p(nx1) superstructures of Pb on Cu(110)

The structures of the p (n x 1) superstructures (n = 4, 5, and 9) of Pb on Cu(110) in the coverage range between Theta = 0.75 and 0.8 are revealed by atomically resolved scanning tunneling microscopy. All three superstructures are formed by substitution of every nth row of Cu atoms (n = 4, 5, and 9) in the [001] direction by Pb atoms. The Pb atoms in between are lined up in the [<(1) over bar 10>] direction. The p(4 x 1) structure appears in two different modifications: one with substitutional rows of Pb atoms and one with a simple overlayer structure without substituted rows of Cu atoms. Alternating succession of these two modifications results in p(12 x 1) domains. It is further shown that the p(9 x 1) structure is not a succession of p(4 x 1) and p(5 x 1) but a superstructure on its own. The p(5 x 1) structure proposed here agrees with previous x-ray-diffraction data at least as well as the quasihexagonal model proposed earlier. We have, in addition, identified the nature of the phase that has been described incommensurate obtained by desorption of Pb upon annealing above 600 K.