29 research outputs found
Raman spectra of misoriented bilayer graphene
We compare the main feature of the measured Raman scattering spectra from
single layer graphene with a bilayer in which the two layers are arbitrarily
misoriented. The profiles of the 2D bands are very similar having only one
component, contrary to the four found for commensurate Bernal bilayers. These
results agree with recent theoretical calculations and point to the similarity
of the electronic structures of single layer graphene and misoriented bilayer
graphene. Another new aspect is that the dependance of the 2D frequency on the
laser excitation energy is different in these two latter systems
A single NV defect coupled to a nanomechanical oscillator
A single Nitrogen Vacancy (NV) center hosted in a diamond nanocrystal is
positioned at the extremity of a SiC nanowire. This novel hybrid system couples
the degrees of freedom of two radically different systems, i.e. a
nanomechanical oscillator and a single quantum object. The dynamics of the
nano-resonator is probed through time resolved nanocrystal fluorescence and
photon correlation measurements, conveying the influence of a mechanical degree
of freedom given to a non-classical photon emitter. Moreover, by immersing the
system in a strong magnetic field gradient, we induce a magnetic coupling
between the nanomechanical oscillator and the NV electronic spin, providing
nanomotion readout through a single electronic spin. Spin-dependent forces
inherent to this coupling scheme are essential in a variety of active cooling
and entanglement protocols used in atomic physics, and should now be within the
reach of nanomechanical hybrid systems
Field emission measure of the time response of individual semiconducting nanowires to laser excitation
International audienceA simple technique is explored to determine the temporal photo-response, s, of individual semiconducting SiC and Si nanowires (NWs), with a high time resolution. Laser-assisted field emission (LAFE) from the NWs is first shown to be highly sensitive to continuous laser illumination. Pulsed illumination is then combined with measurements of the total energy distributions to determine s which were rather large, 4-200 ls. The time response scaled roughly with the square of the NWs length and could be attributed to laser-induced heating. LAFE is thus a new tool for quantifying rapid thermo-optical effects in such nano-objects
Universal Vectorial and Ultrasensitive Nanomechanical Force Field Sensor
Miniaturization of force probes into nanomechanical oscillators enables
ultrasensitive investigations of forces on dimensions smaller than their
characteristic length scale. Meanwhile it also unravels the force field
vectorial character and how its topology impacts the measurement. Here we
expose an ultrasensitive method to image 2D vectorial force fields by
optomechanically following the bidimensional Brownian motion of a singly
clamped nanowire. This novel approach relies on angular and spectral tomography
of its quasi frequency-degenerated transverse mechanical polarizations:
immersing the nanoresonator in a vectorial force field does not only shift its
eigenfrequencies but also rotate eigenmodes orientation as a nano-compass. This
universal method is employed to map a tunable electrostatic force field whose
spatial gradients can even take precedence over the intrinsic nanowire
properties. Enabling vectorial force fields imaging with demonstrated
sensitivities of attonewton variations over the nanoprobe Brownian trajectory
will have strong impact on scientific exploration at the nanoscale
Effect of rotational stacking faults on the Raman spectra of folded graphene
International audienceThe Raman spectral signature of folded graphene layers for one to six layers was studied. Folding allows realization of rotational disorder in otherwise perfect samples. We show that the two-dimensional Raman band of the folded sample is up shifted compared to the unfolded sample. The evolution of the spectral signature with increasing number of layers is discussed
Reply to "Comment on 'Raman spectra of misoriented bilayer graphene' "
Revue internationale à comité de lectureInternational audienceIn their Comment, Ni et al. show new data as supporting their hypothesis, i. e., the two-dimensional band blueshift between graphene and misoriented bilayer is caused by a reduction in the Fermi velocity. In the first part of our reply, we will demonstrate that the exhibited data, which typically shows a constant blueshift for various excitation energies are in contradiction with a change in Fermi velocity. In the second part we will explain how charge transfer from the substrate that affects the phonon-dispersion curve can account for the observed discrepancies and how this hypothesis is supported by experimental observations
Ultrahigh interlayer friction in multiwalled boron nitride nanotubes
International audienceFriction at the nanoscale has revealed a wealth of behaviours that depart strongly from the long-standing macroscopic laws of Amontons–Coulomb. Here, by using a ‘Christmas cracker’-type of system in which a multiwalled nanotube is torn apart between a quartz-tuning-fork-based atomic force microscope (TF–AFM) and a nanomanipulator, we compare the mechanical response of multiwalled carbon nanotubes (CNTs) and multiwalled boron nitride nanotubes (BNNTs) during the fracture and telescopic sliding of the layers. We found that the interlayer friction for insulating BNNTs results in ultrahigh viscous-like dissipation that is proportional to the contact area, whereas for the semimetallic CNTs the sliding friction vanishes within experimental uncertainty. We ascribe this difference to the ionic character of the BN, which allows charge localization. The interlayer viscous friction of BNNTs suggests that BNNT membranes could serve as extremely efficient shock-absorbing surfaces
Experimental Nanofluidics inside an individual nanotube
Building new devices that benefit from the strange transport behavior of fluids at nanoscales is an open and worthy challenge that may lead to new scientific and technological paradigms. We present here a new class of nanofluidic device, made of individual Boron-Nitride (BN) nanotube inserted in a pierced membrane and connecting two macroscopic reservoirs. We explore fluidic transport inside a single BN nanotube under electric fields, pressure drops, chemical gradients, and combinations of these. We measured in this transmembrane geometry that currents induced by a salinity contrast exceed by two orders of magnitude their pressure-driven counterpart. This result is ascribed to the remarkably large, pH dependent, surface charge bared by the BN nanotube. It corresponds to a produced power density in the kW/m2 range, orders of magnitude higher than reported with classical exchange membranes, and demonstrates the unique potential of BN nanotube membranes for energy conversion
Signal amplification in a synchronized field emission NEMS
International audienceWe present in this paper a study on highly resistive SiC nanowires in a singly clamped geometry. We demonstrate that these field emission nanoelectromechanical systems (NEMS) can be synchronized ton an external AC signal and act as an amplifier