Abstract
Low power consumption, fast response and quick recovery times are important parameters for gas sensors performance. Herein, we report the experimental and theoretical studies of ZnO and Cr doped ZnO nanostructures used in low temperature (50 °C) sensors for the detection of CO. The synthesized films were characterized by XRD, UV-Vis, FE-SEM and EDX. The XRD patterns for the ZnO and 0.5 wt% Cr/ZnO films confirm the formation of a single-phase hexagonal wurtzite structure. The reduction of the ZnO optical band gap from 3.12 eV to 2.80 eV upon 0.5 wt% Cr doping is well correlated with the simulation data. The FE-SEM images of the films show spherical morphology with the estimated particle sizes of about ~40 nm and ~ 25 nm were recorded for the ZnO and 0.5 wt% Cr/ZnO films, respectively. Enhanced gas sensing performance is achieved with Cr doping and the sensitivity of ZnO increases from 9.65% to 65.45%, and simultaneously decreasing the response and recovery times from 334.5 s to 172.3 s and from 219 s to 37.2 s, respectively. These improvements in gas sensing performance are due to the reduction in particle size and optical band gap, and an increase in specific surface area.
Highlights
ZnO as a semiconductor material has been shown to exhibit a wide range of properties for various applications
This paper presents the experimental work for Cr doped ZnO NSs gas sensor and it is complimented by density functional theory (DFT) calculations for the ZnO (Zn12O12) and Cr-ZnO (CrZn11O12) nano-cages
ZnO (Pure) and 0.5 wt% Cr/ZnO NS sensors have been successfully synthesized by sol-gel method
Summary
ZnO as a semiconductor material has been shown to exhibit a wide range of properties for various applications. ZnO NS doped with Mn is found to be effective for detecting a wide range of reducing substances, such as acetone, ethanol and acetic acid at temperatures above 400 °C10 This remarkable sensitivity obtained from the above study is attributed to the presence of lower ionization energy of Mn as compared to the ZnO NS material, and the ability of the Mn to reduce the activation energy of the surface chemisorbed gases. For CO gas sensing, the ZnO doped with In3+ system has been found to improve the response time of the CO detection at 300 °C This is attributed to the reduction of the energy band gap, as well as, the ability of the In3+ to act as donor species leading to the formation of more adsorption sites, which mainly consist of In atoms and oxygen vacancies[8]
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