Impedance Spectroscopy Analysis of Structural Defects in Sputtered ZnO Films

The degradation of sputtered columnar ZnO layers under DC polarization was studied by using electrochemical impedance spectroscopy and electron microscopy. It was found that the structure of the as‐deposited ZnO film was dense at the nanoscale. An equivalent circuit model including de Levie impedance accounted for the localized propagation of microscale cracks towards the copper substrate. This generates a capacitance (CZnO) that represents the crack surface area in contact with the electrolyte. CZnO is small enough not to be obscured by the double layer capacitance at the top of the layers and increases with increasingly negative potential and time. These results were compared to nanoporous ZnO layers that behave differently and exhibit a large CZnO. The combination of in situ EIS analysis with the ex situ structural information provided by electron microscopy proved to be an efficient methodology to characterize very different microstructures of conductive coatings. Crack on: The degradation of sputtered columnar ZnO layers is investigated by using electrochemical impedance spectroscopy and scanning transmission electron microscopy. The localized propagation of microscale cracks in the film that are dense at the nanoscale generates a small capacitance (CZnO) that can be extracted by using a simple equivalent circuit including de Levie impedance. CZnO is associated with the development of crack surface area in contact with the electrolyte and increases with time.