IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Friday Sessions
       Session SS1-FrM

Invited Paper SS1-FrM3
Vacancies in Solids and the Stability of Surface Morphology

Friday, November 2, 2001, 9:00 am, Room 120

Session: Dynamics of Metal Surfaces
Presenter: K.F. McCarty, Sandia National Laboratories
Authors: K.F. McCarty, Sandia National Laboratories
J.A. Nobel, Sandia National Laboratories
N.C. Bartelt, Sandia National Laboratories
Correspondent: Click to Email
We have examined the kinetics of island decay on the NiAl (110) surface using low-energy electron microscopy (LEEM). Remarkably, the decay rates are constant in time and totally independent of the local environment (e.g., the width of the immediately adja cent terraces and degree of island curvature). Given the lack of surface current between islands of different curvature, we conclude that surface diffusion is not important to the smoothing process. Instead, we find unambiguous evidence that bulk vacancie s are responsible -- we visibly observe exchange between bulk vacancies and the surface when the sample temperature is changed. For a temperature increase, the surface steps advance. For a temperature decrease, the surface steps recess. These changes result from the increase (decrease) in bulk vacancy concentration for a temperature increase (decrease). Remarkably, the size change accompanying a temperature change is strictly proportional to the perimeter (step length) of the island, and again is totally independent of the local environment. Thus, we conclude that the atoms at surface steps undergo direct exchange with bulk vacancies. We will present simple mathematical models showing how this mechanism quantitatively describes the constant-rate kinetics as well as the bulk-derived flux associated with a temperature change. The complete independence of the surface dynamics on the local environment results from the fact that the steps are interacting directly with the bulk, and thus, the local step density and curvature are largely irrelevant. We will also present results illustrating how the bulk/surface exchange affects NiAl oxidation. This work was performed under the U.S. Department of Energy contract DE-AC04-94AL85000 and supported by the Office of Basic Energy Sciences-Division of Materials Sciences.