1,008 research outputs found
Amplitude calibration of 2D mechanical resonators by nonlinear optical transduction
Contactless characterization of mechanical resonances using Fabry-Perot
interferometry is a powerful tool to study the mechanical and dynamical
properties of atomically thin membranes. However, amplitude calibration is
often not performed, or only possible by making assumptions on the device
parameters such as its mass or the temperature. In this work, we demonstrate a
calibration technique that directly measures the oscillation amplitude by
detecting higher harmonics that arise from nonlinearities in the optical
transduction. Employing this technique, we calibrate the resonance amplitude of
two-dimensional nanomechanical resonators, without requiring knowledge of their
mechanical properties, actuation force, geometric distances or the laser
intensity
Graphene Squeeze-Film Pressure Sensors
The operating principle of squeeze-film pressure sensors is based on the
pressure dependence of a membrane's resonance frequency, caused by the
compression of the surrounding gas which changes the resonator stiffness. To
realize such sensors, not only strong and flexible membranes are required, but
also minimization of the membrane's mass is essential to maximize responsivity.
Here, we demonstrate the use of a few-layer graphene membrane as a squeeze-film
pressure sensor. A clear pressure dependence of the membrane's resonant
frequency is observed, with a frequency shift of 4 MHz between 8 and 1000 mbar.
The sensor shows a reproducible response and no hysteresis. The measured
responsivity of the device is 9000 Hz/mbar, which is a factor 45 higher than
state-of-the-art MEMS-based squeeze-film pressure sensors while using a 25
times smaller membrane area
Investigating laser induced phase engineering in MoS2 transistors
Phase engineering of MoS2 transistors has recently been demonstrated and has
led to record low contact resistances. The phase patterning of MoS2 flakes with
laser radiation has also been realized via spectroscopic methods, which invites
the potential of controlling the metallic and semiconducting phases of MoS2
transistors by simple light exposure. Nevertheless, the fabrication and
demonstration of laser patterned MoS2 devices starting from the metallic
polymorph has not been demonstrated yet. Here, we study the effects of laser
radiation on 1T/1T'-MoS2 transistors with the prospect of driving an in-situ
phase transition to the 2H-polymorph through light exposure. We find that
although the Raman peaks of 2H-MoS2 become more prominent and the ones from the
1T/1T' phase fade after the laser exposure, the semiconducting properties of
the laser patterned devices are not fully restored and the laser treatment
ultimately leads to degradation of the transport channel
Static capacitive pressure sensing using a single graphene drum
To realize nanomechanical graphene-based pressure and gas sensors, it is
beneficial to have a method to electrically readout the static displacement of
a suspended graphene membrane. Capacitive readout, typical in
micro-electro-mechanical systems (MEMS), gets increasingly challenging as one
starts shrinking the dimensions of these devices, since the expected
responsivity of such devices is below 0.1 aF/Pa. To overcome the challenges of
detecting small capacitance changes, we design an electrical readout device
fabricated on top of an insulating quartz substrate, maximizing the
contribution of the suspended membrane to the total capacitance of the device.
The capacitance of the drum is further increased by reducing the gap size to
110 nm. Using external pressure load, we demonstrate successful detection of
capacitance changes of a single graphene drum down to 50 aF, and pressure
differences down to 25 mbar
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