Modeling the optical properties of self-organized arrays of liquid crystal defects

International audienceLocal full Mueller matrix measurements in the Fourier plane of a microscope lens were used to determine the internal anisotropic ordering in periodic linear arrays of smectic liquid crystal defects, known as 'oily streaks'. We propose a single microstructure-dependent model taking into account the anisotropic dielectric function of the liquid crystal that reproduces the smectic layers orientation and organization in the oily streaks. The calculated Mueller matrix elements are compared to the measured data to reveal the anchoring mechanism of the smectic oily streaks on the substrate and evidence the presence of new type of defect arrangement. Beyond the scientific inquiry, the understanding and control of the internal structure of such arrays offer technological opportunities for developing liquid-crystal based sensors and self-assembled nanostructures

Suppression of the thermal hysteresis in magnetocaloric MnAs thin film by highly charged ion bombardment

We present the investigation on the modifications of structural and magnetic properties of MnAs thin film epitaxially grown on GaAs induced by slow highly charged ions bombardment under well-controlled conditions. The ion-induced defects facilitate the nucleation of one phase with respect to the other in the first-order magneto-structural MnAs transition with a consequent suppression of thermal hysteresis without any significant perturbation on the other structural and magnetic properties. In particular, the irradiated film keeps the giant magnetocaloric effect at room temperature opening new perspective on magnetic refrigeration technology for everyday use

Magnetic properties changes of MnAs thin films irradiated with highly charged ions

We present the first investigation on the effect of highly charged ion bombardment on a manganese arsenide thin film. The MnAs films, 150 nm thick, are irradiated with 90 keV Ne$^{9+}$ ions with a dose varying from $1.6\times10^{12}$ to $1.6\times10^{15}$ ions/cm$^2$. The structural and magnetic properties of the film after irradiation are investigated using different techniques, namely, X-ray diffraction, magneto-optic Kerr effect and magnetic force microscope. Preliminary results are presented. From the study of the lattice spacing, we measure a change on the film structure that depends on the received dose, similarly to previous studies with other materials. Investigations on the surface show a strong modification of its magnetic properties

Etude par Microscopie a Effet Tunnel de polymeres conjugues: adsorbats sur graphite, films electropolymerises sur or et sur graphite, defauts de surface du graphite

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 84253 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Etude des capacités d'intégration sensorielle toucher-vision chez des enfants présentant des troubles des apprentissages

The thesis aims to assess whether the transfer of information on the form between touch and vision are properly among children with oral language (dysphasia) or written (dyslexia) or unrest praxia (dyspraxia). In the first study, we conducted a neuropsychological evaluation in order to clarify what level of information processing are possible difficulties. This study shows auditivo-verbal working memory disorder within the three pathologies. More specifically, sequential processing disorders in children with dyslexia, oral language disorders expressive, and unrest visuo-constructifs among dysphasia children, and unrest motor, visuo-perception, visuo-construct and a low spatial memory among dyspraxia children. In a second study, we evaluated a group of child aged 4 to 8 years. The results show an evolving capacities of intramodal T-T and crossmodal TV and V-T of 4 to 8 years with performances almost perfect dice 5 years for simple geometric shapes and performance clearly moving towards 6-7 years for forms oriented.The latest study assesses the capacity for transfer into learning disorders. It showed sensory integration capabilities between touch and vision and efficiency but limited by the slowing cognitive disorders each pathology.Cette thèse a pour objectif d'évaluer si le transfert des informations sur la forme entre le toucher et la vision se fait adéquatement chez des enfants présentant des troubles du langage oral (dysphasiques) ou écrit (dyslexiques) ou des troubles praxiques (dyspraxiques). Dans une première étude, nous avons effectué une évaluation neuropsychologique afin de préciser à quel niveau de traitement des informations se situent les éventuelles difficultés. Cette étude montre des troubles de mémoire de travail auditivoverbale dans les trois pathologies. Plus spécifiquement, des troubles de traitement séquentiel chez les enfants dyslexiques, des troubles du langage oral expressif, et des troubles visuo-constructifs chez les enfants dysphasiques, et des troubles praxiques gestuels, visuo-perceptifs, visuo-constructifs, ainsi qu'une faible mémoire spatiale chez les enfants dyspraxiques. Dans une deuxième étude, nous avons évalué un groupe d'enfant tout-venant âgé de 4 à 8 ans. Les résultats montrent une évolution des capacités de transfert intramodal T-T et intermodal T-V et V-T de 4 à 8 ans avec des performances presque parfaites dés 5 ans pour des formes géométriques simples et des performances évoluant nettement vers 6-7 ans pour des formes composites orientées. La dernière étude évalue les capacités de transfert dans les troubles des apprentissages. Elle montre des capacités d'intégration sensorielle entre le toucher et la vision efficience mais limitée et ralentit par les troubles cognitifs de chaque pathologie

Directed assembly of nanoparticles monitored by liquid crystal topological defects for advanced optical properties of the composites (Conference Presentation)

International audienceDirected assembly of nanoparticles is a promising alternative for original nanoparticle organizations. New kinds of optical properties are expected when semi-conductive or metallic nanoparticles are concerned. Using liquid crystal matrices oriented by their interfaces, it is possible to induce anisotropic nanoparticle organizations. We can then investigate the influence of these matrices on the optical properties of the nanoparticles. I will show how to create hierarchical arrays of oriented topological defects in thin smectic films that act as efficient traps for a specific localization and orientation of nanoparticles [1]. I will show how specific nanoparticle assemblies can be obtained, depending on the nanoparticle size and shape. Fluorescent nanorods trapped in smectic dislocations become strictly oriented along a single direction, providing, a fine control of the polarization of the emmitted single photons [2]. Similarly the orientation of gold nanorods leads to the control of their luminescence as well as of their plasmon resonance by light polarization. I will show that, when the nanoparticle concentration is increased, single chains are formed, and can lead to a strong anisotropic electromagnetic coupling between the particles [3]. We are not only capable of linearly confining the particles, but also of varying the inter-particle interactions and thus modifing their optical properties which are sensitive to the inter-particle distance [4]. [1] D. Coursault, Soft Matter 12 (2016) 629. [2] L. Pelliser et al, Adv. Funct. Mat. 25 (2015) 1719. [3] D. Coursault et al., Adv. Mat. 24 (2012) 1461. [4] D. Coursault et al., ACSNano 9 (2015) 11678

A model for the structure of crystalline adsorbed organic monolayers with application to nCB

In order to understand the structure of nCB monolayers adsorbed on MoS2 as observed by STM, we have built a 2D phenomenological model through which the observed structures can be interpreted in term of a commensurate-incommensurate transition monitored by the molecular length. This model is derived from the theory of frustrated smectics; it demonstrates that the two main parameters governing the structure of such monolayers are the frustration of the adsorbed monolayers and the strength of the substrate-molecule interaction, similarly to the case of physisorbed rare gas monolayers. More generally, various STM results on monolayers of elongated molecules physisorbed on a substrate can be reinterpreted which emphasizes the role of molecule-substrate interaction