39 research outputs found
Adhesion energy of single wall carbon nanotube loops on various substrates
The physics of adhesion of one-dimensional nano structures such as nanotubes,
nano wires, and biopolymers on different material substrates is of great
interest for the study of biological adhesion and the development of nano
electronics and nano mechanics. In this paper, we present force spectroscopy
experiments of a single wall carbon nanotube loop using our home-made
interferometric atomic force microscope. Characteristic force plateaux during
the peeling process allows us to access to quantitative values of the adhesion
energy per unit length on various substrates: graphite, mica, platinum, gold
and silicon. By combining a time-frequency analysis of the deflexion of the
cantilever, we access to the dynamic stiffness of the contact, providing more
information on the nanotube configurations and its intrinsic mechanical
properties
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
Frequency modulated self-oscillation and phase inertia in a synchronized nanowire mechanical resonator
Synchronization has been reported for a wide range of self-oscillating
systems. However, even though it has been predicted theoretically for several
decades, the experimental realization of phase self-oscillation, sometimes
called phase trapping, in the high driving regime has been studied only
recently. We explored in detail the phase dynamics in a synchronized field
emission SiC nanoelectromechanical system with intrinsic feedback. A richer
variety of phase behavior has been unambiguously identified, implying phase
modulation and inertia. This synchronization regime is expected to have
implications for the comprehension of the dynamics of interacting
self-oscillating networks and for the generation of frequency modulated signals
at the nanoscal
Role of fluctuations and nonlinearities on field emission nanomechanical self-oscillators
A theoretical and experimental description of the threshold, amplitude, and
stability of a self-oscillating nanowire in a field emission configuration is
presented. Two thresholds for the onset of self-oscillation are identified, one
induced by fluctuations of the electromagnetic environment and a second
revealed by these fluctuations by measuring the probability density function of
the current. The ac and dc components of the current and the phase stability
are quantified. An ac to dc ratio above 100% and an Allan deviation of 1.3x10-5
at room temperature can be attained. Finally, it is shown that a simple
nonlinear model cannot describe the equilibrium effective potential in the
self-oscillating regime due to the high amplitude of oscillations
Self-oscillations in field emission nanowire mechanical resonators: a nanometric DC-AC conversion
We report the observation of self-oscillations in a bottom-up
nanoelectromechanical system (NEMS) during field emission driven by a constant
applied voltage. An electromechanical model is explored that explains the
phenomenon and that can be directly used to develop integrated devices. In this
first study we have already achieved ~50% DC/AC (direct to alternative current)
conversion. Electrical self-oscillations in NEMS open up a new path for the
development of high speed, autonomous nanoresonators, and signal generators and
show that field emission (FE) is a powerful tool for building new
nano-components
Current Saturation in Field Emission from H-Passivated Si Nanowires
International audienceThis paper explores the field emission (FE) properties of highly crystalline Si nanowires (NWs) with controlled surface passivation. The NWs were batch-grown by the vapor_liquid_solid process using Au catalysts with no intentional doping. The FE current_voltage characteristics showed quasi-ideal current saturation that resembles those predicted by the basic theory for emission from semiconductors, even at room temperature. In the saturation region, the currents were extremely sensitive to temperature and also increased linearly with voltage drop along the nanowire. The latter permits the estimation of the doping concentration and the carrier lifetime, which is limited by surface recombination. The conductivity could be tuned over 2 orders of magnitude by in situ hydrogen passivation/desorption cycles. This work highlights the role of dangling bonds in surface leakage currents and demonstrates the use of hydrogen passivation for optimizing the FE characteristics of Si NWs
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
Femtosecond Laser Induced Resonant Tunneling in an Individual Quantum Dot Attached to a Nanotip
Quantized nano-objects offer a myriad of exciting possibilities for
manipulating electrons and light that impact photonics, nanoelectronics, and
quantum information. In this context, ultrashort laser pulses combined with
nanotips and field emission have permitted renewing nano-characterization and
control electron dynamics with unprecedented space and time resolution reaching
femtosecond and even attosecond regimes. A crucial missing step in these
experiments is that no signature of quantized energy levels has yet been
observed. We combine in situ nanostructuration of nanotips and ultrashort laser
pulse excitation to induce multiphoton excitation and electron emission from a
single quantized nano-object attached at the apex of a metal nanotip.
Femtosecond induced tunneling through well-defined localized confinement states
that are tunable in energy is demonstrated. This paves the way for the
development of ultrafast manipulation of electron emission from isolated
nano-objects including stereographically fixed individual molecules and high
brightness, ultrafast, coherent single electron sources for quantum optics
experiments
Nonlinear polarization coupling in freestanding nanowire/nanotube resonators
In this work, we study the nonlinear coupling between the transverse modes of nanoresonators such as nanotubes or nanowires in a singly clamped configuration. We previously showed that at high driving, this coupling could result in a transition from independent planar modes to a locked elliptical motion, with important modifications of the resonance curves. Here, we clarify the physical origins, associated with a 1:1 internal resonance, and study in depth this transition as a function of the relevant parameters. We present simple formulae that permit to predict the emergence of this transition as a function of the frequency difference between the polarizations and the nonlinear coefficients and give the “backbone curves” corresponding to the elliptical regime. We also show that the elliptical regime is associated with the emergence of a new set of solutions of which one branch is stable. Finally, we compare single and double clamped configurations and explain why the elliptical transition appears on different polarizations