CINaM - Centre Interdisciplinaire de Nanoscience de Marseille

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Accueil du site > Séminaires > A venir ...

A venir ...

 
Jeudi 29 Juin 2017
Juris Purans
Institute of Solid State Physics, University of Latvia, Latvia
Recent achievement in Synchrotron Radiation X-ray absorption spectroscopy: Near field X-ray SPM - new tool for nanoscience
In the last years, the X-ray absorption (XAS) techniques have undergo remarkable development: (i) experiments with unprecedented femtometer accuracy [1], (ii) experiments with nanoscale lateral resolution. Nevertheless, investigations of complex nanostructured materials used in modern technologies require special X-ray experimental techniques able to imaging simultaneously topography and chemical mapping on the nanometer scale. Near Field X-ray Spectromicroscopy is a fully new approach for the detailed investigation of nanostructures down to the nanometer level. The extremely high lateral resolution of Local Probe Microscopies (LPM, AFM, STM) makes them among the most largely used in nanoscience. However, these tools suffer of a lack in chemical sensitivity. On the other hand, far field X-ray spectroscopy probes the chemical and structural properties of materials. A combination of X-ray spectroscopies and LPM is the ideal answer to many problems in nanosciences. The combination of XAS and scanning near-field optical microscopy (SNOM) as a local detector was proposed by Purans et.al. [2,3]. We have started with three types of experiments: (i) XAS-AFM: X-ray excited secondary electrons detection by conductive tip in AFM mode; (ii) XAS-SNOM: X-ray excited optical luminescence (XEOL) detection by SNOM in AFM mode; (iii) XAS-SCM/AFM: X-ray excited capacitance or/and photoconductivity of sample detection by conductive tip in SCM, KFM or AFM mode. The new instrumentation developed within this project offers the possibility to carry out a selective structural analysis of the sample surface with the subwavelength spatial resolution determined by the SNOM probe aperture. The apex of the optical fibre plays the role of a topographic probe, and chemical and topographic mappings can be simultaneously recorded. References 1. J. Purans, N. D.Afify, G.Dalba, R.Grisenti, S.De Panfilis, A.Kuzmin, V.I.Ozhogin, F.Rocca, A.Sanson, S. I. Tiutiunnikov, P.Fornasini, Phys. Rev. Lett. 100, 055901 (2008) 2. J. Purans, Proc. TXRF2003 Sat. meeting on micro X-ray beam analysis, 13.09.2003, Osaka, Japan 3. S. Larcheri, F. Rocca, F. Jandard, D. Pailharey, R. Graziola, A. Kuzmin and J. Purans, Rev. Sci. Instrum. 79 013702 (2008)

Jeudi 6 Juillet 2017
Fabien DUROLA
Centre de Recherche Paul Pascal (CRPP), Bordeaux
Controlled organic syntheses of large polycyclic aromatic compounds, from Scholl to Perkin strategies
The Scholl reaction is a popular tool for bottom-up organic syntheses of large polycyclic aromatic hydrocarbons, or nanographenes, since it allows the formation of numerous carbon-carbon bonds in one step. Nevertheless this well-known reaction remains unpredictable and can sometimes lead to surprising results, such as rearrangements or unexpected regioselectivities that lead to highly twisted helicenic arenes instead of their flat isomers. With the aim to avoid fully apolar hydrocarbons which are often very difficult to purify, we developed a complementary synthetic approach for the formation of large carboxy-substituted polycyclic aromatic compounds. This strategy relies on Perkin reactions for the synthesis of flexible precursors, followed by various cyclization reactions. This new synthetic approach has been optimized and can now be applied to the formation of interesting compounds such as poly-helicenes, columnar liquid crystals or macrocycles, as precursors of short carbon nanotubes.

Vendredi 7 Juillet 2017
Yutaka WAKAYAMA
International Center for Materials Nanoarchitectonics - National Institute for Materials Science
Photochromism in organic field-effect transistor for optical switching and circuits patterning
We developed an optically controllable organic field-effect transistor (OFET) by employing photochromic diarylethene (DAE) molecules as a transistor channel layer. DAE molecules undergo typical photochromic reaction, i.e., reversible conformational change between closed- and open-ring isomers by alternating ultraviolet (UV) and visible (VIS) light irradiation. We found that the drain current in the DAE-based OFET also showed reversible change accompanied by the conformational change; the closed-ring isomer exhibited a transistor operation under appropriate bias voltages, meanwhile the open-ring isomer showed no drain current. As a result, a remarkably high on/off ratio of 1,000 was achieved. The drain current modulation can be attributed to the drastic transformation in the π-conjugation in association with the photoisomerization. These results give us two important messages. The first one is that this compound can be regarded as a new material, which has dual properties: organic semiconductor and photochromism. The second is that a phase transition between semiconductor and insulator can be induced by light irradiation. Based on these achievements, we demonstrate laser drawing of one-dimensional (1D) transistor channels on the photochromic DAE layer. This technique will open new possibilities of various optically reconfigurable organic transistor circuits.

Jeudi 07 Septembre 2017
Ekaterina OBRAZTSOVA

Jeudi 28 Septembre 2017
Fabien SILLY

Jeudi 12 Octobre 2017
Olivier Pouliquen
IUSTI, CNRS - Aix-Marseille Université