288 research outputs found
A Graphene Field-Effect Device
In this letter, a top-gated field effect device (FED) manufactured from
monolayer graphene is investigated. Except for graphene deposition, a
conventional top-down CMOS-compatible process flow is applied. Carrier
mobilities in graphene pseudo-MOS structures are compared to those obtained
from top-gated Graphene-FEDs. The extracted values exceed the universal
mobility of silicon and silicon-on-insulator MOSFETs.Comment: 12 pages, 3 figure
Creep-Fatigue Relationship in Polymer: Molecular Dynamics Simulations Approach
The creep‐tensile fatigue relationship is investigated using MD simulations for amorphous polyethylene, by stepwise increasing the R‐ratio from 0.3 for fatigue to an R‐ratio = 1 for creep. The simulations can produce similar behavior as observed in experiments, for instances strain‐softening behavior and hysteresis loops in the stress‐strain curves. The simulations predict the molecular mechanisms of creep and fatigue are the same. Fatigue and creep cause significant changes of the van der Waals and dihedral potential energies. These changes are caused by movements of the polymer chains, creating more un‐twisted dihedral angles and the unfolding of polymer chain
Effects of temperature and strain rate on the deformation of amorphous polyethylene: a comparison between molecular dynamics simulations and experimental results
Molecular dynamics simulations are used to investigate the effects of
temperature and strain rate on the deformation of amorphous polyethylene.
The simulations predict the effects of temperature and strain rate on the
stress-strain responses, Youngs modulus and Poissons ratio similar to those observed in laboratory experiments performed by other researchers. The time-temperature superposition principle is applied to the Youngs modulus and Poissons ratio to form a master curve to address the discrepancies in strain rates between the simulations and the experiments. Differences in the numbers of monomers and chains, the degree of crystallinity and molecular orientation lead to discrepancies in the Youngs modulus and Poissons ratio between simulations and experiments
Bistability and oscillatory motion of natural nano-membranes appearing within monolayer graphene on silicon dioxide
The recently found material graphene is a truly two-dimensional crystal and
exhibits, in addition, an extreme mechanical strength. This in combination with
the high electron mobility favours graphene for electromechanical
investigations down to the quantum limit. Here, we show that a monolayer of
graphene on SiO2 provides natural, ultra-small membranes of diameters down to 3
nm, which are caused by the intrinsic rippling of the material. Some of these
nano-membranes can be switched hysteretically between two vertical positions
using the electric field of the tip of a scanning tunnelling microscope (STM).
They can also be forced to oscillatory motion by a low frequency ac-field.
Using the mechanical constants determined previously, we estimate a high
resonance frequency up to 0.4 THz. This might be favorable for
quantum-electromechanics and is prospective for single atom mass spectrometers.Comment: 9 pages, 4 figure
Molecular dynamics simulations of strain-controlled fatigue behaviour of amorphous polyethylene
Fatigue of amorphous polyethylene under low strain was simulated using molecular dynamics. The united atom approach and the Dreiding force field were chosen to describe the interaction between monomers. Molecular dynamics simulations resembling strain-controlled loading fatigue tests in tension-tension mode were performed to study the effect of the R-ratio and mean strain on the mechanical responses. Laboratory fatigue experiments in strain/displacement control were performed at room temperature, and the results were compared to the simulation results. The simulations are able to produce qualitatively similar behaviour to the experimental results, for instance, mean stress relaxation, hysteresis loops in the stress�strain curve, and change in the cyclic modulus. They also show that stress relaxation is enhanced by cyclic loading. The simulations show that cyclic loading changes the total potential energies of the system, especially the van der Waals potential. The changes in the van der Waals potential energy contribute significantly to the increasing of the stiffness of the system. Some changes in dihedral angles with lower energy configurations are observed; however, bond distances and angles do not change significantly. The chains tend to unfold slightly along the loading axis as the fatigue loading progresses
The effects of the van der Waals potential energy on the Young’s modulus of a polymer: comparison between molecular dynamics simulation and experiment
Molecular dynamics simulation were employed to investigate the effect of changing the potential energies describing primary and secondary bonds on the Young’s modulus of a polymer. The energies were changed by arbitrarily modifying the parameters of the potential energy model function. The parameters influence the structure of the polymer and its global energy, eventually causing changes to the Young’s modulus. The van der Waals energy describing secondary bonds gives the most significant contribution to the changes. Increasing the energy increases the density and Young’s modulus. The trends are in agreement with experimental data
Visible and infrared photocurrent enhancement in a graphene-silicon Schottky photodetector through surface-states and electric field engineering
The design of efficient graphene-silicon (GSi) Schottky junction
photodetectors requires detailed understanding of the spatial origin of the
photoresponse. Scanning-photocurrent-microscopy (SPM) studies have been carried
out in the visible wavelengths regions only, in which the response due to
silicon is dominant. Here we present comparative SPM studies in the visible
( = 633nm) and infrared ( = 1550nm) wavelength regions for a
number of GSi Schottky junction photodetector architectures, revealing the
photoresponse mechanisms for silicon and graphene dominated responses,
respectively, and demonstrating the influence of electrostatics on the device
performance. Local electric field enhancement at the graphene edges leads to a
more than ten-fold increased photoresponse compared to the bulk of the
graphene-silicon junction. Intentional design and patterning of such graphene
edges is demonstrated as an efficient strategy to increase the overall
photoresponse of the devices. Complementary simulations and modeling illuminate
observed effects and highlight the importance of considering graphene's shape
and pattern and device geometry in the device design
Non-volatile switching in graphene field effect devices
The absence of a band gap in graphene restricts its straight forward
application as a channel material in field effect transistors. In this letter,
we report on a new approach to engineer a band gap in graphene field effect
devices (FED) by controlled structural modification of the graphene channel
itself. The conductance in the FEDs is switched between a conductive "on-state"
to an insulating "off-state" with more than six orders of magnitude difference
in conductance. Above a critical value of an electric field applied to the FED
gate under certain environmental conditions, a chemical modification takes
place to form insulating graphene derivatives. The effect can be reversed by
electrical fields of opposite polarity or short current pulses to recover the
initial state. These reversible switches could potentially be applied to
non-volatile memories and novel neuromorphic processing concepts.Comment: 14 pages, 4 figures, submitted to IEEE ED
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