Abstract
Silver-based low-emissivity (low-E) coatings are applied on architectural glazing to cost-effectively reduce heat losses, as they generally consist of dielectric/Ag/dielectric multilayer stacks, where the thin Ag layer reflects long- wavelength infrared (IR), while the dielectric layers both protect the Ag and act as an anti-reflective barrier. The architecture of the multilayer stack influences its mechanical properties and it is strongly dependent on the residual stress distribution in the stack. Residual stress evaluation by combining focused ion beam (FIB) milling and digital image correlation (DIC), using the micro-ring core configuration (FIB-DIC), offers micron-scale lateral resolution and provides information about the residual stress variation with depth, i.e., it allows depth profiling for both equibiaxial and non-equibiaxial stress distributions and hence can be effectively used to characterize low-E coatings. In this work, we propose an innovative approach to improve the depth resolution and surface sensitivity for residual stress depth profiling in the case of ultra-thin as-deposited and post-deposition annealed Si3N4/Ag/ZnO low-E coatings, by considering different fractions of area for DIC strain analysis and accordingly developing a unique influence function to maintain the sensitivity of the technique at is maximum during the calculation. Residual stress measurements performed using this novel FIB-DIC approach revealed that the individual Si3N4/ZnO layers in the multilayer stack are under different amounts of compressive stresses. The magnitude and orientation of these stresses changes significantly after heat treatment and provides a clear explanation for the observed differences in terms of scratch critical load. The results show that the proposed FIB-DIC combined-areas approach is a unique method for accurately probing non-equibiaxial residual stresses with nano-scale resolution in thin films, including multilayers.
Highlights
Glass is widely used in many applications such as optoelectronics, construction and decoration, medicine, automotive, aerospace, and solar energy harvesting [1,2,3,4,5,6]
This article presented an improved procedure for nano-scale residual stress evaluation in multilayer thin films with non-equibiaxial stress states
The use of focused ion beam incremental nano-scale milling experiments was combined with optimized digital image correlation (DIC) and eigenstrain analysis procedures
Summary
Glass is widely used in many applications such as optoelectronics, construction and decoration, medicine, automotive, aerospace, and solar energy harvesting [1,2,3,4,5,6]. Glass used in building and vehicle windows is often coated with low-emissivity multilayer thin films. These coatings offer high transmission and low emissivity, allowing more sunlight to pass through while blocking the infrared (IR) radiation to minimize undesirable interior heating. 22 of of 16 infrared (IR) radiation to minimize undesirable interior heating Are often are formed depositing a reflectivealayer (e.g., layer silver)(e.g., ontosilver) the glass surface. To improve coatings oftenbyformed by depositing reflective onto the glass surface.
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