The optical applications of 3D sub-wavelength block-copolymer nanostructured functional materials

TL;DR

This paper presents a novel nanostructuring method using block-copolymer templating to engineer the refractive indices of various materials in the deep sub-wavelength regime, enabling advanced optical applications like anti-reflection coatings and hydrogen sensors.

Contribution

It introduces a wet processing route for precise refractive index control in 3D nanostructures, expanding capabilities for optical design and sensor development.

Findings

Refractive indices from 1.17 to 2.2 achieved in nanostructured materials.

Anti-reflection coatings reduced reflection from 38% to ~3%.

High-temperature hydrogen sensor demonstrated with enhanced sensitivity.

Abstract

A method to engineer the refractive indices of functional materials (TiO2, ZnO, SnO2, SiO2), by nanostructuring in the deep sub-wavelength regime (<20nm), is presented. Block-copolymer templating combined with a wet processing route is used to realize 3D functional nanostructures with continuously adjustable refractive indices from 1.17 to 2.2. Wet processing accessed refractive index engineering can be applied to address a variety of realizability concerns in attaining design specified refractive index values and refractive index gradients in 1D, 2D, and 3D that arise as the results of optical design techniques such as thin film optimization methods, transformation optics and conformal mapping. Refractive index optimized multi-layer anti-reflection coatings on crystalline silicon, which reduce light reflections from 38% down to ~3% with a wide angular span, are demonstrated with the developed wet processing route. A high temperature oxygen free fiber optic hydrogen sensor realized by accessing nano-engineering enabled refractive indices is also presented. The functionality of the sensor is characterized with a fiber Bragg grating, transmission based interrogation, and optical frequency domain reflectometry. The latter demonstrates the potential of the developed sensor for the detection of chemical gradients for applications such as in high temperature hydrogen driven fuel cells.