Abstract
Conductometric gas sensors facilitated by photons have been investigated for decades. Light illumination may enhance device attributes including operational temperature, sensing sensitivity and selectivity. This paper aims to provide an overview on the progress of light-activated gas sensors, with a specific focus on sensors based on metal oxides. The material systems that have been studied include pure metal oxides, heterostructures of semiconductor-metal oxides and metal-metal oxides, and metal oxides with dopant. Other reported works on the use of different nanostructures such as one-dimensional and porous nanostructures, study of sensing mechanisms and the interplay between various factors are also summarized. Possible directions for further improvement of sensing properties, through optimizing the size of nanomaterials, film thickness, light intensity and wavelength are discussed. Finally, we point out that the main challenge faced by light-activated gas sensors is their low optical response, and we have analyzed the feasibility of using localized surface plasmon resonance to solve this drawback. This article should offer readers some key and instructive insights into the current and future development of light-activated gas sensors.
Highlights
Gas sensors play an important role in various disciplines ranging from personal safety, medical diagnosis, environmental monitoring to industrial process control [1,2,3,4,5,6]
This review aims to provide a summary on recent development of light-activated conductometric gas sensors that are based on metal oxide semiconductors
We have reviewed the progress of light-activated conductometric gas sensors based on metal oxides
Summary
Gas sensors play an important role in various disciplines ranging from personal safety, medical diagnosis, environmental monitoring to industrial process control [1,2,3,4,5,6]. For n-type sensing materials like ZnO and SnO2, the resistance decreases upon exposure to reductive gases such as CO, H2, ethanol vapor and increases upon exposure to oxidizing gas like O2, NO2, O3. Consequent to the generation of oxygen ions, which governs the operation of conventional conductometric gas sensors based on metal oxide semiconductors, one typically needs to heat the sensing element to a working temperature of at least 150 ◦C [2,3,6]. High working temperatures sacrifices device lifetime and Micromachines 2017, 8, 333 long-term stability of sensing performance as this will result in regrowth of nanomaterials It will limit the sensor’s application in the detection of flammable or explosive analytes because of safety issues. An outlook on the potential development of plasmon-assisted conductometric gas sensors is presented
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