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. 2021 Feb 11;11(2):456.
doi: 10.3390/nano11020456.

Morphology of Ga2O3 Nanowires and Their Sensitivity to Volatile Organic Compounds

Affiliations

Morphology of Ga2O3 Nanowires and Their Sensitivity to Volatile Organic Compounds

Maciej Krawczyk et al. Nanomaterials (Basel). .

Abstract

Gas sensitive structures made of nanowires exhibit extremally large specific surface area, and a great number of chemically active centres that can react with the ambient atmosphere. This makes the use of nanomaterials promising for super sensitive gas sensor applications. Monoclinic β-Ga2O3 nanowires (NWs) were synthesized from metallic gallium at atmospheric pressure in the presence of nitrogen and water vapor. The nanowires were grown directly on interdigitated gold electrodes screen printed on Al2O3 substrates, which constituted the gas sensor structure. The observations made with transmission electron microscope (TEM) have shown that the nanowires are monocrystalline and their diameters vary from 80 to 300 nm with the average value of approximately 170 nm. Au droplets were found to be anchored at the tips of the nanowires which may indicate that the nanowires followed the Vapor-Liquid-Solid (VLS) mechanism of growth. The conductivity of β-Ga2O3 NWs increases in the presence of volatile organic compounds (VOC) even in the temperature below 600 °C. The gas sensor based on the synthesized β-Ga2O3 NWs shows peak sensitivity to 100 ppm of ethanol of 75.1 at 760 °C, while peak sensitivity to 100 ppm of acetone is 27.5 at 690 °C.

Keywords: acetone; chemical gas sensors; chemiresistors; ethanol; gallium oxide; metal oxide; nanomaterials; nanowires; thermal synthesis; volatile organic compounds.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Al2O3 substrate with β-Ga2O3 nanowires grown on Au interdigitated electrodes. Pt meander-type heater was screen printed on the bottom side of the substrate.
Figure 2
Figure 2
The temperature-controlled conductance measurement setup.
Figure 3
Figure 3
(a) SEM image of the top surface of the substrate with gold interdigitated electrodes and β-Ga2O3 nanowires; (b) ×1000 magnified image of β-Ga2O3 nanowires grown on the surface of Au electrode.
Figure 4
Figure 4
SEM image of the inter-electrode area/surface of the substrate with visible agglomerates formed by β-Ga2O3 nanowires.
Figure 5
Figure 5
TEM image of (a) β-Ga2O3 nanowire; (b) Droplet of Au or Au-Ga alloy droplet at the top of the nanowire.
Figure 6
Figure 6
The chemical composition of β-Ga2O3 nanowire.
Figure 7
Figure 7
The chemical composition of Ga-Au alloy droplet anchored at the top of the nanowire.
Figure 8
Figure 8
The diffraction pattern of an electron beam passing through β-Ga2O3 nanowire. The pattern reveals a monocrystalline structure of the nanowire.
Figure 9
Figure 9
(a) X-ray diffractogram of β-Ga2O3 nanowires; (b) The most prominent peaks of the diffractogram in (a). All peaks in the diffractogram are shifted by, approximately, less than −0.20°.
Figure 10
Figure 10
The Williamson–Hall plot of the β-Ga2O3 nanowires.
Figure 11
Figure 11
Survey spectrum of β-Ga2O3 nanowires.
Figure 12
Figure 12
Core-level spectra of: (a) Ga3d; (b) Ga2p.
Figure 13
Figure 13
Core-level spectra of O1s region.
Figure 14
Figure 14
Core-level spectra of Au4f region.
Figure 15
Figure 15
Change of conductance of β-Ga2O3 nanowires as a function of temperature in ambient air, and ethanol or acetone with the concentration of 100 ppm.
Figure 16
Figure 16
Sensitivity of β-Ga2O3 nanowires to volatile organic compounds: (a) The peak sensitivity to ethanol is at approximately 760 °C, (b) to acetone is at approximately 690 °C.
Figure 17
Figure 17
The sensitivity of β-Ga2O3 nanowires as a function of ethanol or acetone partial pressure.

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