Nanostructural ZnO based coplanar gas sensor arrays from the injection of metal chloride solutions: Device processing, gas-sensing properties and selectivity in liquors applications

A new coplanar gas sensor array of ZnO was fabricated by injecting different volumes of 0.01 mol/L AlCl3, CuCl2, SnCl4, TiCl4, PdCl2 and WCl6 solutions and post treatment to improve the selectivity in liquor. The new four-sensor array was optimized by maximizing Sum of Euclidean distances (SED) of the gases of liquor. The morphology of films was characterized by field-emission scanning electron microscopy (FESEM). The results showed that ZnO nanostructures were formed on the surface of films after the injecting process. Nanowires, 100 nm in diameter and 3 μm in length, were found when the solutions included AlCl3, CuCl2, SnCl4 and PdCl2. However, when the injecting solution was TiCl4, nanotowers with 500 nm in diameter and 4 μm in length appeared. No new structures appeared when the WCl6 solution was injected. The results of testing gases of liquor revealed that the injecting process could improve the response of the sensors array effectively. Through calculating the value of the SED, the best array was confirmed whose SED value would be three times the worst one.