Study on the surface segregation evolution of Ag-TiOx nanocomposite coatings

Abstract

The objective of this study is to systematically investigate the evolution of silver surface segregation of silver/titanium oxide nanocomposite coatings produced by reactive sputtering process. Different thickness barrier layers were deposited on the surface of Ag-TiOx two-dimensional (2D) and three-dimensional (3D) composite coatings at different deposition rates. In 2D mode, the SEM images and XPS patterns clearly show that the still strong silver segregation occurred even 50 nm thickness barrier coated with very low deposition rate (3 nm/min), while a sharp decrease of silver surface segregation can be achieved when high barrier deposition rate (20 nm/min) was applied. The high angle annular dark field (HAADF) STEM images reveal that the high silver mobility can be effectively suppressed under high barrier deposition rate. Similar phenomenon can be observed in 3D Ag-TiOx composite coatings. Moreover, the comparable study of the metallic titanium barrier layers show that a 30 nm barrier layer is enough to cover all the silver NPs, and silver atoms diffusion onto the surface was stopped under pure Ar atmosphere. The silver surface segregation evolution indicates that silver segregation could be the result of the combined effect of sputtering plasma and activated oxygen environment.