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. 2023 Mar 15;13(6):1064.
doi: 10.3390/nano13061064.

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

Shao-Yu Chu  1 , Mu-Ju Wu  1 , Tsung-Han Yeh  2 , Ching-Ting Lee  1   3 , Hsin-Ying Lee  1
Affiliations

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

Shao-Yu Chu et al. Nanomaterials (Basel). .

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%.

Keywords: Ga2O3 nanorods; NO2 gas sensors; X-ray diffraction; X-ray photoelectron spectroscopy; field emission scanning electron microscope; hydrothermal synthesis method.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic configuration of NO2 gas sensors with Ga2O3 nanorod sensing membrane.
Figure 2
Figure 2
Schematic configuration of measurement system of NO2 gas sensors.
Figure 3
Figure 3
XRD spectra of SnO2 seed layers with various thicknesses.
Figure 4
Figure 4
FE-SEM top-view and cross-section images of GaOOH nanorods grown on SnO2 seed layers with a thickness of (a) 50 nm, (b) 100 nm, and (c) 200 nm.
Figure 5
Figure 5
FE-SEM top-view and cross-section images of GaOOH nanorods grown using various precursor concentrations of (a) 6 mM/5 mM, (b) 12 mM/10 mM, and (c) 18 mM/15 mM.
Figure 6
Figure 6
XPS spectra of O1s core-level spectra of (a) as-grown GaOOH nanorods and annealed Ga2O3 nanorods treated at (b) 300 °C (c) 400 °C, and (d) 500 °C.
Figure 7
Figure 7
Temperature dependence of resistance for NO2 gas sensors with Ga2O3 nanorod sensing membranes annealed at various temperatures.
Figure 8
Figure 8
Responsivity versus operating temperature of NO2 gas sensors with Ga2O3 nanorod sensing membranes annealed at various temperatures.
Figure 9
Figure 9
(a) Response time and (b) recovery time of NO2 gas sensors with Ga2O3 nanorod sensing membranes annealed at various temperatures under 10 ppm NO2 gas concentration.
Figure 10
Figure 10
Dynamic gas responsivity of NO2 gas sensor with 400 °C-annealed Ga2O3 nanorod sensing membrane under various NO2 concentrations at an operating temperature of 275 °C.
Figure 11
Figure 11
Responsivity of gas sensor with 400 °C-annealed Ga2O3 nanorod sensing membrane under various target gases.
See this image and copyright information in PMC

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