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Morphologie de surface et ordre chimique : Faces vicinales d'alliage cuivre-palladium

Abstract : The aim of this experimental study is to characterise the step structure on a vicinal surface of an ordered alloy (L12) Cu-17%-Pd(1,1,11). This alloy present a chemical order-disorder transition at Tc=778K (Tc) (1sr order). At room temperature, we have observed by scanning tunnelling microscopy (STM) that the equilibrium surface morphology exhibits a regular distribution of paired steps. We have shown, by helium diffraction (TEAS), that this morphology evolves continuously to an unpaired steps structure close to Tc.

By using in situ synchrotron x-ray diffraction at ESRF, the unpairing process was found to be linear with surface in plane component of the chemical order parameter. For a sample shortly aged below Tc, direct observations by scanning tunnelling microscopy pointed out domains of paired steps, separated by walls. With atomic resolution images, we identify these surface walls with the emergence of bulk antiphase boundaries. We show, by TEAS and STM, that domains of paired steps allow us to measure the surface chemical ordering kinetic of an alloy. The characteristic surface domain size grows during aging as A(T).t1/2. An Arrhenius plot of the time scaling factor A(T) settled an activation energy of 2 eV for surface and bulk ordering.

Finally, in order to compare thin surface alloy structure and surface of bulk alloy, we have performed a study of palladium adsorption on vicinal Cu(1,1,11) face. We have shown, by TEAS, that 0.5 ML and annealing at 340K induced a paired steps structure similar than in bulk alloy Cu3Pd. However, the so obtained morphology exhibits is poorly ordered. This could be due by lack of surface chemical long range order.
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Submitted on : Wednesday, February 6, 2008 - 5:36:20 PM
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  • HAL Id : tel-00243115, version 1

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Sylvain Goapper. Morphologie de surface et ordre chimique : Faces vicinales d'alliage cuivre-palladium. Analyse de données, Statistiques et Probabilités [physics.data-an]. Université de Marne la Vallée, 1998. Français. ⟨tel-00243115⟩

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