Luis Reinaudi

Work function calculation for thick metal slabs with local pseudopotentials

A new model for the calculation of the work functions of simple metals is presented, taking into account the type of single-crystal surface. It joins elements common to a number of other previous successful models employing density functional theory, namely finite metal slabs, local pseudopotentials and the self-consistent solution of an effective Schrodinger equation. Results are presented for the low-index crystal faces of aluminium and lead, and the compact faces of Zn and Mg. Comparison is made with previous results from other authors.

Monte Carlo simulation of elongating metallic nanowires in the presence of surfactants

Nanowires of different metals undergoing elongation were studied by means of canonical Monte Carlo simulations and the embedded atom method representing the interatomic potentials. The presence of a surfactant medium was emulated by the introduction of an additional stabilization energy, represented by a parameter Q. Several values of the parameter Q and temperatures were analyzed. In general, it was observed for all studied metals that, as Q increases, there is a greater elongation before the nanowire breaks. In the case of silver, linear monatomic chains several atoms long formed at intermediate values of Q and low temperatures. Similar observations were made for the case of silver-gold alloys when the medium interacted selectively with Ag.

Inclusion of symmetry for the enhanced determination of crystalline structures from powder diffraction data using simulated annealing

Significant improvements compared with the results obtained by other authors are achieved when space symmetry information obtainable from powder diffraction data is applied to the calculation of the TiO2(anatase) and TiO2- (rutile) structure; imposing symmetry conditions increases the number of times that the correct structure is generated in a set of runs and leads to more accuracy in the atomic positions.

Applications of Underpotential Deposition on Bulk Electrodes as a Model System for Electrocatalysis

The underpotential deposition (upd) of metals may modify the catalytic activity of substrates in several ways. For the sake of simplicity, we divide the types of impacts that upd metals can produce in four types, although they all can in principle be acting on a given reaction at the same time.

Experimental Techniques and Structure of the Underpotential Deposition Phase

The electrochemical deposition of metals on foreign substrates is a complex process which includes a number of phase formation phenomena. The very initial electrodeposition stages of a metal, M, on a foreign substrate, S, involve adsorption reactions as well as two- and/or three-dimensional nucleation and growth processes. The most important factors determining the mechanism of electrochemical M phase formation on S are the binding energy between the metal adatoms (Mads) and S, as well as the crystallographic misfit between the 3D M bulk lattice parameters and S. As we have shown in Fig. 1.3, when the binding energy between the depositing M-adatoms and the substrate atoms exceeds that between the atoms of the deposited metal, low dimensional iD metal phases (i = 0, 1 and 2) are formed onto the foreign metal substrate. This phenomenon, introduced in Chap. 1 as underpotential deposition (upd) [1–4], has been known for a long time and it has been intensively subject of study in the past decades since 1970s. This has been demonstrated by many studies of the upd process of different metals on mono- and polycrystalline substrates as well as reviews on the subject. The understanding of the nature of this phenomenon as conceived in the middle 1990s can be found in the book of Lorenz et al. [1]. Reviews available in the literature include the works of Kolb et al., Abruna et al., Sudha and Sangaranarayanan, Aramata [5–8], and the work of Szabo [3] concerning the theoretical aspects of upd, updated by Leiva [9], and also the works of Adžic [10] and Kokkinidis [11], concerning mainly the catalytic effects of upd adatoms.

Underpotential Deposition and Related Phenomena at the Nanoscale: Theory and Applications

Macroscopic materials composed by transition metals such as Ag, Au, Cu, Pd, and Pt are ductile, malleable, display excellent electrical and heat conductivity and high optical reflectivity. These properties have allowed these materials to be widely used in several areas, such as electrical contacts and conductors and the catalysis of chemical reactions. When the size of these materials decreases to the nanometric scale, these particles show unique properties, which cannot be observed in macroscopic-sized materials. The number of synthesis methods of these nanomaterials and their new and possible technological applications has increasingly grown during the last decade. This progress has inevitably led to the commercialization of several nanomaterials. For example, Ag nanoparticles (NPs) have been used as a type of antimicrobial reactive of broad spectrum in Medicine, in mass consumer products, in antiseptic aerosols of domestic use, in antimicrobial water filters coatings, etc. [1]. Apart from these commercial applications, nanomaterials are largely used in the field of research, e.g. Plasmonics, Medicine, reactivity, combustion cells, etc. [2, 3].

What Is Coming Next

In the following sections we will discuss on some tendencies and prospects concerning underpotential deposition (upd) research, related to both theoretical and experimental works.

Modelling of Underpotential Deposition on Bulk Electrodes

As discussed in Chaps. 2 and 3, a wide variety of experimental techniques have allowed to obtain a wealth of information of upd systems. This information concerns:

Phenomenology and Thermodynamics of Underpotential Deposition

As can be found from the other chapters of this book, underpotential deposition shows a wide variety of behaviors, which involve the occurrence of several surface phases, formation of submonolayers, monolayers (ML) and eventually the formation of bilayers. Adsorption may be commensurate or incommensurate, where the ML may undergo compression, and metal adatoms may coadsorb with anions to generate new phases. To start the discussion and briefly go into the history of the development of thermodynamics models for upd, we consider a relatively “simple” system, as shown in Fig. 3.1, which corresponds to Ag deposition on Pt(111) [1]. The voltammogram shown there presents three cathodic and three anodic peaks, which correspond to ML formation/desorption(3), bilayer formation/desorption(2) and bulk deposition/oxidation(1) of Ag. The peak potentials of the complementary processes do not coincide, denoting that at the present sweep rate a quasi equilibrium state has still not been reached. For the discussion below, we choose the anodic peaks, that we will denote with E 1, E 2 and E 3 (see Fig. 3.1). At the sight of the features of this voltammogram, and although the abscissa axis gives a measure for the of electrons at the working electrode, it may be appealing to use the position of the peaks found there as a measure for the stability of the different upd ad-phases being formed. In this spirit, Kolb et al. [2–4] introduced in the 1970s the concept of underpotential shift, ΔE upd.

Improvement in determining the crystal structure of inorganic compounds using powder diffraction data

In the last 18 years, determining the structure of inor-ganic solids from only chemical composition and unit cellhas become a great challenge. The usual approach to thisproblem is to find the global minimum of a certain cost func-tion that depends on the atomic coordinates, and for which itis reasonable to suppose that the configuration that yields theglobal minimum corresponds to that of the correct structure.This cost function may be based on the potential energy ofthe system Pannetier