Peer-reviewed Publications |
Bocquet, F. C., Giovanelli, L., Ksari, Y., Ovramenko, T., Mayne, A. J., Dujardin, G., Spillebout, F., Sonnet, P., Bondino, F., Magnano, E., & Themlin, J. - M. (2018). Peculiar covalent bonding of C60/6H-SiC(0001)-(3 × 3) probed by photoelectron spectroscopy. J. Phys. Condens. Matter., 30(50), 505002.
Résumé: High resolution photoemission with synchrotron radiation was used to study the interface formation of a thin layer of C60 on 6H-SiC(0 0 0 1)-(3 × 3), characterized by protruding Si-tetramers. The results show that C60 is chemisorbed by orbital hybridization between the highest-occupied molecular orbital (HOMO) and the p z orbital of Si adatom at the apex of the tetramers. The covalent nature of the bonding was inferred from core level as well as valence band spectra. The Si 2p spectra reveal that a large fraction (at least 45%) of the Si adatoms remain unbound despite the reactive character of the associated dangling bonds. This is consistent with a model in which each C60 is attached to the substrate through a single covalent C60–Si bond. A binding energy shift of the core levels associated with sub-surface Si or C atoms indicates a decrease of the SiC band bending caused by a charge transfer from the C60 molecules to the substrate via the formation of donor-like interface states.
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Kalashnyk, N., Amiaud, L., Dablemont, C., Lafosse, A., Bobrov, K., & Guillemot, L. (2018). Strain relaxation and epitaxial relationship of perylene overlayer on Ag(110). The Journal of Chemical Physics, 148(21), 214702.
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Kölsch, S., Fritz, F., Fenner, M.A., Kurch, S., Wöhrl, N., Mayne, A.J., Dujardin, G. & Meyer, C. (2018). Kelvin probe force microscopy studies of the charge effects upon adsorption of carbon nanotubes and C60 fullerenes on hydrogen-terminated diamond. J. Appl. Phys., 123(1), 15103.
Résumé: Hydrogen-terminated diamond is known for its unusually high surface conductivity that is ascribed to its negative electron affinity. In the presence of acceptor molecules, electrons are expected to transfer from the surface to the acceptor, resulting in p-type surface conductivity. Here, we present Kelvin probe force microscopy (KPFM) measurements on carbon nanotubes and C60 adsorbed onto a hydrogen-terminated diamond(001) surface. A clear reduction in the Kelvin signal is observed at the position of the carbon nanotubes and C60 molecules as compared with the bare, air-exposed surface. This result can be explained by the high positive electron affinity of carbon nanotubes and C60, resulting in electron transfer from the surface to the adsorbates. When an oxygen-terminated diamond(001) is used instead, no reduction in the Kelvin signal is obtained. While the presence of a charged adsorbate or a difference in work function could induce a change in the KPFM signal, a charge transfer effect of the hydrogen-terminated diamond surface, by the adsorption of the carbon nanotubes and the C60 fullerenes, is consistent with previous theoretical studies.
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Roncin, P., Debiossac, M., Oueslati, H., & Raouafi, F. (2018). Energy loss and inelastic diffraction of fast atoms at grazing incidence. NIM-B, 427, 100–107.
Résumé: The diffraction of fast atoms at grazing incidence on crystal surfaces (GIFAD) was first interpreted only in terms of elastic diffraction from a perfectly periodic rigid surface with atoms fixed at equilibrium positions. Recently, a new approach has been proposed, referred here as the quantum binary collision model (QBCM). The QBCM takes into account both the elastic and inelastic momentum transfers via the Lamb-Dicke probability. It suggests that the shape of the inelastic diffraction profiles are log-normal distributions with a variance proportional to the nuclear energy loss deposited on the surface. For keV Neon atoms impinging on a LiF(001) surface under an incidence angle θ, the predictions of the QBCM in its analytic version are compared with numerical trajectory simulations. Some of the assumptions such as the planar continuous form, the possibility to neglect the role of lithium atoms and the influence of temperature are investigated. A specific energy loss dependence ΔE θ ∝ 7 is identified in the quasi-elastic regime merging progressively to the classical onset ΔE θ ∝ 3. The ratio of these two predictions highlights the role of quantum effects in the energy loss.
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Sala, L., Szymańska, I. B., Dablemont, C., Lafosse, A., & Amiaud, L. (2018). Response under low-energy electron irradiation of a thin film of a potential copper precursor for focused electron beam induced deposition (FEBID). Beilstein J. Nanotechnol., 9, 57–65.
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Tchalala, M. R., Kara, A., Lachgar, A., Yagoubi, S., Foy, E., Vega, E., Nitsche, S., Chaudanson, D., Aufray, B., EL Firdoussi, L., Ali, M. A., & Oughaddou, H. (2018). Silicon nanoparticles synthesis from calcium disilicide by Redox assisted chemical exfoliation. Materials Today Communications, 16, 281–284.
Résumé: We report the preparation of single-crystal silicon nanoparticles with 15 to 22 nm diameter from calcium disilicide (CaSi2) by redox assisted chemical exfoliation using solution phase synthesis route. Silicon nanoparticles are found to be highly oriented with a predominant size of 18 nm. X-Ray diffraction, as well as transmission electron microscopy studies, confirm that the silicon nanoparticles are a diamond type and highly crystalline.
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Tchalala, R. M., Enriquez, H., Mayne, A. J., Kara, A., Dujardin, G., & Oughaddou, H. (2018). First steps of silicene growth on Ag(111). Journal of Physics: Conference Series, 1081, 012005.
Résumé: In this paper we report on the first steps of silicene growth on Ag(111) using scanning tunneling microscopy. We show that the topmost atomic layer is composed of both silicon and silver. The STM observations are consistent with an exchange process between the silicon and silver atoms preferentially taking place at the step edges of the Ag substrate. In addition, silicon stripes are observed as precursors of the formation of the silicene sheet.
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Tong, Y., Jiang, T., Qiu, S., Koshmak, K., Giglia, A., Kubsky, S., Bendounan, A., Chen, L., Pasquali, L., Esaulov, V. A., & Hamoudi, H. (2018). ZnO Functionalization: Metal–Dithiol Superstructures on ZnO(0001) by Self-Assembly. JOURNAL OF PHYSICAL CHEMISTRY C, 122(5), 2880–2889.
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Uribe J. D., M. M., Fierro B., Cardoso-Gil R., Abril I., Garcia-Molina R., Valdés J. E., Esaulov V. A. (2018). Proton energy loss in multilayer graphene and carbon nanotubes. RADIATION EFFECTS AND DEFECTS IN SOLIDS, 173(1-2), 93–101.
Résumé: Results of a study of electronic energy loss of low keV protons interacting with multilayer graphene targets are presented. Proton energy loss shows an unexpectedly high value as compared with measurements in amorphous carbon and carbon nanotubes. Furthermore, we observe a classical linear behavior of the energy loss with the ion velocity but with an apparent velocity threshold around 0.1 a.u., which is not observed in other carbon allotropes. This suggests low dimensionality effects which can be due to the extraordinary graphene properties.
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Zhang, W., Enriquez, H., Tong, Y., Bendounan, A., Kara, A., Seitsonen, A. P., Mayne, A. J., Dujardin, G., & Oughaddou, H. (2018). Epitaxial Synthesis of Blue Phosphorene. SMALL, 14, 1804066.
Résumé: Phosphorene is a new 2D material composed of a single or few atomic layers of black phosphorus. Phosphorene has both an intrinsic tunable direct bandgap and high carrier mobility values, which make it suitable for a large variety of optical and electronic devices. However, the synthesis of single-layer phosphorene is a major challenge. The standard procedure to obtain phosphorene is by exfoliation. More recently, the epitaxial growth of single-layer phosphorene on Au(111) was investigated by molecular beam epitaxy and the obtained structure described as a blue phosphorene sheet. In the present study, large areas of high-quality monolayer phosphorene, with a bandgap value equal to at least 0.8 eV, are synthesized on Au(111). The experimental investigations, coupled with density functional theory calculations, give evidence of two distinct phases of blue phosphorene on Au(111), instead of one as previously reported, and their atomic structures are determined.
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Zhao, M., Almarzouqi, F., Duverger, E., Sonnet, P., Dujardin, G., & Mayne, A. J. (2018). Sub-molecular spectroscopy and temporary molecular charging of Ni-phthalocyanine on graphene with STM. Phys. Chem. Chem. Phys., 20(29), 19507–19514.
Résumé: In this study, the self-assembled molecular network and electronic properties of Ni-phthalocyanine (NiPc) molecules on monolayer graphene (MLG)/6H-SiC(0001) were studied by room temperature Scanning Tunnelling Microscopy (STM) and Density Functional Theory (DFT) calculations. In this study, a very weak electronic coupling between the graphene and the NiPc molecules is found. This is due to the very small charge transfer of only 0.035e- per molecule. The weak molecule-graphene interaction has two observable consequences: sub-molecular resolution was obtained in the STM spectroscopy at room-temperature with the molecules adsorbed directly on the graphene, and the occupied and unoccupied molecular resonance peaks were observed to shift their position in energy as a function of the tip-surface distance. This is due to the temporary local charging (either positive or negative) that is achieved by decreasing the surface voltage under the STM tip. This may have important consequences for future studies of the opto-electronic properties of such hybrid graphene-molecule systems.
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