1,720,975 research outputs found
Electronic anisotropy at vicinal Ag(11 n) surfaces: Work function changes induced by steps and hydrogen adsorption
Full text linkWe have systematically analyzed both the electrical dipole originated by the presence of steps and that produced by the H-Ag bond at different sites of the vicinal Ag(11n) surfaces. We have considered both basal planes as reference systems. We have taken into account relaxation, coverage, and structural effects. An anisotropy of the electronic properties has been found along the terraces between steps. Long-range interactions and localization effects have been identified.Fil: Juarez, Maria Fernanda. Universidad de Ulm; AlemaniaFil: Santos, Elizabeth del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universitat Ulm; Alemani
Electronic Anisotropy at Vicinal Ag(1 1 n) Surfaces: Energetics of Hydrogen Adsorption
Full text linkWe have investigated the adsorption and diffusion of hydrogen atoms at planar (1 0 0), (1 1 1), and stepped (1 1 n) silver surfaces by density functional theory. At low coverage, hydrogen atoms tend to adsorb on step sites rather than on the terrace. The adsorption energy for hydrogen on steps stays almost the same for all (1 1 n) surfaces, showing the local character of the orbitals on these sites. However, the situation is different on the terrace. The adsorption depends on both the position and the length of the terrace. The stability of hydrogen is higher on the middle of the terrace. In contrast to the planar (1 0 0) surface, the adsorption energy decreases when the coverage on the steps increases. Small activation barriers for the up- or downward diffusion show that hydrogen atoms can reach the steps easily at room temperature.Fil: Juarez, Maria Fernanda. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Santos, Elizabeth del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universitat Ulm; Alemania. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentin
Structure and stability of graphene edges in O2 and H2 environments from ab initio thermodynamics
Full text linkEdges play a determining role in the electronic and transport properties of graphene, how-ever, their actual morphology and configuration remain unknown. Using ab initio thermo-dynamics, we have systematically studied the stability and structure of armchair andzigzag edges of graphene in pure O2and combined O2and H2environments. In total, 81different nanostructures were investigated, however, only a few of them domain the phasediagram. Our calculations show that zigzag edges are less stable than armchair edges.Nonetheless, the former exhibit a much richer diversity in terms of structures. The oxy-gen-terminated edges occupy the largest regions in the phase stability diagram in compar-ison with hydrogen-oxygen-terminated edges, which correspond to carboxyl and alcoholfunctional groupsFil: Soldano, Germán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Juarez, Maria Fernanda. Ulm University; AlemaniaFil: Teo, Barry W. T.. National University of Singapore; SingapurFil: Santos, Elizabeth del Carmen. Ulm University; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin
Screening of ions in carbon and gold nanotubes: A theoretical study
Full text linkWe examine the insertion of alkali ions into narrow nanotubes of graphite and gold by density functional theory. The surrounding tubes screen the ionic charge very effectively; the resulting image energy compensates well for the loss of solvation. In addition, ion–ion interactions are strongly reduced. These effects are stronger for gold than for graphite tubes. Our results explain at an atomic level, why narrow tubes store charge so effectivelyFil: Goduljan, Aleksej. Universitat Ulm; AlemaniaFil: Juarez, Maria Fernanda. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Mohammadzadeh, Leila. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Quaino, Paola Monica. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Santos, Elizabeth del Carmen. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Schmickler, Wolfgang. Universitat Ulm; Alemani
Quantum mechanical investigation of the influence of the local environment on the vibrational properties of hydrogenated Si(111)
Full text linkPeriodic density functional calculations were performed to investigate the vibrational properties of hydrogenated and grafted Si(111) surfaces as a function of surface coverage and subsurface oxidation. Surfaces terminated with - CH3, - CCH, and - Cl groups were considered. Subsurface oxidation was taken into account by oxidizing one, two, and three silicon back bonds. The effect of anharmonicity was considered in the calculation of the stretching frequencies of the Si - H and C - H groups. The effect of the different adsorbates on the polarization of the electron density of the SiH group and on the electronic structure of the surface was investigated by means of electron density difference and density of states analyses. The Si - H stretching frequency increases with the surface coverage of - CCH and - Cl species, and it decreases with the increase in the surface coverage of - CH3. Positive (negative) frequency shifts correlate with the increase (decrease) of electron density along the Si - H bond. The Si - H stretching frequency shows a very good correlation with the Si - H bond length for all the systems investigated. The Si - C, C - H, and Si - Cl stretching frequencies increase linearly with the surface coverage of the - CH3, - CCH, and - Cl groups. The back-bond oxidation of a SiH group produces an increase in its stretching frequency and a decrease of the stretching frequency of the surrounding unoxidized SiH groups. All the calculated frequencies show very good agreement with the experimental values.Fil: Juarez, Maria Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Patrito, Eduardo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Paredes Olivera, Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin
Defying Coulomb's law: A lattice-induced attraction between lithium ions
Full text linkNormally ions with the same charge repel each other, but in very rare cases an intervening medium can produce an apparent attraction. We have studied the adsorption of Li-ions on semiconducting carbon nanotubes by density functional theory, one ion being inside, the other outside. The tube shields the direct Coulomb interaction between the ions, but the presence of the ion inside facilitates the adsorption of the ion outside, thus producing an apparent attraction. We give a quantitative explanation based on the electronic band structure of the tube, and surmise, that the same effect will hold on other carbon materials. Our results may explain the apparent attraction of Li-ions that has been observed in Li-batteries.Fil: Juarez, Maria Fernanda. Universitat Ulm; AlemaniaFil: Dominguez Flores, Fabiola. Universitat Ulm; AlemaniaFil: Goduljan, Aleksej. Universitat Ulm; AlemaniaFil: Mohammadzadeh, Leila. Universitat Ulm; Alemania. Universidad de Basilea; SuizaFil: Quaino, Paola Monica. Universidad Nacional del Litoral. Instituto de Química Aplicada del Litoral. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Química Aplicada del Litoral.; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; ArgentinaFil: Santos, Elizabeth del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Universitat Ulm; AlemaniaFil: Schmickler, Wolfgang. Universitat Ulm; Alemani
Interaction of hydrogen with au modified by Pd and Rh in view of electrochemical applications
Full text linkHydrogen interaction with bimetallic Au(Pd) and Au(Rh) systems are studied with the density functional theory (DFT)-based periodic approach. Several bimetallic configurations with varying concentrations of Pd and Rh atoms in the under layer of a gold surface(111) were considered. The reactivity of the doped Au(111) toward hydrogen adsorption and absorption was related to the property modifications induced by the presence of metal dopants. DFT-computed quantities, such as the energy stability, the inter-atomic and inter-slab binding energies between gold and dopants, and the charge density were used to infer the similarities and differences between both Pd and Rh dopants in these model alloys. The hydrogen penetration into the surface is favored in the bimetallic slab configurations. The underlayer dopants affect the reactivity of the surface gold toward hydrogen adsorption in the systems with a dopant underlayer, covered by absorbed hydrogen up to a monolayer. This indicates a possibility to tune the gold surface properties of bimetallic electrodes by modulating the degree of hydrogen coverage of the inner dopant layer(s)Fil: Juarez, Maria Fernanda. Universidad de Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Soldano, Germán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Universidad de Ulm; AlemaniaFil: Santos, Elizabeth del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Guesmi, Hazar. Institut Charles Gerhardt Montpellier; FranciaFil: Tielens, Frederik. Universite de Paris I Pantheon - Sorbonne; FranciaFil: Mineva, Tzonka. Institut Charles Gerhardt Montpellier; Franci
Spontaneous formation of metallic nanostructures on highly oriented pyrolytic graphite (HOPG): an ab initio and experimental study
Full text linkWe have investigated the decoration of step-edges of HOPG by Ag, Au and Pt using experimental and theoretical approaches. Metallic nanowires can be formed on bare or functionalized step-edges. Energy dispersion analysis indicates the presence of oxygenated groups. The experiments showed that nanowires can be obtained with the three metals along the step-edges, but the shapes and morphologies are very different. We have found that the interaction between the metal wires and the carbon follows the sequence: Pt > Au > Ag. The electronic redistribution between the atoms participating in the bond between the metallic nanowire and the step-edges shows a complicated pattern. The density of electronic states projected on the different atoms indicates that there are different orbitals participating in the bonds.Fil: Juarez, Maria Fernanda. Ulm University; AlemaniaFil: Fuentes, Ana Silvina. Universidad Nacional de Catamarca. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Soldano, Germán. Ulm University; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Avalle, Lucia Bernardita. Universidad Nacional de Catamarca. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Santos, Elizabeth del Carmen. Ulm University; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin
A scenario for oxygen reduction in alkaline media
Full text linkWe investigate oxygen reduction in alkaline solution with the focus on gold and silver electrodes. On the basis of theoretical considerations we propose a detailed mechanism, which we support by explicit calculations. In accordance with previous suggestions we conclude that the first step is an outer-sphere electron transfer to the oxygen molecule. The breaking of he oxygen-oxygen bond involves adsorption of OH on the electrode surface. This is much stronger on Au(100) than on Au(111), which explains why the former is a better catalyst.Fil: Ignaczak, Anna. University of Lodz; PoloniaFil: Nazmutdinov, Renat. Kazan National Research Technological University; RusiaFil: Goduljan, Aleksej. Universitat Ulm; AlemaniaFil: Moreira de Campos Pinto, Leandro. Universidade Federal do Mato Grosso do Sul; Brasil. Universitat Ulm; AlemaniaFil: Juarez, Maria Fernanda. Universitat Ulm; AlemaniaFil: Quaino, Paola Monica. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Santos, Elizabeth del Carmen. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Schmickler, Wolfgang. Universitat Ulm; Alemani
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