Published online by Cambridge University Press: 06 July 2010
With background information about the kinetic and experimental aspects of surface diffusion in hand we will now turn our attention to the atomistics of diffusion about which much has been learned through modern instrumentation. The usual picture of surface diffusion, which seems to agree at least qualitatively with experiments on diffusivities, is that atoms carry out random jumps between nearest-neighbor sites. Is this picture correct? Has it been tested in reasonable experiments? What can be said about the jumps which move an atom in surface diffusion? What is the nature of the sites at which atoms are bound? These are among the topics that will be considered at length now.
In these matters the geometry of the various surfaces studied plays an important role, and at the very start we therefore show hard-sphere models of planes that will emerge as significant. Presented first are channeled surfaces, bcc (211) and (321) in Fig. 3.1, as well as fcc(110), (311), and (331) in Fig. 3.2. These are followed in Fig. 3.3 by fcc(100) and (111) and bcc(100), (110), and (111) planes in Fig. 3.4. Their structures are sometimes quite similar, but their diffusion behavior may be quite different.
Adatom binding sites
Location
Where on a surface are metal adatoms bonded? That is an important question for understanding how atoms progress over a surface in diffusion. LEED has been very important in providing information about the geometry of adsorbed layers.
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