المؤلفون: Heeg, Sebastian, Clark, Nick, Vijayaraghavan, Aravind

مصطلحات موضوعية: Condensed Matter - Mesoscale and Nanoscale Physics

الوصف: We present a two-step procedure to probe hotspots of plasmon-enhanced Raman scattering with carbon nanotubes. Dielectrophoretic deposition places a small carbon nanotube bundle on top of plasmonic Au nanodimer. After 'pre-characterising' both the nanotubes and dimer structure, we subsequently use the tip of an AFM to push the bundle into the plasmonic hotspot located in the 25nm wide dimer gap, characterize its location inside the gap, and observe the onset of plasmon-enhanced Raman scattering. Evidence for the activation of the carbon nanotube's double-resonant D-mode by the near-field of the plasmonic hotspot is discussed.
Comment: accepted for publication at Nanotechnology

الوصول الحر: http://arxiv.org/abs/1809.02884Test

المؤلفون: Shao, Yizhen, Nie, Kaiwen, Iliut, Maria, Box, Finn, Luan, Dai, Shen, Yuan, Wang, Weimiao, Sampson, William, Dierking, Ingo, Vijayaraghavan, Aravind

المصدر: Shao , Y , Nie , K , Iliut , M , Box , F , Luan , D , Shen , Y , Wang , W , Sampson , W , Dierking , I & Vijayaraghavan , A 2023 , ' Tuneable electrohydrodynamics of core-shell graphene oxide vortex rings ' , Journal of Molecular Liquids . https://doi.org/10.1016/j.molliq.2023.121341Test

مصطلحات موضوعية: Graphene oxide, Vortex ring effect, Electrohydrodynamics, CTAB, Hydrogel, Aerogel

الوصف: The vortex ring (VR) effect occurs when fluid droplets impact on another fluid, leading to toroidal flow within the impacting droplet due to viscous friction, resulting in a wide variety of flow-induced morphologies. When applied to dispersions of 2-dimensional materials, such as graphene oxide (GO) in water, the VR effect can be used to generate 3-dimensional assemblies of GO flakes. Here, we have taken advantage of the surface charge on GO flakes in water, interacting with cationic aqueous surfactant systems, to generate an electrohydrodynamic VR effect. This yields GO hydrogel and aerogel microparticles with complex axially symmetric shapes, with a core-shell structure featuring a shell of aligned GO flakes. Using high frame-rate optical imaging, we have captured the real-time self-assembly of GO core-shell hydrogel microparticles shaped like spheres, donuts and jellyfish. We describe, both qualitatively and quantitatively, the electrohydrodynamics that drive the formation of such shapes. We also demonstrate how the underlying processes can be tuned by varying parameters such as GO concentration, flake size and drop velocity, and surfactant chemistry and concentration to produce a wide variety of controllable exterior and interior morphologies. Indeed, we show that the formation regimes of the different shapes are determined by dimensionless Weber and Ohnesorge numbers. Lastly, we demonstrate how these microparticles can be used for the efficient adsorption and removal of anionic contaminants in water, with tuneable adsorption capacity.

الإتاحة: https://doi.org/10.1016/j.molliq.2023.121341Test
https://research.manchester.ac.uk/en/publications/9aed01fe-9926-41eb-9405-f89460d733bcTest

المؤلفون: Verre, Andrea Francesco, Faroni, Alessandro, Iliut, Maria, Silva, Claudio, Muryn, Cristopher, Reid, Adam J, Vijayaraghavan, Aravind

مصطلحات موضوعية: Physics - Biological Physics, 92

الوصف: There is urgent clinical need to improve the clinical outcome of peripheral nerve injury. Many efforts are directed towards the fabrication of bioengineered conduits, which could deliver stem cells to the site of injury to promote and guide peripheral nerve regeneration. The aim of this study is to assess if graphene and related nanomaterials can be useful in the fabrication of such conduits. A comparison is made between GO and reduced GO substrates. Our results show that the graphene substrates are highly biocompatible, and the reduced GO substrates are more effective in ncreasing the gene expression of the biomolecules involved in the regeneration process compared to the other substrates studied.
Comment: 15 pages, 3 figures

الوصول الحر: http://arxiv.org/abs/1706.09110Test

المؤلفون: Mueller, Niclas S., Heeg, Sebastian, Alvarez, Miriam Peña, Kusch, Patryk, Wasserroth, Sören, Clark, Nick, Schedin, Fred, Parthenios, John, Papagelis, Konstantinos, Galiotis, Costas, Kalbáč, Martin, Vijayaraghavan, Aravind, Huebner, Uwe, Gorbachev, Roman, Frank, Otakar, Reich, Stephanie

مصطلحات موضوعية: Condensed Matter - Materials Science

الوصف: Raman spectroscopy is a powerful tool for characterizing the local properties of graphene. Here, we introduce a method for evaluating unknown strain configurations and simultaneous doping. It relies on separating the effects of hydrostatic strain (peak shift) and shear strain (peak splitting) on the Raman spectrum of graphene. The peak shifts from hydrostatic strain and doping are separated with a correlation analysis of the 2D and G frequencies. This enables us to obtain the local hydrostatic strain, shear strain and doping without any assumption on the strain configuration prior to the analysis. We demonstrate our approach for two model cases: Graphene under uniaxial stress on a PMMA substrate and graphene suspended on nanostructures that induce an unknown strain configuration. We measured $\omega_\mathrm{2D}/\omega_\mathrm{G} = 2.21 \pm 0.05$ for pure hydrostatic strain. Raman scattering with circular corotating polarization is ideal for analyzing strain and doping, especially for weak strain when the peak splitting by shear strain cannot be resolved.

الوصول الحر: http://arxiv.org/abs/1703.09592Test

المؤلفون: Kusch, Patryk, Heeg, Sebastian, Lehmann, Christian, Müller, Niclas S., Wasserroth, Sören, Oikonomou, Antonios, Clark, Nick, Vijayaraghavan, Aravind, Reich, Stephanie

مصطلحات موضوعية: Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics

الوصف: We report plasmon-enhanced Raman scattering in graphene coupled to a single plasmonic hotspot measured as a function of laser energy. The enhancement profiles of the G peak show strong enhancement (up to $10^5$) and narrow resonances (30 meV) that are induced by the localized surface plasmon of a gold nanodimer. We observe the evolution of defect-mode scattering in a defect-free graphene lattice in resonance with the plasmon. We propose a quantum theory of plasmon-enhanced Raman scattering, where the plasmon forms an integral part of the excitation process. Quantum interferences between scattering channels explain the experimentally observed resonance profiles, in particular, the marked difference in enhancement factors for incoming and outgoing resonance and the appearance of the defect-type modes.
Comment: Keywords: plasmon-enhanced Raman scattering, SERS, graphene, quantum interferences, microscopic theory of Raman scattering. Content: 22 pages including 5 figures + 11 pages supporting information

الوصول الحر: http://arxiv.org/abs/1503.03835Test

المؤلفون: Vassaux, Maxime, Müller, Werner, Suter, James, Vijayaraghavan, Aravind, Coveney, Peter

المساهمون: Department of Chemistry UCL, London, University College of London London (UCL), Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), University of Manchester Manchester

المصدر: ISSN: 2574-0970 ; ACS Applied Nano Materials ; https://hal.science/hal-03899666Test ; ACS Applied Nano Materials, 2022, ⟨10.1021/acsanm.2c03955⟩.

مصطلحات موضوعية: electromechanical systems, ultrasonic transducers, graphene nanocomposite, molecular dynamics, interfacial stress, pressure sensors, polymer deposition, [PHYS.MECA.MEMA]Physics [physics]/Mechanics [physics]/Mechanics of materials [physics.class-ph]

الوصف: International audience ; Advanced nanoelectromechanical systems made from polymer dielectrics deposited onto 2d-nanomaterials such as graphene are increasingly popular as pressure and touch sensors, resonant sensors, and capacitive micromachined ultrasound transducers (CMUTs). 1 However, durability and accuracy of layered nanocomposites depends on the mechanical stability of the interface between polymer and graphene layers. Here we used molecular dynamics computer simulations to investigate the interface between a sheet of graphene and a layer of parylene-C thermoplastic polymer during large numbers of high-frequency (MHz) cycles of bending relevant to the operating regime. We find that important interfacial sliding occurs almost immediately in usage conditions, resulting in more than 2% expansion of the membrane, a detrimental mechanism which requires repeated calibration to maintain CMUTs accuracy. This irreversible mechanism is caused by relaxation of residual internal stresses in the nanocomposite bi-layer, leading to the emergence of self-equilibrated tension in the polymer and compression in the graphene. It arises as a result of deposition-polymerization processing conditions. Our findings demonstrate the need for particular care to be exercised in overcoming initial expansion. The selection of appropriate materials chemistry including low electrostatic interactions will also be key to their successful application as durable and reliable devices.

العلاقة: hal-03899666; https://hal.science/hal-03899666Test; https://hal.science/hal-03899666/documentTest; https://hal.science/hal-03899666/file/_acs_an__mechanically_stable_ultra_thin_layered_graphene_nanocomposites_alleviate_residual_interfacial_stresses.pdfTest

الإتاحة: https://doi.org/10.1021/acsanm.2c03955Test
https://hal.science/hal-03899666Test
https://hal.science/hal-03899666/documentTest
https://hal.science/hal-03899666/file/_acs_an__mechanically_stable_ultra_thin_layered_graphene_nanocomposites_alleviate_residual_interfacial_stresses.pdfTest

المؤلفون: Ligorio, Cosimo, Vijayaraghavan, Aravind, Hoyland, Judith A., Saiani, Alberto

مصطلحات موضوعية: pH effect, Peptide hydrogels, 3D cell culture, Nucleus pulposus

الوصف: Extracellular pH can have a profound effect on cell metabolism, gene and protein expression. Nucleus pulposus (NP) cells, for example, under acidic conditions accelerate the production of degradative enzymes and pro-inflammatory cytokines, leading ultimately to intervertebral disc degeneration, a major cause of back pain. Self-assembling peptide hydrogels constitute a well-established class of biomaterials that could be exploited as pH-tunable platform to investigate cell behaviour under normal and non-physiological pH. In this paper we formulated acidic (pH = 4) and basic (pH = 9) hydrogels, from the same octapeptide FEFKFEFK (F8) (F = phenyalanine, E = glutamic acid, K = lysine), to test the effect of non-physiological pH on encapsulated NP cells. Similarly, graphene oxide-containing F8 hydrogels (GO-F8) were formulated as stiffer analogues. Acidic and basic hydrogels showed peculiar morphologies and rheological properties, with all systems able to buffer within 30 minutes of exposure to cell culture media. NP cells seeded in acidic F8 hydrogels showed a more catabolic phenotype compared to basic hydrogels, with increased gene expression of degradative enzymes (MMP-3, ADAMTS-4), neurotrophic factors (NGF and BDNF) and NF-κB p65 phosphorylation. Acidic GO-F8 hydrogels also induced a catabolic response, although milder than basic counterparts and with the highest gene expression of characteristic NP-matrix components, aggrecan and collagen II. In all systems, the cellular response had a peak within 3 days of encapsulation, thereafter decreasing over 7 days, suggesting a ‘transitory’ effect of hydrogel pH on encapsulated cells. This work gives an insight on the effect of pH (and pH buffering) on encapsulated NP cells and offers new designs of low and high pH peptide hydrogels for 3D cell culture studies.

العلاقة: https://nottingham-repository.worktribe.com/output/27854514Test; Acta Biomaterialia; Volume 143; Pagination 145-158; https://nottingham-repository.worktribe.com/file/27854514/1/Advance%20%20Chk%20Titlecnt%20%20%20Ne%20Acidic%20And%20Basic%20Self-assembling%20Peptide%20And%20Peptide-graphene%20Oxide%20Hydrogels%20%20Characterisation%20And%20Effect%20On%20Encapsulated%20Nucleus%20Pulposus%20Cells%20Global%20%20Chk%20Titlecnt%20%20%20ZTest

الإتاحة: https://doi.org/10.1016/j.actbio.2022.02.022Test
https://nottingham-repository.worktribe.com/file/27854514/1/Advance%20%20Chk%20Titlecnt%20%20%20Ne%20Acidic%20And%20Basic%20Self-assembling%20Peptide%20And%20Peptide-graphene%20Oxide%20Hydrogels%20%20Characterisation%20And%20Effect%20On%20Encapsulated%20Nucleus%20Pulposus%20Cells%20Global%20%20Chk%20Titlecnt%20%20%20ZTest
https://nottingham-repository.worktribe.com/output/27854514Test

المؤلفون: Jorio, Ado, Kasperczyk, Mark, Clark, Nick, Neu, Elke, Maletinsky, Patrick, Vijayaraghavan, Aravind, Novotny, Lukas

مصطلحات موضوعية: Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics

الوصف: Twisted-bilayer graphene (tBLG) exhibits van Hove singularities in the density of states that can be tuned by changing the twisting angle $\theta$. A $\theta$-defined tBLG has been produced and characterized with optical reflectivity and resonance Raman scattering. The $\theta$-engineered optical response is shown to be consistent with persistent saddle-point excitons. Separate resonances with Stokes and anti-Stokes Raman scattering components can be achieved due to the sharpness of the two-dimensional saddle-point excitons, similar to what has been previously observed for one-dimensional carbon nanotubes. The excitation power dependence for the Stokes and anti-Stokes emissions indicate that the two processes are correlated and that they share the same phonon.
Comment: 5 pages, 6 figures

الوصول الحر: http://arxiv.org/abs/1406.7344Test

المؤلفون: Lukas, Maya, Meded, Velimir, Vijayaraghavan, Aravind, Song, Li, Ajayan, Pulickel M., Fink, Karin, Wenzel, Wolfgang, Krupke, Ralph

مصطلحات موضوعية: Condensed Matter - Mesoscale and Nanoscale Physics

الوصف: Catalytic hydrogenation of graphite has recently attracted renewed attention, as a route for nano-patterning of graphene and to produce graphene nano-ribbons. These reports show that metallic nanoparticles etch surface layers of graphite, or graphene anisotropically along the crystallographic zigzag <11-20> or armchair <1010> directions. On graphene the etching direction can be influenced by external magnetic fields or the substrate. Here we report the sub-surface etching of highly oriented pyrolytic graphite (HOPG) by Ni nanoparticles, to form a network of tunnels, as seen by SEM and STM. In this new nanoporous form of graphite, the top layers bend inward on top of the tunnels, while their local density of states remains fundamentally unchanged. Engineered nanoporous tunnel networks in graphite allow further chemical modification and may find applications in storage or sensing.

الوصول الحر: http://arxiv.org/abs/1207.1617Test

المؤلفون: Vijayaraghavan, Aravind, Sciascia, Calogero, Dehm, Simone, Lombardo, Antonio, Bonetti, Alessandro, Ferrari, Andrea C., Krupke, Ralph

المصدر: ACS Nano, 2009, 3(7), 1729 - 1734.

مصطلحات موضوعية: Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science

الوصف: We establish the use of dielectrophoresis for the directed parallel assembly of individual flakes and nanoribbons of few-layer graphene into electronic devices. This is a bottom-up approach where source and drain electrodes are prefabricated and the flakes are deposited from a solution using an alternating electric field applied between the electrodes. These devices are characterized by scanning electron microscopy, atomic force microscopy, Raman spectroscopy and electron transport measurements. They are shown to be electrically active and their current carrying capacity and subsequent failure mechanism is revealed. Akin to carbon nanotubes, we show that the dielectrophoretic deposition is self-limiting to one flake per device and is scalable to ultra-large-scale integration densities, thereby enabling the rapid screening of a large number of devices.
Comment: ACS Nano, (2009) In Press

الوصول الحر: http://arxiv.org/abs/0906.1013Test