Jean-Marc Roussel

On the estimation of SRO effects on surface segregation

The free-energy concentration expansion method (FCEM) is introduced and applied to the elucidation of short-range order (SRO) effects on surface segregation in alloys. This statistical-mechanical analytical approach, based on the Ising model Hamiltonian energetics, is verified by Monte Carlo (MC) simulations. In particular, calculations performed for the (100) surface of fcc solid solution show that the FCEM agrees with MC results much better than the Bragg-Williams (BW) theory, including the prediction of an increase in equilibrium segregation level with temperature, associated with SRO/segregation competition. FCEM is quite accurate and simple to apply, demanding much less computational effort compared to MC simulations or the cluster variation method. It can replace the corresponding BW formulae in theoretical evaluation of various surfaces as well as bulk phenomena, allowing systematic studies of SRO effects in alloys.

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

Abstract Recent experiments on systems such as Rh Ag or Ni Ag have shown that, in an intermediate range of temperature, competition between the flux of the deposited adatoms and the interdiffusion between the deposit and the substrate can lead to an original growth mode in which a floating mono- or bi-substrate layer buries the deposited film. This surfactant effect has been previously modelled, in the simplified situation of successive flashes of a complete monolayer, in the framework of the kinetic tight-binding Ising model. We show here that the extension of this model to the case of a continuous incoming flux leads to a wide variety of behaviours concerning the depth and spatial extension of the buried film as a function of the flux.