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The growth of NiO epitaxial thin films on Ag(001) has been studied by XPS and STM techniques in the 0.3-3ML range. Ni atoms were evaporated in atomic oxygen ambient keeping the substrate at 190°C. Ni 2p XPS analysis reveals the absence of metallic Ni cluster on the surface. Moreover, the intensity ratio of characteristic nickel and oxygen spectral peaks with similar kinetic energy, such as the Ni 2p XPS to O KLL Auger peaks, are identical to those measured in-situ under the same conditions on cleaved NiO, thus showing a good stoichiometric composition of the grown NiO films. The XPS spectra excludes the oxidation of Ag substrate. At 0.3ML NiO one-dimensional and bi-dimensional structures nucleate embedded in the Ag substrate. These structures are monoatomic and oriented along the [110] crystallographic direction, and they appear as depressions. Their apparent height is independent from the applied bias voltage, suggesting that, at very low coverage, the electronic properties of the film are different with respect to bulk NiO. Further deposition leads to the disappearance of one-dimensional structures due to percolation. After the depositions Ag steps appear straight and [110]-oriented and they are decorated with NiO structures. The 3ML film completely covers the substrate, tracing the underneath Ag morphology. It is characterized by a roughness of about 0.2 nm, suggesting a layer by layer growth mode. |