Surface diffusion on metals

Extensive computer simulations have been caiTied out on the near-surface and surface behaviour of materials having a simple cubic lattice structure. The interaction potential between pairs of atoms which has frequently been used for inert gas solids, such as solid argon, takes die Lennard-Jones form where d is the inter-nuclear distance, is the potential interaction energy at the minimum conesponding to the point of 

A/tt = Q.Ky where y is the surface free energy/cm and K is the surface curvature 

The Einstein flux equation for surface diffusion in this situation is 

When 6, die groove angle is small, die widdr between die two maxima, W, on eidrer side of a surface groove is obtained from die values 

Note here drat at a grain boundaiy, if 6 is small, 

Note here that at a grain boundary, if 9 is small, tan 9 = sin 9 = 

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H.P. Bonzel. Surface Diffusion on Metals. In H. Mehrer, editor. Diffusion in Metals and Alloys. Springer-Verlag, New York, 1990. 

Bonzel, H.P. "Surface Diffusion on Metals", in Diffusion in Solid Metals and Alloys. Landolt-Bomstein (New Series) III/26. Mehrer, H. (ed.), Berlin Springer-Verlag, 1993, p. 717-747. 

Prior to starting a full MC simulation, a thermodynamic eqnilibrinm must be estabUshed by rumiing a large number of initial MC steps. Final MC ran may require well over 10 steps. Surface diffusion on metals in the framework of lattice gas potentials is outUned by Uebing et al. [97Uebl]. For semiconductors, either a three-body PES or ab initio PES can used [96Kaxl]. 

Some cautions need to be issued with respect to surface cleanliness. Most of the experiments for insulators were not conducted under ultrahigh vacuum conditions. Hence, many of the surfaces were contaminated to vaiying degrees with atmospheric oxidation products and other species. Contamination can have major effects on surface diffusion on metals [91Bonl], and may be similarly important on insulators. However, since much of the methodology for diffusion studies on insulators has been rather erode and indireef the contamination effects are probably rarely worse than the inherent weaknesses of the methodology. 

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