Encapsulation of low-refractive-index SiO2 nanorods by Al2O3 with atomic layer deposition

Thin films composed of SiO2 nanorods or nanoporous SiO2 (npSiO(2)) are attractive for use as a low refractive index material in various types of optical coatings. However, the material properties of these films are unstable because of the high porosity of the films. This is particularly apparent in dry versus humid atmospheres where both the refractive index and coefficient of thermal expansion (CTE) vary dramatically. In this article, we demonstrate that np-SiO2 can be encapsulated by depositing Al2O3 with Atomic Layer Deposition (ALD), stabilizing these properties. In addition, this encapsulation ability is demonstrated successfully in a 4-pair distributed Bragg reflector (DBR) design. It is hoped that this technique will be useful in patterning specific regions of a film for optical and mechanical stability while other portions are ambient-interactive for sensing. (c) 2007 Optical Society of America.