An atomistic view of the dynamic behavior of the (001) surface was presented. The atomic processes which were involved in the dissolution of the surface layer were isolated, and their mechanisms and energetics were studied quantitatively. At temperatures above 400K, lattice-step atoms could move along the (mainly <110>) steps. Step atoms could also dissociate to the terraces. The equilibrium shape of the surface layer could be reached via the diffusion, dissociation, and re-absorption of step-atoms. At about 400K, this shape was a square with its 4 sides parallel to the <110> close-packed atomic row directions. Step atoms dissociated from edge sites, kink sites, ledge sites, and recessed sites with similar probability. Therefore, the dissociation was not orderly, and the steps were roughened at temperatures above about 500K. The diffusion energy of ledge-site atoms along the <110> lattice steps was measured to be 0.62eV. This diffusion occurred via atomic hopping. On the other hand, self-diffusion on the (001) terrace occurred via atomic replacement in the <001> directions. The dissociation energies of edge-site atoms and other step atoms were measured to be 1.35 and 1.40eV, respectively. The line-energy density of the <110> step was 3.2 x 10-10J/m, and the self-adsorption energy was 6.37eV. Hollow clusters and so-called sponge-like 2-dimensional surface layers were also found on the (001) surface.

C.Chen, T.T.Tsong: Physical Review B, 1993, 47[23], 15852-9