Adsorption of fullerene and azafullerene on Cu(111) studied by electron energy loss spectroscopy

Fullerene and azafullerene films were studied by electron energy loss spectroscopy in reflection geometry. Compared to C60, (C59N)2 multilayers show additional vibrational modes that are characteristic of the dimer structure. The (C59N)2 is semiconductor-like and giant optically allowed excitonic transitions are found in the gap in drastic contrast with C60. The azafullerene monolayer on Cu(111) no longer shows the presence of dimers, indicating monomer adsorption. Similarly to C60, azafullerene molecules in contact with the metal substrate receive a transferred charge between two and three electrons. However, the C59N appears more covalently bound to Cu because it decomposes when heated above 660 K while C60 only desorbs.

O adsorption and incipient oxidation of the Mg(0001) surface

First principles density functional calculations are used to study the early oxidation stages of the Mg(0001) surface for oxygen coverages 1/16 <= Theta <= 3 monolayers. It is found that at very low coverages O is incorporated below the topmost Mg layer in tetrahedral sites. At higher oxygen-load the binding in on-surface sites is increased but at one monolayer coverage the on-surface binding is still about 60 meV weaker than for subsurface sites. The subsurface octahedral sites are found to be unfavorable compared to subsurface tetrahedral sites and to on-surface sites. At higher coverages oxygen adsorbs both under the surface and up. Our calculations predict island formation and clustering of incorporated and adsorbed oxygen in agreement with previous calculations. The calculated configurations are compared with the angle-scanned x-ray photoelectron diffraction experiment to determine the geometrical structure of the oxidized Mg(0001) surface.Comment: 10 pages, 5 figure

Plasma functionalization of AFM tips for measurement of chemical interactions

In this paper, a new, fast, reproducible technique for atomic force microscopy (AFM) tips functionalization used for chemical interaction measurements is described. Precisely, the deposition of an aminated precursor is performed through plasma-enhanced chemical vapor deposition (PECVD) in order to create amine functional groups on the AFM tip and cantilever. The advantages of the precursor, aminopropyltriethoxysilane (APTES), were recently demonstrated for amine layer formation through PECVD deposition on polymeric surfaces. We extended this procedure to functionalize AFM probes. Titration force spectroscopy highlights the successful functionalization of AFM tips as well as their stability and use under different environmental conditions. © 2010 Elsevier Inc

Récent développement de la spectroscopie vibrationnelle de perte d'énergie d'électrons lents à haute résolution. Analyse de matériaux isolants

The use of an auxiliary électron gun allows us to apply High Resolution Electron Energy Loss Spectroscopy (HREELS) to the study of non-conducting samples. Expérimental results are presented for crystalline surfaces : MgO (001), α-Al2O 3 (001), and LiF (001). The infrared optical constants of these materials are obtained by data processing with the dielectric theory describing the interaction of an electron with surface phonons (Fuchs-Kliewer type). These results are compared to data obtained by infrared spectroscopy and the specificity of HREELS is emphasized as far as surface properties are concerned. Two examples of non-crystalline materials are presented : the study of a semiconductor-oxide interface (SO2/Si) and of an organic polymer (polyethylene).L'utilisation d'un canon à électrons auxiliaire permet d'appliquer la spectroscopie de perte d'énergie d'électrons lents à haute résolution (HREELS), à l'étude d'échantillons non conducteurs. On présente des résultats expérimentaux pour les surfaces cristallines MgO (001), α-Al2O3 (001) et LiF (001). Les constantes optiques infrarouges de ces matériaux sont obtenues par ajustement de spectres synthétiques produits par la théorie diélectrique décrivant l'interaction d'un électron avec des phonons de surface de type Fuchs-Kliewer. Ces résultats sont comparés aux données obtenues par la spectroscopie infrarouge et on met l'accent sur la spécificité de l'HREELS quant à la mise en évidence de propriétés superficielles. Deux exemples de matériaux non cristallins sont proposés : l'étude d'une interface oxyde-semiconducteur (SiO2/Si) et d'un polymère organique (polyéthylène)