Fabrication and Characterization of SnO2, TiO2, Composite SnO2/TiO2 Chemiresistive Devices for Sodium and Calcium-sensing

Semiconductor metal oxides have demonstrated sensing-based applications, and to improve the electrical properties of these materials, modifications such as metal-based functionalization and vacuum deposition techniques are typically done. Alternatively, a more cost-effective method is using solution processing techniques. In this study, we used solution-processed semiconductor metal oxides to investigate their sensitivity for cations in aqueous solution and without the additional metallization. Specifically, solution- processed SnO2, TiO2 and a composite of SnO2/TiO2 were deposited on fluorine-doped tin oxide (FTO) glass and these were tested for their chemiresistive properties when exposed to cationic species in solution. Techniques such as Grazing Incidence X-ray diffraction (GIXRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and UV-Vis (for optical bandgap), and the surface profiler were utilized to characterize the metal oxide films. Fabrication factors such as the electrode gap, annealing temperature, precursor concentration and film thickness were studied with respect to the electrical response of the films when exposed to Na+ and Ca2+ ions in solution. The I-V curves before and after ion exposure were measured yielding straight lines implying that the metal oxide films before and after exposure to ions have Ohmic response behavior. Overall, the variation of factors such as crystallinity, and structural features (fibrous, Ca2+, versus non- fibrous, Na+ ) are suggestive of the differences in the electrical responses across the deposited solution-processed metal oxide films which may be useful in sensor array applications