All niobia Bragg stacks for optical sensing of vapors

Vapor responsive all Nb₂O₅ Bragg stacks were prepared using spin-coating of alternating dense and porous films with quarter-wavelength thickness. The required porosity in the films was achieved by soft-templating method using micellar solution of Pluronic copolymer as an organic template. The surface morphology and structure of the films were studied by transmission electron microscopy and selected area electron diffraction, respectively, while optical characterization was performed by combination of ellipsometric and reflectance measurements. Vapor sensing response of the films was tested by reflectance measurements of the samples prior to and after exposure to acetone vapors selected as probe molecules. Incorporation of “defect” layer in the multilayered structures was firstly simulated theoretically and then realized experimentally aiming at improvement of the optical response to volatile organic compounds. Furthermore, the potential of all niobia stacks consisting of alternating dense and porous sol–gel Nb₂O₅ films as chemical sensors with optical read-out is demonstrated and discussed.