106 research outputs found
Functionalized AFM probes for force spectroscopy: eigenmodes shape and stiffness calibration through thermal noise measurements
The functionalization of an Atomic Force Microscope (AFM) cantilever with a
colloidal bead is a widely used technique when the geometry between the probe
and the sample must be controlled, particularly in force spectroscopy. But some
questions remain: how does a bead glued at the end of a cantilever influence
its mechanical response ? And more important for quantitative measurements, can
we still determine the stiffness of the AFM probe with traditional techniques?
In this article, the influence of a colloidal mass loading on the eigenmodes
shape and resonant frequency is investigated by measuring the thermal noise on
rectangular AFM microcantilevers with and without a bead attached at their
extremities. The experiments are performed with a home-made ultra-sensitive
AFM, based on differential interferometry. The focused beam from the
interferometer probes the cantilever at different positions and the spatial
shapes of the modes are determined up to the fifth resonance, without external
excitation. The results clearly demonstrate that the first eigenmode almost
doesn't change by mass loading. However the oscillation behavior of higher
resonances present a marked difference: with a particle glued at its extremity,
the nodes of the mode are displaced towards the free end of the cantilever.
These results are compared to an analytical model taking into account the mass
and the inertial moment of the load in an Euler-Bernoulli framework, where the
normalization of the eigenmodes is explicitly worked out in order to allow a
quantitative prediction of the thermal noise amplitude of each mode. A good
agreement between the experimental results and the analytical model is
demonstrated, allowing a clean calibration of the probe stiffness
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
Logical and thermodynamical reversibility: optimized experimental implementation of the NOT operation
The NOT operation is a reversible transformation acting on a 1-bit logical
state, and should be achievable in a physically reversible manner at no
energetic cost. We experimentally demonstrate a bit-flip protocol based on the
momentum of an underdamped oscillator confined in a double well potential. The
protocol is designed to be reversible in the ideal dissipationless case, and
the thermodynamic work required is inversely proportional to the quality factor
of the system. Our implementation demonstrates an energy dissipation
significantly lower than the minimal cost of information processing in
logically irreversible operations. It is moreover performed at high speed: a
fully equilibrated final state is reached in only half a period of the
oscillator. The results are supported by an analytical model that takes into
account the presence of irreversibility. The Letter concludes with a discussion
of optimization strategies
Resonance frequency shift of strongly heated micro-cantilevers
In optical detection setups to measure the deflection of micro-cantilevers,
part of the sensing light is absorbed, heating the mechanical probe. We present
experimental evidences of a frequency shift of the resonant modes of a
cantilever when the light power of the optical measurement set-up is increased.
This frequency shift is a signature of the temperature rise, and presents a
dependence on the mode number. An analytical model is derived to take into
account the temperature profile along the cantilever, it shows that the
frequency shifts are given by an average of the profile weighted by the local
curvature for each resonant mode. We apply this framework to measurements in
vacuum and demonstrate that huge temperatures can be reached with moderate
light intensities: a thousand {\textdegree}C with little more than 10 mW. We
finally present some insight into the physical phenomena when the cantilever is
in air instead of vacuum
High Resolution Viscosity Measurement by Thermal Noise Detection
An interferometric method is implemented in order to accurately assess the
thermal fluctuations of a micro-cantilever sensor in liquid environments. The
power spectrum density (PSD) of thermal fluctuations together with Sader's
model of the cantilever allow for the indirect measurement of the liquid
viscosity with good accuracy. The good quality of the deflection signal and the
characteristic low noise of the instrument allow for the detection and
corrections of drawbacks due to both the cantilever shape irregularities and
the uncertainties on the position of the laser spot at the fluctuating end of
the cantilever. Variation of viscosity below 0.03 mPas was detected with
the alternative to achieve measurements with a volume as low as 50 L.Comment: Sensors, MDPI, 201
Direct measurement of spatial modes of a micro-cantilever from thermal noise
International audienceMeasurements of the deflection induced by thermal noise have been performed on a rectangular atomic force microscope cantilever in air. The detection method, based on polarization interferometry, can achieve a resolution of 1E-14 m/rtHz in the frequency range 1 kHz â 800 kHz. The focused beam from the interferometer probes the cantilever at different positions along its length and the spatial modes' shapes are determined up to the fourth resonance, without external excitation. Results are in good agreement with theoretically expected behavior. From this analysis accurate determination of the elastic constant of the cantilever is also achieved
Reliability and operation cost of underdamped memories during cyclic erasures
The reliability of fast repeated erasures is studied experimentally and
theoretically in a 1-bit underdamped memory. The bit is encoded by the position
of a micro-mechanical oscillator whose motion is confined in a double well
potential. To contain the energetic cost of fast erasures, we use a resonator
with high quality factor : the erasure work is close to
Landauer's bound, even at high speed. The drawback is the rise of the system's
temperature due to a weak coupling to the environment. Repeated erasures
without letting the memory thermalize between operations result in a continuous
warming, potentially leading to a thermal noise overcoming the barrier between
the potential wells. In such case, the reset operation can fail to reach the
targeted logical state. The reliability is characterized by the success rate
after successive operations. , and
are studied experimentally as a function of the erasure
speed. Above a velocity threshold, soars while
collapses: the reliability of too fast erasures is low. These experimental
results are fully justified by two complementary models. We demonstrate that
is optimal to contain energetic costs and maintain high
reliability standards for repeated erasures at any speed
Thermal noise calibration of functionalized cantilevers for force microscopy: effects of the colloidal probe position
Colloidal probes are often used in force microscopy when the geometry of the
tip-sample interaction should be well controlled. Their calibration requires
the understanding of their mechanical response, which is very sensitive to the
details of the force sensor consisting of a cantilever and the attached
colloid. We present analytical models to describe the dynamics of the
cantilever and its load positioned anywhere along its length. The thermal noise
calibration of such probes is then studied from a practical point of view,
leading to correction coefficients that can be applied in standard force
microscope calibration routines. Experimental measurements of resonance
frequencies and thermal noise profiles of raw and loaded cantilevers
demonstrate the validity of the approach
Simultaneous and accurate measurement of the dielectric constant at many frequencies spanning a wide range
We present an innovative technique which allows the simultaneous measurement
of the dielectric constant of a material at many frequencies, spanning a four
orders of magnitude range chosen between 10 --2 Hz and 10 4 Hz. The sensitivity
and accuracy are comparable to those obtained using standard single frequency
techniques. The technique is based on three new and simple features: a) the
precise real time correction of the amplication of a current amplier; b) the
specic shape of the excitation signal and its frequency spectrum; and c) the
precise synchronization between the generation of the excitation signal and the
acquisition of the dielectric response signal. This technique is useful in the
case of relatively fast dynamical measurements when the knowledge of the time
evolution of the dielectric constant is needed
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