SURFACE PHASES OF RECONSTRUCTED TUNGSTEN (100) AND MOLYBDENUM (100)

After several decades of experimental and theoretical work it has beco me clear that on most solids, including metals, the surface is subject to reconstruction, i.e. the outermost substrate atoms rearrange in re sponse to changes in temperature, adsorbate coverage, or other variabl es. Studies of W(100) and Mo(100) have been very useful in this develo pment. Early LEED studies of adsorption on these surfaces revealed a l arge number of distinct phases and it proved impossible to explain the ir formation in terms of conventional models which assumed the substra te to be ''passive''. The subsequent discovery that the surface is rec onstructed in these phases necessitated a reinterpretation of the resu lts and showed that the effective adatom-substrate and adatom-adatom i nteractions depend on metal atom displacements. It has been found that , in general, substrate structural changes have a strong-sometimes dom inant-influence on the kinetic and thermodynamic surface properties.