33 research outputs found
Arbitrary distribution and nonlinear modal interaction in coupled nanomechanical resonators
We propose a general one-dimensional {\em continuous} formulation to analyze
the vibrational modes of antenna-like nanomechanical resonators consisting of
two symmetric arrays of cantilevers affixed to a central nano-beam. The
cantilever arrays can have arbitrary density and length profile along the beam.
We obtain the secular equation that allows for the determination of their
frequency spectrum and illustrate the results on the particular examples of
structures with constant or alternating cantilever length profiles. We show
that our analytical results capture the vibration spectrum of such resonators
and elucidate key relationships that could prove advantageous for experimental
device performance. Furthermore, using a perturbative approach to treat the
nonlinear and dissipative dynamics of driven structures, we analyze the
anharmonic coupling between two specific widely spaced modes of the
coupled-element device, with direct application to experiments.Comment: 8 pages, 5 figures, additional info can be found at
http://nano.bu.ed
Evidence for Quantized Displacement in Macroscopic Nanomechanical Oscillators
We report the observation of discrete displacement of nanomechanical
oscillators with gigahertz-range resonance frequencies at millikelvin
temperatures. The oscillators are nanomachined single-crystal structures of
silicon, designed to provide two distinct sets of coupled elements with very
low and very high frequencies. With this novel design, femtometer-level
displacement of the frequency-determining element is amplified into collective
motion of the entire micron-sized structure. The observed discrete response
possibly results from energy quantization at the onset of the quantum regime in
these macroscopic nanomechanical oscillators.Comment: 4 pages, two-column format. Related papers available at
http://nano.bu.edu
Quantum Friction in Nanomechanical Oscillators at Millikelvin Temperatures
We report low-temperature measurements of dissipation in megahertz-range,
suspended, single-crystal nanomechanical oscillators. At millikelvin
temperatures, both dissipation (inverse quality factor) and shift in the
resonance frequency display reproducible features, similar to those observed in
sound attenuation experiments in disordered glasses and consistent with
measurements in larger micromechanical oscillators fabricated from
single-crystal silicon. Dissipation in our single-crystal nanomechanical
structures is dominated by internal quantum friction due to an estimated number
of roughly 50 two-level systems, which represent both dangling bonds on the
surface and bulk defects.Comment: 5 pages, two-column format. Related papers available at
http://nano.bu.ed
Coherent Signal Amplification in Bistable Nanomechanical Oscillators by Stochastic Resonance
Stochastic resonance is a counter-intuitive concept[1,2], ; the addition of
noise to a noisy system induces coherent amplification of its response. First
suggested as a mechanism for the cyclic recurrence of ice ages, stochastic
resonance has been seen in a wide variety of macroscopic physical systems:
bistable ring lasers[3], SQUIDs[4,5], magnetoelastic ribbons[6], and
neurophysiological systems such as the receptors in crickets[7] and
crayfish[8]. Although it is fundamentally important as a mechanism of coherent
signal amplification, stochastic resonance is yet to be observed in nanoscale
systems. Here we report the observation of stochastic resonance in bistable
nanomechanical silicon oscillators, which can play an important role in the
realization of controllable high-speed nanomechanical memory cells. Our
nanomechanical systems were excited into a dynamic bistable state and modulated
in order to induce controllable switching; the addition of white noise showed a
marked amplification of the signal strength. Stochastic resonance in
nanomechanical systems paves the way for exploring macroscopic quantum
coherence and tunneling, and controlling nanoscale quantum systems for their
eventual use as robust quantum logic devices.Comment: 18 pages, 4 figure
Nonlinear response of a driven vibrating nanobeam in the quantum regime
We analytically investigate the nonlinear response of a damped doubly clamped
nanomechanical beam under static longitudinal compression which is excited to
transverse vibrations. Starting from a continuous elasticity model for the
beam, we consider the dynamics of the beam close to the Euler buckling
instability. There, the fundamental transverse mode dominates and a quantum
mechanical time-dependent effective single particle Hamiltonian for its
amplitude can be derived. In addition, we include the influence of a
dissipative Ohmic or super-Ohmic environment. In the rotating frame, a
Markovian master equation is derived which includes also the effect of the
time-dependent driving in a non-trivial way. The quasienergies of the pure
system show multiple avoided level crossings corresponding to multiphonon
transitions in the resonator. Around the resonances, the master equation is
solved analytically using Van Vleck perturbation theory. Their lineshapes are
calculated resulting in simple expressions. We find the general solution for
the multiple multiphonon resonances and, most interestingly, a bath-induced
transition from a resonant to an antiresonant behavior of the nonlinear
response.Comment: 25 pages, 5 figures, submitted to NJ
Nanomechanical Detection of Itinerant Electron Spin Flip
Spin is an intrinsically quantum property, characterized by angular momentum.
A change in the spin state is equivalent to a change in the angular momentum or
mechanical torque. This spin-induced torque has been invoked as the intrinsic
mechanism in experiments ranging from the measurements of angular momentum of
photons g-factor of metals and magnetic resonance to the magnetization reversal
in magnetic multi-layers A spin-polarized current introduced into a nonmagnetic
nanowire produces a torque associated with the itinerant electron spin flip.
Here, we report direct measurement of this mechanical torque and itinerant
electron spin polarization in an integrated nanoscale torsion oscillator, which
could yield new information on the itinerancy of the d-band electrons. The
unprecedented torque sensitivity of 10^{-22} N m/ \sqrt{Hz} may enable
applications for spintronics, precision measurements of CP-violating forces,
untwisting of DNA and torque generating molecules.Comment: 14 pages, 4 figures. visit http://nano.bu.edu/ for related paper
Response Spectrum of Coupled Nanomechanical Resonators
International audienceWe develop a simple continuum model to analyze the vibrational modes of a nanomechanical multielement structure. In this model, arrays of submicron cantilevers located symmetrically on both sides of the central clamped-clamped nanobeam are replaced by a continuum. In this approach, the equations of motion of the structure become exactly solvable. Our analytical results capture the main features of the vibrational modes observed both numerically and experimentally and can be applied to a general class of scale-independent elasticaly coupled resonator structures
СИНТЕЗ ФТОРОВМІСНИХ АНАЛОГІВ НОВОКАЇНАМІДУ
Methods for the synthesis of (2-N,N-diethylaminoethyl)amides of meta- and parapentafluoroethoxybenzoic acids starting with respective ethyl pentafluoroethoxybenzoates have been developed. Firstly, ethyl m- and p-pentafluoroethoxybenzoates were treated with sodium hydroxide in aqueous-alcoholic solution. The mixture obtained was acidified with concentrated hydrochloric acid giving respective meta- or para-pentafluoroethoxybenzoic acids. The acids obtained were dried and treated with excess of thionyl chloride giving respective acid chlorides that further reacted with N,N-diethylethylene-1,2-diamine. N,N-diethylethylenediamine was obtained by treating N,N-diethyl-2-chloro-ethylamine hydrochloride with aqueous ammonia solution (25%). The resulting product contained secondary and tertiary amines that could not be separated by distillation. In order to purify N,N-diethylethylene-1,2-diamine the mixture was treated with phthalic anhydride, the desired product was separated in the form of respective phthalimide and then phthalimide protecting group was removed by hydrazinolysis. After such purification N,N-diethylethylene-1,2-diamine contained no secondary or tertiary amines. The condensation of meta- and parapentafluoroethoxybenzoic acid chlorides with N,N-diethylethylenediamine was conducted in 1,2-dichloroethane solution with a little molar excess of triethylamine that was used as HCl scavenger. The reaction mixture was heated for two hours, cooled to room temperature, the residue was filtered off and volatile compounds were removed under reduced pressure. It should be noted that triethylamine is necessary, because otherwise the reaction mixture gets dark brown color and the desired product can’t be isolated. Procainamide analogues, obtained in the present paper, were tested for local anesthetic activity in capsaicin test. Both (2-N,N-diethyl-aminoethyl)amides of meta- and para-pentafluoroethoxybenzoic acids showed better local anesthetic activity, compared to anesthesine.Розроблено методи синтезу (N,N-діетил-2-аміноетил)амідів м- та п-пентафторетоксибензойних кислот, які є фторовмісними аналогами новокаїнаміду. Показано, що синтезовані аналоги мають більш високу місцевоанестезуючу активність, ніж анестезин