Published online by Cambridge University Press: 06 July 2010
Starting in the 1970s, considerable work was done on dimers and trimers and their surface diffusion, but there were no experimental studies of larger clusters, containing twenty or more atoms, since they were assumed to be immobile at the surface. This changed in 1984, with the work of Fink using the FIM, in which he assembled a cluster of twenty or more palladium atoms on the (110) plane of tungsten. At 390 K, this large cluster moved over the surface as a unit, as shown in Fig. 9.1, demonstrating its diffusivity. Large clusters turn out to be mobile at relatively low temperatures and their movement needed to be investigated, since it influences the stability of nanostructures and thin film growth kinetics. With the invention of the scanning tunneling microscope, large clusters were rediscovered a few years later, and work began to unravel how diffusion occurred, many of the studies focusing on the dependence of diffusivity on cluster size. This effort will be surveyed, arranged according to the type of the surface. Study of large clusters began with the examination of movement on a bcc surface, on W(110), but this work was not continued later; instead fcc surfaces were investigated in detail.
Large clusters on fcc(100) surfaces
Theoretical investigations of large clusters on fcc(100) surfaces started in 1980 with the work of Binder and Kalos, which initiated a number of discussions of how the cluster diffusivity D was affected by the size and the specific mechanism of diffusion.
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