Abstract:

The chemisorption of isocyanate (NCO) species on Pd(1 0 0) was studied within the density functional formalism (DFT) using a periodic slab model. The NCO was adsorbed on top, bridge and hollow sites of the metal surface at different coverages. At low coverages, the adsorption energies are in the range of -2.5/-3.0 eV, indicating an important adsorbate-substrate interaction for the three sites studied. The lateral repulsive interaction between neighboring NCO species is almost negligible or weak at lower and intermediate coverages, and very strong at complete monolayer. At low coverages, both bridge and hollow sites are energetically preferred; yet the bridge site becomes the only favoured site at intermediate and complete coverages. Work function and dipole moment calculations can be interpreted by an important charge transfer from the metal surface to NCO. Interestingly, while on hollow site the charge taken by NCO is essentially the same over all the range of coverage, an increasing depolarization is observed on bridge and top sites as the coverage increases. Symmetric and asymmetric NCO stretching modes were also calculated and compared with recent infrared spectroscopy measurements. © 2009 Elsevier B.V. All rights reserved.

Author affiliation: Belelli, Patricia Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina

Author affiliation: Branda, Maria Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina

Author affiliation: Garda, Graciela Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina

Author affiliation: Ferullo, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur. Departamento de Química; Argentina

Author affiliation: Castellani, Norberto Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina

Abstract:

Thin diamond-like carbon films were subjected to fluorination with gaseous XeF2 under ultrahigh vacuum conditions in order to increase the work function of the diamond-like carbon surface. Changes in the work function and surface composition were monitored with UV photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy (XPS), respectively. Successive XeF2 exposures raised the work function by as much as 1.55 eV. Surprisingly, approximately half of the increase in the work function occurred while the coverage of fluorine remained below 0.02 monolayers (ML). This suggests that initial doses of XeF2 remove extrinsic adsorbates from the diamond-like carbon film and that fluorine desorbs with the reaction products. Increasing the exposure of the diamond-like carbon to XeF2 leads to the expected covalent fluorination of the surface, which saturates at fluorine coverages of 6 F atoms/nm2 (~0.3 ML). Annealing of the diamond-like carbon to temperatures above 850 K was required to reduce the surface fluorine concentration to undetectable levels. This did not, however, cause the work function to return to its original, pre-fluorination value.

Author affiliation: Tarditi, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentina

Author affiliation: Kondratyuk, Petro. University of Carnegie Mellon; Estados Unidos

Author affiliation: Wong, Pak Kin. Sae Technology Centre; China

Author affiliation: Gellman, Andrew J.. University of Carnegie Mellon; Estados Unidos. Institute For Advanced Energy Studies;

Abstract:

The adsorption of isocyanate (- NCO) species on Cu(100) was studied using the density functional theory (DFT) and the periodic slab model. The calculations indicate that at low and intermediate coverages NCO adsorbs preferentially on bridge and hollow sites. Work function and dipole moment changes show a significant negative charge transfer from Cu to NCO. The resulting charged NCO species interact repulsively among themselves being these dipole-dipole interactions particularly intensive when they are adsorbed in adjacent sites. Consequently, isocyanates tend to be separated from each other generating the vacant sites required for the dissociation to N and CO. This condition for NCO dissociation has been suggested in the past from experimental observations. A comparison was also performed with the NCO adsorption on Pd(100). In particular, the calculated minimal energy barrier for NCO dissociation was found to be higher on Cu(100) than on Pd(100) in accord with the well known higher NCO stability on Cu(100). © 2011 Elsevier B.V.

Author affiliation: Belelli, Patricia Gabriela. Universidad Nacional del Sur. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina

Author affiliation: Garda, Graciela Raquel. Universidad Nacional del Sur. Departamento de Física; Argentina

Author affiliation: Ferullo, Ricardo. Universidad Nacional del Sur. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina

Abstract:

We study the dependence of the magnetic properties of NiPd and CoPd segregated nanoclusters and slabs as a function of the 3d magnetic component concentration (x), the chemical order, and size. In the case of clusters we consider 3d cores coated by Pd atoms (3d/Pd) and also onion-like (Pd/3d/Pd) configurations. For the slabs we consider different possible segregated structures of the 3d and 4d atoms and study the evolution of the magnetic properties on these different configurations. We show that Pd coating gives rise to an enhancement of the average magnetic moment of the Ni or Co core atoms and of the Pd atoms as well. Larger values of the average magnetic moments are obtained in the onion-like structures (Pd/3d/Pd) than in the core/shell (3d/Pd) configuration. We compare with theoretical and experimental results available in the literature.

Se estudia la dependencia de las propiedades magnéticas de nanocúmulos segregados y películas de NiPd y CoPd como función de la concentración de la componente magnética 3d (x), del orden químico y del tamaño. En el caso de los cúmulos, se consideran núcleos 3d cubiertos por átomos Pd (3d/Pd) y también configuraciones por capas tipo cebolla (Pd/3d/Pd). Para las películas se consideran diferentes posibles estructuras segregadas de los átomos 3d y 4d y se estudia la evolución de las propiedades magnéticas de las diferentes configuraciones. Se muestra que la cubierta de Pd da lugar a un incremento del momento magnético promedio de los átomos del núcleo de Ni o Co así como de los átomos de Pd también. Se obtienen valores más grandes de los momentos magnéticos promedio en las estructuras por capas (Pd/3d/Pd) que en las configuraciones núcleo/cubierta (3d/Pt). Se compara con resultados experimentales disponibles en la literatura.

Author affiliation: Guevara, Alejandro Javier. Universidad Nacional de San Martín; Argentina. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Llois, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Comisión Nacional de Energía Atómica; Argentina

Author affiliation: Aguilera Granja, Faustino. Universidad Autónoma de San Luis Potosí; México

Author affiliation: Montejano Carrizales, Juan Martín. Universidad Autónoma de San Luis Potosí; México

Abstract:

Self-assembled monolayers (SAMs) containing electroactive functional groups are excellent model systems for the formation of electronic devices by self-assembly. In particular ferrocene-terminated alkanethiol SAMs have been extensively studied in the past. However, there are still open questions related with their electronic structure including the influence of the ferrocene group in the SAM-induced work function changes of the underlying metal. We have thus carried out a thorough experimental and theoretical investigation in order to determine the molecular and electronic structure of ferrocene-terminated alkanethiol SAMs on Au surfaces. In agreement with previous studies we found that the Fc-containing alkanethiol molecules adsorb forming a thiolate bond with the Au surface with a molecular geometry 30 degrees tilted with respect to the surface normal. Measured surface coverages indicate the formation of a compact monolayer. On the other hand, contrary with previous observations, we found that the ferrocene group has little influence on the observed work function decrease which is largely determined by the alkanethiol. Furthermore, the ferrocene moiety lies 14 Å above the metal surface covalently bonded to the alkanethiol SAM and its HOMO is located at -1.6 eV below the Fermi level. Our results provide new valuable insight into the molecular and electronic structure of electroactive SAMs which are of fundamental importance in the field of molecular electronics.

Author affiliation: Méndez de Leo, Lucila Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires; Argentina

Author affiliation: de la Llave, Ezequiel Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires; Argentina

Author affiliation: Scherlis Perel, Damian Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires; Argentina

Author affiliation: Williams, Federico Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires; Argentina

Abstract:

Surface topography and work function maps were simultaneously obtained for carbon surfaces modified by a dendritic molecule: 3,5-Bis (3,5-dinitrobenzoylamino) benzoic acid. The dendrons were spontaneously assembled onto highly ordered pyrolytic graphite samples, exhibiting an increase in the surface potential. This fact is consistent with the incorporation of an electron-acceptor functional group that remains electroactive on the surface.

Author affiliation: Farias, Eliana Desiree. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto de Investigaciones en Físicoquímica de Córdoba; Argentina

Author affiliation: Brunetti, Veronica. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto de Investigaciones en Físicoquímica de Córdoba; Argentina

Author affiliation: Paez, Julieta Irene. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Orgánica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentina

Author affiliation: Strumia, Miriam Cristina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Orgánica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentina

Author affiliation: Passeggi, Mario Cesar Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Física del Litoral; Argentina. Universidad Nacional del Litoral; Argentina

Author affiliation: Ferron, Julio. Universidad Nacional del Litoral. Facultad de Ingenieria Quimica. Departamento de Materiales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Física del Litoral; Argentina