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11 results on '"Arfaoui I."'

6. Evidence for a large enrichment of interstitial oxygen atoms in the nanometer-thick metal layer at the NbO/Nb (110) interface.

Author

Arfaoui, I., Guillot, C., Cousty, J., and Antoine, C.

Subjects
*INTERFACES (Physical sciences), *OXYGEN, *NIOBIUM, *ANNEALING of metals
Abstract

The oxide/metal interface induced by surface segregation of oxygen during the annealing of a Nb single crystal in UHV has been studied by photoemission spectroscopy with synchrotron radiation. With 260 and 350 eV photons, four well-resolved peaks A, B, C, D are found in spectra within the 200-210 eV range of binding energy. One couple of peaks (A and C) is associated with 3d[sup 5/2] and 3d[sup 3/2] core levels of Nb atoms in the metal while the other one (B and D), shifted by 1.4 eV when compared to A and C, corresponds to 3d levels of oxidized Nb atoms. The metal peak A at 202.3 eV is formed by three 3d[sup 5/2] components: a peak due to a metallic state (202.1 eV) and two components shifted by 0.2 and 0.5 eV, which are attributed to Nb[sub 6]O and Nb[sub 4]O compounds due to interstitial atoms of oxygen, respectively. The estimated concentration of the interstitial oxygen atoms in the nanometer-thick metal skin underlying the NbO/Nb interface corresponds to a large enrichment when compared to the one in the Nb bulk. [ABSTRACT FROM AUTHOR]

Published
2002
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8. Controlling Molecular Organization for the Realization of Sub-Wavelength Light Sources.

Author

FIORINI-DEBUISSCHERT, C., BERLINE, I., METGÉ, G., APETREI, A., ARFAOUI, I., DOUILLARD, L., CHARRA, F., BLEGER, D., KREHER, D., MATHEVET, F., and ATTIAS, A.-J.

Subjects
LIGHT sources, MOLECULES, SCANNING tunneling microscopy, LUMINESCENCE, NANOSTRUCTURED materials, ELECTRIC fields, SECOND harmonic generation
Abstract

The possibility to use the tip of a scanning tunneling microscope (STM) for the realization of a highly localized molecular light source is discussed. Engineering rules for the control of single molecule luminescence at metallic interfaces are first presented: we report controlled patterning of graphite substrates with well-defined 3D molecular nanostructures using the steered arrangement of multilayered [2.2] paracyclophane-based building blocks. Their in-plane self-assembly is shown to allow exact positioning of vertical structural elements with precisely defined nanoscale spacing both in the substrate plane and in a direction perpendicular to it. In a second part, we demonstrate that electric field induced second harmonic generation (SHG) processes can also be taken into profit to get localized light emission through controlled local electric field application using the STM tip as an electrode. Efficient SHG emission at the tip can be observed when the tip is immersed in a solution of highly nonlinear molecules: the electric field present at the tip apex is shown to lead to local noncentrosymmetry following molecular orientation. [ABSTRACT FROM AUTHOR]

Published
2010

11. Improvements in the characterization of the crystalline structure of acid-terminated alkanethiol self-assembled monolayers on Au(111)

Author

Imad Arfaoui, Francesco Paolucci, Petra Rudolf, Simone Zanarini, Sandra M. Mendoza, Mendoza S. M., Arfaoui I., Zanarini S., Paolucci F., Rudolf P., Zernike Institute for Advanced Materials, and Surfaces and Thin Films

Subjects
PHOTOELECTRON-SPECTROSCOPY, SURFACE, Superlattice, Analytical chemistry, FILMS, law.invention, ELECTROCHEMISTRY, SUPERLATTICE, Contact angle, MOLECULES, X-ray photoelectron spectroscopy, law, Monolayer, General Materials Science, GOLD, Spectroscopy, CARBOXYLIC-ACID, Chemistry, Hexagonal phase, SCANNING-TUNNELING-MICROSCOPY, THIOL MONOLAYERS, Self-assembled monolayer, Surfaces and Interfaces, Condensed Matter Physics, Scanning tunneling microscope, Cyclic voltammetry
Abstract

We report a study of acid-terminated self-assembled monolayers of alkanethiols of different length, 11-mercaptoundecanoic acid (11-MUA) and 16-mercaptohexadecanoic acid (16-MHDA), on Au(111). Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and contact angle techniques were used for characterization, and the results were compared with those obtained from n-alkanethiols of similar chain length, providing a detailed description of the two-dimensional crystalline structure. Molecular resolution STM images show that 11-MUA forms a dense-packed monolayer arranged in a (square root 3 x square root 3)R30 degrees structure with a c(2 x 4) superlattice, where the simple hexagonal phase, the c(2 x 4) superlattice, and nonordered areas coexist. 16-MHDA assembles in a uniform monolayer with similar morphology to that of 11-MUA, but molecular resolution could not be reached in STM due to both the hydrophilicity of the acid groups and the poor conductivity of the thick monolayer. Nevertheless, the monolayer thicknesses estimated by XPS and electrochemistry and the highly blocking character of the film observed by electrochemistry as well as the low water contact angle are consistent with 16-MHDA molecules forming a compact monolayer on the Au(111) substrate with fully extended alkyl chains and acid groups pointing away from the surface. The results obtained for 16-MHDA were reproducible under different preparation conditions such as the addition or omission of acetic acid to the ethanolic solution. Contrary to other reports, we demonstrate that ordered acid-terminated self-assembled monolayers are obtained with the same preparation conditions as those of the methyl-terminated ones, without any additional treatment.

Published
2007

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