Dependency of Ag wetting on the oxygen nonstoichiometry of oxide surfaces

Abstract

Oxide substrates are frequently modified to have either an oxygen deficiency or excess to synthesize a completely continuous, ultrathin metal layer on them by strengthening the metal–oxide adhesion. However, conventional surface treatments using ionic irradiation inevitably induce detrimental structural irregularities, along with chemical modification, on the surface of oxide substrates. This study explores the dependency of Ag wetting on the oxygen deficiency and excess on the surface of a ZnO substrate. The favorable contribution of the increased oxygen deficiency and excess of ZnO surfaces in improving Ag wetting during the inceptive growth stages is evidenced by both experimental results and numerical interpretations. This improved Ag wetting is attributed to a significant reduction in free energy at the Ag–ZnO interfaces, whereas pinholes remain in thicker Ag layers on the ZnO surfaces. This finding extends earlier studies, reporting a favorable role of an increased oxygen deficiency on Ag wetting, with the point that oxygen excess beyond a threshold value is also helpful in improving Ag wetting. Our findings redefine the underlying Ag wetting mechanisms of the nonstoichiometric surface of oxide substrates. Moreover, the study provides guidelines for implementing a continuous ultrathin Ag layer while avoiding ion-induced damage to the oxide substrates.