NANOSCALE METAL/OXIDE SYSTEMS
People
Paola Luches
Sergio D’Addato
Stefania Benedetti
Sergio Valeri
This activity aims at the fundamental understanding and design of metal/oxide materials with optimized properties for the application in catalysis, energy conversion, and magnetism. The goal is achieved through the study of the atomic scale interactions between metals and oxides in reduced dimensionality. The research is focused on the study of ultrathin films of metals, metal nanoparticles on oxide surfaces and core-shell nanoparticles. Ultrathin oxide films on metals show new phases - stabilized by epitaxial growth - with properties different from the bulk due to mechanisms such as uncompensated polarity, increased reducibility, charge transfer to/from the substrate and interfacial effects in general.
Metal nanoparticles on oxide surfaces are studied as models of dispersed catalysts on which the basic mechanisms responsible for the activity of the material (e.g., charge transfer from/to the oxide, interaction with defects, interfacial phases) are studied and optimized. The plasmonic properties of metal nanoparticles on semiconducting oxides are also being studied in view of obtaining materials for dye-sensitized solar cells with increased efficiency.
Core-shell nanoparticles are produced and studied in structure, morphology, and chemical states at the core-shell interface for applications in catalysis and nanomagnetism.
The research is performed in two UHV apparatus equipped with MBE growth facilities, an inert gas aggregation source, and facilities for in-situ electronic, morphologic and structural characterization, such as XPS, UPS, XPD, LEED, AES, STM/AFM. The activity also involves the use of TEM and synchrotron radiation facilities.
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Fig 1: STM images of CeO2 films of different thicknesses grown on Pt(111). The surface shows atomic-scale flat terraces several nm wide with defects of different types. a) b) 2.85 ML CeO2, c) 3.4 ML CeO2, d) - f) 9.3 ML CeO2.
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Fig 2: Experimental (a) and simulated (b) photoelectron diffraction stereogram of a Ni cluster ?lm of 7 ML nominal thickness grown on 10 ML MgO/Mo(001). The data are taken at the Ni 2p core level (Ekin = 1187 eV).
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Fig 3: HR-TEM image of a single particle of Ni nanoparticles co-deposited with MgO: (a) tMgO = 5 nm, scale bar length, l = 5 nm. Indicated fringe spacing values are d = 0.24 nm (blue) and d = 0.12 nm (yellow). (b) tMgO = 2 nm, l = 2 nm. The circles indicate the MgO region outside the first shell. (c) Sample without MgO and with reduced air oxidation, l = 2 nm. (d) Atomistic model of the Mackay icosahedron oriented as in panel b. (e) Multislice simulation using a nine-shell icosahedron with orientation as in panel b. (f) Geometric phase analysis of the lattice parameter expansion relative to panel a in the direction indicated by arrows.
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Publications
Competition Between Polar and Non-Polar Growth of MgO Thin Films on Au(111)
S. Benedetti, N. Nilius, P. Torelli, G. Renaud, H.-J. Freund, and S. Valeri
J. Phys. Chem. C 115, 23043–23049 (2011)
Change of the surface electronic structure of Au(111) by a monolayer MgO(001) film
Y. Pan, S. Benedetti, N. Nilius, and H.-J. Freund
Phys. Rev. B 84, 075456 (2011)
Assembly and Fine Analysis of Ni/MgO Core/Shell Nanoparticles
S. D'Addato, V. Grillo, S. Altieri, S. Frabboni, F. Rossi, and S. Valeri
J. Phys. Chem. C 115, 14044 (2011)
Morphology, Stoichiometry, and Interface Structure of CeO2 Ultrathin Films on Pt(111)
P. Luches, F. Pagliuca, and S. Valeri
J. Phys. Chem. C 115, 10718 (2011)
Structure and stability of nickel/nickel oxide core-shell nanoparticles
S. D'Addato,V. Grillo, S. Altieri, R. Tondi, S. Valeri, and S. Frabboni
J. Phys: Condens. Matter 23, 175003 (2011)
Growth and morphology of metal particles on MgO/Mo(001): A comparative STM and diffraction study
S. Benedetti, P. Myrach, A. di Bona, S. Valeri, N. Nilius, and H.-J. Freund
Phys. Rev. B 83, 125423 (2011)
Spontaneous Oxidation of Mg Atoms at Defect Sites in an MgO Surface
S. Benedetti, N. Nilius, P. Myrach, I. Valenti, H.-J. Freund, and S. Valeri
J. Phys. Chem. C 115, 3684 (2011)
X-ray Photoemission Study of the Charge State of Au Nanoparticles on Thin MgO/Fe(001) Films
P. Torelli, L. Giordano, S. Benedetti, P. Luches, E. Annese, S. Valeri and G. Pacchioni
J. Phys. Chem. C 113, 19957 (2009)
Growth of oxide-metal interfaces by atomic oxygen: Monolayer of NiO(001) on Ag(001)
A. Rota, S. Altieri, and S. Valeri
Phys. Rev. B 79, 161401 (2009)