Abstract
A relation between the boundary curvature κ and the wrinkle wavelength λ of a thin suspended film under boundary confinement is demonstrated. Experiments were performed with nanocrystalline diamond films of approximate thickness 184 nm grown on glass substrates. By removing portions of the substrates after growth, suspended films with circular boundaries of radius 30–811 μm were fabricated. Due to residual stresses, the portions of the film bonded to the substrate are of approximate compressive prestrain 11×10−4 and the suspended portions of the film are azimuthally wrinkled at their boundary. Measurements show that λ decreases monotonically with κ, and a simple model that is in line with this trend is proposed. The model can be applied to design devices with functional wrinkles and can be adapted to gain insight into other systems such as plant leaves. A method for measuring residual compressive strain in thin films, which complements standard strain characterization methods, is also described.
Highlights
Where t is the film thickness and e is a strain that induces wrinkling.[10,11,12] Efforts to investigate the effect of the boundary curvature on the wrinkling of thin films began only recently
Experiments were performed with nanocrystalline diamond films of approximate thickness 184 nm grown on glass substrates
The portions of the film bonded to the substrate are of approximate compressive prestrain 11 Â 10À4 and the suspended portions of the film are azimuthally wrinkled at their boundary
Summary
Where t is the film thickness and e is a strain that induces wrinkling.[10,11,12] Efforts to investigate the effect of the boundary curvature on the wrinkling of thin films began only recently. By removing portions of the substrates after growth, suspended films with circular boundaries of radius 30–811 lm were fabricated. The portions of the film bonded to the substrate are of approximate compressive prestrain 11 Â 10À4 and the suspended portions of the film are azimuthally wrinkled at their boundary.
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