Abstract
A composite metal oxide semiconductor (MOS) sensor array based on tin dioxide (SNO2) and zinc oxide (ZnO) has been fabricated using a straight forward mechanical mixing method. The array was characterized using X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy and X-ray diffraction. The array was evaluated against a number of environmentally important reducing and oxidizing gases across a range of operating temperatures (300–500 °C). The highest response achieved was against 100 ppm ethanol by the 50 wt% ZnO–50 wt% SnO2 device, which exhibited a response of 109.1, a 4.5-fold increase with respect to the pure SnO2 counterpart (which displayed a response of 24.4) and a 12.3-fold enhancement with respect to the pure ZnO counterpart (which was associated with a response of 8.9), towards the same concentration of the analyte. Cross sensitivity studies were also carried out against a variety of reducing gases at an operating temperature of 300 °C. The sensors array showed selectivity towards ethanol. The enhanced behaviour of the mixed oxide materials was influenced by junction effects, composition, the packing structure and the device microstructure. The results show that it is possible to tune the sensitivity and selectivity of a composite sensor, through a simple change in the composition of the composite.
Highlights
The use of mixtures of semiconducting metal oxide gas-sensitive materials based on semiconducting metal oxides is a relatively recent field of research within chemical sensors [1]
Scanning electron microscopy (SEM) imaging characterisation of all seven sensors in the SnO2 -zinc oxide (ZnO) composite array was carried out to gauge the microstructure of each material
The morphology of the SnO2 material observed in Figure 1m,n was attributed to smooth and jagged rock-like clumps ranging from a size of 0.25 μm to as large as
Summary
The use of mixtures of semiconducting metal oxide gas-sensitive materials based on semiconducting metal oxides is a relatively recent field of research within chemical sensors [1]. The use of metal oxide composites or mixtures of metal oxides can lead to novel materials that display many of these highly desirable properties [1,3,4,5,6,7,8] The use of such composite material systems in gas sensing has been reported in a number of papers in the literature [2,7,9,10,11,12], suggesting that enhanced gas response behaviour is promoted as a result of synergistic effects between the two different composite components. We discuss the influence of various chemical and physical properties, such as sensor operating temperature, analyte gas concentration, sensor device composition and microstructure, as well as infering hetero-junction and packing structure effects on the gas response characteristics
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