227 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
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
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
Intrinsic and extrinsic corrugation of monolayer graphene deposited on SiO2
Using scanning tunneling microscopy (STM) in ultra high vacuum and atomic
force microscopy, we investigate the corrugation of graphene flakes deposited
by exfoliation on a Si/SiO2 (300 nm) surface. While the corrugation on SiO2 is
long-range with a correlation length of about 25 nm, some of the graphene
monolayers exhibit an additional corrugation with a preferential wave length of
about 15 nm. A detailed analysis shows that the long range corrugation of the
substrate is also visible on graphene, but with a reduced amplitude, leading to
the conclusion that the graphene is partly freely suspended between hills of
the substrate. Thus, the intrinsic rippling observed previously on artificially
suspended graphene can exist as well, if graphene is deposited on SiO2.Comment: 10 pages, 11 figures, including supplementary materia
Anisotropic photoconductivity in graphene
We investigate the photoconductivity of graphene within the relaxation time
approximation. In presence of the inter-band transitions induced by the
linearly polarized light the photoconductivity turns out to be highly
anisotropic due to the pseudospin selection rule for Dirac-like carriers. The
effect can be observed in clean undoped graphene samples and be utilized for
light polarization detection.Comment: 4 pages, 2 figure
Minimum Information about a Neuroscience Investigation (MINI) Electrophysiology
This module represents the formalized opinion of the authors and the CARMEN consortium, which identifies the minimum information required to report the use of electrophysiology in a neuroscience study, for submission to the CARMEN system (www.carmen.org.uk).

Mars Colonization Problems
In this article, graphene is investigated with respect to its electronic properties when introduced into field effect devices (FED). With the exception of manual graphene deposition, conventional top-down CMOS-compatible
processes are applied. Few and monolayer graphene sheets are
characterized by scanning electron microscopy, atomic force
microscopy and Raman spectroscopy. The electrical properties of
monolayer graphene sandwiched between two silicon dioxide films are studied. Carrier mobilities in graphene
pseudo-MOS structures are compared to those obtained from
double-gated Graphene-FEDs and silicon metal-oxide-semiconductor field-effect-transistors (MOSFETs)
Nonperturbative harmonic generation in graphene from intense midinfrared pulsed light
In solids, high harmonic radiation arises from the subcycle dynamics of electrons and holes under the action of an intense laser field. The strong-field regime opens new opportunities to understand and control carrier dynamics on ultrafast time scales, including the coherent dynamics of quasiparticles such as massless Dirac fermions. Here, we irradiate monolayer and few-layer graphene with intense infrared light to produce nonperturbative harmonics of the fundamental up to the seventh order. We find that the polarization dependence shows surprising agreement with gas-phase harmonics. Using a two-band model, we explore the nonlinear current due to electrons near the Dirac points, and we discuss the interplay between intraband and interband contributions to the harmonic spectrum. This interplay opens new opportunities to access ultrafast and strong-field physics of graphene.Peer reviewed: YesNRC publication: Ye
Surface energy engineering of graphene
Contact angle goniometry is conducted for epitaxial graphene on SiC. Although
only a single layer of epitaxial graphene exists on SiC, the contact angle
drastically changes from 69{\deg} on SiC substrates to 92{\deg} with graphene.
It is found that there is no thickness dependence of the contact angle from the
measurements of single, bi, and multi layer graphene and highly ordered
pyrolytic graphite (HOPG). After graphene is treated with oxygen plasma, the
level of damage is investigated by Raman spectroscopy and correlation between
the level of disorder and wettability is reported. By using low power oxygen
plasma treatment, the wettability of graphene is improved without additional
damage, which can solve the adhesion issues involved in the fabrication of
graphene devices
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