Investigation of High-Sensitivity NO2 Gas Sensors with Ga2O3 Nanorod Sensing Membrane Grown by Hydrothermal Synthesis Method

Abstract

In this work, Ga2O3 nanorods were converted from GaOOH nanorods grown using the hydrothermal synthesis method as the sensing membranes of NO2 gas sensors. Since a sensing membrane with a high surface-to-volume ratio is a very important issue for gas sensors, the thickness of the seed layer and the concentrations of the hydrothermal precursor gallium nitrate nonahydrate (Ga(NO3)3·9H2O) and hexamethylenetetramine (HMT) were optimized to achieve a high surface-to-volume ratio in the GaOOH nanorods. The results showed that the largest surface-to-volume ratio of the GaOOH nanorods could be obtained using the 50-nm-thick SnO2 seed layer and the Ga(NO3)3·9H2O/HMT concentration of 12 mM/10 mM. In addition, the GaOOH nanorods were converted to Ga2O3 nanorods by thermal annealing in a pure N2 ambient atmosphere for 2 h at various temperatures of 300 °C, 400 °C, and 500 °C, respectively. Compared with the Ga2O3 nanorod sensing membranes annealed at 300 °C and 500 °C, the NO2 gas sensors using the 400 °C-annealed Ga2O3 nanorod sensing membrane exhibited optimal responsivity of 1184.6%, a response time of 63.6 s, and a recovery time of 135.7 s at a NO2 concentration of 10 ppm. The low NO2 concentration of 100 ppb could be detected by the Ga2O3 nanorod-structured NO2 gas sensors and the achieved responsivity was 34.2%.

Sensing Mechanism and Characterization of NO2 Gas Sensors Using Gold-Black NP-Decorated Ga2O3 Nanorod Sensing Membranes

“…Activation energy (E A ) is an important characteristic factor for affecting the reaction rate and operating temperature of gas sensors, which is calculated using the following Arrhenius equation 38,50…”

“…Activation energy ( E A ) is an important characteristic factor for affecting the reaction rate and operating temperature of gas sensors, which is calculated using the following Arrhenius equation , R s ( T ) = R 0 e E A / kT ln [ R normals false( T false) ] = ln nobreak0em0.25em⁡ ( R 0 ) + ( E A 1000 K ) true( 1000 T true) where R s ( T ), R 0 , and K are the resistance of NO 2 gas sensors at absolute temperature T , pre-exponential factor, and Boltzmann constant, respectively. Figure illustrates the Arrhenius plot ( R s ( T ) vs 1000/ T ) of the various NO 2 gas sensors.…”

“…Next, using Ga­(NO 3 ) 3 ·9H 2 O with a concentration of 12 mM and C 6 H 12 N 4 with a concentration of 10 mM, GaOOH nanorods were grown on the SnO 2 seed layer by the hydrothermal synthesis method at 180 °C for 4 h. After the sample was annealed in a pure N 2 atmosphere furnace at 400 °C for 2 h, the GaOOH nanorods were converted to Ga 2 O 3 nanorods. The properties of the SnO 2 seed layer and the Ga 2 O 3 nanorods were reported previously . The completed sample with Ga 2 O 3 nanorods was then affixed to a liquid nitrogen-cooled holder, and Au ingots were loaded into a tungsten boat in a vapor cooling condensation system.…”

“…The properties of the SnO 2 seed layer and the Ga 2 O 3 nanorods were reported previously. 38 The completed sample with Ga 2 O 3 nanorods was then affixed to a liquid nitrogencooled holder, and Au ingots were loaded into a tungsten boat in a vapor cooling condensation system. The setup of the vapor cooling condensation system has been reported in previous studies.…”

Engineering Charge Separation in α-Ga2O3 Nanorod Arrays for Photoelectrochemical UV Detection

“…Their research findings suggest that devices treated with N 2 annealing show a notable enhancement in the photo-to-dark current ratio (PDCR), attributed to the introduction of N doping and a suitable concentration of O V . This is attributed to the fact that O V serves as active sites for gas adsorption . These findings collectively highlight the multifaceted role of O V in influencing the properties and performance of Ga 2 O 3 -based devices.…”