CuO thin films deposited by the dip-coating method as acetone vapor sensors: Effect of their thickness and precursor solution molarity

Abstract

The superficial morphology and porosity of metal oxide films play an important role in their sensing response to the presence of organic vapors. For films deposited from precursor solutions, both can be modified by varying the solution's molarity and thickness; however, their effect on the film's sensitivity has been scarcely studied in p-type materials. In this work, CuO p-type nanostructured films on glass substrates were obtained from three precursor solutions at different molarities. The films were deposited by dip-coating, varying the coats to obtain thicknesses in the 100–1700 nm wide range. Scanning electron microscopy images show surfaces with higher porous presence as the film's thickness and precursor solution molarity increase. The CuO films were tested as acetone-vapor sensors in a wide concentration range from 1 to 2000 ppm at a sample temperature Ts = 300 °C. Their sensitivity (S) grows as the film thickness increases, regardless of the solution molarity, associated with a higher porosity, calculated from refractive index values. The highest response is obtained for CuO thickest film (τ = 1670 nm) deposited from the solution at the highest molarity. S values of 1.3, 3.4, 4.75, and 7.4 are obtained at 1, 100, 300, and 2000 ppm acetone-vapor concentrations, respectively. These S values are inside the reported ones using more sophisticated techniques and processes.