Fabrication of a porous SiO2 thin film with an ultralow refractive index for anti-reflective coatings

Anti-reflective (AR) coatings are used in various optical products, such as lenses, filters, and transparent conductive films. High-performance multilayer AR coatings can be achieved by reducing the refractive index of the top layer. Preventing light scattering by forming finely structured film is a...

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Bibliographic Details
Published in:Journal of sol-gel science and technology 2023-06, Vol.106 (3), p.860-868
Main Author: Suzuki, Ryoko
Format: Article
Language:English
Subjects:
Antireflection coatings
Ceramics
Chemistry and Materials Science
Composites
Fluid filters
Glass
Hydrophobicity
Inorganic Chemistry
Lenses
Light scattering
Materials Science
Multilayers
Nanotechnology
Natural Materials
Optical and Electronic Materials
Optical instruments
Original Paper: Sol-gel and hybrid materials for optical
photonic and optoelectronic applications
Refractivity
Silicon dioxide
Sol-gel processes
Solvents
Thin films
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Summary:Anti-reflective (AR) coatings are used in various optical products, such as lenses, filters, and transparent conductive films. High-performance multilayer AR coatings can be achieved by reducing the refractive index of the top layer. Preventing light scattering by forming finely structured film is also important for a high-performance antireflection film. In this study, porous SiO 2 thin films with ultralow refractive indices were prepared using a simple sol–gel method. A high-quality porous SiO 2 thin film with an ultralow refractive index of 1.17 bearing a fine porous structure was fabricated by carefully selecting the solvent and base species. Observation and simulation of the film structure revealed the factors responsible for the low scattering of light and the ultralow refractive index exhibited by the film. Hydrophobic treatment of the film was conducted to reduce the fluctuation of optical performance caused by changes in the refractive index owing to the water adsorbed. Therefore, porous SiO 2 thin films can be used in the lenses and filters of various optical instruments. Graphical abstract A transparent film with low refractive index was obtained. The film has porous structure, consisting of silica particles of a few nm in size. The pores size was found to be a few nm by image analysis. Thin films with low refractive index and low scattering for optics were successfully prepared by a simple sol–gel method. Highlights Ultralow refractive index porous silica film, n  = 1.17, was prepared using a simple sol–gel method. Decreasing of light scattering was achieved by choice of basic catalyst and solvent. Hydrophobic treatment successfully reduced the fluctuation of the refractive index of the film.
ISSN:0928-0707
1573-4846
DOI:10.1007/s10971-023-06108-8