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•Interaction of ultra-short pulses with epsilon-near-zero materials is studied.•Split-step Fourier method is implemented.•Propagation of pulses is governed by the nonlinear Schrödinger equation.•Numerical simulations that support the results are discussed.

Micro-electromechanical systems (MEMS) made of organic materials have attracted efforts for the development a new generation of physical, chemical, and biological sensors, for which the electromechanical sensitivity is the current major concern. Here, we present an organic MEMS made of a rubrene single-crystal air-gap transistor. Applying mechanical pressure on the semiconductor results in high variations in drain current: an unparalleled gauge factor above 4000 has been measured experimentally. Such a high sensitivity is induced by the modulation of charge injection at the interface between the gold electrode and the rubrene semiconductor as an unusual transducing effect. Applying these devices to the detection of acoustic pressure shows that force down to 230 nN can be measured with a resolution of 40 nN. This study demonstrates that MEMS based on rubrene air-gap transistors constitute a step forward in the development of high-performance flexible sensors.

The relationship between charge transport and surface morphology is investigated by utilizing rubrene single crystals of varying thicknesses. In the case of pristine crystals, the surface conductivities decrease exponentially as the crystal thickness increases until ∼4 μm, beyond which the surface conductivity saturates. Investigation of the surface morphology using optical and atomic force microscopy reveals that thicker crystals have a higher number of molecular steps, increasing the overall surface roughness compared with thin crystals. The density of molecular steps as a surface trap is further quantified with the subthreshold slope of rubrene air-gap transistors. This thickness-dependent surface conductivity is rationalized by a shift from in-plane to out-of-plane transport governed by surface roughness. The surface transport is disrupted by roughening of the crystal surface and becomes limited by the slower vertical crystallographic axis on molecular step edges. Separately, we investigate surface-doping of rubrene crystals by using fluoroalkyltrichrolosilane and observe a different mechanism for charge transport which is independent of surface roughness. This work demonstrates that the correlation between crystal thickness, surface morphology, and charge transport must be taken into account when measuring organic single crystals. Considering the fact that these molecular steps are universally observed on organic/inorganic and single/polycrystals, we believe that our findings can be widely applied to improve charge transport understanding.

La maîtrise de la cavitation hydrodynamique au coeur de 'laboratoires sur puces' nous a conduit à développer une métrologie inédite basée sur la sensibilité en température de nanoparticules fluorescentes. Les petites dimensions du système étudié nous ont permis d'effectuer, à l'aide d'un microscope confocal, une cartographie thermique tridimensionnelle de la phase liquide. On a ainsi observé que la transition d'un régime d'écoulement monophasique vers un régime cavitant s'accompagne d'une augmentation de température au cœur de la zone tourbillonnaire. Ce gradient thermique peut s'élever jusqu'à 105 K/m. Un premier modèle explique cette augmentation par la forte densité de puissance dissipée consécutivement à la transition vers un régime cavitant. Par ailleurs, l'influence d'effets thermosensibles associés à la condensation de la vapeur en aval de l'écoulement doit également être considérée.

Organic semiconductors are intensively studied as promising materials for the realisation of low-cost flexible electronic devices. The flexibility requirement implies either performance stability towards deformation, or conversely, detectable response to the deformation itself. The knowledge of the electromechanical response of organic semiconductors to external stresses is therefore not only interesting from a fundamental point of view, but also necessary for the development of real world applications. To this end, in this work we predict and measure the variation of charge carrier mobility in rubrene single crystals as a function of mechanical strain, applied selectively along the crystal axes. We find that strain induces simultaneous mobility changes along all three axes, and that in some cases the response is higher along directions orthogonal to the mechanical deformation. These variations cannot be explained by the modulation of intermolecular distances, but only by a more complex molecular reorganisation, which is particularly enhanced, in terms of response, by π-stacking and herringbone stacking. This microscopic knowledge of the relation between structural and mobility variations is essential for the interpretation of electromechanical measurements for crystalline organic semiconductors, and for the rational design of electronic devices.

Cet article conclut la démarche expérimentale entreprise il y a deux ans destinée à mesurer les pertes de charge d’un liquide circulant dans un microcanal. La réalisation de microcanaux silicium-Pyrex équipés de jauges de contraintes micro – usinées pour la mesure locale de pertes de charges amène au constat suivant : les lois classiques d’écoulement pour de l’eau de différentes conductivités (de 0,1 µS/cm à 70 µS/cm ) sont vérifiées dans des microcanaux à parois lisses de hauteur comprise entre 7 µm et 21 µm et sur une plage de nombre de Reynolds comprise entre 0,3 et 200. Pour les configurations à parois rugueuses, l’incertitude expérimentale sur la profondeur du canal augmente la marge d’erreur des résultats qui restent cependant cohérents

Several studies have examined the efficacy of nutrients in enhancing skin health, function and appearance, yet the strength of evidence to support benefit of use is questionable. Stacey Lockyer and Ayela Spiro share the findings of the British Nutrition Foundation's recent review of commonly used ingredients, such as collagen and carotenoids, in skin nutraceuticals

While there is much focus on obesity as a major health issue, malnutrition remains under-treated and under-recognised. With the majority of malnourished people being aged over 75, Ayela Spiro offers some advice on the treatment and management of this condition

We present the piezoresistive transduction of an all-organic microelectromechanical system (MEMS) based resonant sensor fabricated through a low-cost and highly versatile process. The MEMS resonator consists of a U-shaped cantilever beam resonator made of a thin layer of a piezoresistive nanocomposite (SU/8 epoxy resin filled with industrially produced carbon nanotubes, or CNTs) deposited on flexible substrates such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and paper. The structures have been fabricated using a commercially available vinyl cutting machine. External piezoelectric actuation has been used to drive the devices into resonance while integrated piezoresistive transduction has been chosen as the resonance sensing approach. The achieved measurements validate the concept of dynamic piezoresistive-transduced organic MEMS. The sensitivity to temperature is comparable with that of state-of-the-art inorganic temperature sensors, thus confirming the high accuracy level of the new resonators. As an example of a sensing application, the present MEMS sensors are employed as microdynamical mechanical analyzers enabling the rapid, low-cost and accurate characterization of the viscoelastic properties of organic materials.

Di‐ and triblock non‐ionic copolymers based on poly(ethylene oxide) and poly(propylene oxide) were studied for the stabilization of nanoparticles in water at high ionic strength. The effect of the molecular architecture (di‐ vs. triblock) of these amphiphilic copolymers was investigated by using gold nanoparticles (AuNPs) as probes for colloidal stability. The results demonstrate that both di‐ and triblock copolymers can provide long term stability, and that in both cases AuNPs are individually embedded within globules of polymers. However, in the case of diblock copolymers, the colloidal stability was related to the formation of micelles, in contrast with the case of triblock copolymers, which were previously shown to provide good stability even at concentrations at which micelles do not form. Quartz crystal microbalance (QCM) experiments showed that the presence of the hydrophobic block in the structure of the polymer is important to ensure quantitative adsorption upon a gold surface and to limit desorption. We demonstrate that with an appropriate choice of polymer, the polymer/AuNP hybrids can also undergo filtration and freeze‐drying without noticeable aggregation, which can be very convenient for further applications. Finally, preliminary studies of the cytotoxicity effect on fibroblast cells show that the polymer/AuNP hybrids were not cytotoxic. TEM micrographs on ultrathin sections of cells after incubation with the colloidal solutions show that the nanoparticles were internalized into the cells, conserving their initial size and shape.

No Abstract

Experiments were performed in 2-D microchannels of varying height from 1 mm to 100 ?m. For smooth surfaces of the channels, the results did not demonstrate any scale effect. On the contrary, roughness hass been found ta have large effects on the laminar regime of microflows. In that case, friction factor results are consistently higher than values predicted by macroscale correlations but exhibit a classical trend Po vs Re. For microchannels of height below 100 ?m we have developed microfabricated systems devoted to local pressure measurements and we have successfully tested silicon strain gauges.

Monitoring hydrodynamic cavitation of liquids through “labs on a chip” (i.e. microchannels with a shrinkage, such as microdiaphragms or microventuris) is an improvement in experimental approaches devoted to study the mechanisms involved in these multiphase flows. The small sizes of the reactors do not require big substructures. Flow rates of around 1 L/h make possible the characterisation of rare, toxic or expensive pure fluids or mixtures. Moreover, because of that microfluidic approach, an unique inception of the cavitation from a laminar flow regime is also possible, that provides precious databases for simulation or modelisation. Lastly, “labs on a chip” are an extremely versatile solution to perform novel experiments, as they are embeddable in tools basically designed to proceed with small samples (confocal microscopy, spectroscopy). We present here a summary of the former experiments performed by our team, concerning the fundamental aspects of hydrodynamic cavitation in a microchannel. We have recorded, with thermosensitive nanoparticles dispersed in water, the thermal signature of the growth and collapse of bubbles. We were also able to monitor the cavitation flow regime from a laminar single liquid phase. We are currently involved in applicative studies of hydrodynamic cavitation in microchannels, and preliminary results concerning liquid phase exfoliation of graphene will be also presented.

A novel magnetic sensor is under investigation. This device is a bidimensional generalization of vibrating reed magnetometers, and is intended to be sensitive to very low magnetic fields (about 1013THz1/2) and to very low magnetic moments. This sensor uses the magnetic force which acts on a sample of total magnetization Msubmitted to a magnetic field gradient gradB. The deformation caused by the force applied to a thin silicon membrane can be capacitively detected. When the field gradient is an alternating one at the resonance frequency of the membrane, the deformation is enhanced by the Q-factor. With such a device, one could perform magnetic measurements with unsurpassed sensitivities over a wide range of temperature. An experimental set-up to perform Qmeasurements on Si membranes submitted to an alternating electrostatic force is also described.

GASTROENTEROLOGY 1999;116:504