High-temperature stability of Ag film grown on Ni–Cr substrate

Abstract

The behaviour of Ag films grown on Ni–Cr substrate subjected to high-temperature annealing was studied to determine their microstructural, mechanical and chemical stability. Several buffer layers, including native oxide, MgO, CeO₂ and Pd, were used to hinder Ag film degradation. Ag films, as well as the employed buffer layers, were deposited by e-beam evaporation. Ag film thickness ranged from tenths up to several μm. The main degradation of the Ag film after annealing in air is the formation of micrometric holes by film dewetting. The behaviour of films grown on oxidized Ni–Cr is in broad agreement with results reported in literature, whereas the use of either MgO or CeO₂ layers strongly suppressed hole formation. Both oxides, and particularly the latter, were demonstrated to be effective barriers against Ni and Cr diffusion towards the Ag layer. However, these architectures showed poor adhesion and blister formation occurred. Moreover, severe delamination in long samples was observed. The use of an additional Pd layer prior to Ag film deposition was revealed to be beneficial for both dewetting suppression and film adhesion enhancement.

Keywords:

• Ag film
• dewetting
• self-diffusion
• film adhesion

Acknowledgments

This work has been accomplished in the framework of ENEA/Edison collaboration. The authors wish to thank U. Baffi for technical assistance, L. Gentili for English revision and F. Clarelli for useful discussions.