Andrés Saúl

Alloy surfaces: segregation, reconstruction and phase transitions

Abstract Surface segregation in alloys, i.e., concentration modulation in the surface selvedge at thermodynamical equilibrium, can be viewed as resulting from two kinds of competition or synergy. The first one is between surface and bulk interactions, i.e., surface energy versus bulk alloying interactions, whereas the second one is between these chemical forces and the atomic size-mismatch. Modelling the phenomenon then requires to account for all these forces on the same level. This leads to use both realistic energetic models derived from electronic structure and efficient statistical tools, from mean–field approximation to Monte Carlo simulations. A particular attention must be payed to the possible multisolution character of the problem. Actually, the possible coexistence of stable and metastable solutions may be at the origin of superficial phase transitions, in which the surface acts as a precursor of bulk order–disorder transitions: layering transitions, concentration profile transitions, surface induced order or disorder. All these phenomena are illustrated here on some specific systems and analyzed with tools derived from tight-binding formalism. Finally, the strong coupling between surface segregation and atomic reconstructions is illustrated in the case of strong size-mismatch by means of molecular dynamics calculations.

Different wavelength oscillations in the conductance of 5d metal atomic chains

Combining ab initio and self-consistent parametrized tight-binding calculations we analyze the conductance properties of atomic chains of

Charge redistribution at Pd surfaces: Ab initio grounds for tight-binding interatomic potentials

5d

Link between the surface wetting in Cu(Ag) and the layer-by-layer dissolution mode of a thick Ag deposit on a Cu substrate

elements like Au, Pt and Ir. It is shown that, in addition to the even-odd parity oscillations characteristic of Au, conduction channels associated with the almost full

Competition or synergy between surface segregation and bulk ordering: the CuPd system

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Kinetics of segregation and dissolution in Cu1−cAgc and surface phase transition: comparison between mean field and Monte Carlo calculations

bands in Pt and Ir give rise to longer periods which could be observed in sufficiently long chains. The results for short chains are in good agreement with recent experimental measurements.

Electronic structure of copper oxide clusters in the high TC superconductors: Relation to some recent experimental data

A simplified tight-binding description of the electronic structure is often necessary for complex studies of surfaces of transition-metal compounds. This requires a self-consistent parametrization of the charge redistribution, which is not obvious for late transition series elements (such as Pd, Cu, Au), for which not only

Grain effect in electronic properties of silicon epitaxial nanostructures

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Theoretical study of surface alloy formation through generation and annihilation of vacancies

but also

Flux dependence of the surfactant effect in NiAg(100): a theoretical study

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