Peer-reviewed Publications |
Amiaud, L., Fillion, J. - H., Dulieu, F., Momeni, A., & Lemaire, J. - L. (2015). Physisorption and desorption of H2, HD and D2 on amorphous solid water ice. Effect on mixing isotopologue on statistical population of adsorption sites. Phys Chem Chem Phys, 17(44), 30148–30157.
Résumé: We study the adsorption and desorption of three isotopologues of molecular hydrogen mixed on 10 ML of porous amorphous water ice (ASW) deposited at 10 K. Thermally programmed desorption (TPD) of H2, D2 and HD adsorbed at 10 K have been performed with different mixings. Various coverages of H2, HD and D2 have been explored and a model taking into account all species adsorbed on the surface is presented in detail. The model we propose allows to extract the parameters required to fully reproduce the desorption of H2, HD and D2 for various coverages and mixtures in the sub-monolayer regime. The model is based on a statistical description of the process in a grand-canonical ensemble where adsorbed molecules are described following a Fermi-Dirac distribution.
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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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Houplin, J., Amiaud, L., Dablemont, C., & Lafosse, A. (2015). DOS and electron attachment effects in the electron-induced vibrational excitation of terphenylthiol SAMs. Phys Chem Chem Phys, 17(45), 30721–30728.
Résumé: Low energy electron scattering on terphenylthiol (TPT, HS-(C6H4)2-C6H5) self-assembled monolayers (SAMs) deposited onto gold was investigated using high resolution electron energy loss spectroscopy (HREELS) by recording specular elastic and inelastic excitation functions. The electron elastic reflectivity could be directly compared to the sample density-of-states (DOS) above vacuum level. A high reflectivity region was observed in the range 7.2-8.6 eV. Inelastic excitation functions were studied to get insights into the mechanisms involved in the excitation of a selection of vibrational modes (dipolar and impact scattering). In particular, a resonant mechanism was observed in the excitation of the stretching mode nu(CC) at 196 meV. The purely resonant contribution to the electron-induced excitation of the stretching modes nu(CH) (379 meV) could be extracted from the overtone excitation. It is located at 7.2 eV above the vacuum level and is characterized by a width of 3.4 eV.
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Houplin, J., Amiaud, L., Sedzik, T., Dablemont, C., Teillet-Billy, D., Rougeau, N., & Lafosse, A. (2015). A combined DFT/HREELS study of the vibrational modes of terphenylthiol SAMs. Eur. Phys. J. D, 69(9), 9 pp.
Résumé: Self-assembled monolayers of p-terphenylthiol (TPT, HS-(C6H4)(2)-C6H5) deposited onto gold can serve as model systems for aromatic lithography resists. Such thin molecular films are suitably probed using high resolution electron energy loss spectroscopy, due to its high surface sensitivity. Extended energy loss spectra were measured at different probing energies. The TPT monolayer overlapping.(CH) stretching modes could be modelled by a single effective anharmonic oscillator sustained by a Morse potential energy curve, thanks to the resonant excitation of the associated overtone series at 6 eV. A remarkably good agreement was obtained between the TPT monolayer energy loss spectrum and the computer-simulated infrared vibrational spectrum of the isolated TPT molecule. Density Functional Theory calculations for TPT, fully deuterated TPT and benzenethiol isolated molecules were performed with the exchange correlation functional B3LYP and a dispersion correction, using a triple zeta+ polarisation basis set. By comparing the vibrational patterns obtained for these parent systems, (re-) assignments of all the features observed in the TPT self-assembled monolayer energy loss spectrum are discussed. The obtained vibrational assignments can be confidently transposed to other related systems, such as benzenethiol and biphenyl self-assembled monolayers.
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Houplin, J., Dablemont, C., Sala, L., Lafosse, A., & Amiaud, L. (2015). Electron Processing at 50 eV of Terphenylthiol Self-Assembled Monolayers: Contributions of Primary and Secondary Electrons. Langmuir, 31(50), 13528–13534.
Résumé: Aromatic self-assembled monolayers (SAMs) can serve as platforms for development of supramolecular assemblies driven by surface templates. For many applications, electron processing is used to locally reinforce the layer. To achieve better control of the irradiation step, chemical transformations induced by electron impact at 50 eV of terphenylthiol SAMs are studied, with these SAMs serving as model aromatic SAMs. High-resolution electron energy loss spectroscopy (HREELS) and electron-stimulated desorption (ESD) of neutral fragment measurements are combined to investigate electron-induced chemical transformation of the layer. The decrease of the CH stretching HREELS signature is mainly attributed to dehydrogenation, without a noticeable hybridization change of the hydrogenated carbon centers. Its evolution as a function of the irradiation dose gives an estimate of the effective hydrogen content loss cross-section, sigma = 2.7-4.7 x 10(-17) cm(2). Electron impact ionization is the major primary mechanism involved, with the impact electronic excitation contributing only marginally. Therefore, special attention is given to the contribution of the low-energy secondary electrons to the induced chemistry. The effective cross-section related to dissociative secondary electron attachment at 6 eV is estimated to be 1 order of magnitude smaller. The 1 eV electrons do not induce significant chemical modification for a 2.5 mC cm(-2) dose, excluding their contribution.
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Jia, J., Kara, A., Pasquali, L., Bendounan, A., Sirotti, F., & Esaulov, V. A. (2015). On sulfur core level binding energies in thiol self-assembly and alternative adsorption sites: An experimental and theoretical study. J.Phys.Chem C, 143(10), 104702.
Résumé: Characteristic core level binding energies (CLBEs) are regularly used to infer the modes of molecular adsorption: orientation, organization, and dissociation processes. Here, we focus on a largely debated situation regarding CLBEs in the case of chalcogen atom bearing molecules. For a thiol, this concerns the case when the CLBE of a thiolate sulfur at an adsorption site can be interpreted alternatively as due to atomic adsorption of a S atom, resulting from dissociation. Results of an investigation of the characteristics of thiol self-assembled monolayers (SAMs) obtained by vacuum evaporative adsorption are presented along with core level binding energy calculations. Thiol ended SAMs of 1,4-benzenedimethanethiol (BDMT) obtained by evaporation on Au display an unconventional CLBE structure at about 161.25 eV, which is close to a known CLBE of a S atom on Au.Adsorption and CLBE calculations for sulfur atoms and BDMT molecules are reported and allow delineating trends as a function of chemisorption on hollow, bridge, and atop sites and including the presence of adatoms. These calculations suggest that the 161.25 eV peak is due to an alternative adsorption site, which could be associated to an atop configuration. Therefore, this may be an alternative interpretation, different from the one involving the adsorption of atomic sulfur resulting from the dissociation process of the S–C bond. Calculated differences in S(2p) CLBEs for free BDMT molecules, SH group sulfur on top of the SAM, and disulfide are also reported to clarify possible errors in assignments.
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Lupone, S., Damoy, S., Husseen, A., Briand, N., Debiossac, M., Tall, S., & Roncin, P. (2015). A large open ratio, time and position sensitive detector for time of ight measurements in UHV. RSI, 86, 126115.
Résumé: We report on the construction of an UHV compatible 40 mm active diameter detector based on micro channel plates and assembled directly on the feed-throughs of a DN63CF flange. It is based on the charge division technique and uses a standard 2 inch Si wafer as a collector. The front end electronic is placed directly on the air side of the flange allowing excellent immunity to noise and a very good timing signal with reduced ringing. The important aberrations are corrected empirically
providing an absolute positioning accuracy of 500 μm while a 150 μm resolution is measured in the center.
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Oughaddou, H., Enriquez, H., Tchalala, M.R., Yildirim, H., Mayne, A.J., Bendounan, A., Dujardin, G., Ait Ali, M. & Kara, A. (2015). Silicene: A promising new 2D material. PROGRESS IN SURFACE SCIENCE, 90, 46–83.
Résumé: Silicene is emerging as a two-dimensional material with very attractive electronic properties for a wide range of applications; it is a particularly promising material for nano-electronics in silicon-based technology. Over the last decade, the existence and stability of silicene has been the subject of much debate. Theoretical studies were the first to predict a puckered honeycomb structure
with electronic properties resembling those of graphene. Though these studies were for free-standing silicene, experimental fabrication of silicene has been achieved so far only through epitaxial growth on crystalline surfaces. Indeed, it was only in 2010 that researchers presented the first experimental evidence of the formation
of silicene on Ag(110) and Ag(111), which has launched silicene in a similar way to graphene. This very active field has naturally led to the recent growth of silicene on Ir(111), ZrB2(0001)and Au(110) substrates. However, the electronic properties of epitaxially grown silicene on metal surfaces are influenced by the
strong silicene–metal interactions. This has prompted experimental studies of the growth of multi-layer silicene, though the nature of its ‘‘silicene’’ structure remains questionable. Of course, like graphene, synthesizing free-standing silicene represents the ultimate challenge. A first step towards this has been reported recently through chemical exfoliation from calcium disilicide (CaSi2). In this review, we discuss the experimental and theoretical studies of silicene performed to date. Special attention is given to different experimental studies of the electronic properties of silicene on metal substrates. New avenues for the growth of silicene on other substrates with different chemical characteristics are presented along with foreseeable applications such as nano-devices and novel batteries.
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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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Zugarramurdi, A., Momeni, A., Debiossac, M., Lunca-Popa, P., Mayne, A.J., Borisov, A.G., Mu, Z., Roncin, P. & Khemliche, H. (2015). Determination of the geometric corrugation of graphene on SiC(0001) by grazing incidence fast atom diffraction. Appl. Phys. Lett., 106(10), 101902.
Résumé: We present a grazing incidence fast atom diffraction (GIFAD) study of monolayer graphene on 6H-SiC(0001). This system shows a Moiré-like 13x13 superlattice above the reconstructed carbon buffer layer. The averaging property of GIFAD results in electronic and geometric corrugations that are well decoupled; the graphene honeycomb corrugation is only observed with the incident beam parallel to the zigzag direction while the geometric corrugation arising from the superlattice is revealed along the armchair direction. Full-quantum calculations of the diffraction patterns show the very high GIFAD sensitivity to the amplitude of the surface corrugation. The best agreement between the calculated and measured diffraction intensities yields a corrugation height of 0.27 +- 0.3A° .
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