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Paramagnetic centers in amorphous GeO2
Luigi Giacomazzi, Layla Martin-Samos, Nicolas Richard, 2015, published scientific conference contribution

Keywords: germanium dioxide, defects, density-functional theory, EPR
Published in RUNG: 03.10.2018; Views: 3677; Downloads: 0
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Characterization of Mg low-index surfaces by first-principles
Miha Gunde, 2017, master's thesis

Abstract: In this work, three surfaces, namely, Mg(0001), Mg(10 ̄1 0) and Mg(11 ̄2 0) are investigated by means of Density Functional Theory and Generalized Gradient Approximation first-principle calculations. The surfaces have been characterized in terms of their interlayer distances, surface energies, Projected Density of States and Surface Core Level Shifts. Contrary to what was found in previous studies based on Density Functional Theory-Local Density Approximation, the use of Generalized Gradient Approximation exchange correlation functional unravels the oscillatory behavior of both interlayer distances and Surface Core Level Shifts of Mg(10 ̄1 0). Moreover, the Projected Density Of States of un-reconstructed Mg(11 ̄2 0) exhibit the typical quantisation of electronic levels associated to a 2D-confinement of a 3D nearly-free electron gas, as observed in nano-wires, and a Peierls instability along the unconfined direction. Different possible reconstructions on Mg(11 ̄2 0) have then been investigated. In particular, it is found that the surface energy of (2X1) and (3X1) reconstructions is almost degenerate and lower than the surface energy of the unreconstructed Mg(11 ̄2 0) surface. Because of the quasi-degeneracy of surface energies, Mg(11 ̄2 0) surface should be composed by a combination of all the quasi degenerate phases.
Keywords: Density Functional Theory, first-principle calculations, Mg surface, Surface Core-Level Shift, surface relaxation, surface reconstruction
Published in RUNG: 04.07.2017; Views: 6150; Downloads: 2104
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Formation of Hybrid Electronic States in FePc Chains Mediated by the Au(110) Surface
Maria Grazia Betti, Pierluigi Gargiani, Carlo Mariani, Stefano Turchini, Nicola Zema, Sara Fortuna, Arrigo Calzolari, Stefano Fabris, 2012, original scientific article

Abstract: Iron–phthalocyanine (FePc) molecules deposited on the Au(110) surface self-organize in ordered chains driven by the reconstructed Au channels. The interaction process induces a rehybridization of the electronic states localized on the central metal atom, breaking the 4-fold symmetry of the molecular orbitals of the FePc molecules. The molecular adsorption is controlled by a symmetry-determined mixing between the electronic states of the Fe metal center and of the Au substrate, as deduced by photoemission and absorption spectroscopy exploiting light polarization. DFT calculations rationalize this mixing of the Fe and Au states on the basis of symmetry arguments. The calculated electronic structure reproduces the main experimental spectral features, which are associated to a distorted molecular structure displaying a trigonal bipyramidal geometry of the ligands around the metal center.
Keywords: phthalocyanine, Au(110), gold, surface, DFT, density functional theory, calculation, simulation
Published in RUNG: 13.10.2016; Views: 4989; Downloads: 0
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Structural phases of ordered FePc-nanochains self-assembled on Au(110)
Betti Maria Grazia, Pierluigi Gargiani, Carlo Mariani, Roberto Biagi, Jun Fujii, Giorgio Rossi, Andrea Resta, Stefano Fabris, Sara Fortuna, Xavier Torrelles, Manvendra Kumar, Maddalena Pedio, 2012, original scientific article

Abstract: Iron-phthalocyanine molecules deposited on the Au(110) reconstructed channels assemble into one-dimensional molecular chains, whose spatial distribution evolves into different structural phases at increasing molecular density. The plasticity of the Au channels first induces an ordered phase with a 5×5 symmetry, followed by a second long-range ordered structure composed by denser chains with a 5×7 periodicity with respect to the bare Au surface, as observed in the low-energy electron-diffraction (LEED) and grazing incidence X-ray diffraction (GIXRD) patterns. The geometry of the FePc molecular assemblies in the Au nanorails is determined by scanning tunneling microscopy (STM). For the 5×7 phases, the GIXRD analysis identifies a “4-3” rows profile along the [001] direction in the Au surface and an on-top FePc adsorption site, further confirmed by density functional theory (DFT) calculations. The latter also reveals the electronic mixing of the interface states. The chain assembly is driven by the molecule–molecule interaction and the chains interact with the Au nanorails via the central metal atom, while the chain–chain distance in the different structural phases is primarily driven by the plasticity of the Au surface.
Keywords: STM, LEED, DFT, density functional theory, phthalocyanine, Au(110), gold, surface
Published in RUNG: 13.10.2016; Views: 4858; Downloads: 0
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Spin and orbital configuration of metal phthalocyanine chains assembled on the Au(110) surface
Gargiani Pierluigi, Giorgio Rossi, Roberto Biagi, Valdis Corradini, Maddalena Pedio, Sara Fortuna, Arrigo Calzolari, Stefano Fabris, Julio Criginski Cezar, N. B. Brookes, Maria Grazia Betti, 2013, original scientific article

Abstract: The spin and orbital configuration of magnetic metal phthalocyanines (MPcs) deposited on metallic substrates are strongly influenced by the rehybridization of the molecular states with the underlying metal. FePc, CoPc, and CuPc isolated molecules are archetypal systems to investigate the interrelationship between magnetic moments and orbital symmetry after deposition on a metallic substrate. MPcs form long-range ordered chains self-assembled along the reconstructed channels of the Au(110) surface. X-ray magnetic circular dichroism from the L2,3 absorption edges of Fe, Co, and Cu shows that the orbital and spin configuration are strongly modified upon adsorption on the Au(110) surface if the orbitals responsible of the magnetic moment are involved in the interaction process. The magnetic moment for a single layer of molecular chains is completely quenched for the CoPc molecules, fully preserved for the CuPc and reduced for the FePc ones. The modified magnetic configuration is confined to the very interface layer, i.e., to the MPc molecules bound to the metal substrate up to the compact packing of the single layer. The different response can be rationalized in terms of the symmetry/orientation of the metal-ion d states interacting with the substrate states, as indicated by density functional theory calculations in agreement with experimental findings.
Keywords: phthalocyanine, Au(110), gold, self-assembly, pattern, configuration, density functional theory, DFT, CuPc, FePc
Published in RUNG: 12.10.2016; Views: 4837; Downloads: 0
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Phase behaviour of self-assembled monolayers controlled by tuning physisorbed and chemisorbed states: a lattice-model view
Sara Fortuna, David L. Cheung, Karen Johnston, 2016, original scientific article

Abstract: The self-assembly of molecules on surfaces into 2D structures is important for the bottom-up fabrication of functional nanomaterials, and the self-assembledstructure depends on the interplay between molecule-molecule interactions and molecule-surface interactions. Halogenated benzene derivatives on platinum have been shown to have two distinct adsorption states: a physisorbed state and a chemisorbed state, and the interplay between the two can be expected to have a profound effect on the self-assembly and phase behaviour of these systems. We developed a lattice model that explicitly includes both adsorption states, with representative interactions parameterised using density functional theory calculations. This model was used in Monte Carlo simulations to investigate pattern formation of hexahalogenated benzene molecules on the platinumsurface. Molecules that prefer the physisorbed state were found to self-assemble with ease, depending on the interactions between physisorbed molecules. In contrast, molecules that preferentially chemisorb tend to get arrested in disordered phases. However, changing the interactions between chemisorbed and physisorbed molecules affects the phase behaviour. We propose functionalising molecules in order to tune their adsorption states, as an innovative way to control monolayer structure, leading to a promising avenue for directed assembly of novel 2D structures.
Keywords: lattice model, hexagonal lattice, Monte Carlo, DFT, density functional theory, benzene, physisorption, chemisorption, halogenated
Published in RUNG: 11.10.2016; Views: 4632; Downloads: 0
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Molecule-Driven Substrate Reconstruction in the Two-Dimensional Self-Organization of Fe-Phthalocyanines on Au(110)
Sara Fortuna, Pierluigi Gargiani, Maria Grazia Betti, Carlo Mariani, Arrigo Calzolari, Silvio Modesti, Stefano Fabris, 2012, original scientific article

Abstract: The structural patterns formed by molecular self-assembly at surfaces are usually controlled by the relative strengths of the intermolecular and molecule–substrate interactions. An additional steering effect is present when the substrate can easily reconstruct upon molecular adsorption, which therefore drives a self-templating effect on the metal support. This is here demonstrated for the model case of Fe-phthalocyanine molecules adsorbed on the Au(110) surface. Scanning tunneling microscopy shows that molecular adsorption promotes a local (1 × 5) surface reconstruction, which drives the assembly of molecular chains along the [11̅0] direction. The order and periodicity of the molecular assemblies are determined with low energy electron diffraction patterns. Density functional theory calculations reveal the energetic origins of the molecule-driven substrate reconstruction. Since the function of molecular overlayers at surfaces is strongly correlated to their structure, these results have implications in the design of new metal/molecular interfaces.
Keywords: self-assembly, phthalocyanine, Au(110), DFT, density functional theory, simulation, surface, recontruction
Published in RUNG: 11.10.2016; Views: 4767; Downloads: 0
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