| | | | | | | webmail : intra-extra| Accès VPN| Accès IST| Contact | Français

Headlines 2007

Dec 19, 2007
H. Gilles, S. Girard, M. Laroche, A. Belarouci CIMAP, Caen

The SNOM (Scanning Near-field Optical Microscopy) allows to reach a spatial resolution well below the wavelength of the light used. Indeed, thanks to the "near-field" illumination (when the distance between the object and the source is much less than the wavelength) it becomes possible to avoid the diffraction inherent to every optical system. Measurement of the evanescent field at the back side of a total-reflection interface allows obtaining a SNOM image with a resolution well below one micrometer.

Nov 13, 2007

Clusters consists in a set of several up to million atoms in condensed phase with nanometric finite size. The investigation of their properties as the function of their increasing size is sometimes presented as one way to build a macroscopic condensed world from a gas. This often appears to be too simplistic, because the static and dynamic behavior of clusters has often no equivalence at the macroscopic scale, as they are controlled by their high specific surface and their finite size. These concerns the physical chemistry of the mesoscopic world, as illustrated by the recent experimental study driven by the "Reaction dynamics" group of DRECAM/SPAM-Laboratoire Francis Perrin in collaboration with a theoretician team from Paris VI University.

Mar 23, 2007
V. Brenner, F. Piuzzi, I. Dimicoli, B. Tardivel, and M. Mons

One of the great mysteries of life is its lack of symmetry at the molecular scale. Many biological molecules, like amino acids, exist a priori in two asymmetrical forms, "right” and “left”. Such molecules are referred to as “chiral” . Like the two hands, these forms cannot be superimposed but are mirror images of each other (Fig.). However, in living organisms, proteins are exclusively built up from “left” amino acids. This selection of only one form remains one of the great scientific enigmas, which physicists, chemists and biologists try to solve.

Proteins are extremely long chains of amino acids. Each amino acid is added by formation of a peptide bound (CONH) and release of a water molecule, leaving a residue attached to the chain. Within the cells, the proteins thus formed are folded and their function depends not only on their sequence but also on their conformation. This makes the studies of the fundamental mechanisms of protein folding of strong interest.
By studying both experimentally and theoretically the folding of simple peptides, made of two amino acids, researchers from the "Service des Photons, Atomes et Molécules” of CEA-Saclay have obtained new results documenting the issue of chirality of the living world.

Mar 16, 2007
J.M. Mestdagh, L. Poisson, I. Fischer, P. D’Oliveira
Service des Photons, Atomes et Molécules DRECAM/SPAM

The very new laser of the "Plateforme Laser Femtoseconde Accordable, PLFA" began to be installed last year within the Service of Photons Atoms and Molecules (SPAM). It belongs to the infrastructure SLIC, member of the European network LASERLAB-EUROPE and is thus accessible to European scientists. It was designed according to several bets: high repetition rate (1 Khz), strong pulse energy (up to 13mJ, at 800nm), broad accordability (500-750nm) and ultra-fast pulses (<35 fs = 35 10-15 s).

The requirement of a wide wavelength range, even difficult to realize, is necessary to allow decisive progress in physico-chemistry of fast reactions. The requirements in pulse duration were chosen to probe efficiently the dynamics of reactions.

Research in that field began within DRECAM at the beginning of the 90's. They led to a revolution in physico-chemistry: the duration of the energy flow within organic or bio-organic molecules often scales within the sub-picosecond time range. This was at variance with the models usually used of redistribution of energy by coupling between electronic excitation and vibration.

The PLFA project is essential to offer a more complete approach: it allows at the same time energy studies, by adjusting the quantity of energy deposited in the system, selectivity by the accordability of the source and time studies at the femtosecond scale.

Apr 11, 2007
S. Petit, F. Moussa, M. Hennion et S. Pailhès (DRECAM/LLB CEA-Saclay)
L. Pinsard-Godard, Laboratoire de Chimie du Solide, Paris XI
A. Ivanov, ILL, BP 156 F-38042 Grenoble

Multi-ferroïcs are exceptional materials whose fundamental state is both magnetic and ferro-electric [1]. Moreover, in such materials, magnetism and ferroelectricity maintains close links: as for example the manganese oxide YMnO3 [2], can see its magnetization modified by the action of an electric field, or its electric polarization by the action of a magnetic field (magnetoelectric effect). Muli-ferroïcity is a complex problem in physics of condensed matter; it also represents an important stake for the applications, and for example for “technologies for the information and health” developed at the CEA (development of new concepts of memorizing the information or spin electronics).

The last research on these materials tends to show that the coupling between magnetism and ferro-electricity occurs via important deformations of the crystal lattice. It is known for example that in the case of the compound YMnO3, the transition (TN = 72K) towards the magnetic phase (and thus multi-ferroïc) is the seat of magnetostrictive effects that reveals the strong coupling between atomic displacements, magnetic ferroelectricity and moments.

Jun 27, 2007

Researchers at the Institute of Electronics, Microelectronics and Nanotechnologie (IEMN / CNRS – Universités Lille 1 and Valenciennes, Institut supérieur de l’électronique et du numérique-ISEN) and  the Solid-state Physics Division at the French Atomic Energy Agency (CEA), have succeeded in making transistors from carbon nanotubes on a silicon substrate. The transistors, which are mainly used as automatic switches, can reach cutoff frequencies of 30 GHz [1]which improves by a factor of 4 the previous record obtained by the same teams in August 2006. This result opens up new prospects for mainstream applications which require high operating frequencies.

Jun 08, 2007
Nuclear magnetic resonance (NMR) is an indispensable technique for studying matter. It can be applied to medical imaging (MRI) to obtain 2D and 3D images of the human body. While it opens the door to a wealth of physicochemical information by harnessing the fundamental properties of matter, NMR remains a technique with poor sensitivity, making it very difficult to use on small quantities of solid or heterogeneous material. A group of scientists from the CEA research department dedicated to condensed matter, atoms and molecules (DRECAM) is pushing back this limit by using miniaturised mobile detectors to capture the NMR signal with high resolution and a 10-fold increase in sensitivity for sample volumes of a few hundred nanolitres.

To increase in sensitivity on small samples, it is necessary to approach as much as possible the detector (coils surrounding the sample). So, the difficulty to obtain a spectrum high resolution seems insurmountable since it would be necessary to place the sample in a micro-capillary tube and then spun at several thousand revolutions per second in a stable and reproducible way inside a micro-detector (coil) with an interior diameter of a few hundred microns. To meet this challenge, the CEA team (D. Sakellariou, G. LeGoff and J.-F. Jacquinot) came up with an innovative solution by spinning the micro-detector (coil) and sample in one piece, with power to the detector supplied via induction from an exterior coil, which also enabled the (wireless) transmission of the desired signal. The whole system spins at thousands of revolutions per second, and probably constitutes the world's fastest set of rotating antennas.

Mar 28, 2007
M.-A. Dubois1, L. H. Emmons2, L. Cournac3, P. Chatelet4, N. C. A. Pitman5, V. Vilca5, & L.-F. del Aguila6

1CEA Saclay, DSM/DRECAM/Service de Physique de l ’Etat Condensé, L ’Orme des Merisiers, 91191 Gif sur Yvette, France
2Department of Zoology NHB 390 MRC 108, Smithsonian Institution, P.O.Box 37012,Washington, DC 20013-7012 USA
3CEA Cadarache, DSV/DEVM/Laboratoire d ’Ecophysiologie de la Photosynthèse, 13108 Saint Paul Lez Durance Cedex, France
4CNRS/URA 1183,Muséum National d ’Histoire Naturelle,
4 avenue du Petit Château,91800 Brunoy, France
5Asociación para la Conservación de la Cuenca Amazonía,
Calle Cuzco 499, Puerto Maldonado, Madre de Dios, Perú
6Fundación Amigos de la Naturaleza, Santa Cruz de la Sierra, Bolivia

Feb 07, 2007

M. Roger1, D.J.P Morris2, D.A. Tennant3,4, M.J. Gutmann5, J.P. Goff2, J.-U. Hoffmann3, R. Feyerherm3, E. Dudzik3, D. Prabhakaran6, A.T. Boothroyd6, N. Shannon7, B. Lake3,4 & P.P. Deen8.

1Service de Physique de l’Etat Condensé (CNRS/MIPPU/URA 2464), DSM/DRECAM/SPEC, CEA Saclay, P.C. 135, F-91191 Gif sur Yvette, France.
2Dept. of Physics, University of Liverpool, Oliver Lodge Laboratory, Liverpool L69 7ZE, UK.
3Hahn-Meitner Institute, Glienicker Strasse 100, Berlin D-14109 Germany.
4Institute für Festkörperphysik, Technische Universität Berlin, Hardenbergstrasse 36, Berlin D-10623 Germany,
5ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 OQX, UK.
6Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK.
7H.H Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK.
8European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France.

Jan 27, 2007
A. Chiffaudel, F. Daviaud, B. Dubrulle, C. Gasquet, R. Monchaux, V. Padilla, avec la participation de L. Marié et F. Ravelet, DSM/DRECAM/SPEC
Collaboration VKS : CEA – ENS Lyon – ENS Paris -

Many research teams aim at understanding of the origin and behavior of the magnetic field of planets and stars. The VKS1 collaboration (gathering researchers at CEA, CNRS, Ecoles normales supérieures in Lyon and Paris) has succeeded in generating a magnetic field from a highly turbulent liquid sodium flow in a laboratory experiment. Although the extreme conditions specific to astrophysical and geophysical media are out of reach in the laboratory, the observed magnetic field shares remarkable similarities with cosmic fields. Their observations are reported in the January 26th issue of Physical Review Letters (see also the "Physical review Focus").

Visit the WEB site of the GIT DRECAM/SPEC !


Retour en haut