CINaM - Centre Interdisciplinaire de Nanoscience de Marseille


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A venir ...

Jeudi 15 Octobre 2015
Pierre SENS
Physicochimie Curie - UMR 168, Institut Curie, Paris
Physical models of crawling cell motility
Cell motility is generally powered by actin polymerization and acto-myosin contraction. When moving over a flat and rigid substrate, cells usually develop thin and broad protrusions at their front, called lamellipodia, where actin polymerisation generates a protrusive force pushing the front edge of the cell forward. The lamellipodium often displays interesting dynamics, including normal and lateral waves, possibly relevant to cell polarisation and the initiation of motion. Crawling cells move by generating traction forces on their surrounding, which can be measured by traction force microscopy. These forces often exhibit interesting spatio-temporal patterns which are crucial to the cell’s ability to move, including periodic oscillations that may be related to the lamellipodial waves discussed above. This talk will be divided in two relatively unconnected parts. - I will first described a model of lamellipodium dynamics where the stochastic adhesion of actin filaments to the substrate by mechano-sensitive linkers produces a stick-slip behaviour with alternative phases of forward and backward edge motion. This stick-slip behaviour confers bistability to lamellipodium fragments and possibly to entire cells, which may either be symmetric and static or polarised and motile. This model explains the existence of radial and lateral lamellipodium waves which were observed experimentally, and highlights the role of the plasma membrane tension in regulating lamellipodium dynamics and cell polarisation. - I will then discuss a conceptual model of cell motility where the traction forces exerted by the cell are modelled as oscillating force multipoles. I will show how mechanical interactions mediated by the cytosol or the substrate may lead to synchronisation between the different parts of the cell, giving rise to polarisation and motion. I will also discussed the effect of noise on the persistence of cell motion, and the insight that such a model gives to the process of chemotaxis. The seminar will be in english

Jeudi 29 Octobre 2015
Jean-Marie DUBOIS
Institut Jean Lamour (UMR 7198 CNRS – Université de Lorraine), Parc de Saurupt, CS50840, F-54011 Nancy

Push-Pull Alloys and the Legacy of Dan Shechtman
With his famous discovery of quasicrystalline order in 1982-84, Dan Shechtman, the 2011 Nobel Laureate for Chemistry, has granted us with a fascinating field in materials science that has nowadays spread out to a variety of domains in metallurgy, geology, polymer science, artificial nanostructured materials, low temperature physics, and art. Push-pull alloys stand at the heart of the heritage and teach us a lot about the roots of order in Nature, its influence on properties, and by the way open new niches for applications. A short review of the most salient features of this domain will be given. We will begin with a simplified view at the way atomic order may be described in complex intermetallics and quasicrystals. The talk will continue with electron transport properties, which provide a signature of the breakdown of periodic order in those systems made of metals. We will then examine surface properties, with a view at the potential application niches and one, yet commercially available, application will be addressed. The talk will merely draw attention to A-B-C ternary alloys, in which the elemental constituents A, B and C are chosen in such a way that B-C interactions are repulsive, but A-B and A-C are attractive in the respective binary systems. I call such alloys “push-pull alloys” in reminiscence of push-pull amplifiers that are designed to amplify an electric signal. Push-pull alloys amplify complexity, forming complex intermetallics with tens to thousands atoms per unit cell. Few of them lead to the ultimate degree of complexity, when quasiperiodic order substitutes for crystal periodicity, which opens the way to discovering unprecedented properties such as heat insulation in Al62Cu25Fe13 (at. %). Many more compounds are known today, which share the same elemental characteristics (the picture may be extended to specific binary alloys). The results will be interpreted in terms of self-organized criticality [1]. In order to promote discussion about the essence of the quasicrystalline state (“why are the atoms where they are?”), a preliminary model will be suggested. It is based on the assumption that d-like electrons, facing the energy gaps opened at the boundaries of the Jones zone via Mizutani’s interference rule [2], impose a second wavelength to the scattering mechanism that is different from the one characteristic of the (orthogonal) s-p wave functions. Appropriate tuning of the two interference systems may cancel periodicity as predicted by the Lifshitz-Petrich model [3]. 1. P. Bak, How Nature works: the science of self-organized criticality (Copernicus Press, New York, 1996). 2. U. Mizutani et al., Chem. Soc. Rev. 41 (2012) 6799-6820. DOI: 10.1039/c2cs35161g. 3. R. Lifshitz and D.M. Petrich, Phys. Rev. Lett. 79-7 (1997) 1261-1264.

Jeudi 12 Novembre 2015
Paola Luches
Istituto Nanoscienze, Consiglio Nazionale delle Ricerche, Modena, Italy
Understanding reversible reduction processes in cerium oxide ultrathin films
Reducible oxides are compounds in which the cations can quickly and reversibly change their oxidation state between two or more states. This property makes reducible oxide - based materials very interesting in view of the applications, for example in catalysis, energy conversion and biomedicine. The combination between reducible oxides and metals, either as dopants or as supported nanoparticles, typically improves the performance of the material, compared to the individual components. The interaction between the oxide and the metal induces in fact important modifications in the structure and in the electronic properties of the combined system. I will discuss the results of our recent studies of cerium oxide ultrathin epitaxial films, studied as reducible oxide model systems [1-5]. I will focus on the interface between the cerium oxide film and the Pt(111) substrate, discussing the atomic scale structure and the occurrence of charge transfer effects [1,5]. I will also describe the electronic, structural and morphological modifications induced in the films by reduction and oxidation cycles through thermal treatments in vacuum and in oxygen partial pressure [2]. The results will be discussed considering the reduced dimensionality and the influence of the interface with the metallic substrate. The structure, morphology and charge transfer induced in Ag nanoparticles supported on epitaxial cerium oxide films will also be discussed [3,4]. The studies were performed using surface science techniques (XPS, LEED, STM), combined with high-resolution XANES and aberration-corrected STEM, and interpreted with the help of DTF+U calculations. References [1] P. Luches, F. Pagliuca, S. Valeri, F. Boscherini, J. Phys. Chem. C 117, 1030 (2013). [2] P. Luches, F. Pagliuca, S. Valeri, Phys. Chem. Chem. Phys. 16, 18848 (2014). [3] P. Luches, F. Pagliuca, S. Valeri, F. Illas, G. Preda, G. Pacchioni, J. Phys. Chem. C 116, 1122 (2012). [4] F. Benedetti, P. Luches, M. C. Spadaro, G. Gasperi, S. D’Addato, S. Valeri, F. Boscherini, J. Phys. Chem. C 119, 6024 (2015). [5] P. Luches, L. Giordano, V. Grillo, G. C. Gazzadi, S. Prada, M. Campanini, G. Bertoni, C. Magen, F. Pagliuca, G. Pacchioni, S. Valeri, Adv. Mater. Interf. (2015), in press.

Jeudi 19 Novembre 2015
Khalifa AGUIR
Institut Matériaux Microélectronique Nanosciences de Provence, IM2NP, UMR CNRS 7334, Universités d'Aix-Marseille et de Toulon, Campus de St. Jérôme, 13397 Marseille, France
De l'intérêt de la miniaturisation des capteurs pour le suivi de la qualité de l'air
Les capteurs dédiés au suivi de la qualité de l’air utilisent comme couche sensible des matériaux dont la conductivité peut varier en présence de gaz, vapeurs et de manière générale des polluants atmosphériques. La qualité de la réponse des capteurs est directement liée à la structure des matériaux utilisés, à l’échelle nanométrique. En effet, les capteurs les plus étudiés et les plus développés aujourd’hui, utilisent le plus souvent des oxydes semiconducteurs nanostructurés comme matériau sensible. Ceci permet d’augmenter le nombre de sites d’adsorption et donc d’augmenter la réponse du capteur. Cependant la nano-structuration seule du matériau sensible n’est pas suffisante. Elle doit s’accompagner d’une réduction de la taille de la couche sensible dans son ensemble, couche mince, nanofils, nanotubes, ajouts de nanograins catalytiques. Dans tous les cas, il faut privilégier l’effet de la surface sur celui du volume. La réaction entre le gaz et le capteur doit rester essentiellement un phénomène de surface, à l’échelle des nanograins qui constituent la couche sensible ou qui s’ajoutent à celle-ci pour modifier la réponse vis-à-vis de tel ou tel gaz. L’amélioration de la réponse des capteurs est indispensable si l’on veut respecter les normes en vigueur sur la qualité de l’air. Pour certains polluants, il est nécessaire de disposer de capteurs qui présentent des seuils de détection de l’ordre du ppb voire moins. Par ailleurs, la diminution de la taille des dispositifs et l’utilisation de microcapteurs permet de réduire la consommation et de pouvoir fabriquer des systèmes portables, autonomes, …

Jeudi 14 Janvier 2016
Roberta Poloni
INP, Grenoble
Metal Organic Framework for carbon capture