Interface roughening in wrinkly metal
We report a study on the roughening process in wrinklymetal film (aluminium) for thicknesses ranging from 35 to 1000 nm. The spatial and temporal scaling behaviours have been investigated by using atomic force microscopy. We show that fast diffusion is a part of the buckling process on a viscoelastic substrate due to Grinfeld-type instability. Power spectral density analysis reveals that the roughness exponent α is ∼0.85 for all thicknesses. This value is consistent with the fact that fast diffusion is the underlying process. The films exhibit slow temporal evolution, i.e. W ∼ t0 (β = 0.15 ± 0.02, Z = 5.66 ± 0.5), as the film thickness increases. The wavelength or correlation length also changes as ξ = t0.19±0.04 (Z = 5.26 ± 1) with the thickness. Deposition through a 400 μm × 1 cm (35 nm thickness) window shows a very organized wrinkled pattern with chain-like island attachment parallel to a surface with a smaller length scale (400 μm). We propose a model explaining why deposited atoms would move parallel to a surface with a shorter length scale to create ordered chain-like structures.