refractive indices of monolayer SiO2 are tuned from 1.46 to 1.08 by changing the deposition angle (α) from 0 to 88°. The fabricated bilayer SiO2 AR (BSAR) film possess high optical omnidirectional broadband transparency and tunability at a desired wavelength range showing <1% reflectance. The present AR design is flexible and practically applicable to various supporting substrate materials (η varies from 1.45 to 1.9). Furthermore, the omnidirectional BSAR films show multiple functions including enhanced mechanical strength, the thermal stability (up to 300 °C), and hydrophobic capability with a water contact angle (CA) of 147° to withstand under humid environment. This multipurpose coating provides an intriguing route in optics field for imminent research.

Silicon Nanocone Arrays via Pattern Transfer of Mushroomlike SiO2 Nanopillars for Broadband Antireflective Surfaces

“…The design and fabrication of broadband antireflective surfaces are crucial aspects of maximizing the performance of devices in a wide range of applications, including solar cells, photodetectors, light-emitting diodes (LEDs), and display panels. − In particular, nanoscale silicon (so-called black silicon) is considered to be the most promising candidate for realizing broadband antireflection. , This material contains subwavelength-scale nanostructures that effectively suppress light reflection while enhancing light absorption over wide ranges of wavelengths. Furthermore, the nanoscale texture increases the surface area, which is advantageous in a variety of photofunctional applications.…”

Omnidirectional SiO2 AR Coatings

“…After, annealing at 350 • C, a clear shift of reflectance minima is observed in comparison with as deposit AR coating. The, AR efficacy of SiO 2 AR coating at 350 • C deteriorates due to structural defects, lattice stresses, increased packing density or crystallization [34]. Overall, the SiO 2 AR films are thermally stable up to 300 • C without any deterioration in AR efficiency.…”

“…Overall, the SiO 2 AR films are thermally stable up to 300 • C without any deterioration in AR efficiency. Beyond, this temperature (350 • C), there is a slight increment in AR efficiency due to induced crystallinity, which influences packing density of thin films in the declining of the AR efficacy [34]. …”

“…In, our experiments, we deposit bilayer SiO 2 AR coatings comprised of a dense layer and a porous layer on top of the dense layer to reduce the reflectance of BK7 glass substrate less than 1 percent in the visible region. Firstly, the dense film is deposited on the forward-facing side at deposition angle 0 • having a refractive index of 1.46 at 550 nm wavelength [34]. On, the top of the dense film, a porous vertical nanostructure having lower η than the bottom layer was deposited at an oblique angle (α) of 80 • .…”

“…The, main shortcoming of the sol-gel fabrication method is the narrow choice of supporting substrates. Previously, most of SiO 2 AR coating was assembled on K9 or glass substrates via sol-gel technique [34]. The, pore densification step requires high sintering temperature (200-500 • C), which restricts the fabrication to few substrates [35].…”