On the ground state structure of monolayers on the (100) face of fcc crystals

While the (classical) ground state structure of an atomic monolayer adsorbe d at a smooth substrate with negligible corrugation potential is trivial, n amely, a triangular lattice with a spacing given by the minimum of the inte ratomic (Lennard-Jones) potential, nontrivial ground state structures occur on corrugated substrate surfaces. Assuming as a substrate surface the (100 ) plane of a face-centered cubic crystal, the possible (classical) ground s tate structures of the monolayer are studied by Monte Carlo simulation, var ying both the density of the adsorbed film and the strength of the potentia l due to the surface. Different incommensurate structures are found, which can be interpreted as (two-dimensional) patterns of domain walls separating commensurate regions. Typically the heavy walls are oriented along the fac e diagonals of the square substrate lattice. This nonuniform order also is reflected in the distribution of distances of the adsorbed atoms from the s ubstrate surface plane, which is not a delta function but may even display a bimodal character. (C) 2001 American Institute of Physics.