Copper growth on the O-terminated ZnO(000(1)over-bar) surface: Structure and morphology - art. no. 085424

The effects of copper deposition or). the ZnO(000 (1) over bar) O-terminate d surface at 300 K have been studied by surface x-ray diffraction (SXRD). T erraces about 550 Angstrom wide, presenting a (1 x 1) bulk-derived order, w ere obtained on the clean surface after repeated cycles of Ar+ sputtering-a nnealing. The SXRD data show that inward relaxation takes place in the two topmost planes (-0.2 Angstrom for the first O plane) while the site occupan cy in the second Zn plane is reduced by one quarter. Upon copper adsorption , a full derelaxation of the O surface is observed. In addition, the ordere d fraction of atoms in the top O plane is reduced by one quarter, a feature that may be associated to some O-Cu interaction. The Cu adatoms involved i n such interaction could be responsible for the surface derelaxation throug h a charge transfer, No change is detected concerning the CuZnO(000 (1) ove r bar)-(1 x 1) surface up to an equivalent of several monolayers of deposit ed copper. Copper aggregates into flat islands, with two orientational rela tionships, at 180 degrees from each other: Cu(111)//ZnO(000 (1) over bar) w ith Cu[(1) over bar 10]//ZnO[100]. The islands are not strained on the subs trate, even at very early stages of growth. The rodlike signal from the (11 1) facet is already measured for an equivalent of 5 Cu ML. The lateral grow th proceeds preferentially along the ZnO[210] axis. Additional diffraction signals, attributed to copper islands nucleating at the ZnO bilayer step ed ges, are detected.