AVS 47th International Symposium
    Surface Science Monday Sessions
       Session SS3-MoA

Paper SS3-MoA7
Shape Relaxation of Crystals via Layer-by-Layer Pealing Observed in Real Time

Monday, October 2, 2000, 4:00 pm, Room 210

Session: Surface Diffusion and Wetting
Presenter: K. Thürmer, University of Maryland
Authors: K. Thürmer, University of Maryland
J.E. Reutt-Robey, University of Maryland
E.D. Williams, University of Maryland
Correspondent: Click to Email
How does a small faceted crystal adjust its shape to a changing temperature and is it possible to reach its equilibrium shape? A positive answer to the latter question would allow an elegant experimental determination of absolute values of surface and step free energies.@footnote 1@ Small defect-free crystals near equilibrium experience an energy barrier for both growth and removal of atomic layers on a facet. Under growth conditions the 2D nucleation barrier gives rise to shape oscillations.@footnote 2@ Recently Mullins et al.@footnote 3@ concluded that for crystals larger than a few nm the magnitude of this barrier prevents surface free energy driven reshaping. We studied µm sized Lead crystals with an variable temperature STM under UHV-conditions. By tracking several crystals during a temperature increase from 110°C up to 205°C we confirmed Mullins suggestion that these crystallites are immobilized in their initial shapes. To investigate how a crystal establishes its shape we quenched the sample to temperatures between 65 and 110°C. STM observations of the (111) top facet starting shortly after the quench reveal a scenario of facet growth, where all layers smaller than a critical size peal off one-by-one. Uwaha@footnote 4@ treated the kinetics of such a collapse of step loops applying a constant critical size. Our experiments indicate a modification of the critical radius by a slow redistribution of atoms over the curved region of the crystal. @FootnoteText@ Work supported by NSF-MRSEC @footnote 1@ H.P. Bonzel et al, to be published @footnote 2@ J. Tersoff et al, Phys Rev. Lett. 70, 1143 (1993) @footnote 3@ W.W. Mullins et al, J. Am. Ceram. Soc., 83, 214 (2000) @footnote 4@ M. Uwaha, J. Phys. Soc. Jap., 57, 1681 (1988).