207 research outputs found
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
Antibody-mediated inhibition of syndecan-4 dimerisation reduces interleukin (IL)-1 receptor trafficking and signalling.
OBJECTIVE: Syndecan-4 (sdc4) is a cell-anchored proteoglycan that consists of a transmembrane core protein and glucosaminoglycan (GAG) side chains. Binding of soluble factors to the GAG chains of sdc4 may result in the dimerisation of sdc4 and the initiation of downstream signalling cascades. However, the question of how sdc4 dimerisation and signalling affects the response of cells to inflammatory stimuli is unknown. METHODS: Sdc4 immunostaining was performed on rheumatoid arthritis (RA) tissue sections. Interleukin (IL)-1 induced extracellular signal-regulated kinases (ERK) phosphorylation and matrix metalloproteinase-3 production was investigated. Il-1 binding to sdc4 was investigated using immunoprecipitation. IL-1 receptor (IL1R1) staining on wild-type, sdc4 and IL1R1 knockout fibroblasts was performed in fluorescence-activated cell sorting analyses. A blocking sdc4 antibody was used to investigate sdc4 dimerisation, IL1R1 expression and the histological paw destruction in the human tumour necrosis factor-alpha transgenic mouse. RESULTS: We show that in fibroblasts, the loss of sdc4 or the antibody-mediated inhibition of sdc4 dimerisation reduces the cell surface expression of the IL-1R and regulates the sensitivity of fibroblasts to IL-1. We demonstrate that IL-1 directly binds to sdc4 and in an IL-1R-independent manner leads to its dimerisation. IL-1-induced dimerisation of sdc4 regulates caveolin vesicle-mediated trafficking of the IL1R1, which in turn determines the responsiveness to IL-1. Administration of antibodies (Ab) against the dimerisation domain of sdc4, thus, strongly reduces the expression IL1R1 on arthritic fibroblasts both in vitro and an animal model of human RA. CONCLUSION: Collectively, our data suggest that Ab that specifically inhibit sdc4 dimerisation may support anti-IL-1 strategies in diseases such as inflammatory arthritis
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
Intrinsic Terahertz Plasmons and Magnetoplasmons in Large Scale Monolayer Graphene
We show that in graphene epitaxially grown on SiC the Drude absorption is
transformed into a strong terahertz plasmonic peak due to natural nanoscale
inhomogeneities, such as substrate terraces and wrinkles. The excitation of the
plasmon modifies dramatically the magneto-optical response and in particular
the Faraday rotation. This makes graphene a unique playground for
plasmon-controlled magneto-optical phenomena thanks to a cyclotron mass 2
orders of magnitude smaller than in conventional plasmonic materials such as
noble metals.Comment: to appear in Nano Letter
Electrical Control of Plasmon Resonance with Graphene
Surface plasmon, with its unique capability to concentrate light into
sub-wavelength volume, has enabled great advances in photon science, ranging
from nano-antenna and single-molecule Raman scattering to plasmonic waveguide
and metamaterials. In many applications it is desirable to control the surface
plasmon resonance in situ with electric field. Graphene, with its unique
tunable optical properties, provides an ideal material to integrate with
nanometallic structures for realizing such control. Here we demonstrate
effective modulation of the plasmon resonance in a model system composed of
hybrid graphene-gold nanorod structure. Upon electrical gating the strong
optical transitions in graphene can be switched on and off, which leads to
significant modulation of both the resonance frequency and quality factor of
plasmon resonance in gold nanorods. Hybrid graphene-nanometallic structures, as
exemplified by this combination of graphene and gold nanorod, provide a general
and powerful way for electrical control of plasmon resonances. It holds promise
for novel active optical devices and plasmonic circuits at the deep
subwavelength scale
Generation of photovoltage in graphene on a femtosecond time scale through efficient carrier heating
Graphene is a promising material for ultrafast and broadband photodetection.
Earlier studies addressed the general operation of graphene-based
photo-thermoelectric devices, and the switching speed, which is limited by the
charge carrier cooling time, on the order of picoseconds. However, the
generation of the photovoltage could occur at a much faster time scale, as it
is associated with the carrier heating time. Here, we measure the photovoltage
generation time and find it to be faster than 50 femtoseconds. As a
proof-of-principle application of this ultrafast photodetector, we use graphene
to directly measure, electrically, the pulse duration of a sub-50 femtosecond
laser pulse. The observation that carrier heating is ultrafast suggests that
energy from absorbed photons can be efficiently transferred to carrier heat. To
study this, we examine the spectral response and find a constant spectral
responsivity between 500 and 1500 nm. This is consistent with efficient
electron heating. These results are promising for ultrafast femtosecond and
broadband photodetector applications.Comment: 6 pages, 4 figure
Wafer-scale synthesis and transfer of graphene films
We developed means to produce wafer scale, high-quality graphene films as
large as 3 inch wafer size on Ni and Cu films under ambient-pressure and
transfer them onto arbitrary substrates through instantaneous etching of metal
layers. We also demonstrated the applications of the large-area graphene films
for the batch fabrication of field-effect transistor (FET) arrays and
stretchable strain gauges showing extraordinary performances. Transistors
showed the hole and electron mobilities of the device of 1,100 cm2/Vs and 550
cm2/Vs at drain bias of -0.75V, respectively. The piezo-resistance gauge factor
of strain sensor was ~6.1. These methods represent a significant step toward
the realization of graphene devices in wafer scale as well as application in
optoelectronics, flexible and stretchable electronics.Comment: 18 page
Graphene plasmonics
Two rich and vibrant fields of investigation, graphene physics and
plasmonics, strongly overlap. Not only does graphene possess intrinsic plasmons
that are tunable and adjustable, but a combination of graphene with noble-metal
nanostructures promises a variety of exciting applications for conventional
plasmonics. The versatility of graphene means that graphene-based plasmonics
may enable the manufacture of novel optical devices working in different
frequency ranges, from terahertz to the visible, with extremely high speed, low
driving voltage, low power consumption and compact sizes. Here we review the
field emerging at the intersection of graphene physics and plasmonics.Comment: Review article; 12 pages, 6 figures, 99 references (final version
available only at publisher's web site
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