Oxygen-dosage effect on the structure and composition of ultrathin NiO layers reactively grown on Ag(001)

NiO ultrathin films have been prepared under UHV conditions on Ag(001) substrate by metal deposition inO2 atmosphere. The films were prepared by deposition of the amount of metal correspondent to 1 ML monolayerof NiO in the presence of different oxygen-to-metal flux ratios, to investigate the oxygen dosage effecton the structure and composition of the growing layer and on the stoichiometry of Ni oxide. Thicker films (upto 20 ML) were also prepared. The structure has been monitored both in reciprocal and direct space bylow-energy electron diffraction and primary-beam diffraction-modulated electron emission. Core-level x-rayphotoemission spectroscopy has been used to study film chemistry and composition. At low coverage (below2 ML) a dramatic dependence of structure and composition on the oxygen-to-nickel flux ratio has beenobserved. Low oxygen dosage induces a (231) reconstruction in the 1-ML films that evolves to a (131)phase as the dosage and/or the film thickness increases. In the layers prepared at low oxygen dosage a largefraction of metallic Ni coexists with the Ni oxide, but the oxidized fraction largely prevails for high oxygendosage. The oxygen dosage during the growth also affects thicker films. The mosaic formation, which has beenascribed to misfit strain relaxation, is related to a low oxygen-to-nickel flux ratio.