laboratoire de physique statistique
 
 
laboratoire de physique statistique

Publications

Rechercher
 
2016
Contact gating at GHz frequency in graphene - Wilmart, Q. and Inhofer, A. and Boukhicha, M. and Yang, W. and Rosticher, M. and Morfin, P. and Garroum, N. and Feve, G. and Berroir, J. -M. and Placais, B.
SCIENTIFIC REPORTS 6 (2016) 
LPS


Abstract : The paradigm of graphene transistors is based on the gate modulation of the channel carrier density by means of a local channel gate. This standard architecture is subject to the scaling limit of the channel length and further restrictions due to access and contact resistances impeding the device performance. We propose a novel design, overcoming these issues by implementing additional local gates underneath the contact region which allow a full control of the Klein barrier taking place at the contact edge. In particular, our work demonstrates the GHz operation of transistors driven by independent contact gates. We benchmark the standard channel and novel contact gating and report for the later dynamical transconductance levels at the state of the art. Our finding may find applications in electronics and optoelectronics whenever there is need to control independently the Fermi level and the electrostatic potential of electronic sources or to get rid of cumbersome local channel gates.
A specific flagellum beating mode for inducing fusion in mammalian fertilization and kinetics of sperm internalization - Ravaux, Benjamin and Garroum, Nabil and Perez, Eric and Willaime, Herve and Gourier, Christine
SCIENTIFIC REPORTS 6 (2016) 
LPS


Abstract : The salient phases of fertilization are gamete adhesion, membrane fusion, and internalization of the spermatozoon into the oocyte but the precise timeline and the molecular, membrane and cell mechanisms underlying these highly dynamical events are far from being established. The high motility of the spermatozoa and the unpredictable location of sperm/egg fusion dramatically hinder the use of real time imaging optical techniques that should directly provide the dynamics of cell events. Using an approach based on microfluidics technology, the sperm/egg interaction zone was imaged with the best front view, and the timeline of the fertilization events was established with an unparalleled temporal accuracy from the onset of gamete contact to full sperm DNA decondensation. It reveals that a key element of the adhesion phase to initiate fusion is the oscillatory motion of the sperm head on the oocyte plasma membrane generated by a specific flagellum-beating mode. It also shows that the incorporation of the spermatozoon head is a two steps process that includes simultaneous diving, tilt, and plasma membrane degradation of the sperm head into the oocyte and subsequent DNA decondensation.
 
2015
Search for Dislocation Free Helium 4 Crystals - Souris, F. and Fefferman, A. D. and Haziot, A. and Garroum, N. and Beamish, J. R. and Balibar, S.
JOURNAL OF LOW TEMPERATURE PHYSICS 178149-161 (2015) 
LPS


Abstract : The giant plasticity of He crystals has been explained as a consequence of the large mobility of their dislocations. Thus, the mechanical properties of dislocation free crystals should be quite different from those of usual ones. In 1996-1998, Ruutu et al. published crystal growth studies showing that, in their helium 4 crystals, the density of screw dislocations along the c-axis was less than 100 per cm, sometimes zero. We have grown helium 4 crystals using similar growth speeds and temperatures, and extracted their dislocation density from their mechanical properties. We found dislocation densities that are in the range of 10-10 per cm, that is several orders of magnitude larger than Ruutu et al. Our tentative interpretation of this apparent contradiction is that the two types of measurements are somewhat indirect and concern different types of dislocations. As for the dislocation nucleation mechanism, it remains to be understood.
Stability of C12Ej Bilayers Probed with Adhesive Droplets - Astafyeva, Ksenia and Urbach, Wladimir and Garroum, Nabil and Taulier, Nicolas and Thiam, Abdou R.
LANGMUIR 316791-6796 (2015) 
LPS


Abstract : The stability of model surfactant bilayers from the poly(ethylene glycol) mono-n-dodecyl ether (C12Ej) family was probed. The surfactant bilayers were formed by the adhesion of emulsion droplets. We generated C12Ej bilayers by forming water-in-oil (w/o) emulsions with saline water droplets, covered by the surfactant, in a silicone and octane oil mixture. Using microfluidics, we studied the stability of those bilayers. C12E1 allowed only short-lived bilayers whereas C12E2 bilayers were stable over a wide range of oil mixtures. At high C12E2 concentration, a two-phase region was displayed in the phase diagram: bilayers formed by the adhesion of two water droplets and Janus-like particles consisting of adhering aqueous and amphiphilic droplets. C12E8 and C12E25 did not mediate bilayer formation and caused phase inversion leading to o/w emulsion. With intermediate C12E4 and C12E5 surfactants, both w/o and o/w emulsions were unstable. We provided the titration of the C12E2 bilayer with C12E4 and C12E5 to study and predict their stability behavior.
 
2014
Design, fabrication and characterization of a monolithic focusing piezoceramic transducer for an anisotropic material - Souris, Fabien and Grucker, Jules and Garroum, Nabil and Leclercq, Arnaud and Isac, Jean-Michel and Dupont-Roc, Jacques and Jacquier, Philippe
REVIEW OF SCIENTIFIC INSTRUMENTS 85 (2014) 
LPS


Abstract : Piezoceramic transducers shaped as spherical caps are widely used to focus ultrasound waves in isotropic materials. For anisotropic materials, the sound wave surface is not spherical and the transducer surface should be adjusted to reproduce a portion of this wave surface to focus the emitted sound properly. In this article, we show how to design such a transducer and how to fabricate it in lab on a standard machine from a rod of raw piezo ceramic material. The main features of its electrical impedance response are well reproduced by a numerical model, allowing the identification of most of its vibrational modes. We finally measured the sound field emitted by such a transducer and found its focusing efficiency similar to that of spherical caps in isotropic media. (C) 2014 AIP Publishing LLC.