Solitonic-exchange mechanism of surface~diffusion

We study surface diffusion in the framework of a generalized Frenkel-Kontorova model with a nonconvex transverse degree of freedom. The model describes a lattice of atoms with a given concentration interacting by Morse-type forces, the lattice being subjected to a two-dimensional substrate potential which is periodic in one direction and nonconvex (Morse) in the transverse direction. The results are used to describe the complicated exchange-mediated diffusion mechanism recently observed in MD simulations [J.E. Black and Zeng-Ju Tian, Phys. Rev. Lett. {\bf 71}, 2445-2448(1993)].Comment: 22 Revtex pages, 9 figures to appear in Phys. Rev.

A vitrifying structure transition in the Dy/Mo(112) adsorption system

Annealing-driven irreversible structural transitions are studied by low-energy electron diffraction in submonolayer Dy films adsorbed on the Mo(112) surface. In a wide coverage range θ>0.07, Dy overlayers deposited at low temperatures (T≈100 K) are ordered and keep their structure upon annealing up to 350–600 K. Near θ=0.68, the overlayers are stable to high-temperature annealing (Ta=1000 K) as well, whereas the denser films are metastable and transform to more stable ordered structures. An unusual annealing effect is found for θ<0.58: the initially ordered metastable phases are replaced by phases having no extended order, which are assumed to be two-dimensional glasses. © 2001 American Institute of Physics