Pascal Aubert

Strain-controlled magnetic domain wall propagation in hybrid piezoelectric/ferromagnetic structures

The control of magnetic order in nanoscale devices underpins many proposals for integrating spintronics concepts into conventional electronics. A key challenge lies in finding an energy-efficient means of control, as power dissipation remains an important factor limiting future miniaturization of integrated circuits. One promising approach involves magnetoelectric coupling in magnetostrictive/piezoelectric systems, where induced strains can bear directly on the magnetic anisotropy. While such processes have been demonstrated in several multiferroic heterostructures, the incorporation of such complex materials into practical geometries has been lacking. Here we demonstrate the possibility of generating sizeable anisotropy changes, through induced strains driven by applied electric fields, in hybrid piezoelectric/spin-valve nanowires. By combining magneto-optical Kerr effect and magnetoresistance measurements, we show that domain wall propagation fields can be doubled under locally applied strains. These results highlight the prospect of constructing low-power domain wall gates for magnetic logic devices.

A multiscale approach to assess the complex surface of polyurethane catheters and the effects of a new plasma decontamination treatment on the surface properties.

Polyurethane catheters made of Pellethane 2363-80AE® were treated with a low temperature plasma developed for the decontamination of reusable polymer devices in hospitals. We investigated the modifications of the polymer surface by studying the topographic modifications, the chemical modifications, and their consequences on the wettability and bacterial adhesion. This study showed that plasma treatment modified the topography and grafted oxygen and nitrogen species onto the surface, resulting in an increase in the surface polarity. This effect could be correlated to the number of nitrogen atoms interacting with the surface. Moreover, this study demonstrated the significance of multiscale heterogeneities, and the complexity of industrial medical devices made from polymers. Their surface can be heterogeneous, and they contain additives that can migrate and change the surface composition.

Memristive and neuromorphic behavior in a Li x CoO 2 nanobattery

The phenomenon of resistive switching (RS), which was initially linked to non-volatile resistive memory applications, has recently also been associated with the concept of memristors, whose adjustable multilevel resistance characteristics open up unforeseen perspectives in cognitive computing. Herein, we demonstrate that the resistance states of LixCoO2 thin film-based metal-insulator-metal (MIM) solid-state cells can be tuned by sequential programming voltage pulses, and that these resistance states are dramatically dependent on the pulses input rate, hence emulating biological synapse plasticity. In addition, we identify the underlying electrochemical processes of RS in our MIM cells, which also reveal a nanobattery-like behavior, leading to the generation of electrical signals that bring an unprecedented new dimension to the connection between memristors and neuromorphic systems. Therefore, these LixCoO2-based MIM devices allow for a combination of possibilities, offering new perspectives of usage in nanoelectronics and bio-inspired neuromorphic circuits.

Modification of a cyclo-olefin surface by radio-sterilization: Is there any effect on the interaction with drug solutions?

A cyclo-olefin copolymer was subjected to an e-beam ionizing treatment. Two doses were studied: one corresponding to the recommended dose for the sterilization of pharmaceutical packaging (25 kGy), and a greater one to enhance the modifications caused by the treatment (150 kGy). The surface modifications were studied by X-ray photoelectron spectroscopy (XPS), contact angle measurements and atomic force microscopy (AFM). The roughness and the wettability of the surface were enhanced by the treatment. The consequences of the surface modifications on the drug interaction with the polymer were studied.

Direct Evidence of Lithium Ion Migration in Resistive Switching of Lithium Cobalt Oxide Nanobatteries

Lithium cobalt oxide nanobatteries offer exciting prospects in the field of nonvolatile memories and neuromorphic circuits. However, the precise underlying resistive switching (RS) mechanism remains a matter of debate in two-terminal cells. Herein, intriguing results, obtained by secondary ion mass spectroscopy (SIMS) 3D imaging, clearly demonstrate that the RS mechanism corresponds to lithium migration toward the outside of the Lix CoO2 layer. These observations are very well correlated with the observed insulator-to-metal transition of the oxide. Besides, smaller device area experimentally yields much faster switching kinetics, which is qualitatively well accounted for by a simple numerical simulation. Write/erase endurance is also highly improved with downscaling - much further than the present cycling life of usual lithium-ion batteries. Hence very attractive possibilities can be envisaged for this class of materials in nanoelectronics.