Confined wrinkling: impact on pattern morphology and periodicity

Wrinkling instabilities are observed in compressed multilayers made of materials with contrasted properties. Here, we study the influence of confinement, i.e. using foundations with dimensions smaller than 50 nm, on the wrinkled patterns. We show that confinement generates a change in morphology from labyrinths to a dotted pattern with hexagonal symmetry. This transition occurs when the amplitude of the wrinkles becomes comparable to the thickness of the upper membrane, i.e. A ≃ h. For very thin foundations (h < 100 nm), a drastic deviation from the usual evolution of the wavelength with the foundation thickness is observed. This new regime was explained by considering the van der Waals interactions between the metal layer and the substrate. The VDW energy term was involved in a new scaling law model that agrees with the experimental data.