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Sensors 2018, 18(3), 735; https://doi.org/10.3390/s18030735

The Effect of Film Thickness on the Gas Sensing Properties of Ultra-Thin TiO2 Films Deposited by Atomic Layer Deposition

1
Christopher Ingold Laboratories, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
2
National Institute of Materials Physics, Atomistilor, 405A, P.O. Box MG-7, 077125 Bucharest-Măgurele, Romania
3
School of Engineering, University of Warwick, Coventry CV4 7AL, UK
*
Author to whom correspondence should be addressed.
Received: 9 January 2018 / Revised: 20 February 2018 / Accepted: 20 February 2018 / Published: 1 March 2018
(This article belongs to the Special Issue Gas Sensors based on Semiconducting Metal Oxides)
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Abstract

Analyte sensitivity for gas sensors based on semiconducting metal oxides should be highly dependent on the film thickness, particularly when that thickness is on the order of the Debye length. This thickness dependence has previously been demonstrated for SnO2 and inferred for TiO2. In this paper, TiO2 thin films have been prepared by Atomic Layer Deposition (ALD) using titanium isopropoxide and water as precursors. The deposition process was performed on standard alumina gas sensor platforms and microscope slides (for analysis purposes), at a temperature of 200 °C. The TiO2 films were exposed to different concentrations of CO, CH4, NO2, NH3 and SO2 to evaluate their gas sensitivities. These experiments showed that the TiO2 film thickness played a dominant role within the conduction mechanism and the pattern of response for the electrical resistance towards CH4 and NH3 exposure indicated typical n-type semiconducting behavior. The effect of relative humidity on the gas sensitivity has also been demonstrated. View Full-Text
Keywords: gas sensing; sensors; ALD; TiO2; titanium isopropoxide; thin films; debye length gas sensing; sensors; ALD; TiO2; titanium isopropoxide; thin films; debye length
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Wilson, R.L.; Simion, C.E.; Blackman, C.S.; Carmalt, C.J.; Stanoiu, A.; Di Maggio, F.; Covington, J.A. The Effect of Film Thickness on the Gas Sensing Properties of Ultra-Thin TiO2 Films Deposited by Atomic Layer Deposition. Sensors 2018, 18, 735.

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