Marie-Cécile de Weerd

Self-Organized Molecular Films with Long-Range Quasiperiodic Order

Self-organized molecular films with long-range quasiperiodic order have been grown by using the complex potential energy landscape of quasicrystalline surfaces as templates. The long-range order arises from a specific subset of quasilattice sites acting as preferred adsorption sites for the molecules, thus enforcing a quasiperiodic structure in the film. These adsorption sites exhibit a local 5-fold symmetry resulting from the cut by the surface plane through the cluster units identified in the bulk solid. Symmetry matching between the C60 fullerene and the substrate leads to a preferred adsorption configuration of the molecules with a pentagonal face down, a feature unique to quasicrystalline surfaces, enabling efficient chemical bonding at the molecule-substrate interface. This finding offers opportunities to investigate the physical properties of model 2D quasiperiodic systems, as the molecules can be functionalized to yield architectures with tailor-made properties.

Al3AuIr: A New Compound in the Al-Au-Ir System.

A new ternary phase with a composition of Al3AuIr has been found in the Al-rich area of the Al-Au-Ir system. Differential thermal analysis indicates a melting point of 990 °C, and single-crystal X-ray diffraction measurements reveal that this ternary phase adopts a Ni2Al3 structure type (space group P3̅m1) with a = 4.2584(5) Å and c = 5.1991(7) Å. This compound is isostructural to the Al3Cu1.5Co0.5 phase also found in the Al-rich part of the Al-Cu-Co ternary diagram. Experimental evidence combined with ab initio calculations point toward an Al3AuIr phase stabilized by a Hume-Rothery mechanism. Quantum chemical calculations indicate two-center and multicenter interactions in the Al3AuIr phase. Layered distribution of two-center interactions separated by regions with four- and five-center bonds suggests a preferential cleavage of the material at puckered planes perpendicular to the [001] direction.

Growth and structure of ultrathin alumina films on the (1 1 0) surface of γ-Al4Cu9 complex metallic alloy

The first stages of oxidation of the (1 1 0) surface of a γ-Al(4)Cu(9) complex metallic alloy were investigated by combining x-ray photoemission spectroscopy, low energy electron diffraction and scanning tunnel microscopy studies. Oxidation at room temperature in the 2 × 10(-8) to 2 × 10(-7) mbar oxygen pressure range occurs in two steps: a fast regime is followed by a much slower one, leading to the formation of a thin aluminium oxide film showing no long range order. Cu-O bonds are never observed, due to fast oxygen induced aluminium segregation. The low value of the estimated activation energy for aluminium diffusion (0.65 ± 0.12 eV at(-1)) was ascribed to the presence of two vacancies in the γ-Al(4)Cu(9) structure. Annealing at 925 K the oxide film formed at room temperature leads to the formation of small crystallized domains with a sixton structure similar to structures reported in the literature following the oxidation of Cu-9% Al(1 1 1), NiAl (1 1 0) and FeAl(1 1 0) surfaces as well as ultrathin Al films deposited onto Cu(1 1 1) or Ni(1 1 1) surfaces. Two contributions were observed in the O1s peaks, which have been ascribed to loosely bound oxygen species and oxygen belonging to the sixton structure respectively.

Intermetallic compounds as potential alternatives to noble metals in heterogeneous catalysis: The partial hydrogenation of butadiene on alpha-Al4Cu9(110)

Recently, non‐noble intermetallic compounds have shown promising catalytic performances in the partial hydrogenation of alkynes and alkenes. In this work, the properties of γ‐Al4Cu9(1 1 0) toward the gas‐phase hydrogenation of butadiene were investigated at total pressures of 2–20 mbar and temperatures of 110–180 °C. The model catalyst is active and 100 % selective to butenes. Moreover, although less active than Al13Fe4(0 1 0), which was evaluated previously for the same reaction, it is more selective and more stable. The combination of catalytic tests with pre‐ and postreaction Auger electron spectroscopy measurements and comparative tests with Cu(1 1 0) shows that Cu governs the reaction on γ‐Al4Cu9(1 1 0). However, the lower activity of the (more Cu‐rich) sputtered Al4Cu9 surface with respect to the annealed one and the differences between Al4Cu9 and Cu surfaces in terms of butene isomer distribution, butene conversion kinetics, and sensitivity to poisons, demonstrate the unique character of the intermetallic compound.

Quasi-ordered C60 molecular films grown on the pseudo-ten-fold (1 0 0) surface of the Al13Co4 quasicrystalline approximant.

The growth of C60 films on the pseudo-ten-fold (1 0 0) surface of the orthorhombic Al13Co4 quasicrystalline approximant was studied experimentally by scanning tunneling microscopy, low-energy electron diffraction and photoemission spectroscopy. The (1 0 0) surface terminates at bulk-planes presenting local atomic configurations with five-fold symmetry-similar to quasicrystalline surfaces. While the films deposited at room temperature were found disordered, high-temperature growth (up to 693 K) led to quasi-ordered molecular films templated on the substrate rectangular unit mesh. The most probable adsorption sites and geometries were investigated by density functional theory (DFT) calculations. A large range of adsorption energies was determined, influenced by both symmetry and size matching at the molecule-substrate interface. The quasi-ordered structure of the film can be explained by C60 adsorption at the strongest adsorption sites which are too far apart compared to the distance minimizing the intermolecular interactions, resulting in some disorder in the film structure at a local scale. Valence band photoemission indicates a broadening of the molecular orbitals resulting from hybridization between the substrate and overlayer electronic states. Dosing the film at temperature above 693 K led to molecular damage and formation of carbide thin films possessing no azimuthal order with respect to the substrate.