Landolt-Börnstein - Group III Condensed Matter

13.8 Systematics of surface diffusion coefficients

Abstract

This chapter briefly discusses the systematics of surface diffusion coefficients. The activation enthalpy of migration of a single adatom is defined as the enthalpy difference between the equilibrium site and the saddle point configuration. Both of these enthalpies are related to the bond strength between two atoms of this material (energy of cohesion). This latter quantity can to a first approximation be derived from the enthalpy of sublimation (or evaporation at TM) of the solid, ΔHsub. Therefore one expects the enthalpy of migration to be a certain fraction of the enthalpy of sublimation. This is easy to understand for self-diffusion but for hetero-diffusion of different species on the same substrate metal one assumes a similar relationship to hold because changes in the adsorption enthalpy of different species are related to changes in their sublimation enthalpies. A good demonstration of the utility of such a relationship are intrinsic surface diffusion data for several adatoms on W(211). The same principal approach has been applied to mass transfer surface self-diffusion data in order to derive a general material-independent expression for the temperature dependence of Ds. Although in this case the activation enthalpy is equal to the sum of migration and formation enthalpy, both of these quantities are related to the interatomic bond strength and hence ΔHsub which by itself is proportional to TM.

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Title
13.8 Systematics of surface diffusion coefficients
Book Title
Diffusion in Solid Metals and Alloys
In
13 Surface diffusion on metals
Book DOI
10.1007/b37801
Chapter DOI
10.1007/10390457_139
Part of
Landolt-Börnstein - Group III Condensed Matter
Volume
26
Editors
  • H. Mehrer
  • Authors
  • H. P. Bonzel
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