Effect of substrate elasticity on thin film buckle morphologies: A phase diagram

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Thin films submitted to internal/external stresses are known to undergo buckling over a critical stress level. In the case of a rigid substrate, depending on the stress anisotropy, three elementary buckling structures are expected: straight-sided, bubble or telephone cord buckles. In this context, the effect of the substrate elasticity on the expected buckled morphologies is explored. The post-buckling equilibrium shapes that develop on parallel delaminated stripes of films for a biaxial compressive stress state are studied. Finite elements methods calculations are carried out to simulate the various equilibrium configurations. A morphological map is extracted and plotted as a function of the stress components in the longitudinal ( i.e. along the stripe direction) and transversal direction ( i.e. perpendicular to the stripe direction). It is shown that the stability domains of the elementary buckles are shifted down to lower stresses as the substrate stiffness is decreased. In addition, the stability domain of the telephone cord buckles is shown to be enlarged. Finally, an intermediate domain between bubbles and both straight-sided and telephone cord buckles is evidenced on the morphological map. The buckles are in this case characterized by hook-like or bone-like structures. This latter buckling structure has been experimentally observed by atomic force microscopy on nickel/polycarbonate systems. • Effect of substrate elasticity on buckled morphologies • Significant shift down towards low stresses of the stability domain of buckles • Evidencing of an intermediate stability domain between straight-sided and telephone cord buckles