Surface wrinkling of a rigid capping layer on a freestanding thin elastic film

Periodic wrinkling of a rigid capping layer on a deformable substrate is a ubiquitous example of pattern formation in nature. Many experiments have studied wrinkle formation during the compression of thin rigid films on relatively thick soft elastic substrates. The resulting wrinkling wavelength and amplitude can be predicted theoretically by minimizing the bending energy of the rigid film and the deformation energy of the soft substrate. To date, most studies have focused on the regime where the substrate thickness can be considered semi-infinite relative to that of the rigid film. In this work we use optical and atomic force microscopy to study the wrinkling behavior of thin rigid films upon compression by a pre-strained freestanding elastic substrates which cannot be considered semi-infinite. As the ratio of substrate to rigid film thickness is decreased, deviations from the typical semi-infinite behaviour are observed as periodic deformations of the entire substrate film become significant.