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Agradecimentos: We thank Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP-07/54829-5) and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) for financial support. Special thanks to Prof. G. Tremiliosi-Filho for lending the Au(332) crystal. M.J.P. and E.A.C. thank FAPESP and CNPq for the fellowships granted (Proc. FAPESP 2011/12.566-3; Proc. CNPq 150192/2014-2). We also thank the Brazilian Synchrotron Light Source for the beam time and the PGM-beamline staff for support during the experiments Abstract: The reactivity of the Pt/Au(332) surface was studied using high-resolution photoelectron spectroscopy and carbon monoxide adsorption at 3.5 x 10(-3) mbar. The characterization of Pt/Au(332) indicates the formation of a Au-Pt surface alloy at the topmost atomic layer of the (332) crystal due to an atomic exchange mechanism at both terrace and step edge. The amount of alloyed Au atoms has proven to be dependent on the amount of Pt deposited in the coverage range investigated. The activation of Au atoms by alloying is detected by comparing the ability of the surface to adsorb CO at high pressures. By analyzing the C 1s and O 1s photoemission lines it is possible to conclude that CO adsorption is both dissociative and molecular on the PtAu/Au(332) surface, differently from the behavior observed for Au and Pt single crystals. Also, by rising the temperature of the COads-PtAu/Au(332) surface, a dissociative reaction path is followed by the accumulation of graphitic carbon on the surface and the oxygen/carbon dioxide desorption. Thus, our results show not only the differential catalytic behavior of Pt@Au/Au(hkl) model surfaces but also that Au atoms have an active role on the reaction mechanism FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Aberto

Agradecimentos: Authors thank Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP-07/54829-5) and Conselho Nacional de Pesquisa (CNPq) for financial support. Specially thank to L. H. Lima for experimental assistance with STM measurements and Prof. G. Tremiliosi-Filho for lending the Au(332) crystal. MJP, SF and EAC thank FAPESP and CNPq for the fellowships granted (Procs. FAPESP 2011/12.566-3 and 2012/16860-6; Proc. CNPq 160172/2011-0) Abstract: Two single crystalline surfaces of Au vicinal to the (111) plane were modified with Pt and studied using scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) in ultra-high vacuum environment. The vicinal surfaces studied are Au(332) and Au(887) and different Pt coverage (yPt) were deposited on each surface. From STM images we determine that Pt deposits on both surfaces as nanoislands with heights ranging from 1 ML to 3 ML depending on yPt. On both surfaces the early growth of Pt ad-islands occurs at the lower part of the step edge, with Pt ad-atoms being incorporated into the steps in some cases. XPS results indicate that partial alloying of Pt occurs at the interface at room temperature and at all coverage, as suggested by the negative chemical shift of Pt 4f core line, indicating an upward shift of the d-band center of the alloyed Pt. Also, the existence of a segregated Pt phase especially at higher coverage is detected by XPS. Sample annealing indicates that the temperature rise promotes a further incorporation of Pt atoms into the Au substrate as supported by STM and XPS results. Additionally, the catalytic activity of different PtAu systems reported in the literature for some electrochemical reactions is discussed considering our findings FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: Authors would like to thank Conselho Nacional de Pesquisa (CNPq) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for financial support. Special thanks to L. H. Lima for discussions during STM measurements and Prof. G. Tremiliosi-Filho for lending the Au crystal. MJP thanks FAPESP for the fellowship granted (Proc. 2011/12.566-3). EAC thanks CNPq for the fellowship granted (Proc. 160172/2011-0) Abstract: Co nanoislands were grown on (332) vicinal surface of Au in UHV using the e-beam evaporation technique. Scanning tunneling microscopy results reveal that Co deposition occurs following an islanding mode for ?Co ranging from 0.17 to 0.64 ML. At low coverage nanoislands show a monolayer height, while at higher Co loadings, islands have a maximum bilayer height. XPS measurements rule out the possibility of alloy formation provided that binding energy of Co2p core lines remains unchanged as cobalt loading increases. Also, XPS data reveals that, when subjected to thermal annealing, Co atoms diffuse into Au crystal retaining its chemical nature as before the annealing. Finally, NO adsorption experiments show that Co nanostructures are partially oxidized upon adsorption, as evidenced by changes in core photoemission lineshapes of the Co2p lines. Also, NO adsorption seems to inhibit Co atom diffusion into Au crystal during moderate thermal treatment FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado