The Effect of Anodization Time on the Properties of TiO 2 Nanotube Humidity Sensors
- PDF / 358,603 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 57 Downloads / 244 Views
The Effect of Anodization Time on the Properties of TiO2 Nanotube Humidity Sensors Reshmi Raman, Oscar A. Jaramillo, and Marina E. Rincón* CIE-UNAM, Priv. Xochicalco S/N, Col. Centro, Temixco, Mor. 62580. *Corresponding author: [email protected] ABSTRACT In this paper, the effect of anodization time on the properties of TiO2 nanotube humidity sensors is reported. TiO2 nanotube arrays were grown by anodization of Ti foil using diethylene glycol and ammonium fluoride. Highly ordered TiO2 nanotube arrays were obtained, with the length of tube increasing from 4 to 20 Pm as the time of anodization increases, at the expense of nanotube integrity. Humidity sensors based on TiO2 nanotube arrays were fabricated in impedance mode with ITO as top contact. The results revealed that sensor performance does not correlate with anodization time, regardless of enhanced area, showing an optimum morphology at 4h and 10h. The increase resistivity of the sensors upon water exposure, a donor molecule, is explained by the lack of TiO2 stoichiometry and the fluctuations in the concentration of oxygen vacancies. Keywords: sensor, nanostructures, morphology INTRODUCTION Humidity monitoring is very important for environmental control, industrial production, agriculture, food storage, and physicochemical processes in pharmaceuticals. In recent years, attention has been devoted to the development of high performance humidity sensors based on metal oxides [1–6], polymers [7–9], and inorganic/organic composite materials [10]. Humidity sensors require high sensitivity, low hysteresis, linear response, fast response and recovery behavior, wide humidity detection range, low cost, and excellent long-term stability [1-6, 11]. Of these sensors, the impedance type humidity sensors [3, 4, 11] are becoming more prevalent, in terms of quality and cost, than field effect transistors and fiber optic sensors. Furthermore, the thin film humidity sensors having nanosized grains and nanoporous structures have drawn much interest because of the high surface exposure for adsorption of water molecules. The adsorption of a water molecule on the surface of a metal oxide nanostructured semiconductor can be treated as a chemical–electronic process, in which charge transfer occurs between the adsorbed species and the dielectric matrix. This process can be greatly enhanced considering the low dimension and high surface-to-volume ratio of the nanostructured materials, which can cause a prominent change in the electrical conductivity or capacitance. Due to the advantages of the high surface to volume ratio of many one-dimensional (1D) metal oxides, 1D-TiO2 nanostructures such as nanofibers [12], nanowires [13], or nanotubes [4, 14], have also been synthesized for sensor applications. One-dimensional TiO2 nanostructures, especially TiO2 nanotubes arrays (TNA) formed by anodization of Ti foil, are structured by densely bundled nanotubes, which make the sponge-like films show large surface–volume ratio. They show excellent adsorptive ability for water vapor, which is criticall
Data Loading...
