Dissociative adsorption of N2 on W(110): Theoretical study of the dependence on the incidence angle

5 páginas, 2 figuras.-- El Pdf del artículo es la versión post-print.The dissociative adsorption of N2 on W(110) is studied using classical dynamics on a six-dimensional potential energy surface obtained from density functional theory calculations. Two distinct channels are identified in the dissociation process: a direct one and an indirect one. It is shown that the direct channel is inhibited for low energy molecules (Ei < 400 meV) and low incidence angles. The indirect channel includes long-lasting dynamic trapping of the molecule at the surface before dissociation. The dependence of the sticking coefficient on the initial incidence angle is analyzed. The theoretical results compare well with values measured using molecular beam techniques.We acknowledge partial support by the University of the Basque Country UPV/EHU (Grant No. 9/UPV 00206.215-13639/2001), and the Spanish MCyT (Grant No. FIS2004-06490-CO3-00). M.A. acknowledges financial support by the Gipuzkoako Foru Aldundia, and H.F.B. and A.S. by the DIPC.Peer reviewe

Low sticking probability in the nonactivated dissociation of N2 molecules on W(110)

The six-dimensional potential energy surface for the dissociation of N2 molecules on the W(110) surface has been determined by density functional calculations and interpolated using the corrugation reducing procedure. Examination of the resulting six-dimensional potential energy surface shows that nonactivated paths are available for dissociation. In spite of this, the dissociation probability goes to a very small value when the impact energy goes to zero and increases with increasing energy, a behavior usually associated with activated systems. Statistics on the dynamics indicate that this unconventional result is a consequence of the characteristics of the potential energy surface at long distances. Furthermore, two distinct channels are identified in the dissociation process, namely, a direct one and an indirect one. The former is responsible for dissociation at high energies. The latter, which includes long-lasting dynamic trapping in the vicinity of a potential well above the W top position, is the leading mechanism at low and intermediate energies.© 2006 American Institute of Physics.The authors acknowledge partial support by the Basque Departamento de Educación, Universidades e Investigación, the University of the Basque Country UPV/EHU (Grant No. 9/UPV 00206.215-13639/2001), and the Spanish MCyT (Grant No. FIS2004-06490-CO3-00). One of the authors (M.A.) acknowledges financial support by the Gipuzkoako Foru Aldundia.Peer Reviewe

Normal and off-normal incidence dissociative dynamics of O 2 ( v , J ) on ultrathin Cu films grown on Ru(0001)

The dissociative adsorption of molecular oxygen on metal surfaces has long been controversial, mostly due to the spin-triplet nature of its ground state, to possible non-adiabatic effects, such as an abrupt charge transfer from the metal to the molecule, or even to the role played by the surface electronic state. Here, we have studied the dissociative adsorption of O2on CuML/Ru(0001) at normal and off-normal incidence, from thermal to super-thermal energies, using quasi-classical dynamics, in the framework of the generalized Langevin oscillator model, and density functional theory based on a multidimensional potential energy surface. Our simulations reveal a rather intriguing behavior of dissociative adsorption probabilities, which exhibit normal energy scaling at incidence energies below the reaction barriers and total energy scaling above, irrespective of the reaction channel, either direct dissociation, trapping dissociation, or molecular adsorption. We directly compare our results with existing scanning tunneling spectroscopy and microscopy measurements. From this comparison, we infer that the observed experimental behavior at thermal energies may be due to ligand and strain effects, as already found for super-thermal incidence energies.Fil: Fallaque, J. G.. Universidad Autónoma de Madrid; España. Instituto Madrileño de Estudios Avanzados en Nanociencia; EspañaFil: Ramos Acevedo, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Martín, F.. Universidad Autónoma de Madrid; España. Instituto Madrileño de Estudios Avanzados en Nanociencia; EspañaFil: Díaz, C.. Universidad Complutense de Madrid; Españ

Energy dissipation to tungsten surfaces upon hot-atom and Eley-Rideal recombination of H 2

Adiabatic and nonadiabatic quasi-classical molecular dynamics simulations are performed to investigate the role of electron-hole pair excitations in hot-atom and Eley-Rideal H 2 recombination mechanisms on H-covered W(100). The influence of the surface structure is analyzed by comparing with previous results for W(110). In the two surfaces, hot-atom abstraction cross sections are drastically reduced due to the efficient energy exchange with electronic excitations at low incident energies and low coverage, while the effect on Eley-Rideal reactivity is negligible. As the coverage increases, the projectile energy is more efficiently dissipated into the other adsorbates. Consequently, the effect of electronic excitations is reduced. As a result, the reactivity and final energy distributions of the formed H 2 molecules are similar for both abstraction mechanisms.Fil: Galparsoro, Oihana. Centre National de la Recherche Scientifique; Francia. Universite de Bordeaux; FranciaFil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Martinez, Alejandra Elisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Juaristi, Joseba Iñaki. Donostia International Physics Center; España. Universidad del País Vasco; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Alducin, Maite. Donostia International Physics Center; España. Universidad del País Vasco; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Larregaray, Pascal. Centre National de la Recherche Scientifique; Francia. Universite de Bordeaux; Franci

Environment-driven reactivity of H2 on PdRu surface alloys

The dissociative adsorption of molecular hydrogen on PdxRu1−x/Ru(0001) (0 ≤ x ≤ 1) has been investigated by means of He atom scattering, Density Functional Theory and quasi-classical trajectory calculations. Regardless of their surroundings, Pd atoms in the alloy are always less reactive than Ru ones. However, the reactivity of Ru atoms is enhanced by the presence of nearest neighbor Pd atoms. This environment-dependent reactivity of the Ru atoms in the alloy provides a sound explanation for the striking step-like dependence of the initial reactive sticking probability as a function of the Pd concentration observed in experiments. Moreover, we show that these environment-dependent effects on the reactivity of H2 on single atoms allow one to get around the usual constraint imposed by the Brønsted–Evans–Polanyi relationship between the reaction barrier and chemisorption energy.Fil: Ramos Acevedo, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; ArgentinaFil: Minniti, M.. Universidad Autónoma de Madrid; EspañaFil: Díaz, C.. Universidad Autónoma de Madrid; EspañaFil: Farias, D.. Universidad Autónoma de Madrid; EspañaFil: Miranda, R.. Universidad Autónoma de Madrid; España. Instituto Madrileño de Estudios Avanzados en Nanociencia; EspañaFil: Martín, F.. Universidad Autónoma de Madrid; España. Instituto Madrileño de Estudios Avanzados en Nanociencia; EspañaFil: Martinez, Alejandra Elisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; ArgentinaFil: Busnengo, Heriberto Fabio. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentin

On-surface transmetalation of metalloporphyrins

Increasing the complexity of 2D metal-organic networks has led to the fabrication of structures with interesting magnetic and catalytic properties. However, increasing complexity by providing different coordination environments for different metal types imposes limitations on their synthesis if the controlled placement of one metal type into one coordination environment is desired. Whereas metal insertion into free-base porphyrins at the vacuum/solid interface has been thoroughly studied, providing detailed insight into the mechanisms at play, the chemical interaction of a metal atom with a metallated porphyrin is rarely investigated. Herein, the breadth of metalation reactions is augmented towards the metal exchange of a metalloporphyrin through the deliberate addition of atomic metal centers. The cation of Fe(ii)-tetraphenylporphyrins can be replaced by Co in a redox transmetalation-like reaction on a Au(111) surface. Likewise, Cu can be replaced by Co. The reverse reaction does not occur, i.e. Fe does not replace Co in the porphyrin. This non-reversible exchange is investigated in detail by X-ray absorption spectroscopy complemented by scanning tunneling microscopy. Density functional theory illuminates possible reaction pathways and leads to the conclusion that the transmetalation proceeds through the adsorption of initially metallic (neutral) Co onto the porphyrin and the expulsion of Fe towards the surface accompanied by Co insertion. Our findings have important implications for the fabrication of porphyrin layers on surfaces when subject to the additional deposition of metals. Mixed-metal porphyrin layers can be fabricated by design in a solvent-free process, but conversely care must be taken that the transmetalation does not proceed as an undesired side reaction.Fil: Hötger, Diana. Max Planck Institute for Solid State Research; AlemaniaFil: Abufager, Paula Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Morchutt, Claudius. Max Planck Institute for Solid State Research; Alemania. École Polytechnique Fédérale de Lausanne; SuizaFil: Alexa, Patrick. Max Planck Institute for Solid State Research; AlemaniaFil: Grumelli, Doris Elda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Dreiser, Jan. Paul Scherrer Institute; SuizaFil: Stepanow, Sebastian. ETH Zürich; SuizaFil: Gambardella, Pietro. ETH Zürich; SuizaFil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Etzkorn, Markus. Max Planck Institute for Solid State Research; AlemaniaFil: Gutzler, Rico. Max Planck Institute for Solid State Research; AlemaniaFil: Kern, Klaus. Max Planck Institute for Solid State Research; Alemania. École Polytechnique Fédérale de Lausanne; Suiz

Enhancing hydrogen evolution activity of Au(111) in alkaline media through molecular engineering of a 2D polymer

The electrochemical splitting of water holds promise for the storage of energy produced intermittently by renewable energy sources. The evolution of hydrogen currently relies on the use of platinum as a catalyst—which is scarce and expensive—and ongoing research is focused towards finding cheaper alternatives. In this context, 2D polymers grown as single layers on surfaces have emerged as porous materials with tunable chemical and electronic structures that can be used for improving the catalytic activity of metal surfaces. Here, we use designed organic molecules to fabricate covalent 2D architectures by an Ullmann-type coupling reaction on Au(111). The polymer-patterned gold electrode exhibits a hydrogen evolution reaction activity up to three times higher than that of bare gold. Through rational design of the polymer on the molecular level we engineered hydrogen evolution activity by an approach that can be easily extended to other electrocatalytic reactions.Fil: Alexa, Patrick. Max Planck Institute for Solid State Research; AlemaniaFil: Lombardi, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Abufager, Paula Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Grumelli, Doris Elda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Vyas, Vijay S.. Max Planck Institute for Solid State Research; Alemania. Marquette University; Estados UnidosFil: Haase, Frederik. Max Planck Institute for Solid State Research; Alemania. Kyoto University. Institute for Integrated Cell-Material Sciences; JapónFil: Lotsch, Bettina V.. Max Planck Institute for Solid State Research; Alemania. University of Munich. Department of Chemistry; AlemaniaFil: Gutzler, Rico. Max Planck Institute for Solid State Research; AlemaniaFil: Kern, Klaus. Max Planck Institute for Solid State Research; Alemania. École Polytechnique Fédérale de Lausanne; Suiz

On-surface transmetalation of metalloporphyrins

Increasing the complexity of 2D metal-organic networks has led to the fabrication of structures with interesting magnetic and catalytic properties. However, increasing complexity by providing different coordination environments for different metal types imposes limitations on their synthesis if the controlled placement of one metal type into one coordination environment is desired. Whereas metal insertion into free-base porphyrins at the vacuum/solid interface has been thoroughly studied, providing detailed insight into the mechanisms at play, the chemical interaction of a metal atom with a metallated porphyrin is rarely investigated. Herein, the breadth of metalation reactions is augmented towards the metal exchange of a metalloporphyrin through the deliberate addition of atomic metal centers. The cation of Fe(ii)-tetraphenylporphyrins can be replaced by Co in a redox transmetalation-like reaction on a Au(111) surface. Likewise, Cu can be replaced by Co. The reverse reaction does not occur, i.e. Fe does not replace Co in the porphyrin. This non-reversible exchange is investigated in detail by X-ray absorption spectroscopy complemented by scanning tunneling microscopy. Density functional theory illuminates possible reaction pathways and leads to the conclusion that the transmetalation proceeds through the adsorption of initially metallic (neutral) Co onto the porphyrin and the expulsion of Fe towards the surface accompanied by Co insertion. Our findings have important implications for the fabrication of porphyrin layers on surfaces when subject to the additional deposition of metals. Mixed-metal porphyrin layers can be fabricated by design in a solvent-free process, but conversely care must be taken that the transmetalation does not proceed as an undesired side reaction.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

On-surface transmetalation of metalloporphyrins

Increasing the complexity of 2D metal-organic networks has led to the fabrication of structures with interesting magnetic and catalytic properties. However, increasing complexity by providing different coordination environments for different metal types imposes limitations on their synthesis if the controlled placement of one metal type into one coordination environment is desired. Whereas metal insertion into free-base porphyrins at the vacuum/solid interface has been thoroughly studied, providing detailed insight into the mechanisms at play, the chemical interaction of a metal atom with a metallated porphyrin is rarely investigated. Herein, the breadth of metalation reactions is augmented towards the metal exchange of a metalloporphyrin through the deliberate addition of atomic metal centers. The cation of Fe(ii)-tetraphenylporphyrins can be replaced by Co in a redox transmetalation-like reaction on a Au(111) surface. Likewise, Cu can be replaced by Co. The reverse reaction does not occur, i.e. Fe does not replace Co in the porphyrin. This non-reversible exchange is investigated in detail by X-ray absorption spectroscopy complemented by scanning tunneling microscopy. Density functional theory illuminates possible reaction pathways and leads to the conclusion that the transmetalation proceeds through the adsorption of initially metallic (neutral) Co onto the porphyrin and the expulsion of Fe towards the surface accompanied by Co insertion. Our findings have important implications for the fabrication of porphyrin layers on surfaces when subject to the additional deposition of metals. Mixed-metal porphyrin layers can be fabricated by design in a solvent-free process, but conversely care must be taken that the transmetalation does not proceed as an undesired side reaction.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Dissociative dynamics of spin-triplet and spin-singlet O2 on Ag(100)

10 páginas, 8 figuras.We study the dissociative dynamics of O2 molecules on the Ag(100) surface. Initially, the impinging molecules are either in the spin-triplet ground state or in the spin-singlet excited state. The molecule-surface interaction is obtained in each case by constructing the six-dimensional potential energy surface (PES) from the interpolation of the energies calculated with spin-polarized and non-spin-polarized density functional theories, respectively. Classical trajectory calculations performed in both PESs show that O2 molecules initially in the spin-triplet ground state only dissociate for incidence energies above 1.05 eV. This result is consistent with molecular beam experiments performed in this system. Interestingly, our results also suggest that for the spin-singlet O2 dissociation occurs even for incidence energies as low as 50 meV. We propose the use of spin-singlet excited O2 molecules to improve the otherwise low dissociative reactivity of O2 at clean Ag(100).We acknowledge partial support by the Spanish MEC (Grant No. FIS2007-66711-C02-02), the Basque Government (Grant No. CTP07-P02), and the Basque Departamento de Educación, Universidades e Investigación, the University of the Basque Country UPV/EHU (Grant No. IT-366-07). Computational resources were provided by the SGI/IZO-SGIker at the UPV/EHU (supported by the Spanish Ministry of Education and Science and the European Social Fund) and the DIPC computer center.Peer reviewe