2020 |
El Boujlaidi, A., Rochdi, N., Tchalala, R., Enriquez, H., Mayne, A. J., & Oughaddou, H. (2020). Growth and characterization of nickel oxide ultra-thin films. SURFACES AND INTERFACES, 18, 100433.
Résumé: The oxidation of the Ni(111) surface under ultrahigh-vacuum conditions is studied experimentally with low-energy electron diffraction and high-resolution X-ray photoelectron spectroscopy. Exposure of the clean Ni(111) surface to molecular oxygen at room temperature followed by annealing at 400 K leads to the formation of two different structures (2×2) and (3root3 × 3root3 )R30°, prior to the formation of the NiO(111) monolayer. The O 1s core levels indicate that the obtained oxide is terminated by oxygen atoms while the valence band measurements clearly reveal the band gap of NiO. The energy difference between the Fermi level and the maximum of the valance band is extracted and is found to be 0.47 eV.
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2018 |
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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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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2017 |
Husseen, A., Le Moal, S., Oughaddou, H., Dujardin, G., Mayne, A., & Le Moal, E. (2017). Reaction kinetics of ultrathin NaCl films on Ag(001) upon electron irradiation. Phys. Rev. B, 96(23), 235418.
Résumé: We report on an electron-induced modification of alkali halides in the ultrathin film regime. The reaction kinetics and products of the modifications are investigated in the case of NaCl films grown on Ag(001). Their structural and chemical modification upon irradiationwith electrons of energy 52–60 eV and 3 keV is studied using low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES), respectively. The irradiation effects on the film geometry and thickness (ranging from between two and five atomic layers) are examined using scanning tunneling microscopy (STM).We observe that Cl depletion follows different reaction kinetics, as compared to previous studies on NaCl thick films and bulk crystals. Na atoms produced from NaCl dissociation diffuse to bare areas of the Ag(001) surface, where they form Na-Ag superstructures that are known for the Na/Ag(001) system. The modification of the film is shown to proceed through two processes, which are interpreted as a fast disordering of the film with removal of NaCl from the island edges and a slow decrease of the structural order in the NaCl with formation of holes due to Cl depletion. The kinetics of the Na-Ag superstructure growth is explained by the limited diffusion on the irradiated surface, due to aggregation of disordered NaCl molecules at the substrate step edges.
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2016 |
Dujardin, G., Boer-Duchemin, E., Le Moal, E., Mayne, A. J., & Riedel, D. (2016). DIET (Dynamics at surfaces Induced by Electronic Transitions) at the nanoscale. Surf. Sci., 643, 13–17.
Résumé: We review the long maturing evolution of DIET (Dynamics at surfaces Induced by Electronic Transitions) that began in the 1960s when Menzel, Gomer and Redhead proposed their famous stimulated desorption model. DIET entered the « nanoscale » in the 1990s when researchers at Bell Labs and IBM realized that the Scanning Tunneling Microscope (STM) could be used as an atomic size source of electrons to electronically excite individual atoms and molecules at surfaces. Resonant and radiant Inelastic Electron Tunneling (IET) using the STM have considerably enlarged the range of applications of DIET. Nowadays, « DIET at the nanoscale » covers a broad range of phenomena at the atomic-scale. This includes molecular dynamics (dissociation, desorption, isomerization, displacement, chemical reaction), vibrational spectroscopy and dynamics, spin spectroscopy and manipulation, luminescence spectroscopy, Raman spectroscopy and plasmonics. Future trends of DIET at the nanoscale offer exciting prospects for new methods to control light and matter at the nanoscale.
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Rogez, B., Cao, S., Dujardin, G., Comtet, G., Le Moal, E., Mayne, A. J., & Boer-Duchemin, E. (2016). The mechanism of light emission from a scanning tunnelling microscope operating in air. Nanotechnology, 27(46), 465201.
Résumé: The scanning tunnelling microscope (STM) may be used as a low-energy, electrical nanosource of surface plasmon polaritons and light. In this article, we demonstrate that the optimum mode of operation of the STM for maximum photon emission is completely different in air than in vacuum. To this end, we investigate the emission of photons, the variation in the relative tip-sample distance and the measured current as a function of time for an STM operating in air. Contrary to the case of an STM operating in vacuum, the measured current between the tip and sample for an STM in air is very unstable (rapidly fluctuating in time) when the applied voltage between the tip and sample is in the ∼1.5–3 V range (i.e., in the energy range of visible photons). The photon emission occurs in short (50 μs) bursts when the STM tip is closest to the sample. The current instabilities are shown to be a key ingredient for producing intense light emission from an STM operating in air (photon emission rate several orders of magnitude higher than for stable current). These results are explained in terms of the interplay between the tunnel current and the electrochemical current in the ubiquitous thin water layer that exists when working in air.
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Sonnet, P., Stauffer, L., Gille, M., Bléger, D., Hecht, S., Cejas, C., Dujardin, G., & Mayne, A. J. (2016). Molecular dissociation on the SiC(0001)-3x3 surface. ChemPhysChem, 17(23), 3900–3906.
Résumé: In the framework of density functional theory, the adsorption of the halogenated polycyclic aromatic hydrocarbon 2,11-diiodohexabenzocoronene (HBC-I2) on the SiC(0001) 3×3 surface has been investigated. Nondissociative and dissociative molecular adsorption is considered, and simulated scanning tunneling microscopy (STM) images are compared with the corresponding experimental observations. Calculations show that dissociative adsorption is favorable and reveal the crucial importance of the extended flat carbon core on molecule–surface interactions in dissociative adsorption; the iodine atom–surface interaction is of minor importance. Indeed, removing iodine atoms does not significantly affect the STM images of the central part of the molecule. This study shows that the dissociation of large halogenated polycyclic aromatic hydrocarbon molecules can occur on the SiC surface. This opens up interesting perspectives in the chemical reactivity and functionalization of wide band gap semiconductors.
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2014 |
Yang, H., Mayne, A. J., Comtet, G., Dujardin, G., Kuk, Y., Nagarajan, S., & Gourdon, A. (2014). Single-molecule light emission at room temperature on a wide-band-gap semiconductor. Phys. Rev. B, 90(12), 125427.
Résumé: Room-temperature light emission from single chemisorbed perylene based molecules adsorbed on silicon carbide (SiC) is probed by a scanning tunneling microscopy. A new approach to STM-induced luminescence of a single molecule is explored using a wide band gap semiconductor to decouple electronically the molecule from the surface. After molecular adsorption, the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) both lie within the bulk band gap and below the Fermi level of the substrate. The maximum photon energy of the light emission from the molecule shows a fixed shift of 1.5 eV relative to the maximum energy of the tunnel electrons. This is consistent with the photons being generated by inelastic electron tunneling between the highest occupied molecular orbital and the unoccupied electronic states of the STM tip.
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2013 |
Ovramenko, T., Spillebout, F., Bocquet, F. C., Mayne, A. J., Dujardin, G., Sonnet, P., Stauffer, L., Ksari, Y., & Themlin, J. M. (2013). STM imagery and density functional calculations of C-60 fullerene adsorption on the 6H-SiC(0001)-3x3 surface. Phys. Rev. B, 87(15), 155421.
Résumé: Scanning tunneling microscopy (STM) studies of the fullerene C-60 molecule adsorbed on the silicon carbide SiC(0001)-3 x 3 surface, combined with density functional theory (DFT) calculations, show that chemisorption of individual C-60 molecules occurs through the formation of one bond to one silicon adatom only in contrast to multiple bond formation on other semiconducting surfaces. We observe three stable adsorption sites with respect to the Si adatoms of the surface unit cell. Comprehensive DFT calculations give different adsorption energies for the three most abundant sites showing that van der Waals forces between the C-60 molecule and the neighboring surface atoms need to be considered. The C-60 molecules are observed to form small clusters even at low coverage indicating the presence of a mobile molecular precursor state and nonnegligible intermolecular interactions. DOI: 10.1103/PhysRevB.87.155421
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2012 |
Boudrioua, O., Yang, H., Sonnet, P., Stauffer, L., Mayne, A. J., Comtet, G., Dujardin, G., Kuk, Y., Nagarajan, S., Gourdon, A., & Duverger, E. (2012). Large organic molecule chemisorption on the SiC(0001) surface. Phys. Rev. B, 85(3), 035423.
Résumé: We present a density-functional theory (DFT) study combined with scanning tunneling microscopy (STM) experiments of the chemisorption of the N,N'-bis(1-hexylheptyl) perylene-3,4:9,10-bis(dicarboximide) molecule, noted here as DHH-PTCDI, on the SiC(0001)-3 x 3 surface. Five possible adsorption configurations have been investigated in which molecular adsorption occurs on two adjacent Si adatoms via different pairs of atoms of the molecule. We have calculated the energies, structures, density of states, local density of states, and a calculated STM image and show that chemisorption via two oxygen atoms located on the same side of the molecule on two adjacent Si adatoms is the most favorable, in agreement with the experimental STM images. A comparison between the PTCDI and the adsorption of another large organic molecule (phthalocyanine) on the SiC(0001) surface completes this work.
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Nimmrich, M., Kittelmann, M., Rahe, P., Harneit, W., Mayne, A. J., Dujardin, G., & Kuhnle, A. (2012). Influence of charge transfer doping on the morphologies of C-60 islands on hydrogenated diamond C(100)-(2 x 1). Phys. Rev. B, 85(3), 035420.
Résumé: The adsorption and island formation of C-60 fullerenes on the hydrogenated C(100)-(2 x 1):H diamond surface is studied using high-resolution noncontact atomic force microscopy in ultrahigh vacuum. At room temperature, C-60 fullerene molecules assemble into monolayer islands, exhibiting a hexagonally close-packed internal structure. Dewetting is observed when raising the substrate temperature above approximately 505 K, resulting in two-layer high islands. In contrast to the monolayer islands, these double-layer islands form extended wetting layers. This peculiar behavior is explained by an increased molecule-substrate binding energy in the case of double-layer islands, which originates from charge transfer doping. Only upon further increasing the substrate temperature to approximately 615 K, the wetting layer desorbs, corresponding to a binding energy of the charge transfer-stabilized film of 1.7 eV.
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Spillebout, F., Stauffer, L., Sonnet, P., & Mayne, A. J. (2012). Stability of small chemical groups on hexagonal-SiC(0001) surfaces: A theoretical study. SURFACE SCIENCE, 606(15-16), 1195–1202.
Résumé: Density functional theory (DFT) calculations are used to investigate the stability on SiC(0001) surfaces of different chemical groups -NH2, -NO2, -CH3, -OH, -SH and -CN. The adsorption stability decreases in the order -NO2 > -OH > -NH2 > -SH > -CN > -CH3. The stability of the single molecule-substrate bond is strongly influenced by the polarizability, which in turn depends on different parameters such as the electronegativity, atomic size and chemical environment. In a further step, methyl (-ACH(3)) and phenyl (-AC(6)H(5)) substituted groups are also considered and similar behaviour is observed. The inductive effect of the -CH3 or -C6H5 groups modifies the polarization of the Si adatom-molecule bond and the steric hindrance due to their size influences the molecular orientation. These two parameters affect the calculated adsorption energy, and are more important for -C6H5 substituent. This study provides clear tendencies that can be applied to more complex systems. Comparison of the adsorption of two large molecules, H2Pc (metal-free phthalocyanine) and PTCDI (perylene tetracarboxylic diimide) on the SiC(0001) surface is presented as an example. (C) 2012 Elsevier B.V. All rights reserved.
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Westover, J., Enriquez, H., Oughaddou, H., & Kara, A. (2012). Metallization of the beta-SiC(100) 3x2 surface: A DFT investigation. SURFACE SCIENCE, 606(19-20), 1471–1474.
Résumé: Using density functional theory (DFT) we report results for the electronic structure and vibrational dynamics of hydrogenated silicon carbide (001) (3 x 2) surfaces with various levels of hydrogenation. These results were obtained using density functional theory with a generalized gradient exchange correlation function. The calculations reveal that metallization can be achieved via hydrogen atoms occupying the second silicon layer. Further increase of hydrogen occupation on the second silicon layer sites results in a loss of this metallization. For the former scenario, where metallization occurs, we found a new vibrational mode at 1870 cm(-1), which is distinct from the mode associated with hydrogen atoms on the first layer. Furthermore, we found the diffusion barrier for a hydrogen atom to move from the second to the third silicon layer to be 258 meV. (c) 2012 Elsevier B.V. All rights reserved.
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Yang, H., Boudrioua, O., Mayne, A. J., Comtet, G., Dujardin, G., Kuk, Y., Sonnet, P., Stauffer, L., Nagarajan, S., & Gourdon, A. (2012). The paradox of an insulating contact between a chemisorbed molecule and a wide band gap semiconductor surface. Phys. Chem. Chem. Phys., 14(5), 1700–1705.
Résumé: Controlling the intrinsic optical and electronic properties of a single molecule adsorbed on a surface requires electronic decoupling of some molecular orbitals from the surface states. Scanning tunneling microscopy experiments and density functional theory calculations are used to study a perylene molecule derivative (DHH-PTCDI), adsorbed on the clean 3 x 3 reconstructed wide band gap silicon carbide surface (SiC(0001)-3 x 3). We find that the LUMO of the adsorbed molecule is invisible in I(V) spectra due to the absence of any surface or bulk states and that the HOMO has a very low saturation current in I(z) spectra. These results present a paradox that the molecular orbitals are electronically isolated from the surface of the wide band gap semiconductor even though strong chemical bonds are formed.
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2011 |
Mayne, A. J., & Dujardin, G. (2011). Atomic and Molecular Manipulation (Vol. 2). Frontiers in Nanoscience. A.J. Mayne, G. Dujardin.
Résumé: Work with individual atoms and molecules aims to demonstrate that miniaturized electronic, optical, magnetic, and mechanical devices can operate ultimately even at the level of a single atom or molecule. As such, atomic and molecular manipulation has played an emblematic role in the development of the field of nanoscience. New methods based on the use of the scanning tunnelling microscope (STM) have been developed to characterize and manipulate all the degrees of freedom of individual atoms and molecules with an unprecedented precision. In the meantime, new concepts have emerged to design molecules and substrates having specific optical, mechanical and electronic functions, thus opening the way to the fabrication of real nano-machines. Manipulation of individual atoms and molecules has also opened up completely new areas of research and knowledge, raising fundamental questions of “Optics at the atomic scale”, “Mechanics at the atomic scale”, Electronics at the atomic scale“, ”Quantum physics at the atomic scale“, and ”Chemistry at the atomic scale“. This book aims to illustrate the main aspects of this ongoing scientific adventure and to anticipate the major challenges for the future in ”Atomic and molecular manipulation" from fundamental knowledge to the fabrication of atomic-scale devices.
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Mayne, A. J., Riedel, D., Comtet, G., & Dujardin, G. (2011). Electronic Control of Single Molecule Nanomachines. In Current-Driven Phenomena in Nanoelectronics (pp. 156–188). T. Seideman.
Résumé: Consisting of ten chapters written by some of the world’s leaders in the field, this book combines experimental, theoretical and numerical studies of current-driven phenomena in the nanoscale. The topics covered range from single-molecule, site-specific nanochemistry induced by a scanning tunneling microscope, through inelastic tunneling spectroscopy and current-induced heating, to current-triggered molecular machines. The various chapters focus on experimental and numerical method development, the description of specific systems, and new ideas and novel phenomena.
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Rochdi, N., Liudvikouskaya, K., Descoins, M., Raissi, M., Coudreau, C., Lazzari, J. L., Oughaddou, H., & D'Avitaya, F. A. (2011). Surface morphology and structure of ultra-thin magnesium oxide grown on (100) silicon by atomic layer deposition oxidation. THIN SOLID FILMS, 519(19), 6302–6306.
Résumé: Ultra-thin magnesium oxide layers were elaborated by atomic layer deposition and oxidation process on silicon (100) starting from (2 x 1) thermally-reconstructed or hydrogen-terminated Si surfaces. Low-energy electron diffraction experiments show (2 x 3) and (3 x 3) reconstructions while depositing a magnesium monolayer on Si clean surfaces, and a 3-dimentional growth of the oxide as confirmed by ex-situ atomic force microscopy. For hydrogen-terminated or clean surfaces previously physisorbed by oxygen, uniform cobalt/magnesium-oxide/silicon stacks of layers are observed by transmission electron microscopy. Annealing above 150 degrees C leads to MgO dissolution and formation of an interfacial complex compound by inter-diffusion of Si and Co. (C) 2011 Elsevier B.V. All rights reserved.
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Wang, T., Boer-Duchemin, E., Tranvouez, E., Cartwright, R., Comtet, G., Dujardin, G., & Mayne, A. J. (2011). Low voltage fabrication of sub-nanometer insulating layers on hydrogenated diamond. JOURNAL OF APPLIED PHYSICS, 110(3), 034311.
Résumé: A new regime of electrochemical anodic oxidation with an atomic force microscope (AFM) is introduced for producing insulating layers on a hydrogenated diamond surface. In this new regime, when a low surface voltage (V(S) < +2 V) is applied to the sample, an insulating layer is created without any measurable change in the topography. Insulating layers created in this fashion are shown to preserve the high sub-surface conductance of hydrogenated diamond surfaces, contrary to the oxide layers accompanied by a topographic change, which destroy sub-surface conductance. (C) 2011 American Institute of Physics. [doi:10.1063/1.3615956]
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2010 |
El Asri, T., Raissi, M., Vizzini, S., El Maachi, A., Ameziane, E. L., d'Avitaya, F. A., Lazzari, J. L., Coudreau, C., Oughaddou, H., Aufray, B., & Kaddouri, A. (2010). Inter-diffusion of cobalt and silicon through an ultra thin aluminum oxide layer. APPLIED SURFACE SCIENCE, 256(9), 2731–2734.
Résumé: Optical emission spectroscopy of sputtered species during ion bombardment, Auger electron spectroscopy and high-resolution transmission electron microscopy were used to study the cobalt and silicon diffusion through the interfaces of Co/AlO/Si(0 0 1) hetero-structure. The results are discussed as a function of the annealing temperature of sample and show that the diffusion process at the interfaces starts for annealing temperatures above 200 degrees C without detectable modification of the oxide layer. (C) 2009 Elsevier B. V. All rights reserved.
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Nimmrich, M., Kittelmann, M., Rahe, P., Mayne, A. J., Dujardin, G., von Schmidsfeld, A., Reichling, M., Harneit, W., & Kuhnle, A. (2010). Atomic-resolution imaging of clean and hydrogen-terminated C(100)-(2x1) diamond surfaces using noncontact AFM. Phys. Rev. B, 81(20), 201403.
Résumé: High-purity, type IIa diamond is investigated by noncontact atomic force microscopy (NC-AFM). We present atomic-resolution images of both the electrically conducting hydrogen-terminated C(100)-(2 x 1) : H surface and the insulating C(100)-(2 x 1) surface. For the hydrogen-terminated surface, a nearly square unit cell is imaged. In contrast to previous scanning tunneling microscopy experiments, NC-AFM imaging allows both hydrogen atoms within the unit cell to be resolved individually, indicating a symmetric dimer alignment. Upon removing the surface hydrogen, the diamond sample becomes insulating. We present atomic-resolution images, revealing individual C-C dimers. Our results provide real-space experimental evidence for a (2 x 1) dimer reconstruction of the truly insulating C(100) surface.
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2009 |
Baffou, G., Mayne, A. J., Comtet, G., Dujardin, G., Stauffer, L., & Sonnet, P. (2009). SiC(0001) 3 x 3 Heterochirality Revealed by Single-Molecule STM Imaging. J. Am. Chem. Soc., 131(9), 3210–3215.
Résumé: We report a description of the SiC(0001) 3 x 3 silicon carbide reconstruction based on single-molecule scanning tunneling microscopy (STM) observations and density functional theory calculations. We show that the SiC(0001) 3 x 3 reconstruction can be described as contiguous domains of right and left chirality distributed at the nanoscale, which breaks the to date supposed translational invariance of the surface. While this surface heterochirality remains invisible in STM topographies of clean surfaces, individual metal-free phthalocyanine molecules chemisorbed on the surface act as molecular lenses to reveal the surface chirality in the STM topographies. This original method exemplifies the ability of STM to probe atomic-scale structures in detail and provides a more complete vision of a frequently studied SiC reconstruction.
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Cranney, M., Chalopin, Y., Mayne, A. J., & Dujardin, G. (2009). Adsorption and organisation of para-hexaphenyl molecules on Si(100). Appl. Phys. A, 94(4), 767–773.
Résumé: Para-hexaphenyl molecules (p-6P: C(36)H(26)) can be grown as nanofibres on various surfaces having optical properties of technological relevance. We report here the first observations of the initial stages of adsorption of individual p-6P molecules on Si(100)-(2x1) using room temperature Scanning Tunnelling Microscopy (STM). Depending on the substrate temperature, the hexaphenyl molecules adsorb in two configurations; indicating both weak and strong chemisorption. All six phenyl rings are clearly visible and the molecules are found to adsorb with characteristic angles between the long axis of the molecule and the silicon dimer rows. A statistical analysis of the spatial distribution of the molecules suggests that the clustering required for crystallographic nanofibre growth does not occur at the atomic scale under the experimental conditions used here.
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Riedel, D., Delacour, C., Mayne, A. J., & Dujardin, G. (2009). Very low thermally induced tip expansion by vacuum ultraviolet irradiation in a scanning tunneling microscope junction. Phys. Rev. B, 80(15), 155451.
Résumé: The thermal and photoelectronic processes induced when a vacuum ultraviolet (VUV) laser irradiates the junction of a scanning tunneling microscope (STM) are studied. This is performed by synchronizing the VUV laser shots with the STM scan signal. Compared to other wavelengths, the photoinduced thermal STM-tip expansion is not observed when the VUV radiation is freed from spurious emissions. Furthermore, we demonstrate that the purified VUV photoinduced transient signal detected in the tunnel current is entirely due to photoelectronic emission and not combined with thermionic processes. The ensuing photoelectron emission is shown to be independent of the tip-surface distance while varying linearly with the pure VUV laser intensity. These results illustrate a strong decoupling between phonons and photoelectrons which allows a very weak STM-tip expansion.
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Vizzini, S., Oughaddou, H., Hoarau, J. Y., Biberian, J. P., & Aufray, B. (2009). Y Growth of ultrathin film aluminum oxide on Ag(111). APPLIED PHYSICS LETTERS, 95(17), 173111.
Résumé: Scanning tunneling microscopy (STM) and spectroscopy and electron energy loss spectroscopy were used to characterize ultrathin epitaxial aluminum oxide on Ag(111) which was prepared via a specific deposition and oxidation process. Atomically resolved STM images show self-organized oxide stripes of 4 nm width with excellent homogeneity in depth and chemical composition properties which are crucial for applications of this oxide to magnetic tunnel junctions. We also found that electrons tunnel easily through the oxide film. This oxide has a different spectroscopic signature from that of alumina and has a wide bandgap close to 6.6 eV. (C) 2009 American Institute of Physics. [doi:10.1063/1.3251778]
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2008 |
Baffou, G., Mayne, A. J., Comtet, G., & Dujardin, G. (2008). State selective electron transport through electronic surface states of 6H-SiC(0001)-3 x 3. Phys. Rev. B, 77(16), 165320.
Résumé: We investigate charge transport through electronic surface states of the 6H-SiC(0001)-3 x 3 surface. Three intrinsic surface states are located within the wide bulk band gap, in which two (S(1) and U(1)) arise from strongly correlated electronic states and the third (S(2)) has negligible electron correlation effects. Combined conductance and luminescence experiments with the scanning tunneling microscope show that the Mott-Hubbard surface states (S(1) and U(1)) have a high resistance (1.0 G Omega), while the noncorrelated state (S(2)) has a negligible resistance. Consequently, current can be selectively transported through any of these three surface states.
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Mamatkulov, M., Stauffer, L., Sonnet, P., Mayne, A. J., Comtet, G., & Dujardin, G. (2008). Theoretical simulations of the tip-induced configuration changes of the 4,4 '-diacetyl-p-terphenyl molecule chemisorbed on Si(001). J. Chem. Phys., 128(24), 244710.
Résumé: We have investigated from a theoretical point of view modifications of the 4,4'-diacetyl-p-terphenyl molecule chemisorbed on Si(001) induced by the scanning tunneling microscope (STM). In previous experiments, these modifications were observed to occur preferentially at the end of the molecule after a +4.0 V voltage pulse and at the center after a +4.5 V voltage pulse. In the framework of ab initio simulations, we have realized a systematic energetic study of the dissociative chemisorption of one, two, or three phenyl rings of the substituted p-terphenyl molecule. Charge densities were then calculated for the investigated configurations and compared to the STM topographies. Before manipulation with the STM tip, the substituted p-terphenyl molecule is preferentially adsorbed without phenyl ring dissociation, allowing a partial rotation of the central phenyl ring. Our results show that the STM induced modifications observed at the end of the molecule might originate from the dissociation of two phenyl rings (one central and one external ring), while the modifications occurring at the central part of the molecule can be interpreted as a dissociation of the two external rings. (c) 2008 American Institute of Physics.
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Mayne, A. J., & Dujardin, G. (2008). STM manipulation and Dynamics. In Dynamics (Vol. 3, pp. 681–759). Handbook of Surface Science. E. Hasselbrink and B.I. Lundqvist.
Résumé: This volume of the Handbook of Surface Science covers all aspects of the dynamics of surface processes. Two dozen world leading experts in this field address the subjects of energy exchange in gas atoms, surface collisions, the rules governing dissociative adsorption on surfaces, the formation of nanostructures on surfaces by self-assembly, and the study of surface phenomena using ultra-fast lasers. The chapters are written for both newcomers to the field as well as researchers.
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