Investigation of silver diffusion in TiO2/Ag/TiO2 coatings

Low emissivity (low-E) coatings consisting of dielectric/silver/dielectric multi-layer stacks are applied to large-area architectural glazing to reduce heat losses from buildings. In this work TiO2/Ag/TiO2 stacks were deposited onto soda-lime glass by pulsed DC reactive magnetron sputtering. The coatings were annealed in the range 100–600°C to study silver diffusion through neighbouring layers. Depth-profiling analysis was performed on these samples using time-of-flight secondary ion mass spectrometry and selected samples were also analysed by X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry. Fick’s second diffusion law was used to find diffusion coefficient values and to investigate the temperature dependence of silver diffusion. To investigate film morphology and composition, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were performed. The purpose of this study is the requirement for the understanding of the issue of silver diffusion during annealing treatments used in glass fabrication and the results obtained show that silver diffuses through the adjacent layers in a stack during heat treatment. However, in the temperature range investigated, the diffusion rates did not follow an Arrhenius dependence. At higher temperatures and longer annealing times sodium also diffuses from the glass into the coating, replacing the silver between the titania layers.