root 7R19.1 degrees superlattice of Ar/Ag(111) - art. no. 033407

Recent observations of a higher-order-commensurate lattice of argon physiso rbed on Ag(111) are discussed. The source of the registry energy and the po sitioning of the unit cell with four Ar atoms in hi,oh-symmetry low-coordin ation sites are attributed to a special case of the Novaco-McTague mechanis m for orientational epitaxy. The importance of measurements of the differen ces of adatom-substrate distances in the unit cell is emphasized.