2018 |
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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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2017 |
Kalashnyk N., R. L. A., Li D., Smogunov, Dappe Y.J., Jones T.S. and Guillemot L. (2017). Unraveling Giant Cu(110) Surface Restructuring Induced by a Non-Planar Phthalocyanine. NanoResearch, , 1–7.
Résumé: The surface stability of coinage metals is paramount when they are used as electrode materials for functional electronic devices incorporating organic semiconductors. In this work, it is shown that the adsorption of non-planar vanadyl phthalocyanine molecules on Cu(110) drastically restructured the metal surface at room temperature, which was further enhanced upon moderate annealing. Scanning tunneling microscopy imaging demonstrated that the surface was restructured at step edges into sawtooth features that gradually replaced the (110) terraces. The edges of the modified steps were preferentially composed of chiral (1×6) kink sites decorated with vanadyl phthalocyanine molecules adsorbed in a tilted configuration with the oxygen atom pointing downwards. These results can have a strong impact on the optimization of the performance of organic devices integrated with phthalocyanine molecules.
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2016 |
Bobrov, K., Kalashnyk, N., & Guillemot, L. (2016). Thermodynamic balance of perylene self-assembly on Ag(110). J Chem Phys, 145(15), 154705.
Résumé: We present a room temperature STM study of perylene adsorption on Ag(110) at the monolayer coverage regime. We found that structure and symmetry of the perylene monolayer are settled by thermodynamic balance of the three factors: (i) the ability of perylene molecules to recognize specific adsorption sites on the (110) lattice, (ii) the intermolecular interaction, and (iii) the accommodation of thermal motion of the molecules. The moderate strength of the site recognition and the intermolecular interaction, of the same order of magnitude as kT approximately 25 meV, represents a key feature of the thermodynamic balance. It bestows to this system the unique quality to form the quasi-liquid monolayer of epitaxial as well as self-assembling character. The perylene monolayer accommodates the short-range motion of the molecules instead of quenching it. It precludes the formation of possible solid nuclei and maintains common registry of the included molecules. The surface registry of the quasi-liquid phase is provided by locking of a structure-related fraction of the perylene molecules into specific adsorption sites of the (110) lattice favorable in terms of intermolecular interaction.
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2015 |
Bobrov K., K. N., Guillemot L. (2015). True perylene epitaxy on Ag(110) driven by site recognition effect. J. Chem. Phys., 142(10), 101929.
Résumé: We present a STM study of room temperature perylene adsorption on the Ag(110) surface. We have found a 2D perylene crystalline phase coexisting with the perylene liquid phase under thermal equilibrium. The reversible precipitation of the liquid phase at sub-monolayer coverage reveals the well ordered chiral crystalline phase existing in two enantiomorphic configurations of the ((-2)(3) (5)(2)) and ((2)(3) (5)(-2)) symmetry. This chiral phase is spatially separated into the 2D enantiopure islands of tens of nanometers size randomly distributed on the substrate and surrounded by the liquid medium. Analysis of surface registry of the crystalline phase combined with modeling of the intermolecular interactions indicates that its structure and symmetry is determined by a specific balance between the intermolecular attraction and intrinsic ability of the perylene aromatic board to recognize adsorption sites. The recognition effect was found to be strong enough to pin half of the perylene molecules into defined adsorption sites providing the structure skeleton. The attractive intermolecular interaction was found to be strong enough to bind another half of the molecules to the perylene skeleton shaping the true epitaxial structure.
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Shen, J., Jia, J., Bobrov, K., Guillemot, L., & Esaulov, V. A. (2015). Electron Transfer Processes on Supported Au Nanoclusters and Nanowires and Substrate Effects. J.Phys.Chem.C, 119(27), 15168–15176.
Résumé: The catalytic activity of metal nanoclusters is considered to depend on their size, morphology, and substrate type. Here we address this problem by studying changes in electron transfer processes, that are important in surface chemistry, on the example of the interaction of Li ions with gold nanostructures as a function of their sizes and substrate type. The Au nanoclusters were grown on highly ordered pyrolytic graphite (HOPG) and Al2O3 surfaces. In the case of Al2O3 and sputtered HOPG surface, a wide surface coverage distribution of nanoclusters is formed, whereas on pristine HOPG scanning tunneling microscopy (STM) images show that Au clusters nucleate at step edges and can coalesce into “nanowires”. We found that electron transfer is much more probable on small clusters than on bulk Au surfaces. For distributed clusters, electron transfer is most probable for lateral size is of the order of 2–3 nm and height is in the 1 nm range, that is, of the order of a few atomic layers. Interestingly, larger electron transfer rates were found on cluster chains or nanowires nucleated on HOPG step edges in the case of pristine HOPG than on isolated clusters on HOPG planes. Our results suggest that the main effects that are observed are largely related to cluster size and morphology.
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2013 |
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Bobrov, K., & Guillemot, L. (2013). Autocatalytic effect of Cu nano-islands on the reaction of water with the oxygen covered Cu(110) surface. Surface Science, 611, 32–39.
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Shen, J., Jia, J., Bobrov, K., Guillemot, L., & Esaulov, V. A. (2013). Electron transfer processes on Au nanoclusters supported on graphite. Gold Bull, 46(4), 343–347.
Résumé: Electron transfer processes play an important role in surface chemistry. This paper presents results of a study of changes in resonant electron transfer processes, as a function of gold cluster sizes, on the example of electron transfer between Li+ ions scattered on Au clusters on highly oriented pyrolytic graphite (HOPG). The gold nanoclusters were grown on lightly sputtered HOPG surface in order to obtain a wide coverage distribution of clusters. The growth of clusters was monitored by scanning tunneling microscopy. We found that electron transfer is much more probable on small clusters, whose lateral size is of the order of 2 to 3 nm and height in the 1-nm range, than on bulk Au or thin Au films. A comparison with Au clusters grown on the semiconducting titania did not reveal significant differences with HOPG.
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2011 |
Chen, L., Shen, J., Jia, J. J., Kandasamy, T., Bobrov, K., Guillemot, L., Fuhr, J. D., Martiarena, M. L., & Esaulov, V. A. (2011). Li+-ion neutralization on metal surfaces and thin films. PHYSICAL REVIEW A, 84(5), 052901.
Résumé: Li+ ions with energies ranging from 0.3 to 2 keV are scattered from Au(110) and Pd(100) surfaces and from ultrathin Ag film grown on Au(111) in order to study electron transfer phenomena. We find that neutralization occurs quite efficiently and find an anomalous ion energy dependence of the neutral fraction for Au(110) and Pd(100) surfaces previously noted for Au(111). The dependence of the neutral fraction on the azimuthal angle of the Au(110) and Pd(100) surfaces is reported. In the case of Ag monolayer on Au(111), results are similar to the case of the Ag(111) surface. To understand the anomalous ion energy dependence, we present a theoretical study using density functional theory (DFT) and a linearized rate equation approach, which allows us to follow the Li charge state evolution for the (111) surfaces of Ag, Au, and Cu, and for the Ag-covered Au(111) surface.
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Guillemot, L., & Bobrov, K. (2011). Formation of a Chemisorbed Water-Hydroxyl Phase on Cu(110) Mediated by Surface Transport. JOURNAL OF PHYSICAL CHEMISTRY C, 115(45), 22387–22392.
Résumé: Under ambient conditions, most of the solid surfaces are commonly covered with water and oxygen both playing a crucial role in catalysis, corrosion, and electrochemistry. We present an STM study on water interaction with the oxygen preadsorbed Cu(110)-(2 x 1)-O surface. Under water adsorption at similar to 200 K, the (2 x 1) added-on Cu-O chains are gradually transformed into mobile copper-hydroxyls complexes. Long-range transport and condensation of the complexes induce nucleation and growth of 2D copper islands. Simultaneously the associated hydroxyls self-assemble with oncoming water molecules into a well-ordered 2D water-hydroxyl chemisorbed phase thermally stable up to a room temperature. We found that the assembly of the water-hydroxyl phase could be consistently described in terms of H bonds formation between the adsorbate species. We anticipate that the understanding of the forces driving the chemisorption will stimulate studies on water chemisorption on other metal surfaces, which are still far from being completed.
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Guillemot, L., & Bobrov, K. (2011). Morphological instability of the Cu(110)-(2 x 1)-O surface under thermal annealing. PHYSICAL REVIEW B, 83(7), 075409.
Résumé: We present a scanning tunneling microscope study on reactivity of chemisorbed oxygen on the Cu(110)-(2 x 1)-O surface. We have found that the Cu(110)-(2 x 1)-O surface is intrinsically unstable under thermal annealing in the 400-900 K range. In the 455-570 K range, the surface undergoes faceting. The orientational transition of the adsorbed oxygen phase displays wide [110] terraces, covered by (2 x 1)-O bands self-assembled into a superstructure, as well as bunches of oxygen-free narrow terraces. We found that the wide [110] terraces are intrinsically unstable against further restructuring at their edges. The restructuration is driven by reversible thermal dissociation of the (2 x 1)-O bands. The slightly uneven oxygen band density between terraces, consequently differing in reactivity with respect to Cu-O fragments, induces Cu atom transport between their edges. The interplay between thermal dissociation of the (2 x 1)-O bands and long-range elastic relaxation of the strained surface is suggested to be the origin of the observed inhomogeneous oxygen distribution. In the 570-810 K range the Cu atom transport reveals continuous growth of the oxygenated [110] terraces. We discuss in detail the mechanism of the Cu transport, which results in a rapid propagation of the oxygenated terraces as well as a strain development on the surface.
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2010 |
Bobrov, K., & Guillemot, L. (2010). Strain engineering tunable nanotemplates on the Cu(110)-(2 x 1)-O surface. SURFACE SCIENCE, 604(21-22), 1894–1898.
Résumé: We present an STM study on the domain pattern formation of the Cu(110)-O surface. We found that the separation of the oxygen adsorbate phase into the domain pattern is consistent with a phenomenological model of size-dependent elastic relaxation of the strained surface. We developed a thermally assisted oxygen adsorption procedure aiming to control the size of the two-dimensional (2x1)-O islands nucleated at the surface under oxygen adsorption serving as precursors for domain pattern formation. We engineered wide range tuneable (2x1)-O domain patterns by controlling the nuclei size and the oxygen coverage at the pattern formation stage. (C) 2010 Elsevier B.V. All rights reserved.
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2009 |
Canario, A. R., Guillemot, L., Grizzi, O., Bandurin, Y., & Esaulov, V. A. (2009). Scattering of F atoms and anions on a TiO2(110) surface. SURFACE SCIENCE, 603(8), 1099–1105.
Résumé: Results of a study of energy losses and electron transfer processes for grazing scattering of fluorine atoms and anions scattering along different azimuthal orientations of the TiO2 crystal are presented. We observe strong variations in the overall intensity of scattered particles which are due to channelling effects. The energy losses do not show strong variations as a function of crystal azimuth except for the case of scattering along the (001) direction between the bridging oxygen atom rows, where we also observe differences in the energy losses of scattered ions and neutrals. We attribute this to the fact that larger F- survival occurs for trajectories staying farther from the surface, when also the energy losses remain small. The overall characteristics of energy losses are attributed mainly to trajectory effects due to scattering in regions of different electron density. Measurements of the ratio of scattered ions to the total scattered flux, i.e. the ion fractions which reflect electron capture and loss processes, show that these are not the same for incident anions and atoms. A strong difference for scattering along the (001) direction is observed, where at low incident energies a strong survival of incident ions occurs. These results are tentatively discussed in terms of non resonant electron capture at lattice O- sites and electron loss into the conduction band or by collisional detachment with bridging O atoms. (C) 2009 Elsevier B.V. All rights reserved.
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Guillemot, L., & Bobrov, K. (2009). Chirality induced by surface strain studied using scanning tunneling microscopy. PHYSICAL REVIEW B, 79(20), 201406.
Résumé: We present a scanning tunneling microscopy study of a thermally annealed oxygen covered Cu(110)-(2x1)-O surface. The thermal annealing results in step bunching followed by formation of strained terraces. The mechanical strain causes local compression of the Cu lattice accompanied with reflection symmetry breaking as measured by comparative analysis of the atomically resolved topographies. On the strained terraces the oblique Cu lattice favors oxygen rearrangement into a chiral adsorption phase. Chiral surface organization is evidenced by formation of enantiomorphic domains on the strained terraces.
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2008 |
Bobrov, K., & Guillemot, L. (2008). Interplay between adsorbate-induced reconstruction and local strain: Formation of phases on the Cu(110)-(2x1): O surface. PHYSICAL REVIEW B, 78(12), 121408.
Résumé: We present an STM study on the interplay between adsorbate-induced reconstruction and local strain on the oxygen adsorbed Cu(110) surface. Thermal annealing of the surface resulted in surface terrace ripening revealing larger terraces, uniformly covered by the (2x1)-O reconstructed phase, separated by step bunches. The largest terrace was found to be partially splitted by emerging dislocations inducing strong inhomogeneous strain in their close vicinity. This extra strain caused local conversion of the dominating (2x1)-O phase into oxygen chemisorbed phases drastically different from the dominating phase. A meaningful correlation between lateral evolution of the extra strain and structure of these phases has been found. The symmetry of the discovered phases has been determined and their structural models have been elaborated.
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2007 |
Bobrov, K., & Guillemot, L. (2007). Nanostructure formation by reactions of H2O with pre-adsorbed O on a Ag(110) surface. SURFACE SCIENCE, 601(15), 3268–3275.
Résumé: We present results of an STM investigation of water interaction with an oxygen covered Ag(l 10) in the case of the 0(4 x 1) reconstructed surface. Regarding the formation of one-layer-thick silver nanostructures previously demonstrated, they point to the key role of the surface temperature at which the water dosing is made. Indeed we measure silver nanostructuring for dosing temperatures lower than 235 K. We follow, in real time during the water dosing, the modifications induced at the surface for two temperatures of 200 K and 240 K. Drastic differences are exhibited. At 200 K, after an initial stage of formation of molecular assembly strips along the [0 0 1], the reactive process leading to the conversion to an OH layer occurs clearly going along with the appearance and development of quasi- rectangular silver nanostructures. At 240 K, no such initial phase is evidenced. The complete conversion to an OH row structure of the scanned area occurs with no concomitant silver nanostructure formation. The dynamical behaviour of the reaction front allows the unravelling of the key role of the developing OH row ends intersecting the remaining Ag-O rows as particular reactive adsorption sites for the completion of the OH layer. (c) 2007 Elsevier B.V. All rights reserved.
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Guillemot, L., & Bobrov, K. (2007). On the formation of OH ordered layers by dissociation of H2O on an oxygen covered Ag(110) surface: An STM investigation. SURFACE SCIENCE, 601(3), 871–875.
Résumé: We present results of an STM investigation of water interaction with an oxygen covered Ag(110) on the example of the 0(4 x 1) reconstructed surface. In agreement with numerous previous experimental works, using diffraction techniques, we found that a structure of OH(1 x 2) type, displaying rows in the [1-10] direction, is formed. The new features revealed by this local probe study, is the presence of quasi rectangular islands evenly distributed across the terraces, with a density of 0.22 +/- 0.03 and a mean area of 90 +/- 15 nm(2) at 220 K. They are imaged at an apparent height of 0.14 nm. It is remarkable that the same OH row structure is present on the whole terrace “on top” and “in between” the islands. These features are attributed to silver islands of mono-atomic height, formed by clustering of silver ad-atoms released during reaction of the 0 atoms with the water molecules. These findings point to a more complex behaviour of the reaction dynamics than previously described. They emphasise the key role of the silver ad-atoms, present in the added rows of the initial Ag(110)-O(4 x 1) surface, in the formation of the nanostructures. In turn it is concluded that the rows evidenced by this STM and previous diffraction studies, are formed by OH chains. (c) 2006 Elsevier B.V. All rights reserved.
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