Anodizing charge density controls the porosity of anodic titanium oxide photonic crystals

Abstract

Anodic titanium oxide (ATO) one-dimensional photonic crystals (PhCs) are materials with uniaxial periodic modulation of porosity. A periodic change of an effective refractive index caused by porosity modulation results in the formation of photonic band gaps (PBGs). The non-uniform dissolution of ATO cell walls during the fabrication process hampers the obtaining of a strict optical periodicity of ATO PhCs. Recently it was found that the dissolution of ATO cell walls is accelerated by anodic polarization. However, the main factor controlling the accelerated dissolution of ATO cell walls during anodizing remains unclear. In this study, the correlation between ATO PhC porosity and the charge density is discussed. The dependencies of the spectral photonic band gap (PBG) position and PBG reflectance on the charge density are studied experimentally. The findings open a pathway to the synthesis of ATO PhCs with flawless optical periodicity and high PBG reflectance.