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. 2019 Dec 6;12(24):4073.
doi: 10.3390/ma12244073.

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

N M Shaalan  1   2 , D Hamad  2 , Osama Saber  1   3
Affiliations

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

N M Shaalan et al. Materials (Basel). .

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.

Keywords: 1D-nanostructures; copper-doped tin oxide; methane gas sensor; thermal evaporation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Schematic illustration of the gas sensor measurement equipment with the sample stage. (b) Schematic diagram of the device and electrical connections.
Figure 2
Figure 2
SEM images of the sample prepared at various Cu content of Cu:In; (a) S1, (b) S2, and (c) S3.
Figure 3
Figure 3
XRD charts for the sample prepared at various Cu contents. (a) S1, (b) S2, and (c) S3.
Figure 4
Figure 4
EDX spectra for the sample prepared at various Cu contents. (a) S1, (b) S2, and (c) S3. The table attached in the figure shows the weight and atomic percentage of the OK, CuK, and InL emission.
Figure 5
Figure 5
Summation of Raman scattering spectra for the sample prepared at various Cu contents. (a) S1, (b) S2, and (c) S3.
Figure 6
Figure 6
Change in resistance at operating temperatures of 50–200 °C for the sensor fabricated by the S1 sensing layer.
Figure 7
Figure 7
Change in resistance at operating temperatures of 50–200 °C for the sensor fabricated by the S2 layer.
Figure 8
Figure 8
Output voltage at operating temperatures 100 °C for the sensors fabricated with S1, S2, and S3 sensing layers. Note: the sensing layer of S3 is not sensitive to methane at the operating temperature applied here (50, 150, 200 °C are not shown here).
Figure 9
Figure 9
Sensor response as a function of operating temperatures for the sensors fabricated with S1, S2, and S3 sensing layers. Note: the negative values here are defined as negative sensor response for p-type behavior to be notable compared to n-type behavior.
Figure 10
Figure 10
Schematic diagram of the sensing mechanism (a) with low Cu content, and (b) high Cu content of p-n type materials.
Figure 11
Figure 11
Repeatability sensor signal of the most sensitive S2 layer at 100 °C.
See this image and copyright information in PMC

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