Low temperature solution-processed ZnO nanorod arrays with application to liquid ethanol sensors

ZnO nanorod arrays have been prepared by low-temperature chemical bath deposition method. The lengths and diameters of the high-aspect-ratio ZnO nanorods are around 1.5 μm and 55 nm, respectively. The as-prepared ZnO nanostructures are hexagonal phase with c-axis orientation, and the sensing properties of the ZnO-based sensors against liquid ethanol with different concentrations are investigated using electrical impedance spectroscopy (EIS). The EIS results reveal that the series resistance (Rs) is as low as 27 Ω; the charge-transfer resistance (Rct) remarkably contributes to the sensing properties of the ethanol sensor, and decreases with a decreasing concentration (99.5–1%) from 17.0 kΩ to 2.6 kΩ. An equivalent circuit with capacitors and resistors was developed to investigate the conduction process according to complex impedance (Nyquist) diagrams. In low concentration range, the electron conduction process is dominated by the Rct and a constant phase element (CPE); however, in high concentration ethanol solution, the conduction process is dominated by polarization and decomposition of the absorbed water with larger Rct observed. Also, sensitivity of the ZnO sensor was evaluated from the current–voltage (I–V) characteristics; the results demonstrate that the ZnO nanorod arrays are very promising to fabricate chemical sensors with high sensitivity and low power consumption.

► Liquid ethanol sensors are fabricated based on high-aspect-ratio (∼27) and well-aligned ZnO nanorod arrays.
► Sensing characteristics are investigated using electrical impedance spectroscopy (EIS) and the equivalent circuit is proposed.
► Sensing mechanism involves conduction process and polarization process was investigated over a wide range of ethanol concentration.
► The I–V characteristics were recorded, and the ZnO sensor exhibits high sensitivity with value of ∼1.43 in 1% (v/v) ethanol solution at room temperature.