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Facet evolution on supported nanostructures: Effect of finite height

Fok, Pak-Wing and Rosales, Rodolfo R. and Margetis, Dionisios (2008) Facet evolution on supported nanostructures: Effect of finite height. Physical Review B, 78 (23). Art. No. 235401. ISSN 1098-0121. doi:10.1103/PhysRevB.78.235401.

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The surface of a nanostructure relaxing on a substrate consists of a finite number of interacting steps and often involves the expansion of facets. Prior theoretical studies of facet evolution have focused on models with an infinite number of steps, which neglect edge effects caused by the presence of the substrate. By considering diffusion of adsorbed atoms (adatoms) on terraces and attachment-detachment of atoms at steps, we show that these edge or finite height effects play an important role in the structure's macroscopic evolution. We assume diffusion-limited kinetics for adatoms and a homoepitaxial substrate. Specifically, using data from step simulations and a continuum theory, we demonstrate a switch in the time behavior of geometric quantities associated with facets: the facet edge position in a straight-step system and the facet radius of an axisymmetric structure. Our analysis and numerical simulations focus on two corresponding model systems where steps repel each other through entropic and elastic dipolar interactions. The first model is a vicinal surface consisting of a finite number of straight steps; for an initially uniform step train, the slope of the surface evolves symmetrically about the centerline, i.e., the middle step when the number of steps is odd. The second model is an axisymmetric structure consisting of a finite number of circular steps; in this case, we include curvature effects which cause steps to collapse under the effect of line tension. In the first case, we show that the position of the facet edge, measured from the centerline, switches from O(t^1/4) behavior to O(t^1/5) (where t is time). In the second case, the facet radius switches from O(t^1/4) to O(t). For the axisymmetric case, we also predict analytically through a continuum shock wave theory how the individual collapse times are modified by the effects of finite height under the assumption that step interactions are weak compared to the step line tension.

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Fok, Pak-Wing0000-0001-9655-614X
Additional Information:© 2008 The American Physical Society. (Received 15 April 2008; revised 30 September 2008; published 1 December 2008) The authors thank R.V. Kohn and E.D. Williams for valuable discussions. R.R.R. was partially supported by NSF-DMS under Contract No. 0813648. D.M. was supported in part by NSF-MRSEC under Contract No. DMR0520471 at the University of Maryland and also appreciates the support of the Maryland NanoCenter.
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Subject Keywords:adsorption; entropy; nanostructured materials; numerical analysis; surface diffusion
Issue or Number:23
Record Number:CaltechAUTHORS:FOKprb08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:12458
Deposited By: Archive Administrator
Deposited On:02 Dec 2008 19:36
Last Modified:08 Nov 2021 22:28

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