Optical Detection of VOC Vapors Using Nb2O5 Bragg Stack in Transmission Mode

Rosen Georgiev,Tsvetanka Babeva,Yoana Chorbadzhiyska,Biliana Georgieva,Venelin Pavlov

doi:10.3390/photonics8090399

Abstract

In this study, an emphasis is put on vapor-sensitive Bragg stacks as an important class of optical sensors. All-niobia Bragg stacks were deposited by spin-coating of sol-gel Nb2O5 thin films alternated with mesoporous layers after proper design through optimization of operating wavelength and number of layers in the stack. Mesoporous Nb2O5 films with different morphology and identical structure were obtained using organic templates (Pluronics PE6200 and PE6800) and subsequent annealing. Transmittance measurements were performed as a detection method that offers technological simplicity and accuracy. It was demonstrated that stacks including PE6200 templated films exhibit higher sensitivity than stacks templated with PE6800. It was assumed and verified by computer-aided modelling of experimental data that mesoporous films prepared with addition of PE6200, although less porous, were more stable compared to those templated with PE6800, and did not collapse during the thermal treatment of the stacks. Furthermore, the reproducibility of optical response was studied by sorption and desorption cycles of acetone vapors. The suitability of all-niobia Bragg stacks for optical sensing of VOCs was discussed.

Highlights

Nb2 O5 Bragg Stack in TransmissionConventional Bragg stacks are structures that consist of alternatingly deposited two materials having low and high refractive indices and quarter-wavelength optical thickness, which allow constructive and destructive interference of multiple reflected and transmitted light waves, respectively, engineering a photonic band gap of high reflectance and low transmittance of photons of particular energy
The most common approach in inorganic vapor sensitive Bragg stack deposition is the inclusion of mesoporous material layers, which are inherently extremely sensitive to the environment changes due to their unique properties such as controllable pore size [5,6]
The morphology of films was studied by TEM, while their amorphous structure was confirmed by Selected Area Electron Diffraction (SAED)

Summary

Introduction

Conventional Bragg stacks are structures that consist of alternatingly deposited two materials having low and high refractive indices and quarter-wavelength optical thickness, which allow constructive and destructive interference of multiple reflected and transmitted light waves, respectively, engineering a photonic band gap of high reflectance and low transmittance of photons of particular energy. Those structures have been a focus of research due to their ability to control the propagation of light in various ways [1,2,3]. To the best of our knowledge the most common combination reported in the literature is TiO2 /SiO2 , which is, challenging itself due to the considerable

Methods

Results

Conclusion