AVS 50th International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuM

Paper SS2-TuM4
The Importance of Substrate Steps on the Ripening of 3D Particles: Ag and Cu on Ru(0001)

Tuesday, November 4, 2003, 9:20 am, Room 328

Session: Nucleation and Growth
Presenter: W.L. Ling, Sandia National Laboratories
Authors: W.L. Ling, Sandia National Laboratories
T. Giessel, Sandia National Laboratories
K. Thürmer, Sandia National Laboratories
R.Q. Hwang, Sandia National Laboratories
N.C. Bartelt, Sandia National Laboratories
K.F. McCarty, Sandia National Laboratories
Correspondent: Click to Email
Many hetero-epitaxial systems grow in the Stranski-Krastanov mode, in which material added to a wetting layer results in 3D islands. Once nucleated, and after growth has stopped, these 3D islands can minimize surface and interfacial free energy if they grow taller. However, there can be large free-energy barriers to this vertical growth because of the apparent necessity of nucleating new layers on top of these islands. In fact, Mullins and Rohrer have shown that it is unlikely that such nucleation would occur during ripening.@footnote 1@ In this work, we have studied the evolution of 3D islands of Ag and Cu on Ru(0001) using low-energy electron microscopy. We find that vertical growth does not occur at all during ripening when the Ag or Cu film does not overlay substrate steps. On stepped sufaces, on the other hand, we find vertical growth readily occurs. Using real-time observations, we find that the vertical growth occurs by an unexpected route that does not require nucleation. Islands, which adopt flat tops in an early stage of growth, gain a layer when they descend a monatomic Ru step. In this manner, they maintain the flat tops throughout ripening but grow taller as they migrate downhill on the substrate. We have investigated the vertical growth rate as a function of step spacing and island height. We find that thin islands shrink and tall islands grow, and the growth rate increases with the step density. @FootnoteText@@footnote 1@W.W. Mullins and G.S. Rohrer, J. Am. Ceram. Soc. 83, 214 (2000).