11. Phase behaviour of self-assembled monolayers controlled by tuning physisorbed and chemisorbed states: a lattice-model viewSara Fortuna, David L. Cheung, Karen Johnston, 2016, izvirni znanstveni članek Opis: 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.
Ključne besede: lattice model, hexagonal lattice, Monte Carlo, DFT, density functional theory, benzene, physisorption, chemisorption, halogenated
Objavljeno v RUNG: 11.10.2016; Ogledov: 4521; Prenosov: 0
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12. 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, izvirni znanstveni članek Opis: 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.
Ključne besede: self-assembly, phthalocyanine, Au(110), DFT, density functional theory, simulation, surface, recontruction
Objavljeno v RUNG: 11.10.2016; Ogledov: 4637; Prenosov: 0
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13. Oxalic acid adsorption states on the clean Cu(110) surfaceSara Fortuna, 2016, izvirni znanstveni članek Opis: Carboxylic acids are known to assume a variety of configurations on metallic surfaces. In particular oxalic acid on the Cu(110) surface has been proposed to assume a number of upright configurations. Here we explore with DFT calculations the possible structures that oxalic acid can form on copper 110 at different protonation states, with particular attention at the possibility of forming structures composed of vertically standing molecules. In its fully protonated form it is capable of anchoring itself on the surface thanks to one of its hydrogen-free oxygens. We show the monodeprotonated upright molecule with two oxygens anchoring it on the surface to be the lowest energy conformation of a single oxalic molecules on the Cu(110) surface. We further show that it is possible for this configuration to form dense hexagonally arranged patterns in the unlikely scenario in which adatoms are not involved.
Ključne besede: oxalic acid, oxalate, cu(110), copper, surface, adsorption, density functional theory, DFT
Objavljeno v RUNG: 11.10.2016; Ogledov: 4493; Prenosov: 0
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14. Ge(2), Ge(1) and Ge-E´ centers in irradiated Ge-doped silica : a first-principles EPR studyLayla Martin-Samos, Nicolas Richard, Sylvain Girard, A. Boukenter, Youcef Ouerdane, Luigi Giacomazzi, 2015, izvirni znanstveni članek Ključne besede: silica, density-functional theory, defects
Objavljeno v RUNG: 17.05.2016; Ogledov: 4736; Prenosov: 123
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