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Surfaces d’alliages métalliques complexes : nanostructures et croissance moléculaire

Abstract : Complex metallic alloys (CMAs) are intermetallics with a unit cell characterized by a large number of atoms and a substructure of atomic clusters of high symmetry. Quasicrystals and their periodic approximants are part of this class of materials. Here, we have investigated the atomic and electronic structure of the (100) surface of a cage compound Ce3Pd20Si6 which can be also considered as a CMA. The assembly of Pd12Si6 and Pd16 cages in which guest Ce atoms are located describes its structure. The surface is analyzed using experimental methods under ultrahigh vacuum as well as atomistic simulations based on density functional theory (DFT). The surface forms at corrugated planes of the bulk structure that preserve intact the Pd12Si6 cages, with additional Pd surface atoms. It is concluded that despite this Pd-based cage compound being clearly metallic, stronger interactions between Pd and Si atoms on the host cage structure significantly influence its surface structure. Due to the cage preservation, the surface presents an intrinsic nanostructuration with a periodicity slightly less than one nanometer. This surface is further used as a pattern in an attempt to form self-organized molecular films. First results are presented concerning the self-assembly of C60 and its derivative (PTBC) on different substrates, including Ce3Pd20Si6(100) but also 5-fold surfaces of icosahedral phases i-AlCuFe and i-AgInYb and simple Cu (111) and Au (111) surfaces. Simple models are proposed to describe the structures formed by PTBC on Cu (111) and Au (111). C60 deposited on Ce3Pd20Si6(100) leads to the formation of hexagonal nanodomains,while PTBC leads to amorphous films. For PTBC deposited on quasicrystalline surfaces, preferential adsorption occurs at low coverage at 5-fold symmetric sites, dictated by symmetry matching between molecules and substrates. When the monolayer is saturated however, the film is either amorphous on i-AlCuFe or quasiperiodic on i-AgInYb, but with a large amount of disorder.
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Firas Abdel Hamid. Surfaces d’alliages métalliques complexes : nanostructures et croissance moléculaire. Science des matériaux [cond-mat.mtrl-sci]. Université de Lorraine, 2019. Français. ⟨NNT : 2019LORR0155⟩. ⟨tel-02516851⟩



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