Delamination of functional coatings is an important issue in case of weak interfaces or aggressive environments. Similarly, scratch resistance which is a primary issue for functional thin films is partly controlled by adhesion. However the adhesion between layers in stacks is difficult to measure. Among the tests now existing, some provide only rather qualitative data, such as the scratch test, others cannot be used with thick brittle substrates, like four point bending. For glass substrates, we have previously developed a double cantilever beam method. Recently the stressed superlayer technique has been developed. The method measures the interfacial toughness through the delamination of a superlayer deposited under a large intrinsic stress [1]. At a certain thickness of the superlayer, it becomes thermodynamically favorable to release the stress by breaking an interface and bending the coating into a buckle or blister. This method has several advantages. It shows good reproducibility and is easy to control. Depending on stress and thickness of the superlayer, different mode mixities can be achieved. In this way, we can both probe the interfacial work of adhesion and influence the crack propagation. However a detailed understanding of the experimental relation between superlayer delamination and multilayer adhesion is still lacking. For this purpose, we studied a model interfaces in stacks ZnO/Ag/ZnO capped with superlayers of Mo under compressive stress. Thickness gradient in the superlayer allows us to observe the threshold thickness for delamination process in a single sample. In-situ XPS study is used to identify the interface of rupture in the stack. The results of this method (adhesion energy, interface of rupture) are compared with the results of established double cantilever beam tests [2].
1. M.W. Moon, H.M. Jensen, J.W. Hutchinson, K.H. Oh, and A.G. Evans, J. Mech. Phys. Solids 50 (11), 2355 (2002).
2. E. Barthel, O. Kerjan, P. Nael, and N. Nadaud, Thin Solid Films, 473, 272 (2004).
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