The effect of boundary curvature on the wrinkling of thin suspended films

Wrinkling is a ubiquitous phenomenon in nature that can be used to optimize the performance of devices [1]. However, few basic tools are available to predict the wrinkling of thin films due to the intricate mechanics that are involved [2]. Here, we show a relation between the boundary curvature κ and the wrinkle wavelength λ of a thin suspended film under boundary confinement [3]. Experiments are done with nanocrystalline diamond films of approximate thickness 184 nm that are grown on glass substrates. By etching parts of substrate after growth, suspended films with circular boundaries of radius ranging from 30 to 811 μm are made using recent technologies [4,5]. Due to thermal mismatch, the parts of film attached to the substrate are compressively strained and the suspended parts of film are azimuthally wrinkled. We show that λ monotonically decreases with κ and present a model that predicts this.

[1] J. B. Kim et al. Nature Photon 6, 327–332 (2012)
[2] E. Cerda et al. Phys. Rev. Lett. 90, 074302 (2003)
[3] S. D. Janssens et al. Appl. Phys. Lett. 116, 193702 (2020)
[4] S. D. Janssens et al. Appl. Phys. Lett. 104, 073107 (2014)
[5] S. D. Janssens et al. Diamond Relat. Mater. 98, 107511 (2019)