Co-Evaporated CuO-Doped In2O3 1D-Nanostructure for Reversible CH4 Detection at Low Temperatures: Structural Phase Change and Properties

Abstract

In order to improve the sensitivity and to reduce the working temperature of the CH4 gas sensor, a novel 1D nanostructure of CuO-doped In2O3 was synthesized by the co-evaporation of Cu and In granules. The samples were prepared with changing the weight ratio between Cu and In. Morphology, structure, and gas sensing properties of the prepared films were characterized. The planned operating temperatures for the fabricated sensors are 50–200 °C, where the ability to detect CH4 at low temperatures is rarely reported. For low Cu content, the fabricated sensors based on CuO-doped In2O3 showed very good sensing performance at low operating temperatures. The detection of CH4 at these low temperatures exhibits the potential of the present sensors compared to the reported in the literature. The fabricated sensors showed also good reversibility toward the CH4 gas. However, the sensor fabricated of CuO-mixed In2O3 with a ratio of 1:1 did not show any response toward CH4. In other words, the mixed-phase of p- and n-type of CuO and In2O3 materials with a ratio of 1:1 is not recommended for fabricating sensors for reducing gas, such as CH4. The gas sensing mechanism was described in terms of the incorporation of Cu in the In2O3 matrix and the formation of CuO and In2O3 phases.

Flower-Like ZnO Nanorods Synthesized by Microwave-Assisted One-Pot Method for Detecting Reducing Gases: Structural Properties and Sensing Reversibility

“…To explain the surface activity, we must clarify the reaction of surface species (adsorbed molecules) in air and in air containing gas. It is well-known that ZnO is an n-type semiconductor, and its gas-sensing mechanism belongs to the surface-controlled type (Ruhland et al, 1998 ; Koziej et al, 2007 ; Haridas and Gupta, 2012 ; Shaalan et al, 2019a , b ), and the change in conductivity is dependent on the species type and the amount of chemisorbed oxygen on the surface. The intrinsic resistance of the semiconductor decreases when increasing the temperature; however, we have to consider the transformation of physisorbed oxygen molecules into various oxygen ions when increasing the surface temperature.…”

“…It is well-known that reducing gas prefers to react with atomic oxygen ions O − rather than ions on the surface, which causes the sensor to be active at 200°C (Ruhland et al, 1998 ; Koziej et al, 2007 ; Haridas and Gupta, 2012 ; Shaalan et al, 2019a , b ). Thus, at low temperatures of RT-150°C, the chance of reaction is very low.…”

“…Thus, the dramatic improvement in the response at 200–300°C can be attributed to the light of the formation of oxygen species. As a result of the forming oxygen ions on the oxide, the reducing gas reacts with O − ions and produces neutral compounds (such as H 2 O, and CO 2 depending on the gas type Koziej et al, 2007 ; Haridas and Gupta, 2012 ; Shaalan et al, 2019a , b ) and injects electron charges back to the oxide conduction band, causing a decrease in the resistance due to the increase in the conduction electron density, as follows:…”

A Highly Sensitive Surface-Modified Porous Carbon Nanotube-Based Sensor for Ammonia Gas Detection

“…As a result, several researchers have focused heavily on developing gas sensors using techniques other than those that are costly, like gas chromatography. , Chemical-resistive sensors are straightforward and have benefits of being transforming into a microsensor; − thus, the approach for electrochemical sensors and chemical resistance is appealing, such as a gas sensor employing metal oxides, graphene, − and multilayer carbon tubes. − Due to their sensitivity to a variety of gases, ability to operate at room temperature, incredibly low detection threshold, and low power requirements, CNT chemical resistance sensors are frequently utilized. Due to their high conductivity and internal gas detecting characteristics, CNTs have been utilized as sensors for chemical resistor-based sensors, which have the benefit of forming a compact sensing system. , The efficiency of gas detection may be improved by novel measuring techniques, signal processing, and sensor technology advancements.…”

Low-Temperature Ethanol Sensor via Defective Multiwalled Carbon Nanotubes

“…Therefore, a large number of researchers have paid great attention to the process of creating gas sensors by methods other than those that are expensive techniques such as gas chromatography [13,14], light waves [15,16], and sound waves [17]. The technique for electrochemical sensors and chemical resistance is attractive, such as a gas sensor using metal oxides, graphene, and multilayer carbon tubes [18][19][20][21][22][23][24][25][26][27], as chemical resistance sensors are simple and have the advantage of being integrated into a microsensor. CNT chemical resistance sensors are widely used due to their response to many gases, room temperature operation, extremely low detection feature, and low power consumption [23,25,28].…”