Light-Activated Metal Oxide Gas Sensors: A Review

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.

Improved Synthesis of ZnO Nanowalls: Effects of Chemical Bath Deposition Time and Annealing Temperature

“…In this scenario, the use of UV light represents a promising route since UV light can induce gas desorption kinetics similar to what happens at high temperatures. Moreover, UV photons generate electron-hole pairs in ZnO, and the photo-induced carriers can interact with adsorbed gaseous species [7,9]. This can allow for the realization of gas sensors UV-activated at room temperature using ZnO nanostructures like nanosheets (hexagonal foils with thickness of about 100 nm and length of few micrometers), nanorods (parallelepipeds with a hexagonal base with a diameter greater than 50 nm and length of about 1.5 µm), and nano and microwires (cylindrical structures with length of about 10 µm and diameter of few nanometers and micrometers, respectively) [9][10][11][12][13][14].…”

Comparative Study of ZnO Thin Films Grown on Quartz Glass and Sapphire (001) Substrates by Means of Magnetron Sputtering and High-Temperature Annealing

“…ZnO is of low cost, and Al-doped ZnO is of excellent conductivity as well as cheap, which is considered a superior substitute for the expensive indium tin oxide (ITO) transparent conductive material [14][15][16]. In addition, ZnO is found to be very sensitive to ultraviolet (UV) light, humidity, and gas and has been successfully applied in UV sensors [17], graphic imaging sensors [18], humidity sensors, and gas sensors [19,20]. Last but not least, it has been demonstrated that ZnO with bionic structure level holes is suitable for energy storage and utilization [21].…”

Nanostructured ZnO/Ag Film Prepared by Magnetron Sputtering Method for Fast Response of Ammonia Gas Detection

“…As for the preparation methods, various chemical-reaction-based approaches have been demonstrated to fabricate the nanostructured ZnO layer, such as chemical vapor deposition [13], spray pyrolysis [14], the sol-gel method [15], hydrothermal synthesis [16], etc., while fewer ZnO nanostructures have been demonstrated through the physical fabrication method. To further improve the sensing ability of ZnO, introducing heterojunction with other metal or metal oxide materials is also conventionally proposed [17,18]. For example, Shingange et al demonstrated that ZnO nanorods were functionalized with Au nanoparticles, yielding a high selectivity towards NH 3 compared with CO, CH 4 , and H 2 at the concentration of 100 ppm [8].…”