Elimination of cracks in self-assembled photonic band gap crystals

TL;DR

This study demonstrates that pre-sintering silica spheres prevents cracks in self-assembled photonic band gap crystals, with heat treatment parameters affecting the silica's properties and refractive index.

Contribution

It introduces a method of pre-sintering silica spheres to eliminate cracks in photonic crystals, and explores how heat treatment influences silica's properties and refractive index.

Findings

Pre-sintering silica spheres prevents crack formation.

Heat treatment affects silica's refractive index.

Refractive index can be tuned via temperature.

Abstract

Thin colloidal crystals (or synthetic opals) composed of Stober silica spheres typically develop cracks when they are utilized to obtain photonic band gap crystals (or inverted opals). We find that by sintering the silica spheres prior to assembly of the opal these cracks can be avoided. We report the effects of temperature and duration of the heat treatment on 850 nm silica spheres using electron microscopy, thermogravimetry, and light scattering. We also find a large dependence of the refractive index of the silica on the temperature of the heat treatment. This may allow tuning of the refractive index of silica spheres.