Metal oxide thin films coated evanescent wave based fiber optic VOC sensor

Abstract

Recently, there has been an increase in the demand for sensor devices that monitor the concentration of volatile organic compounds (VOC) for disease severity prognosis. This paper reports an experimental analysis of evanescent wave-based fiber optic VOC sensor utilizing clad modification technique. Zinc oxide (ZnO), aluminum-doped zinc oxide (AZO), and tin oxide (SnO2) thin films are individually deposited over the unclad portion of the optical fiber using Radiofrequency (RF) magnetron sputtering. The deposited metal oxide thin films were characterized using the Scanning Electron Microscope (SEM), Energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Ultraviolet-visible (UV-Vis) spectroscopy, and Ellipsometer device. Spectral characteristics of all three sensor probes were tested for different VOCs: acetone, acetophenone, ethanol, and isopropanol (IPA), with concentrations varying from 0 to 250 ppm. Among them, SnO2 coated sensor probe shows the maximum sensor response of 21.2% towards 250 ppm IPA, with a response and recovery times of ~17 and ~21 s, respectively. In addition to the intensity variation, the prepared sensor probes also exhibit the wavelength shift due to the lossy mode resonance phenomenon. Specifically, SnO2 coated sensor probe shows a maximum wavelength shift of 2.4% towards 250 ppm IPA. The detection limit of the SnO2 coated sensor probe was observed to be 300 ppb.