Structure maps of surface structures

The adatom positions of adsorbates like A = H, Se Xe on (100) or (111) surf aces of bcc or ccp metals and related compounds like hcp metals, NaCl or Zn S form a square, hexagonal, honeycomb or Kagome net. The ordered structures can be characterized by the self-coordination numbers of nearest, next-nea rest and third neighbors T-1, T-2, T-3 and the T-1, T-2 values plotted in s tructure maps for a constant ratio of vacant/occupied sites. Most experimen tal structures have a single coordination of all A atoms. The interactions between A atoms are attractive for chains of A atoms with T-1 = 2 and repul sive for T-1 = 0 or T-1 = T-2 = 0. The structures with intermediate T-1, T- 2 values can be characterized by sequences of structural units like squares or hexagons with a different occupation of the corners by A atoms.