P(NX1) SUPERSTRUCTURES OF PB ON CU(110)

The structures of the p (n x 1) superstructures (n = 4, 5, and 9) of P b on Cu(110) in the coverage range between Theta = 0.75 and 0.8 are re vealed by atomically resolved scanning tunneling microscopy. All three superstructures are formed by substitution of every nth row of Cu ato ms (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 substi tutional rows of Pb atoms and one with a simple overlayer structure wi thout substituted rows of Cu atoms. Alternating succession of these tw o 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) b ut a superstructure on its own. The p(5 x 1) structure proposed here a grees with previous x-ray-diffraction data at least as well as the qua sihexagonal model proposed earlier. We have, in addition, identified t he nature of the phase that has been described incommensurate obtained by desorption of Pb upon annealing above 600 K.