Morphology and chemical activity at the Au/NiO interface

The study of gold/oxide interfaces has increased recently due to its new found catalytic properties. Those properties are strongly dependent on the structure and morphology of the overlayer and on its interaction with the substrate [1, 2]. The tendency of Au to nucleate at oxygen vacancies [3] drives the growth of Au and favors charge transfer between the overlayer and the substrate. The morphology of the substrate surface and the fi rst stage of the Au growth thus result fundamental in determining the properties of gold/oxide systems. We present here a detailed characterization of the Au/NiO interface from a structural and morphological point of view by means of XPD, LEED and STM/AFM. We also investigated the chemical reactions at interface by XPS. The evolution of the Au/NiO system was studied as a function of the Au deposition in the range between 0 and 30 ML, with emphasis on the low deposition (<3 ML). XPS measurements aimed to a quantifi cation of the previously reported NiO reduction [4] induced by Au deposition. STM/AFM measurements were performed in order to establish a relationship between the growth mode and morphology of the Au overlayer and the Ni reduction at interface. We have also carried out similar experiments on the Fe/NiO [5] and Pt/NiO in order to investigate the general features of the metal/NiO systems. [1] Z. Yang et al. Phys. Rev. B 61, 14066 (2000). [2] L. Giordano et al. Surf. Sci. 471 (2001) 21. [3] Y. Zongxian et al. Phys. Rev. B 65, 155407, (2002). [4] R. de Masi et al. Surf. Sci. 515 (2002) 523. [5] P. Luches et al. Surf. Sci. in press.