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Cu(110)
A704 Surface Science 295 (1993) 411-426 North-Holland
Ultrathin reactive metal films on TiO2(l10): growth, interfacial interaction and electronic structure of chromium films Jian-Mei Pan 1, Ulrike Diebold, Lizhong Zhang and Theodore E. Madey * Department of Physics and Astronomy, Laboratory for Surface Modification, Rutgers, The State University of New Jersey, Piscataway, NJ 08855, USA Received 8 January 1993; accepted for publication 23 June 1993 A study of ultrathin Cr films on TIP2(110) surfaces is reported. The combination of low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS) enables us to study quantitatively the growth of reactive metal films on metal oxides, and the chemical interactions at the interface. Ultrathin Cr films grow initially in a quasi-two-dimensional fashion at room temperature. Changes in oxidation states of both Ti and Cr during film formation suggest that strong chemical interactions at the interface are of great importance in the growth of reactive metal films. Cr "wets" the surface more effectively at 300 K than ultrathin films of less reactive metals, Fe and Cu. This suggests that a relation exists between the metal reactivity with oxygen and the wetting of metal films on oxides: The more reactive the metal towards oxygen, the better is the wetting ability. The chemical interaction is accompanied by charge transfer at the interface, causing a reduction of the surface work function. The interracial interaction also causes the interfacial Cr layer to behave differently from the top metallic Cr atoms upon thermal annealing. The top layers of metallic Cr show a strong clustering tendency at 500°C, while the interfacial Cr seems to have less surface mobility and slow bulk diffusion.
Surface Science 295 (1993) 427-432 North-Holland
The unoccupied electronic structure of N a / C u ( l l 0 ) D. Tang, C. Su and D. Heskett Department of Physics, University of Rhode Island, Kingston, RI 02881, USA Received 3 March 1993; accepted for publication 11 June 1993 Using the technique of inverse photoemission spectroscopy (IPES), we have measured the unoccupied electronic states of sodium on Cu(lt0) as a function of Na dose on the Cu(ll0) surface at room temperature. An Na-induced state appears for Na coverages above 0.08 ML for normal incidence, which we assign as the Na unoccupied 3p level. A second peak appears for coverages greater than 1 ML near the Y point. The adsorption of Na also causes shifts and attenuation of Cu(ll0) surface states. We compare our results with studies of related systems.
Surface Science 295 (1993) 433-444 North-Holland
Temperature behavior of tracer di
sion on heterogeneous surfaces
K. Sapag a, V. Pereyra a, J.L. Riccardo ~,b and G. Zgrablich ~.b,, a Departamento de Ffsica, Universidad Nacional de San Luis, CONICET, 5700 San Luis, Argentina b Centro Regional de Estudios Avanzados (CREA), Gobierno de la Provincia de San Luis, CC 256, 5700 San Luis, Argentina Received 22 December 1992; accepted for publication 8 June 1993 The behavior of a tagged particle on a generalized heterogeneous surface is studied by Monte Carlo simulation. Using the dual site-bond model (SBM), the energetic properties of the heterogeneous substrates can be appropriately described through the site and bond energy distributions and the overlapping degree between them. The effect of the adsorptive energy topography on the tracer diffusion coefficient, as well as on the time behavior of the mean-square displacement of the adparticle, are analyzed for different temperatures and energy correlation degrees. The short-time behavior of tracer diffusion is highly sensitive to the surface energy structure. The possibility of using tracer diffusion analysis for a better characterization of the energetic topography of heterogeneous surfaces is discussed.
Ultrathin reactive metal films on TiO2(l10): growth, interfacial interaction and electronic structure of chromium films Jian-Mei Pan 1, Ulrike Diebold, Lizhong Zhang and Theodore E. Madey * Department of Physics and Astronomy, Laboratory for Surface Modification, Rutgers, The State University of New Jersey, Piscataway, NJ 08855, USA Received 8 January 1993; accepted for publication 23 June 1993 A study of ultrathin Cr films on TIP2(110) surfaces is reported. The combination of low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS) enables us to study quantitatively the growth of reactive metal films on metal oxides, and the chemical interactions at the interface. Ultrathin Cr films grow initially in a quasi-two-dimensional fashion at room temperature. Changes in oxidation states of both Ti and Cr during film formation suggest that strong chemical interactions at the interface are of great importance in the growth of reactive metal films. Cr "wets" the surface more effectively at 300 K than ultrathin films of less reactive metals, Fe and Cu. This suggests that a relation exists between the metal reactivity with oxygen and the wetting of metal films on oxides: The more reactive the metal towards oxygen, the better is the wetting ability. The chemical interaction is accompanied by charge transfer at the interface, causing a reduction of the surface work function. The interracial interaction also causes the interfacial Cr layer to behave differently from the top metallic Cr atoms upon thermal annealing. The top layers of metallic Cr show a strong clustering tendency at 500°C, while the interfacial Cr seems to have less surface mobility and slow bulk diffusion.
Surface Science 295 (1993) 427-432 North-Holland
The unoccupied electronic structure of N a / C u ( l l 0 ) D. Tang, C. Su and D. Heskett Department of Physics, University of Rhode Island, Kingston, RI 02881, USA Received 3 March 1993; accepted for publication 11 June 1993 Using the technique of inverse photoemission spectroscopy (IPES), we have measured the unoccupied electronic states of sodium on Cu(lt0) as a function of Na dose on the Cu(ll0) surface at room temperature. An Na-induced state appears for Na coverages above 0.08 ML for normal incidence, which we assign as the Na unoccupied 3p level. A second peak appears for coverages greater than 1 ML near the Y point. The adsorption of Na also causes shifts and attenuation of Cu(ll0) surface states. We compare our results with studies of related systems.
Surface Science 295 (1993) 433-444 North-Holland
Temperature behavior of tracer di
sion on heterogeneous surfaces
K. Sapag a, V. Pereyra a, J.L. Riccardo ~,b and G. Zgrablich ~.b,, a Departamento de Ffsica, Universidad Nacional de San Luis, CONICET, 5700 San Luis, Argentina b Centro Regional de Estudios Avanzados (CREA), Gobierno de la Provincia de San Luis, CC 256, 5700 San Luis, Argentina Received 22 December 1992; accepted for publication 8 June 1993 The behavior of a tagged particle on a generalized heterogeneous surface is studied by Monte Carlo simulation. Using the dual site-bond model (SBM), the energetic properties of the heterogeneous substrates can be appropriately described through the site and bond energy distributions and the overlapping degree between them. The effect of the adsorptive energy topography on the tracer diffusion coefficient, as well as on the time behavior of the mean-square displacement of the adparticle, are analyzed for different temperatures and energy correlation degrees. The short-time behavior of tracer diffusion is highly sensitive to the surface energy structure. The possibility of using tracer diffusion analysis for a better characterization of the energetic topography of heterogeneous surfaces is discussed.