The influence of the barrier layer on the mechanical properties of IR-reflecting (low-E) multilayer systems on glass

Since the 1980's the so called low-E (low emissivity or IR-reflecting) multilayer systems have gained in significance as regards the economical and ecological aspects of reducing the heat loss through window panes. The low-E coatings have to meet the requirements of a high transparency in the visible light range a high IR reflection (i.e.a high electrical conductivity) and mechanical properties, which have to ensure a certain stability and lifetime of the multilayer system, and the specific conditions during the steps of the production of double glazing units. A conventional low-E system consists of a thin silver layer sandwiched between two dielectric layers (e.g.SnO2, TiO2, ZnO etc.). Adding a barrier layer between the silver and the top layer enables an optimized performance of the multilayer system concerning the mentioned properties. Investigations on the nano-hardness (H), the elasticity (E), and the intrinsic stress (S) are presented for different barrrier-layer materials. The correlation between the physical properties (H,E,S) and the results of the qualitative (industrially relevant) "brush Test" (DIN 53778) is given. This study provides a deeper insight in the function of the barrier layer in a low-E mulilayer system and makes a directed selection of the barrier-material and thickness possible.