Facile and rapid synthesis of highly luminescent nanoparticles via Pulsed Laser Ablation in Liquid

This paper demonstrates the usefulness of pulsed laser ablation in liquids as a fast screening synthesis method able to prepare even complex compositions at the nanoscale. Nanoparticles of Y2O3:Eu3+, Lu2O2S: Eu3+, Gd2SiO5:Ce3+ and Lu3TaO7:Gd3+,Tb3+ are successfully synthesized by pulsed laser ablation in liquids. The phase and stoichiometries of the original materials are preserved while the sizes are reduced down to 5-10 nm. The optical properties of the materials are also preserved but show some small variations and some additional structures which are attributed to the specificities of the nanoscale (internal pressure, inhomogeneous broadening, surface states...

Émergence de flaticons dans les fibres optiques

Conférence pouvant être vue sur http://youtu.be/p9OnhcHQ3MwNational audienceNous étudions expérimentalement la propagation non-linéaire d'une onde continue menant à l'émergence d'impulsions au sommet plat et sans dérive de fréquence. Ces impulsions, appelées flaticons, subissent une évolution auto-similaire de leur partie centrale et présentent des oscillations temporelles marquées dans leurs flancs

Dielectric properties of segmented polyurethanes for electromechanical applications

cited By 10International audienceThe paper deals with electromechanical and dielectric properties of polyurethanes (PU) block-copolymers. Most of the works published in the literature only consider electrostriction at room temperature at a given frequency. In this work, it is shown that electrostrictive coefficient ME is divided by 3-10 at increasing frequency over 3 decades of frequency, depending on the ratio of hard to soft segments in PU. Thus it is important to analyze the energy conversion efficiency by investigating the dielectric and viscoelastic properties. This work deals with the study of dielectric properties of 3 PU with different fractions of hard segments. Three relaxation phenomena (β, α and conduction) were investigated for each PU in the temperature-frequency range studied here, in order to optimize the copolymer composition in view of their best efficiency as actuators or mechanical energy harvesting devices

Deformation mechanism of cerium oxide nanocubes - an in situ transmission electron microscopy study

Cerium oxide nanoparticles are used in many industrial products, among which solid oxide fuel cell electrodes or catalysts. However, their mechanical properties are rarely taken into account and few studies dealt with the determination of their deformation mechanism [1, 2]. Please click Download on the upper right corner to see the full abstract

Oriented Attachment of ZnO Nanocrystals

Self-organization of nanoparticles is a major issue to synthesize mesoscopic structures. Among the possible mechanisms leading to self-organization, the oriented attachment is efficient yet not completely understood. We investigate here the oriented attachment process of ZnO nanocrystals preformed in the gas phase. During the deposition in high vacuum, about 60% of the particles, which are uncapped, form larger crystals through oriented attachment. In the present conditions of deposition, no selective direction for the oriented attachment is noticed. To probe the driving force of the oriented attachment, and more specifically the possible influence of the dipolar interaction between particles, we have deposited the same nanocrystals in the presence of a constant electric field. The expected effect was to enhance the fraction of domains resulting from the oriented attachment due to the increased interaction of the particle dipoles with the electric field. The multiscale analytical and statistical analysis (TEM coupled to XRD) shows no significant influence of the electric field on the organization of the particles. We therefore conclude that the dipolar interaction between nanocrystals is not the prominent driving force in the process. Consequently, we argue, in accordance with recent theoretical and experimental investigations, that the surface reduction, possibly driven by Coulombic interaction, may be the major mechanism for the oriented attachment process

In situ nanocompression tests in an environmental TEM to study plasticity of cerium oxides

Cerium oxide plays an important role in several fields, among which catalysis, gas detection or fuel cells [1]. Cerium oxide nanoparticles are also used as superior abrasive particles in chemical mechanical planarization (CMP), which is a key process in semiconductor device fabrication [2]. Most of the current research focus on the synthesis of cerium oxide to optimize CMP, but analysing its deformation mechanisms is also a promising research direction [3]. Please click Additional Files below to see the full abstract

TEM observation and in situ compression tests of transition alumina prepared by high pressure compaction at room temperature

The behavior of ceramics at the nanometer scale strongly differs from the one of the corresponding bulk material. For instance, strong plastic deformation has recently been reported in isolated nanometer-sized alumina nanoparticles or MgO nanocubes, when tested in situ in a transmission electron microscope (TEM). This plastic behavior may also occur in a powder during the compaction process, even at room temperature. Controlling plastic deformation of nanoparticles during the ceramics processing might be a way to enhance their properties or to improve the processing route (compaction and sintering steps, for instance). We present here a comprehensive study of the mechanical behavior of transition alumina in the compacted powder. Please click Additional Files below to see the full abstract

Evidence for the formation of distorted nanodomains involved in the phase transformation of stabilized zirconia by coupling convergent beam electron diffraction and in situ TEM nanoindentation

International audienceThe transformation of zirconia from its tetragonal to its monoclinic phase is an important feature of the zirconia system. First found to be an advantage due to its important toughening effect, it can also be very detrimental when it occurs in the framework of low-temperature degradation, particularly in the case of biomaterial applications. One way to avoid or to control this phase transformation is to understand how it initiates and more particularly the stress states that can trigger it. A new technique available inside a transmission electron microscope seems to be particularly well suited for that type of study: convergent beam electron diffraction, a well-known technique to reveal stresses, was coupled to in situ transmission electron microscopy mechanical nanoindentation. The experiments reveal the presence of sheared nanoregions at grain boundaries. These could act as embryos for tetragonal-to-monoclinic phase transformations. This is an important first step in the understanding of the earliest stage of zirconia phase transformation

From dislocation nucleation to dislocation multiplication in ceramic nanoparticle

Magnesium oxide nanocubes are compressed along the [001] direction in situ in the transmission electron microscope. Incipient plasticity in the smaller samples is characterized by the nucleation of few 1/2{110} dislocations while a larger number of line defects is observed in larger nanocubes. Yield and flow stresses scattered stochastically above a minimum value varying as the inverse of the sample size. The upper bound is given by the reduced number of dislocation sources. Such size-dependent behaviour is justified by a detailed statistical analysis and is fully explained by the deformation mechanism