286 research outputs found
Thermal conductivity of suspended pristine graphene measured by Raman spectroscopy
The thermal conductivity of suspended single-layer graphene was measured as a
function of temperature using Raman scattering spectroscopy on clean samples
prepared directly on a prepatterned substrate by mechanical exfoliation without
chemical treatments. The temperature at the laser spot was monitored by the
frequency of the Raman 2 band of the Raman scattering spectrum, and the
thermal conductivity was deduced by analyzing heat diffusion equations assuming
that the substrate is a heat sink at ambient temperature. The obtained thermal
conductivity values range from 1800 WmK near 325 K to
710 WmK at 500 K.Comment: 4pages, 3 figure
Accurate and Precise Determination of Mechanical Properties of Silicon Nitride Beam Nanoelectromechanical Devices
4-O-Carboxymethylascochlorin Inhibits Expression Levels of on Inflammation-Related Cytokines and Matrix Metalloproteinase-9 Through NFâÎșB/MAPK/TLR4 Signaling Pathway in LPS-Activated RAW264.7 Cells
Toll-like receptor 4 (TLR4) and matrix metalloproteinase-9 (MMP-9) are known to play important roles in inflammatory diseases such as arteriosclerosis and plaque instability. The purpose of this study was to perform the effect of 4-O-carboxymethylascochlorin (AS-6) on MMP-9 expression in lipopolysaccharide (LPS)-induced murine macrophages and signaling pathway involved in its anti-inflammatory effect. Effect of AS-6 on MAPK/NF-ÎșB/TLR4 signaling pathway in LPS-activated murine macrophages was examined using ELISA, Western blotting, reverse transcription polymerase chain reaction (RT-PCR) and fluorescence immunoassay. MMP-9 enzyme activity was examined by gelatin zymography. AS-6 significantly suppressed MMP-9 and MAPK/NF-ÎșB expression levels in LPS-stimulated murine macrophages. Expression levels of inducible nitric oxide synthase (iNOS), COX2, MMP-9, JNK, ERK, p38 phosphorylation, and NF-ÎșB stimulated by LPS were also decreased by AS-6. Moreover, AS-6 suppressed TLR4 expression and dysregulated LPS-induced activators of transcription signaling pathway. The results of this study showed that AS-6 can inhibit LPS-stimulated inflammatory response by suppressing TLR4/MAPK/NF-ÎșB signals, suggesting that AS-6 can be used to induce the stability of atherosclerotic plaque and prevent inflammatory diseases in an in vitro model
Graphene nano-electromechanical mass sensor with high resolution at room temperature
The inherent properties of 2D materialsâlight mass, high out-of-plane flexibility, and large surface areaâpromise great potential for precise and accurate nanomechanical mass sensing, but their application is often hampered by surface contamination. Here we demonstrate a tri-layer graphene nanomechanical resonant mass sensor with sub-attogram resolution at room temperature, fabricated by a bottom-up process. We found that Joule-heating is effective in cleaning the graphene membrane surface, which results in a large improvement in the stability of the resonance frequency. We characterized the sensor by depositing Cr metal using a stencil mask and found a mass-resolution that is sufficient to weigh very small particles, like large proteins and protein complexes, with potential applications in the fields of nanobiology and medicine.</p
Nanoscale Structural Switching of Plasmonic Nanograin Layers on Hydrogel Colloidal Monolayers for Highly Sensitive and Dynamic SERS in Water with Areal Signal Reproducibility
Developing
substrates that enable both reproducible and highly
sensitive Raman detection of trace amounts of molecules in aqueous
systems remains a challenge, although these substrates are crucial
in biomedicine and environmental sciences. To address this issue,
we report spatially uniform plasmonic nanowrinkles formed by intimate
contact between plasmonic nanograins on the surface of colloidal crystal
monolayers. The Au or Ag nanograin layers coated on hydrogel colloidal
crystal monolayers can reversibly wrinkle and unwrinkle according
to changes in the water temperature. The reversible switches are directed
by surface structural changes in the colloidal crystal monolayers,
while the colloids repeat the hydrationâdehydration process.
The Au and Ag nanowrinkles are obtained upon hydration, thus enabling
the highly reproducible detection of Raman probes in water at the
nano- and picomolar levels, respectively, throughout the entire substrate
area. Additionally, the reversible switching of the nanostructures
in the plasmonic nanograin layers causes reversible dynamic changes
in the corresponding Raman signals upon varying the water temperature
Microscopic Quantum Transport Processes of OutâofâPlane Charge Flow in 2D Semiconductors Analyzed by a FowlerâNordheim Tunneling Probe
Abstract Weak interlayer couplings at 2D van der Waals (vdW) interfaces fundamentally distinguish outâofâplane charge flow, the information carrier in vdWâassembled vertical electronic and optical devices, from the inâplane band transport processes. Here, the outâofâplane charge transport behavior in 2D vdW semiconducting transition metal dichalcogenides (SCTMD) is reported. The measurements demonstrate that, in the high electric field regime, especially at low temperatures, either electron or hole carrier FowlerâNordheim (FN) tunneling becomes the dominant quantum transport process in ultrathin SCTMDs, down to monolayers. For fewâlayer SCTMDs, sequential layerâbyâlayer FN tunneling is observed to dominate the charge flow, thus serving as a material characterization probe for addressing the Fermi level positions and the layer numbers of the SCTMD films. Furthermore, it is shown that the physical confinement of the electron or hole carrier wave packets inside the subânm thick semiconducting layers reduces the vertical quantum tunneling probability, leading to an enhanced effective mass of tunneling carriers
Graphene nano-electromechanical mass sensor with high resolution at room temperature
The inherent properties of 2D materialsâlight mass, high out-of-plane flexibility, and large surface areaâpromise great potential for precise and accurate nanomechanical mass sensing, but their application is often hampered by surface contamination. Here we demonstrate a tri-layer graphene nanomechanical resonant mass sensor with sub-attogram resolution at room temperature, fabricated by a bottom-up process. We found that Joule-heating is effective in cleaning the graphene membrane surface, which results in a large improvement in the stability of the resonance frequency. We characterized the sensor by depositing Cr metal using a stencil mask and found a mass-resolution that is sufficient to weigh very small particles, like large proteins and protein complexes, with potential applications in the fields of nanobiology and medicine.Dynamics of Micro and Nano SystemsBN/Chirlmin Joo La
Focused-Laser-Enabled p-n Junctions in Graphene Field-Effect Transistors
With its electrical carrier type as well as carrier-densities highly-sensitive to light,
graphene is potentially an ideal candidate for many opto-electronic applications. Beyond the
direct light-graphene interactions, indirect effects arising from induced charge traps underneath
the photoactive graphene arising from light-substrate interactions must be better understood and
harnessed. Here, we study the local doping effect in graphene using focused-laser irradiation,
which governs the trapping and ejecting behavior of the charge trap-sites in the gate oxide. The local doping effect in graphene is manifested by a large Dirac voltage shifts and/or double Dirac
peaks from the electrical measurements and a strong photocurrent response due to the formation
of a p-n-p junction in gate-dependent scanning photocurrent microscopy. The technique of
focused-laser irradiation on a graphene device suggests a new method to control the chargecarrier
type and carrier concentration in graphene in a non-intrusive manner as well as elucidate
strong light-substrate interactions in the ultimate performance of graphene devices.139411sciescopu
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