Quartz crystal microbalance coated with sol-gel-derived indium-tin oxide thin films as gas sensor for NO detection

This paper presents the possibilities and properties of indium-fin oxide (ITO)-covered quartz crystal microbalances (QCM) as a NOx toxic gas sensors. The starting sol-gel solution was prepared by mixing indium chloride dissolved in acetylacetone and tin chloride dissolved in ethanol (0-20% by weight). The ITO thin films were deposited on the gold electrodes of quartz crystals by spin-coating and annealing and subsequently followed by a standard photolithography to pattern the derived films to ensure all sensors had the same sensing areas. All heat treatment was controlled below 500 degreesC in order to avoid the degradation of the piezoelectric characteristics of quartz crystal (Quartz will lose its piezoelectricity at similar to573 degreesC due to the phase change from alpha to beta). The electrical and structural properties of ITO thin films were characterized with Hall analysis system, TG/DTA, XRD, XPS, SEM, etc. The gas sensor featured ITO thin films of similar to100 nm as the receptor to sense the toxic gas NO and a quartz crystal with frequency of 10 MHz as the transducer to transfer the surface reactions (mass loading, etc.) into a frequency shift. A homemade setup had been employed to measure the sensor response under the static mode. The experimental results indicated that the ITO-coated QCM had good sensitivity for NO gas, similar to12 Hz/100 ppm within 5 min. These results prove that the ITO-covered quartz crystals are usable as a gas sensor and as an analytical device. (C) 2004 Elsevier B.V. All rights reserved.