Optical Gas Sensor based on Al-doped ZnO/ZnTPP hybrid thin film

Abstract

Hybrid optical gas sensors based on Al-doped ZnO/Zinc porphyrin (AZO/ZnTPP) thin films have been fabricated and demonstrated to detect ethanol vapor. Double-sensing layer of AZO and ZnTPP films were deposited on a cleaned glass substrate by RF magnetron sputtering and spin-coating techniques, respectively. We have investigated the influences of Al-doping concentration (0%, 2% and 3 wt% Al2O3) on ZnO structure with regarding to enhancing optical gas sensing properties when exposed the films to the volatile. Structural, electrical and optical properties of the AZO thin films were characterized and related to the optical gas sensing responses. It was found that an increase of Al-doped concentration in ZnO structure can also induce a potentially optical sensing response. These results were mentioned that an enhancement of carrier concentration due to Al3+ substitution in Zn2+ on ZnO structure can generate the adsorbed oxygen ion on the AZO surface as well. Absorption spectra of AZO thin films showed blue shift in near UV region due to releasing of electrons when the adsorbed oxygen ions were interacted with ethanol molecules. According to the introduced the AZO layer to form AZO/ZnTPP sensing film, the results could be demonstrated significantly enhanced the optical responses to the ethanol in broaden range of near UV-visible region at room temperature. Finally, the authors have suggest that the A3ZO/ZnTPP thin film exhibiting a good performance to detect ethanol vapor and overcome a conventional ZnTPP, ZnO/ZnTPP and A2ZO/ZnTPP thin films may be promoted as one of the optical gas sensor in an optoelectronic nose system due to broaden responses at room temperature.