M.E. Pronsato

The electronic effect of carbon and hydrogen in an () edge dislocation core system in bcc iron

Abstract The Fe–C–H interaction in a dislocated bcc structure was studied using qualitative structure calculations in the framework of the atom superposition and electron delocalisation molecular orbital (ASED-MO) theory. Calculations were performed using Fe 85 cluster to simulate a dislocated bcc structure. The cluster geometry and atomic parameters were optimised to make a better approximation to the repulsive energy terms. The most stable position for C atom inside the cluster was determined. Therefore, and H atom was approximated to the minimum energy region where the C atom was previously located. The total energy of the cluster decreases with the C atom near the dislocation core. The a /2[ 1 1 1 ] dislocation creates an energetically favourable zone for accumulation of C. The presence of C in the dislocation core make no favourable H accumulation. The C acts such as an expeller of H and could reduce the weakening of Fe–Fe bonds. In addition, a sort of Fe–C–Fe “bridge” could prevent dislocation displacement if a shear stress would be applied.

DFT study of Rh-decorated pristine, B-doped and vacancy defected graphene for hydrogen adsorption

Rh adatom stability on graphene, with and without defects has been investigated by density functional theory (DFT) calculations to evaluate the feasibility to achieve a uniform dispersion of the metallic atom. Different defects introduced include B dopants, single vacancies and double 585 and 555-777 type vacancies. An energetic analysis of the hydrogen adsorption capacity for the different Rh decorated graphene structures was also performed. Dispersion force contribution to the adsorption energy was determined in order to obtain a quantitative method to know whether H2 molecules adsorbed chemically or the adsorption on the Rh decorated graphene supports is controlled by van der Waals forces. Partial density of states (PDOS) for the different systems, were obtained to understand the Rh–C, H2–Rh (adsorbed) and H–H interactions and magnetic effects, before and after Rh and H2 adsorption. When H2 molecules bind to Rh adatoms, an electrostatic interaction occurs due to a charge transfer from the metal to the graphene surfaces after adsorption. Bonding and Bader charge analysis are also included.

Underpotential deposition and involved alloy formation of cadmium on silver particles modified HOPG substrates

Cadmium underpotential deposition (UPD) on Ag particles modified highly ordered pyrolytic graphite (HOPG) surfaces, and the involved alloy formation were studied by conventional electrochemical techniques. Voltammetric results indicated that the Cd UPD followed an adsorption behavior different from that observed for massive Ag electrodes and Ag particles supported on vitreous carbon. Nanometer-sized bimetallic Cd–Ag particles were characterized by ex situ atomic force microscopy (AFM). Initially, AFM images show Ag deposits of similar size distributed preferably on HOPG step edges. No remarkable morphological changes are observed on the surface after the subsequent Cd deposition, suggesting that the Cd particles are deposited selectively over the Ag crystals. From the analysis of desorption spectra, employing different polarization times, and density functional theory (DFT) calculations, the formation of a Cd–Ag surface alloy could be inferred.

Tungsten oxide nanowire on copper surfaces: a DFT model

We studied a model of a one dimensional tungsten oxide nanowire on a reconstructed Cu(110) surface by density functional theory calculations. The effect of oxygen vacancies on the electronic structure was analyzed (DOS). The nanowire equilibrium geometric configuration corresponds to tungsten oxide strips oriented along the Cu[10] direction, in which W–W distances are similar to the bulk data, in agreement with electron diffraction experiments. Bader charge analysis shows that the electron charge of the W atoms corresponds to a tungsten atom in the 6+ oxidation state. The presence of oxygen vacancies increases the electronic charge of the tungsten atoms. Formation of the oxygen vacancies by removal of terminal oxygen atoms is energetically favorable. Calculated PDOS shows stabilization of the tungsten states to lower energies due to the presence of oxygen vacancies.