Vol.:(0123456789) 1 3 Journal of Materials Science: Materials in Electronics https://doi.org/10.1007/s10854-018-9477-2 TiO 2 thin flm based gas sensors for CO-detection Heberto Gómez Pozos 1  · Karthik Tangirala Venkata Krishna 2  · María de la Luz Olvera Amador 3  · Yuriy Kudriavtsev 3  · Arturo Maldonado Alvarez 3 Received: 19 November 2017 / Accepted: 11 June 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Pure titanium dioxide (TiO 2 ) thin flms were deposited and investigated as gas sensors for carbon monoxide (CO) detec- tion. TiO 2 thin flms were deposited by ultrasonic spray pyrolysis technique, starting from titanium(IV) oxyacetilacetonate, onto soda-lime glass substrates. Structural, morphological, and compositional properties of the TiO 2 flms were obtained utilizing X-ray difractometry, energy dispersive X-ray, scanning electron microscopy, and secondary ion mass spectros- copy techniques, respectively. Films deposited above 400 °C were polycrystalline, and its X-ray pattern ft well to the TiO 2 anatase structure, and no other phases were detected, whereas flms deposited at lower temperatures presented an amorphous structure. The sensitivity of the TiO 2 flms is analyzed by varying both thickness and deposition temperature. In addition, the sensor response was measured for CO concentrations from 1 to 300 ppm at diferent operation temperatures, 100, 200, and 300 °C. The highest sensitivity (~ 300) was obtained for TiO 2 thin flms deposited with the lowest flm thickness, at a substrate temperature of 350 °C. The results obtained in this work show that the TiO 2 flms processed by ultrasonic spray pyrolysis exhibit very promising results for detection of CO. 1 Introduction The control of the main polluting industries, e.g., mining, chemical, and oil [1], it is of global interest, since their emissions of air pollutants afect the health. Therefore, the progress of gas sensors for testing the dangerous and com- bustible gases is vital. The gas sensor measures concentra- tion of gases and convert it into electrical signal which can be interpreted by electronic equipment [2]. Actually, oxide semiconductor gas sensors such as SnO 2 , ZnO, and TiO 2 [3–9] are utilized for monitoring the hazardous gases, for example, C 3 H 8 , C 4 H 10 , CO 2 , H 2 S, CO, among others. Titanium dioxide (TiO 2 ) thin flms are nontoxic, chemi- cally stable, easy, and low-cost preparation. Additionally, TiO 2 crystallizes in three polymorphic forms: brookite (orthorhombic), rutile (tetragonal), and anatase (tetragonal) [10]. Its refractive index for the rutile is higher when com- pared to the anatase phase [11] and rutile is found to be the most thermodynamically stable phase. Formation of a particular phase depends upon the nature of its composi- tion, starting material, deposition conditions, and deposi- tion method. Anatase is stable up to 800 °C, above which it transforms into rutile phase. Physical properties of the flms depend on crystal structure, chemical composition, and surface morphology, among others [12]. TiO 2 have attracted great attention for its applications in optical fl- ters [13], ceramic membrane dye-sensitized solar cells [14], waveguides [15], gas sensors [16], and photocatalysis [17] due to the modulation in its structural, optical, and transport properties. TiO 2 thin flms are the most promising metal oxide for solid state chemical sensors mainly due to its abundant oxy- gen vacancies, high surface area morphology, high reactivity with diverse gases, and high selectivity to CO in the pres- ence of many gases like hydrocarbons [18], H 2 [19], CO 2 [16], LPG [20], C 2 H 8 OH [21], etc. * Heberto Gómez Pozos gpozos@uaeh.edu.mx 1 Área académica de Computación y Electrónica, ICBI, Universidad Autónoma del Estado de Hidalgo, Ciudad del Conocimiento, Carretera Pachuca - Tulancingo, Km. 4.5, 56092 Mineral de la Reforma, Hidalgo, Mexico 2 Ingeniería Industrial Escuela Superior Tepeji del Río, Universidad Autónoma del Estado de Hidalgo, Noxtongo, 42855 Tepeji de Ocampo, Hgo, Mexico 3 Departamento de Ingeniería Eléctrica-SEES, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, CINVESTAV-IPN, Apartado postal 14740, 07360 Mexico City, DF, Mexico