Concept of non-periodic metasurfaces based on positional gradients applied to IR-flat lenses

International audienceWe describe a theoretical study of gradient metasurfaces that – unlike most theoretical designs requiring advanced fabrication techniques – could easily be produced by a simple patterning method, templated microlens lithography (TEMPL). We show here that positional gradients of identical microstructures can lead to a gradient of phase lag across the metasurface. Using a radial gradient in the pitch of a hexagonal array of identical microfabricated resonators, one could thus produce gradient metasurfaces with the ability to focus infrared light. We provide illustrative examples of devices and compare their theoretical capabilities

A surface confined yttrium(III) bis-phthalocyaninato complex: a colourful switch controlled by electrons

AMs of a Y(III) double-decker complex on ITO have been prepared and their electrical and optical properties explored, exhibiting three accessible stable redox states with characteristic absorption bands in the visible spectra, corresponding to three complementary colors (i.e., green, blue and red). These absorption bands are exploited as output signals of this robust ternary electrochemical switch, behaving hence as an electrochromic molecular-based device.This work was funded by ERC StG 2012-306826 e-GAMES, the EU project ITN iSwitch (GA no. 642196), the Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), DGI (Spain) BE-WELL CTQ2013-40480-R, and Generalitat de Catalunya 2014-SGR-17. I. A. acknowledges CIBER-BBN for a grant.Peer reviewe

Magnetic Ordering in Ultrasmall Potassium Ferrite Nanoparticles Grown on Graphene Nanoflakes

Magnetic nanoparticles are central to the development of efficient hyperthermia treatments, magnetic drug carriers, and multimodal contrast agents. While the magnetic properties of small crystalline iron oxide nanoparticles are well understood, the superparamagnetic size limit constitutes a significant barrier for further size reduction. Iron (oxy)hydroxide phases, albeit very common in the natural world, are far less studied, generally due to their poor crystallinity. Templating ultrasmall nanoparticles on substrates such as graphene is a promising method to prevent aggregation, typically an issue for both material characterization and applications. We generate ultrasmall nanoparticles, directly on the carbon framework by the reaction of a graphenide potassium solution, charged graphene flakes, with iron(II) salts. After mild water oxidation, the obtained composite material consists of ultrasmall potassium ferrite nanoparticles bound to the graphene nanoflakes. Magnetic properties as evidenced by magnetometry and X-ray magnetic circular dichroism, with open magnetic hysteresis loops near room temperature, are widely different from classical ultrasmall superparamagnetic iron oxide nanoparticles. The large value obtained for the effective magnetic anisotropy energy density Keff accounts for the presence of magnetic ordering at rather high temperatures. The synthesis of ultrasmall potassium ferrite nanoparticles under such mild conditions is remarkable given the harsh conditions used for the classical syntheses of bulk potassium ferrites. Moreover, the potassium incorporation in the crystal lattice occurs in the presence of potassium cations under mild conditions. A transfer of this method to related reactions would be of great interest, which underlines the synthetic value of this study. These findings also give another view on the previously reported electrocatalytic properties of these nanocomposite materials, especially for the sought-after oxygen reduction/evolution reaction. Finally, their longitudinal and transverse proton NMR relaxivities when dispersed in water were assessed at 37 °C under a magnetic field of 1.41 T, allowing potential applications in biological imaging.IdEx Bordeau

Fabrication of Nonperiodic Metasurfaces by Microlens Projection Lithography

This paper describes a strategy that uses template-directed self-assembly of µm-scale microspheres to fabricate arrays of microlenses for projection photolithography of periodic, quasiperiodic, and aperiodic infrared metasurfaces. This method of “template-encoded microlens projection lithography” (TEMPL) enables rapid prototyping of planar, multi-scale patterns of similarly shaped structures with critical dimensions down to ~ 400 nm. Each of these structures is defined by local projection lithography, with a single microsphere acting as a lens. This paper explores the use of TEMPL for the fabrication of a broad range of two-dimensional lattices with varying types of non-periodic spatial distribution. The matching optical spectra of the fabricated and simulated metasurfaces confirm that TEMPL can produce structures that conform to expected optical behavior.Chemistry and Chemical Biolog

Cyanomethylene-bis(phosphonate)-Based Lanthanide Complexes: Structural, Photophysical, and Magnetic Investigations

10 pagesInternational audienceThe syntheses, structural investigations, magnetic and photophysical properties of a series of 10 lanthanide mononuclear complexes, containing the heteroditopic ligand cyanomethylene-bis(5,5-dimethyl-2-oxo-1,3,2λ5-dioxa-phosphorinane) (L), are described. The crystallographic analyses indicate two structural types: in the first one, [LnIII(L)3(H2O)2]*H2O (Ln = La, Pr, Nd), the metal ions are eight-coordinated within a square antiprism geometry, while the second one, [LnIII(L)3(H2O)]*8H2O (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er), contains seven-coordinated LnIII ions within distorted monocapped trigonal prisms...

Synthesis and properties of multifunctional single molecule magnets

En aquest treball s'ha dut a terme la síntesi i la caracterització química de varis complexos de doble capa de ftalocianines de terbi amb l'objectiu d'estudiar les seves propietats magnètiques en una varietat de configuracions. Es va obtenir una serie de compostos amb propietats físico-químiques distintes, com les d'autoassemblatje en superfície, d'activitat redox o de propietats mesomòrfiques.Las propietats magnètiques dels compostos sintetitzats varen ser caracteritzades via SQUID, dicroisme circular magnètic (MCD) y dicroisme circular magnètic de rajos-X (XMCD), en una varietat d'estats sòlids congelats, en submonocapes sobre grafit i en dissolució en varis estats d'oxidació.En general, es va observar que el comportament d'imant unimolecular (SMM) d'aquests compostos està qualitativament afectat por el estat d'oxidació de la molècula i la superestructura en la que estan integrats,produeixen canvis en la temperatura de bloqueig i en la forma de les histèresis de magnetització. Non obstant, es va constatar que el comportament d'imant unimolecular d'aquest complexos és molt robust ja que ni la substitució química de les ftalocianines, la hibridació amb una superfície de grafit, la oxidació o reducció del sistema o la morfologia del estat sòlid de les mostres va poder destruir aquesta propietat.En este trabajo se ha llevado a cabo la síntesis y la caracterización química de varios complejos de doble capa de ftalocianinas de terbio con el propósito de estudiar las propiedades magnéticas de estos complejos en una variedad de configuraciones. Se obtuvo una serie de compuestos con propiedades físico-químicas distintas, como las de autoensamblaje en superficie, de actividad redox o de propiedades mesomórficas.Las propiedades magnéticas de los compuestos sintetizados fueron entonces caracterizadas vía SQUID, dicroísmo circular magnético (MCD) y dicroísmo circular magnético de rayos-X (XMCD), en una variedad de estados sólidos congelados, en submonocapas sobre grafito y en disolución en varios estados de oxidación.En general, se observó que el comportamiento de imán unimolecular (SMM) de estos compuestos está cualitativamente afectado por el estado de oxidación de la molécula y la superestructura en la que están integrados, produciendo cambios en la temperatura de bloqueo y en la forma de las hysteresis de magnetización. Non obstante, se constató que el comportamiento de imán unimolecular de estos complejos es muy robusto ya que ni la substitución química de las ftalocianinas, la hibridación con una superficie de grafito, la oxidación o reducción del sistema o la morfología del estado sólido de las muestras pudo destruir está propiedad

Concept of non-periodic metasurfaces based on positional gradients applied to IR-flat lenses

We describe a theoretical study of gradient metasurfaces that – unlike most theoretical designs requiring advanced fabrication techniques – could easily be produced by a simple patterning method, templated microlens lithography (TEMPL). We show here that positional gradients of identical microstructures can lead to a gradient of phase lag across the metasurface. Using a radial gradient in the pitch of a hexagonal array of identical microfabricated resonators, one could thus produce gradient metasurfaces with the ability to focus infrared light. We provide illustrative examples of devices and compare their theoretical capabilities.Initiative d'excellence de l'Université de Bordeau

Continuous- versus segmented-flow microfluidic synthesis in materials science

Materials science is a fast-evolving area that aims to uncover functional materials with ever more sophisticated properties and functions. For this to happen, new methodologies for materials synthesis, optimization, and preparation are desired. In this context, microfluidic technologies have emerged as a key enabling tool for a low-cost and fast prototyping of materials. Their ability to screen multiple reaction conditions rapidly with a small amount of reagent, together with their unique physico-chemical characteristics, have made microfluidic devices a cornerstone technology in this research field. Among the different microfluidic approaches to materials synthesis, the main contenders can be classified in two categories: continuous-flow and segmented-flow microfluidic devices. These two families of devices present very distinct characteristics, but they are often pooled together in general discussions about the field with seemingly little awareness of the major divide between them. In this perspective, we outline the parallel evolution of those two sub-fields by highlighting the key differences between both approaches, via a discussion of their main achievements. We show how continuous-flow microfluidic approaches, mimicking nature, provide very finely-tuned chemical gradients that yield highly-controlled reaction–diffusion (RD) areas, while segmented-flow microfluidic systems provide, on the contrary, very fast homogenization methods, and therefore well-defined super-saturation regimes inside arrays of micro-droplets that can be manipulated and controlled at the milliseconds scale. Those two classes of microfluidic reactors thus provide unique and complementary advantages over classical batch synthesis, with a drive towards the rational synthesis of out-of-equilibrium states for the former, and the preparation of high-quality and complex nanoparticles with narrow size distributions for the latter.Initiative d'excellence de l'Université de Bordeau