ABSTRACT
A BiFeO3 film is grown epitaxially on a PrScO3 single crystal substrate which imparts ~ 1.45% of biaxial tensile strain to BiFeO3 resulting from lattice misfit. The biaxial tensile strain effect on BiFeO3 is investigated in terms of crystal structure, Poisson ratio, and ferroelectric domain structure. Lattice resolution scanning transmission electron microscopy, precession electron diffraction, and X-ray diffraction results clearly show that in-plane interplanar distance of BiFeO3 is the same as that of PrScO3 with no sign of misfit dislocations, indicating that the biaxial tensile strain caused by lattice mismatch between BiFeO3 and PrScO3 are stored as elastic energy within BiFeO3 film. Nano-beam electron diffraction patterns compared with structure factor calculation found that the BiFeO3 maintains rhombohedral symmetry, i.e., space group of R3c. The pattern analysis also revealed two crystallographically distinguishable domains. Their relations with ferroelectric domain structures in terms of size and spontaneous polarization orientations within the domains are further understood using four-dimensional scanning transmission electron microscopy technique.
ABSTRACT
Various layer schemes have been developed to protect thin film silver mirrors from tarnish and corrosion. However, the mechanisms by which these additional layers improve mirror durability are not fully understood. Accelerated environmental exposure testing of protected silver mirrors was used to investigate the effects of layer composition on the mechanisms of corrosion feature development and growth. Two model mirror coatings were analyzed in which the composition of the base layer below the silver and the adhesion layer above the silver were varied. Large circular corrosion features formed preferentially along the silver-chromium interfaces, regardless of where this interface was located within the layered structure of the mirror. The corrosion features originated at coating defects in the dielectric protection layer, and their growth was likely driven by the oxidation and chloridation of both silver and chromium at the Ag-Cr interfaces.
ABSTRACT
Various overcoat layers have been developed to protect silver mirrors from tarnish and corrosion. However, the mechanisms by which these protective layers improve mirror durability are not fully understood. Mixed flowing gas exposure was used to investigate the corrosion behavior of plasma beam sputtered silver mirrors with different adhesion layer materials. A small amount of nickel in the adhesion layer had a significant impact on the silver-dielectric interface. Additionally, lateral transport of silver was found to be an important factor in the corrosion process. Better stability at all layer interfaces is suggested to improve mirror durability.
