Abstract
The paper presents a technology for preparation and characterization of titanium dioxide (TiO2) thin films suitable for gas sensor applications. Applying atomic layer deposition (ALD), very thin TiO2 films were deposited on quartz resonators, and their gas sensing properties were studied using the quartz crystal microbalance (QCM) method. The TiO2 thin films were grown using Ti(iOPr)4 and water as precursors. The surface of the films was observed by scanning electron microscopy (SEM), coupled with energy dispersive X-ray analysis (EDX) used for a composition study. The research was focused on the gas-sensing properties of the films. Films of 10-nm thickness were deposited on quartz resonators with Au electrodes and the QCMs were used to build highly sensitive gas sensors, which were tested for detecting NO2. Although very thin, these ALD-grown TiO2 films were sensitive to NO2 already at room temperature and could register as low concentrations as 50 ppm, while the sorption was fully reversible, and the sensors could be fully recovered. With the technology presented, the manufacturing of gas sensors is simple, fast and cost-effective, and suitable for energy-effective portable equipment for real-time environmental monitoring of NO2.
Highlights
TiO2 is one of the most extensively studied transition metal oxides
With 200 atomic layer deposition (ALD) cycles, films with a thickness of ~ 10 nm were grown; the thickness was evaluated based on the UV-Vis reflectometry measurement of the reference TiO2 thin films deposited on Si wafers
The successful deposition of TiO2 was clearly proved by the presence of Ti in the energy dispersive X-ray analysis (EDX) spectrum of the reference TiO2 film grown by ALD on the Si wafer
Summary
TiO2 is one of the most extensively studied transition metal oxides. Nowadays, TiO2, as an n-type semiconductor, is widely explored for photocatalysis, gas sensing and various optical applications [1,2]. Applying atomic layer deposition (ALD), very thin TiO2 films were deposited on quartz resonators, and their gas sensing properties were studied using the quartz crystal microbalance (QCM) method.
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