Scientifiques


Articles publiés dans cette rubrique

Des molécules pour l’électronique  (21 mai 2010)

Pour accéder au stade ultime de miniaturisation de la taille des circuits électroniques, de nombreuses recherches sont actuellement menées pour synthétiser des molécules qui miment les comportements des circuits logiques, systèmes binaires pouvant passer d’un état à un autre. Une équipe du Laboratoire Chimie, Ingénierie Moléculaire d’Angers (CNRS / Université d’Angers), en collaboration avec des chercheurs de l’Institut d’Electronique, de Microélectronique et de Nanotechnologie (CNRS / Université Lille 1), vient de synthétiser de nouveaux systèmes photo-commutables présentant un ratio on/off record. Cette découverte ouvre des perspectives dans la conception de dispositifs électroniques moléculaires.

Confirmation expérimentale des théories sur la surfusion ou pourquoi l’eau ne gèle pas dans les nuages (21 mai 2010)

Des scientifiques de l’INAC, de l’Institut Néel et de l’ ESRF apportent des éléments clés pour expliquer le curieux phénomène de surfusion, cet état de la matière où un liquide ne gèle pas alors même qu’il est à une température inférieure à son point de cristallisation. La surfusion est un phénomène que l’on peut observer au quotidien puisque les nuages sont une accumulation de gouttelettes d’eau en surfusion.

Measurement of quantum phase-slips in a Josephson junction chain (21 mai 2010)

Josephson junction chains attract currently a lot of interest due to their possible applications in metrology or quantum information. For example, under microwave irradiation of frequency f, such chains could exhibit current quantization I=2nef where 2e is the charge of a Cooper pair and n is an integer number. They could be used for the definition of a new quantum current standard. In view of the potential applications, we have measured the ground state of a Josephson junction chain. Here we have analysed our results in terms of “quantum phase-slips”, the central phenomenon governing these superconducting networks.

Heat flux at the nanoscale : beyond the Boltzmann-Stefan law (20 mai 2010)

Does the usual Stephan-Boltzmann theory for blackbody radiation applies to nanometer-size objects ? To answer this question the heat flux in vacuum between two surfaces at different temperature and separated by distances between a micrometer to100 nm have been measured and compared to theory by two CNRS labs (Charles Fabry of Institut d’Optique and Institut Néel). At the nanometer scale, the measurements show large discrepancies with the Stefan-Boltzmann theory which describes this thermal exchange at large distances on the basis of Planck’s law. As well known, in the far field regime the heat flux exchanged between two flat parallel surfaces does not depend upon the distance between the two surfaces. Instead, in the near field regime, the measured variation is strong. The flux increase dramatically as the distance between the two surfaces becomes smaller than about one micrometer.

Quantum forgetfulness of a Single Molecule Magnet (30 avril 2010)

A step critical to the implementation of a quantum computer based on complex magnetic molecules (Single Molecule Magnets) is control of the decoherence mechanisms. Decoherence is the process by which a quantum system “forgets” its quantum nature and become classical when it interacts, even very weakly, with the random fl uctuations of its environment. Simply speaking, a collective quantum system possesses an “internal clock” acting like a pendulum whose amplitude decreases progressively because of these environmental interactions. When the clock’s motion stops, the system is eff ectively at rest and collapses to the classical regime.

Wavefunction symmetry in graphene at the nanometre scale (30 avril 2010)

Graphene is an unconventional two dimensional system with fascinating electronic properties. These properties - for example the half integer Quantum Hall Eff ect - come from the honeycomb crystal structure, which imposes special symmetry relations on the electronic wavefunctions, corresponding to the so-called “electronic chirality”. A priori, this chirality is specific to the ideal graphene plane, but was found to be preserved for graphene on a SiO2 substrate, as shown by magnetotransport measurements. We have found that the property of electronic chirality is also preserved in a single plane of graphene grown epitaxially on a silicon carbide (0001) substrate.

Les nanos c'est:

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