FIM studies of single adsorbed atoms

In a surface diffusion experiment one has to determine the adsorption site and the displacement of an adatom within a heating period from two field ion images, one taken before the heating period and one after. An accurate determination of the image magnification and of distances from 

The diffusion data can also be analyzed in terms of the moments of the displacement distribution used by Ayrault Ehrlich.121 The second moment of a sample set, m2, is given by 

Applications to surface science Table 4.1 Diffusion parameters 

If the activation energies of surface diffusion vary over a wide range from one element to another and from one surface to another, the diffusivity, or the pre-exponential factor, D0, does not. Within the very limited accuracy of the field ion microscope measurements, usually no better than one order of magnitude because of the narrow temperature range within which a measurement can be conveniently done, all measured values of D0 are consistent with eq. (4.22) by taking AS = 0, and v0 = kTIh where h is the Planck constant, or D0 are about a few 10-3 cm2/s. This has been pointed out repeatedly by the author126 since there is 

At a very low temperature where an adatom jumps only occasionally, about one atomic jump in every few seconds, field ion microscope studies conclude that the surface diffusion of adatoms is consistent with a discrete nearest neighbor random walk. However, in molecular dynamic simulations of diffusion phenomena, which are carried out only for high temperature diffusions where atomic jumps are very rapid, i.e. an atomic 

---