Convective Assembly of Antireflective Silica Coatings with Controlled Thickness and Refractive Index

Abstract

Convective assembly at high volume fraction was used to deposit silica nanoparticle coatings onto glass and silicon substrates. By allowing control of the film structure and thickness, this technique provides a means for making large-scale coatings with antireflective properties. The reflectance was reduced by 50% for silicon (at 600 nm) and by 70% for single glass/air surface. Microstructural investigations using SEM, AFM, profilometry, and ellipsometry provided good correlation to the observed macroscopic optical properties. By virtue of the coatings' uniformity, the reflectance and transmission spectra from both substrates could be modeled well by classical reflection relations, using a volume-averaged refractive index. Data analysis showed that the relatively high packing fraction in nanocoatings made from monodisperse spheres is responsible for the limit on antireflective capabilities. To overcome this restriction, low-density silica coatings were made from binary colloidal mixtures of different diameter SiO2 particles. The packing fraction of these coatings was further optimized to yield 88% maximal reduction in the reflectance of glass surfaces. The technique is simple, inexpensive, and scalable.

Synthesis and Characterization of High Refractive Index Polyimides Derived from 4,4′-(p-Phenylenedisulfanyl)dianiline and Various Aromatic Tetracarboxylic Dianhydrides

“…1,2 Recently, much attention has been paid to the applications of PIs in optical devices, including optical waveguides, anti-reflection films, lens, optical image sensors, and so on. [3][4][5][6] The most widely studied PIs for optical applications are fluorinated ones, which exhibit the good processability, thermal stability, low dielectric constants and refractive indices, combined with good transparency in the visible region as well as at the near infrared wavelengths for telecommunication (1.3 mm and 1.55 mm). [7][8][9] Although a variety of PIs for optical applications have been reported, sulfur-containing polyimides have rarely been introduced.…”

Addition of silica nanoparticles to tailor the mechanical properties of nanofibrillated cellulose thin films

“…The distribution of silica nanoparticles in the film as well as the porosity may result in a final value that is far lower than the value of bulk silica. For some optical applications, anti-reflective coatings are of interest in order to maximize the light transmitted and to minimize that reflected through a certain void [31][32][33][34][35][36]. The principle of antireflection is the destructive interference occurring between the reflected beams at the substrate-film interface and that at the film-air interface [37].…”

Preparation of mechanically stable triple-layer interference broadband antireflective coatings with self-cleaning property by sol–gel technique

“…Meanwhile, the sintering process can further improve coating strength and adhesion to glass substrates. 55,56 Therefore, the triple-layer lm, which adopted acid catalyzed coatings as lm material, showed good mechanical property. The lm material of the bottom layer used in this work was acid catalyzed silica-titania composite lm, considered to be robust and have good adhesion to the substrate.…”