ELASTIC STEP INTERACTIONS ON VICINAL SURFACES OF FCC METALS

The structural and energetic properties of [100] and [110] steps on th e (001) surface of fcc metal have been determined by T = 0 atomistic s imulations. The interactions between [100] steps and between [110] ste ps on the (001) surface are determined from the surface energy of a se ries of (01n) and (1BAR1m) surfaces, respectively. For step spacings l arger than three fcc lattice parameters (R > 3a0), we find that the in teraction energy between two similar steps on the (001) surface can be reasonably represented by the functional form R-2, in agreement with the prediction of a simple linear elastic analysis based upon a line d ipole force model of a step. However, we observe qualitative differenc es between the displacement fields determined by the two methods. For R < 3a0, on the other hand, we find that the interaction between steps deviates significantly from the form R-2. These deviations demonstrat e that both dipole and quadrupole force distributions are necessary to account for step-step interactions for spacings as small as a fractio n of a lattice parameter up to infinite step spacings. We show that a [100] step on the (001) surface in Au and Pt (but not in Ag, Au, Cu, o r Pd) may lower the surface energy by transforming into a zig-zagged [ 110] step.