Interface step-induced thin-film delamination and buckling Antoine Ruffini ⇑ , Julien Durinck, Je ´ro ˆ me Colin, Christophe Coupeau, Jean Grilhe ´ Institut P’, CNRS-Universite ´ de Poitiers-ENSMA, De ´partement Physique et Me ´canique des Mate ´riaux, SP2MI-Te ´le ´port 2, F86962 Futuroscope-Chasseneuil Cedex, France Received 28 January 2013; accepted 9 April 2013 Available online 3 May 2013 Abstract Atomistic simulations based on experimental observations provide the first evidence that the interface delamination of a thin film from its substrate may start from interface steps. Buckling of the film after interface gliding from both edges of its delaminated part is also observed. In the framework of the Fo ¨ ppl–von Ka ´rma ´n theory of thin plates, the expression of the critical strain beyond which the film buckles has been then analytically determined as a function of the step height and gliding displacements. Both numerical and analytical results confirm that the formation of blisters is favoured in the neighbourhood of interfacial imperfections. Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Thin films; Buckling; Delamination; Defect; Atomistic simulations 1. Introduction Interface delamination of thin films on substrates is a frequently observed phenomenon which can release the high residual stress generated, for example, during the cre- ation of the structures [1–3]. In the case of compressive stress, buckling of the films has been also observed, which in turn may lead to further growth of delaminated zones [4–6]. Straight-sided blisters [7] or telephone-cord buckles [8] are some examples of structures which have been char- acterized in the framework of the Fo ¨ppl–von Ka ´rma ´n (FvK) theory of thin plates, and the profile as well as the critical strain related to buckling of these structures has been analytically determined [9,10]. The elastic coefficients of various films have been thus determined from the buckle profiles [11,12] and, taking advantage of the delamination process, the adhesion properties of several coated materials have been characterized [13–15]. However, understanding the elementary microscopic plasticity mechanisms involved in the decohesion process remains an important challenge in materials science [16–18]. It is commonly assumed in the literature that delamina- tion usually starts, at the interface, from imperfections such as fracture zones [19,20], topological defects (steps, etc.) [21,22], roughness [23,24] or chemical impurities [25]. In a previous theoretical work, the critical size of prototypical defects beyond which the buckling occurs has been deter- mined [26]. Experimental studies have been then conducted to test the different scenarios of delamination initiation [27,28]. It is the aim of this paper to identify the plasticity mech- anisms, at the microscopic scale, potentially involved in the first stages of the delamination process and to characterize the relations between plasticity, delamination and buckling for a strained thin film deposited on a substrate. After the presentation of the experimental observations of buckles above step-like nanostructures, this paper investigates, in the second part, the influence of interface steps on the ini- tiation of the delamination process by means of atomistic simulations. In the third part, the results are interpreted within the framework of continuum elasticity theory, through the FvK formalism of thin plates. 1359-6454/$36.00 Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.actamat.2013.04.012 ⇑ Corresponding author. Tel.: +33 549 49 68 30; fax: +33 549 49 66 92. E-mail address: antoine.ruffini@univ-poitiers.fr (A. Ruffini). www.elsevier.com/locate/actamat Available online at www.sciencedirect.com Acta Materialia 61 (2013) 4429–4438