1,612 research outputs found
Optically driven ultra-stable nanomechanical rotor
Nanomechanical devices have attracted the interest of a growing
interdisciplinary research community, since they can be used as highly
sensitive transducers for various physical quantities. Exquisite control over
these systems facilitates experiments on the foundations of physics. Here, we
demonstrate that an optically trapped silicon nanorod, set into rotation at MHz
frequencies, can be locked to an external clock, transducing the properties of
the time standard to the rod's motion with the remarkable frequency stability
of . While the dynamics of
this periodically driven rotor generally can be chaotic, we derive and verify
that stable limit cycles exist over a surprisingly wide parameter range. This
robustness should enable, in principle, measurements of external torques with
sensitivities better than 0.25zNm, even at room temperature. We show that in a
dilute gas, real-time phase measurements on the locked nanorod transduce
pressure values with a sensitivity of 0.3%.Comment: 5 pages, 4 figure
Cavity-assisted manipulation of freely rotating silicon nanorods in high vacuum
Optical control of nanoscale objects has recently developed into a thriving
field of research with far-reaching promises for precision measurements,
fundamental quantum physics and studies on single-particle thermodynamics.
Here, we demonstrate the optical manipulation of silicon nanorods in high
vacuum. Initially, we sculpture these particles into a silicon substrate with a
tailored geometry to facilitate their launch into high vacuum by laser-induced
mechanical cleavage. We manipulate and trace their center-of-mass and
rotational motion through the interaction with an intense intra-cavity field.
Our experiments show optical forces on nanorotors three times stronger than on
silicon nanospheres of the same mass. The optical torque experienced by the
spinning rods will enable cooling of the rotational motion and torsional
opto-mechanics in a dissipation-free environment.Comment: 8 page
Full rotational control of levitated silicon nanorods
We study a nanofabricated silicon rod levitated in an optical trap. By
manipulating the polarization of the light we gain full control over the
ro-translational dynamics of the rod. We are able to trap both its
centre-of-mass and align it along the linear polarization of the laser field.
The rod can be set into rotation at a tuned frequency by exploiting the
radiation pressure exerted by elliptically polarized light. The rotational
motion of the rod dynamically modifies the optical potential, which allows
tuning of the rotational frequency over hundreds of Kilohertz. This ability to
trap and control the motion and alignment of nanoparticles opens up the field
of rotational optomechanics, rotational ground state cooling and the study of
rotational thermodynamics in the underdamped regime.Comment: 5 pages, 4 figures, 4 Supplementary pages, 4 Supplementary figure
Multifunctional Devices and Logic Gates With Undoped Silicon Nanowires
We report on the electronic transport properties of multiple-gate devices
fabricated from undoped silicon nanowires. Understanding and control of the
relevant transport mechanisms was achieved by means of local electrostatic
gating and temperature dependent measurements. The roles of the source/drain
contacts and of the silicon channel could be independently evaluated and tuned.
Wrap gates surrounding the silicide-silicon contact interfaces were proved to
be effective in inducing a full suppression of the contact Schottky barriers,
thereby enabling carrier injection down to liquid-helium temperature. By
independently tuning the effective Schottky barrier heights, a variety of
reconfigurable device functionalities could be obtained. In particular, the
same nanowire device could be configured to work as a Schottky barrier
transistor, a Schottky diode or a p-n diode with tunable polarities. This
versatility was eventually exploited to realize a NAND logic gate with gain
well above one.Comment: 6 pages, 5 figure
Biofunctionalized Zinc Oxide Field Effect Transistors for Selective Sensing of Riboflavin with Current Modulation
Zinc oxide field effect transistors (ZnO-FET), covalently functionalized with single stranded DNA aptamers, provide a highly selective platform for label-free small molecule sensing. The nanostructured surface morphology of ZnO provides high sensitivity and room temperature deposition allows for a wide array of substrate types. Herein we demonstrate the selective detection of riboflavin down to the pM level in aqueous solution using the negative electrical current response of the ZnO-FET by covalently attaching a riboflavin binding aptamer to the surface. The response of the biofunctionalized ZnO-FET was tuned by attaching a redox tag (ferrocene) to the 3′ terminus of the aptamer, resulting in positive current modulation upon exposure to riboflavin down to pM levels
Scaling Laws for NanoFET Sensors
The sensitive conductance change of semiconductor nanowires and carbon
nanotubes in response to binding of charged molecules provide a novel sensing
modality which is generally denoted as nanoFET sensors. In this paper, we study
the scaling laws of nanoplate FET sensors by simplifying nanoplates as random
resistor networks with molecular receptors sitting on lattice sites.
Nanowire/tube FETs are included as the limiting cases where the device width
goes small. Computer simulations show that the field effect strength exerted by
the binding molecules has significant impact on the scaling behaviors. When the
field effect strength is small, nanoFETs have little size and shape dependence.
In contrast, when the field-effect strength becomes stronger, there exists a
lower detection threshold for charge accumulation FETs and an upper detection
threshold for charge depletion FET sensors. At these thresholds, the nanoFET
devices undergo a transition between low and large sensitivities. These
thresholds may set the detection limits of nanoFET sensors, while could be
eliminated by designing devices with very short source-drain distance and large
width
A Reusable Impedimetric Aptasensor for Detection of Thrombin Employing a Graphite-Epoxy Composite Electrode
Here, we report the application of a label-free electrochemical aptasensor based on a graphite-epoxy composite electrode for the detection of thrombin; in this work, aptamers were immobilized onto the electrodes surface using wet physical adsorption. The detection principle is based on the changes of the interfacial properties of the electrode; these were probed in the presence of the reversible redox couple [Fe(CN)6]3−/[Fe(CN)6]4− using impedance measurements. The electrode surface was partially blocked due to formation of aptamer-thrombin complex, resulting in an increase of the interfacial electron-transfer resistance detected by Electrochemical Impedance Spectroscopy (EIS). The aptasensor showed a linear response for thrombin in the range of 7.5 pM to 75 pM and a detection limit of 4.5 pM. The aptasensor was regenerated by breaking the complex formed between the aptamer and thrombin using 2.0 M NaCl solution at 42 °C, showing its operation for different cycles. The interference response caused by main proteins in serum has been characterized
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