Effects of crystalline anisotropy on edge retraction and rim pinch-off during solid-state dewetting of single-crystal Ni and Cu thin films

Solid-state dewetting (SSD) leads to morphological evolution to form complex structures with diverse potential technological applications. A key phenomenon that controls the morphology of dewetted films is pinch-off, in which a rim develops at retracting edges and a valley forms ahead of the rim. When the valley comes into contact with the substrate, a wire is formed, and repeated pinch-off events generate regular arrays of parallel wires. Crystalline anisotropy strongly influences morphological evolution during SSD, including whether or not pinch-off occurs. The effects of crystalline anisotropy on pinch-off were investigated using lithographically patterned single-crystal Cu and Ni films with edges of varying in-plane crystallographic orientations. Whether valleys form and pinch-off occurs depends on the epitaxial orientation of the film, the in-plane crystallographic orientation of the patterned edge, and the annealing atmosphere. All these parameters affect the surface energy anisotropy of the rims. The effects of these parameters also differ significantly between Cu and Ni. Surface energy anisotropy of cross sections of dewetted wires or particles were quantified via a Winterbottom analysis. Level-set simulations using experimentally extracted Cahn–Hoffman vectors (ξ-vectors) reproduce morphological evolution observed during the dewetting process for all the investigated conditions.