Periodic mass shedding of a retracting solid film step

• Published in: Acta materialia Vol. 48; no. 8; pp. 1719 - 1728
• Main Authors: Wong, Harris, Voorhees, P.W., Miksis, M.J., Davis, S.H.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 11.05.2000; Elsevier Science
• Subjects: ANNEALING; Condensed matter: structure, mechanical and thermal properties; DIFFUSION; Exact sciences and technology; MASS TRANSFER; MATERIALS SCIENCE; MATHEMATICAL MODELS; Morphological evolution; MORPHOLOGY; Other nonelectronic physical properties; Physical properties of thin films, nonelectronic; Physics; Surface diffusion; SURFACE ENERGY; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); THIN FILMS; Transport modeling; Thin films; Transport modeling; Annealing; Surface diffusion; Morphological evolution; Theoretical study; Transport processes; Contact angle; Diffusion; Contraction
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/S1359-6454(00)00016-1

A semi-infinite, uniform film on a substrate tends to contract from the edge to reduce the surface energy of the system. This work studies the two-dimensional retraction of such a film step, assuming that the film evolves by capillarity-driven surface diffusion. It is found that the retracting film edge forms a thickened ridge followed by a valley. The valley sinks with time and eventually touches the substrate. The ridge then detaches from the film. The new film edge retracts to form another ridge accompanied again by a valley, and the mass shedding cycle is repeated. This periodic mass shedding is simulated numerically for contact angle α between 30 and 180°. For smaller α, a small-slope late-time solution is found that agrees with the numerical solution for α=30°. Thus, the complete range of α is covered. The long-time retraction speed and the distance traveled per cycle agree quantitatively with experiments.