The emergence of rigidity in the amorphous matter, such as glasses and jammed granular matter, is a topic of considerable interest both from fundamental and practical perspectives. Conversely, a satisfactory description of the loss of rigidity when amorphous solids, such as glasses, are subjected to external stress has also received much attention.  Yielding behavior, and plasticity, in glasses has been analysed in analogy with phenomena in the various driving protocol. Probing plastic response to cyclic or oscillatory deformation, using  computer simulations, provides significant insights into the phenomenon, such as the emergence of aging, rejuvenation, ergodicity, shear banding and permits a detailed investigation of nonequilibrium transition. I will describe the results of our computational investigations of these phenomena, and relations their behavior across the yield.

SWCNT functionalization: from molecular electronics to (bio)sensing applications

Single walled carbon nanotubes (SWCNTs) have attracted interest during the last decades due to their exceptional electronic properties. Notably, they can be functionalized through different ways and incorporated in a device configuration to develop new electronics. I will talk about the work performed during my PhD and Postdoc related to the modification and implementation of these nanotubes for the development of gas and bio-sensors. First, SWCNTs have been incorporated on microcantilevers as a sensitive layer for gas sensing application. A continuity of this work was to functionalize the SWCNTs with a molecular receptor (deep cavitand) in order to recognize selectively Benzene vapors. Then, SWCNTs have been wrapped with DNA making them soluble in water and solution processable. By functionalizing their side wall with different aptamers that can selectively bind target molecules, a biosensor has been developed for the recognition of biomarkers responsible of neuro-trauma conditions in human body. Finally, a new route to form molecular junctions between two SWCNTs ends has been performed using aryl diazonium reduction in a single step.

Propriétés électronique de nanotubes de carbone remplis par les fullerènes C60.

Vladimir Prudkovskiy, Georgia Tech/Néel Institute
L'encapsulation de diverses molécules à l'intérieur de nanotubes de carbone (CNT), comme par exemple les fullerènes C60, constitue une des voies prometteuses vers l'accordabilité de la conductance des CNTs. Parmi la grande variété des CNTs remplis, les peapods représentent une structure hybride pionnière découvert en 1998 [1]. Depuis lors, leur structure électronique a fait l’objet d’études théoriques controversées [2,3] avec un nombre limité de réalisations expérimentales [4,5]. Nous avons étudié les propriétés électroniques des peapods individuels en combinant les mesures de spectroscopie micro-Raman et de magnétotransport sur les mêmes échantillons. Nous avons constaté que les C60 encapsulés modifient fortement la structure de bande électronique des nanotubes semi-conducteurs au voisinage du point de neutralité de charge. Cette modification comprend un déplacement rigide de la structure électronique et un remplissage partiel de la bande interdite. Nous avons aussi montré que l’excitation UV sélective des fullerènes conduit à une forte modification du couplage électronique entre les C60 et le CNT induite par la coalescence partielle des C60 et de leur distribution à l'intérieur du tube [6]. Les résultats expérimentaux sont supportés par des simulations numériques de la densité d'états et de la conductance des nanotubes de carbone avec des fullerènes fusionnés à l'intérieur.

[1] B.W. Smith et al. Nature 396, 323 (1998) https://dx.doi.org/10.1038/24521
[2] S. Okada et al. PRL 86, 3835 https://dx.doi.org/10.1103/PhysRevLett.86.3835
[3] A. Rochefort et al. PRB 67, 115401 https://dx.doi.org/ 10.1103/PhysRevB.67.115401
[4] D.J. Hornbaker et al. Science 292, 828 (2002) https://dx.doi.org/10.1126/science.1068133
[5] C.H.L. Quay et al. PRB 76, 073404 (2007) https://dx.doi.org/10.1103/PhysRevB.76.073404
[6] V.S. Prudkovskiy et al. Carbon 57, 498 (2013) https://doi.org/10.1016/j.carbon.2013.02.027

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At low temperature, amorphous solids exhibit an elastic response to small strains(γ) or stresses(σ) and initially display a linear response to a quasistatic external loading with a shear modulus (μ) that relates the stress to the strain. We can write σ = μγ; γ << 1. Upon the increase in the external loading, this linear relation appears to fail. The response of the amorphous solid begins to mix elastic intervals interspersed with plastic events, leading generically to an apparent nonlinear dependence of the stress as a function of the strain. The stress versus strain curves for large values of the strain either end abruptly due to a catastrophic failure of the material or display a regime of “steady state” where the shear modulus appears to vanish. Viewing stress versus strain curves of this type, one is tempted to present them before the onset of the steady state as a nonlinear expansion of the stress in powers of the strain. In this talk, I will explain that such an expansion needs to be reconsidered. I will show the enormous difference between quenched and annealed averages of the stress versus strain curves and propose that a useful description of the mechanical response is given by a stress (or strain) -dependent shear modulus. The elastic response is piecewise linear rather than nonlinear.

Nanogaps consist of a pair of separately addressable electrodes defining the floor and the roof of a <100 nm high channel and provide amplification of faradaic signals via efficient redox cycling. Mass transport in these devices exhibits several properties which are not encountered in conventional configurations. First, even weak molecule-surface interactions can have significant impact due to the high surface-to-volume ratio inherent to the nanochannel geometry. This leads to hindered diffusion and can adversely affect the response time for detection at low flow rates, but can also in principle be exploited for separating species advected along the channel. Second, the ability to locally control the ratio of reduced-to-oxidized species via electrode potentials, coupled with the differences in diffusion coefficients exhibited by the majority of redox couples, can cause spatially varying analyte concentrations along a channel. This in turn leads to counter-intuitive behavior such as the potential at a downstream electrode influencing the response of an upstream detector. While nanogaps provide an ideal tool for studying these effects which are otherwise difficult to observe directly, we expect that the behavior is general and also occurs in other systems where electrochemical conversion takes place in confined fluidic geometries

In the 80’s, the apparition of the Atomic Force Microscopy (AFM) was a revolution which
enabled a dramatic increase in the sensitivity of imaging techniques, up to the ability to “see”
individual atoms. The potential for magnetic measurements was quickly understood leading to
the invention of the Magnetic Force Microscopy (MFM).
Harnessing the recent advances in optomechanics and in the synthesis of nano materials, we
have designed and build a new generation of AFM based on SiC nanowires force sensors. Its
sensitivity lies six order of magnitudes bellow commercial AFM, in the attoNewton range (10-18
N) at room temperature. Moreover the two dimensional vibrations of the nanowire enable
vectorial force field measurements.
These capabilities were first employed to measure the hybrid interaction between a single spin
(a NV center in diamond) and a mechanical mode. Among others, this system would enable
a mechanical readout of a single spin quantum state and pave the way toward the creation of
counter intuitive non classical states of motion.
The outstanding sensitivity of SiC nanowires is also used to probe other types of forces. In
particular the vectorial nature of these force fields can be mapped with great accuracy. This is
of great interests for nanomagnetism in order to detect emerging small and spatially non
uniform spin textures. I will show our first attempts in building a nanowire based MFM.

$T^3$ *
Michele will entertain
us with
"The Bearable Compositeness of Leptons"