Abstract
Reliable environmental monitoring requires cost effective but highly sensitive and selective gas sensors. While the sensitivity of the sensors is improved by reducing the characteristic dimensions of the gas-sensing material, the selectivity is often approached by combining the sensors into multisensor arrays. The development of scalable methods to manufacture such arrays based on low-dimensional structures offers new perspectives for gas sensing applications. Here we examine an approach to produce multisensor array chips based on the TiOx nanotube layers segmented by multiple Pt strip electrodes. We study the sensitivity and selectivity of the developed chip at operating temperatures up to 400 °C towards organic vapors in the ppm range. The results indicate that the titania nanotubes are a promising material platform for novel cost-effective and powerful gas-analytical multisensor units.
Highlights
The development of gas sensors with advanced characteristics is driven by the necessity of fast, reliable and cheap monitoring of the environment[1] which is especially important for various emerging tasks[2]
Metal oxide semiconductors are recognized as materials which fully meet the requirements of commercial gas sensors and have a great potential to advance further, mainly through application of nanotechnologies[9]
Among quasi-1-D structures, NTs are distinguished by their high specific surface due to their hollow structure with inner and outer surfaces that are exposed to the gases which makes it easier to fully deplete the oxide from free carriers due to surface localization under chemisorption and catalytic processes
Summary
The process to employ the titanium dioxide NTs in the multisensor chip includes (Fig. 1) primarily an anodization of the titanium foil in accordance with known protocols[20, 25, 36, 37]. The maximum gas response as a relative resistance change, ΔR/ Rair, in the vapor-enriched air has been observed at 350 °C (Fig. 3b) At this temperature, the median NT array segments response to isopropanol and acetone of 10 ppm concentration is close to 38% while one to 10 ppm of ethanol is about 14%. The surface reactions between the gas molecules (see Fig. 5a) and/or their direct catalysis include a dissociation accompanied by an exchange of charged species that involves different amounts of charge localized by chemisorbed species This explains the higher response of the NTs towards isopropanol and acetone vapors when compared to one versus ethanol. The chip design allows one further advancing the selectivity by application of inhomogeneous heating and/or other external modifications
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