Ordering of Self-Diffusion Barrier Energies on Pt(110)-1x2 Page: 3 of 18
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For Physical Review B, Rapid Comunications
wall. It hops along the cluster, then returns to the channel at its other end. Called
"leapfrog diffusion," the same process occurs in molecular-dynamics simulations
by Montalenti and Ferrando.3
The energetic advantage of leapfrogging is that on the MEP all adatoms but one
occupy high-coordination channel sites. This advantage, however, is shared by a
dissociation-recombination mechanism in which atom 1 at one end of a cluster sep-
arates from the remainder, then, successively, atom 2 catches up to 1, atom 3
catches up to the 1-2 dimer, etc., and eventually the reconstituted cluster is dis-
The focus of this note is the recent Scanning Tunneling Microscopy (STM)
observation4 that dissociation-recombination is not just facile, but the most facile
dimer-diffusion mode at 300-350K. I show that this result conflicts with bond-
counting arguments and ab-initio calculations; both favor leapfrogging over adatom
diffusion and addimer dissociation. The barriers I compute for dimer dissociation
(1.13 eV) and leapfrogging (0.76 eV) imply, e.g., that the former is 106 times less
probable at 300K than dimer leapfrogging, assuming equal prefactors.5 Thus ab-
initio theory suggests revisiting the experimental analysis.
Physical arguments - Leapfrog diffusion of dimers should be more facile than
monomer diffusion because the MEP's for both processes involve moving an ada-
tom from its initial channel-bottom site up a channel wall, along it, then down again
(cf. Figs. 1 and 2). The key distinction is that in the leapfrog case the moving ada-
tom always has one additional neighbor, its partner adatom. Since binding-energy
loss per broken bond varies inversely with the initial number of neighbors,6 barriers
along the leapfrog.path must therefore be lower.
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Feibelman, Peter J. Ordering of Self-Diffusion Barrier Energies on Pt(110)-1x2, article, June 1, 1999; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc707263/m1/3/: accessed September 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.