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Dive into the research topics where V. Fournée is active.

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Featured researches published by V. Fournée.


Surface Science | 2003

Growth of Ag thin films on complex surfaces of quasicrystals and approximant phases

V. Fournée; A. R. Ross; Thomas A. Lograsso; James W. Evans; Patricia A. Thiel

Abstract The nucleation and growth of Ag thin films deposited on structurally complex alloy substrates is studied by scanning tunneling microscopy and low-energy electron diffraction. The substrates are high-symmetry surfaces of either icosahedral or decagonal quasicrystals or of related periodic crystals called approximants. At low coverage, completely different film morphologies are observed depending on the surface free energy of the substrate (relative to Ag). At high coverage, the formation of hexagonal nanocrystals is observed in all cases. These have fcc symmetry and pyramid-like multilayer stacking along the 〈1xa01xa01〉 direction. The constituent hexagonal islands have one, two or five different orientations depending on the rotational symmetry of the substrate on which the growth occurred. The films can be artificially smoothened by O 2 induced coarsening, leading to a patchwork of Ag nanocrystals with a perfect texture, which are separated by grain boundaries.


Surface Science | 2003

Pseudomorphic Starfish: Nucleation of Extrinsic Metal Atoms on a Quasicrystalline Substrate

T. Cai; J. Ledieu; R. McGrath; V. Fournée; Thomas A. Lograsso; A. R. Ross; Patricia A. Thiel

Abstract Direct observation of extrinsic Al atoms on the fivefold surface of icosahedral Al–Cu–Fe indicates that they form pseudomorphic islands resembling starfish. The starfish occupy specific types of sites on the laterally-bulk-terminated quasicrystalline surface. We postulate that the nucleation event consists of a diffusing Al atom dropping into an empty site at the centre of a substrate pentagon. Growth consists of the addition of five Al atoms (nearly) in lattice sites. These 6-atom starfish do not grow laterally as coverage increases, leading to islands of uniform size, and to early roughening.


Surface Science | 2000

A LEED comparison of structural stabilities of the three high-symmetry surfaces of Al-Pd-Mn bulk quasicrystals

Zhi-Xun Shen; W. Raberg; M. Heinzig; Cynthia J. Jenks; V. Fournée; M.A. Van Hove; Thomas A. Lograsso; Dwight W. Delaney; T. Cai; P. C. Canfield; I. R. Fisher; A. I. Goldman; Matthew J. Kramer; Patricia A. Thiel

Abstract It is shown that low-energy electron diffraction (LEED) patterns of the three high-symmetry surfaces (fivefold, threefold and twofold) of icosahedral Al–Pd–Mn are all compatible with quasicrystallinity, under specific conditions of preparation. This conclusion results from comparing symmetries of experimental surface LEED patterns with bulk X-ray diffraction data which are converted to the conditions of the LEED experiment. This conclusion is also based upon an analysis of relative diffraction spot spacings in LEED. Hence, none of the three surfaces exhibits a massive lateral reconstruction, i.e. massive deviation from quasicrystallinity. The LEED pattern of the fivefold surface is distinct from the LEED pattern of the pseudo-tenfold surface of an orthorhombic approximant. We believe that this rules out the possibility that the fivefold surface of the icosahedral quasicrystal reconstructs to an approximant with tenfold or pseudo-10-fold symmetry. The twofold and threefold surfaces facet more readily, indicating qualitatively that they are less stable than the fivefold surface.


Journal of Chemical Physics | 2003

The effect of common gases on nucleation of metal islands: The role of oxygen in Ag(100) homoepitaxy

Anthony R. Layson; James W. Evans; V. Fournée; Patricia A. Thiel

Preexposure to molecular oxygen gas, O2,g, can have a strong effect on the nucleation and growth of Ag islands on Ag(100) at 250 K. At this temperature, molecular oxygen dissociates efficiently at kink sites on steps. Subsequent deposition of Ag produces a far lower density of Agad islands than without oxygen. There is an associated increase in the Ag flux-scaling exponent, from 0.28 for the oxygen-free surface to 0.9 for the preexposed surface. Two-step deposition experiments show that species containing atomic oxygen diffuse freely across terraces and steps at this temperature and on the time scale of deposition. We hypothesize that the nucleating species contains both Ag and O, and that nucleation of islands is highly reversible (critical size i≫1). The diffusion of small islands, if it occurs, is not sufficient to explain the data.


Journal of Physics: Condensed Matter | 2002

Electronic structure of quasicrystals deduced from Auger and x-ray photoelectron spectroscopies

V. Fournée; James W. Anderegg; A. R. Ross; Thomas A. Lograsso; Patricia A. Thiel

Specific features in the electronic structure of Al-transition metal quasicrystals are analysed by a combination of Auger and x-ray photoelectron spectroscopies. We first demonstrate that different degrees of asymmetry in the transition metals 2p core-level lineshape observed across different types of surface structure correspond to variations in the density of states at the Fermi level, DOS(EF). Using this effect, we explore the controversial issue of whether the quasicrystalline, decagonal AlNiCo system is electronically stabilized. We find strong evidence for the presence of a reduced DOS(EF) in this system, as expected for electronically stabilized compounds, and as observed in the quasicrystalline, icosahedral AlPdMn and AlCuFe alloys. Finally, qualitative information on the nature of the electronic states in quasiperiodic structures extracted from the core-valence-valence Auger lines are presented and discussed.


Physical Review Letters | 2005

Quantum size effects in metal thin films grown on quasicrystalline substrates.

V. Fournée; H. R. Sharma; Masahiko Shimoda; An Pang Tsai; Barış Ünal; A. R. Ross; Thomas A. Lograsso; Patricia A. Thiel


Physical Review B | 2003

Nucleation and growth of Ag films on a quasicrystalline AlPdMn surface

V. Fournée; T. C. Cai; A. R. Ross; Thomas A. Lograsso; James W. Evans; Patricia A. Thiel


Physical Review B | 2000

Electronic structure of quasicrystalline surfaces: Effects of surface preparation and bulk structure

V. Fournée; Patrick J. Pinhero; James W. Anderegg; Thomas A. Lograsso; A. R. Ross; Paul C. Canfield; I. R. Fisher; Patricia A. Thiel


Physical Review B | 2002

Surface structures of approximant phases in the Al-Pd-Mn system

V. Fournée; A. R. Ross; Thomas A. Lograsso; James W. Anderegg; C. Dong; Matthew J. Kramer; I. R. Fisher; Paul C. Canfield; Patricia A. Thiel


Surface Science | 2005

Step structure on the fivefold Al–Pd–Mn quasicrystal surface, and on related surfaces

J. Ledieu; Erik J. Cox; R. McGrath; Neville V. Richardson; Qiao Chen; V. Fournée; Thomas A. Lograsso; A. R. Ross; K.J. Caspersen; Barış Ünal; James W. Evans; Patricia A. Thiel

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T. Cai

Iowa State University

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J. Ledieu

University of Lorraine

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