78 research outputs found

    Electrical detection of hyperbolic phonon-polaritons in heterostructures of graphene and boron nitride

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    Light properties in the mid-infrared can be controlled at a deep subwavelength scale using hyperbolic phonons-polaritons (HPPs) of hexagonal boron nitride (h-BN). While propagating as waveguided modes HPPs can concentrate the electric field in a chosen nano-volume. Such a behavior is at the heart of many applications including subdiffraction imaging and sensing. Here, we employ HPPs in heterostructures of h-BN and graphene as new nano-optoelectronic platform by uniting the benefits of efficient hot-carrier photoconversion in graphene and the hyperbolic nature of h-BN. We demonstrate electrical detection of HPPs by guiding them towards a graphene pn-junction. We shine a laser beam onto a gap in metal gates underneath the heterostructure, where the light is converted into HPPs. The HPPs then propagate as confined rays heating up the graphene leading to a strong photocurrent. This concept is exploited to boost the external responsivity of mid-infrared photodetectors, overcoming the limitation of graphene pn-junction detectors due to their small active area and weak absorption. Moreover this type of detector exhibits tunable frequency selectivity due to the HPPs, which combined with its high responsivity paves the way for efficient high-resolution mid-infrared imaging

    Photoluminescence from an individual double-walled carbon nanotube

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    We report direct and unambiguous evidence of the existence of inner semiconducting tube (ISCT) photoluminescence (PL) from measurements performed on four individual freestanding index-identified double-walled carbon nanotubes (DWNTs). Based on thorough Rayleigh scattering, Raman scattering, and PL experiments, we are able to demonstrate that the ISCT PL is observed with a quantum yield estimated to be a few 10-6 independent of the semiconducting or metallic nature of the outer tube. This result is mainly attributed to ultrafast exciton transfer from the inner to outer tube. Furthermore, by carrying out PL excitation experiments on the (14, 1)@(15, 12) DWNT, we show that the ISCT PL can be detected through the optical excitation of the outer tube, indicating that the exciton transfer can also occur in the opposite way

    Ferredoxin containing bacteriocins suggest a novel mechanism of iron uptake in <i>Pectobacterium spp</i>

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    In order to kill competing strains of the same or closely related bacterial species, many bacteria produce potent narrow-spectrum protein antibiotics known as bacteriocins. Two sequenced strains of the phytopathogenic bacterium &lt;i&gt;Pectobacterium carotovorum&lt;/i&gt; carry genes encoding putative bacteriocins which have seemingly evolved through a recombination event to encode proteins containing an N-terminal domain with extensive similarity to a [2Fe-2S] plant ferredoxin and a C-terminal colicin M-like catalytic domain. In this work, we show that these genes encode active bacteriocins, pectocin M1 and M2, which target strains of &lt;i&gt;Pectobacterium carotovorum&lt;/i&gt; and &lt;i&gt;Pectobacterium atrosepticum&lt;/i&gt; with increased potency under iron limiting conditions. The activity of pectocin M1 and M2 can be inhibited by the addition of spinach ferredoxin, indicating that the ferredoxin domain of these proteins acts as a receptor binding domain. This effect is not observed with the mammalian ferredoxin protein adrenodoxin, indicating that &lt;i&gt;Pectobacterium spp.&lt;/i&gt; carries a specific receptor for plant ferredoxins and that these plant pathogens may acquire iron from the host through the uptake of ferredoxin. In further support of this hypothesis we show that the growth of strains of &lt;i&gt;Pectobacterium carotovorum&lt;/i&gt; and &lt;i&gt;atrosepticum&lt;/i&gt; that are not sensitive to the cytotoxic effects of pectocin M1 is enhanced in the presence of pectocin M1 and M2 under iron limiting conditions. A similar growth enhancement under iron limiting conditions is observed with spinach ferrodoxin, but not with adrenodoxin. Our data indicate that pectocin M1 and M2 have evolved to parasitise an existing iron uptake pathway by using a ferredoxin-containing receptor binding domain as a Trojan horse to gain entry into susceptible cells

    Probing the ultimate plasmon confinement limits with a Van der Waals heterostructure

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    Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary MaterialsThe ability to confine light into tiny spatial dimensions is important for applications such as microscopy, sensing and nanoscale lasers. While plasmons offer an appealing avenue to confine light, Landau damping in metals imposes a trade-off between optical field confinement and losses. We show that a graphene-insulator-metal heterostructure can overcome that trade-off, and demonstrate plasmon confinement down to the ultimate limit of the lengthscale of one atom. This is achieved by far-field excitation of plasmon modes squeezed into an atomically thin hexagonal boron nitride dielectric h-BN spacer between graphene and metal rods. A theoretical model which takes into account the non-local optical response of both graphene and metal is used to describe the results. These ultra-confined plasmonic modes, addressed with far-field light excitation, enables a route to new regimes of ultra-strong light-matter interactions.The authors thank Gerasimos Konstantatos and Valerio Pruneri for the intensive use of their respective FTIRs, very insightful discussions with Marco Polini, Thomas Christensen, Asger Mortenson and Javier Aizpurua on non-local effects and with Achim Woessner on simulation and modelling of graphene acoustic plasmonsmodes. Funding: We acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0522), support by Fundacio Cellex Barcelona, the Mineco grants Ramon y Cajal (RYC-2012-12281), Plan Nacional (FIS201347161-P and FIS2014-59639-JIN), and the Government of Catalonia trough the SGR grant (2014-SGR-1535). Furthermore, the research leading to these results has received funding from the European Union H2020 Programme under grant agreement no. 604391 Graphene Flagship, the ERC starting grant (307806, CarbonLight) and project GRASP (FP7-ICT-2013613024-GRASP).D.A.I.acknowledges the FPI gran tBES-2014-068504. N.M.R.P.andE.J.C.D acknowledge support from the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Financing UID/FIS/04650/2013. This work was supported in part by the Center for Excitonics, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award No. de-sc0001088, and the Army Research Office (grant number 16112776). J.-Y.H. and J.K. acknowledge support from the USA FOSRFATEMURI, GrantNo. FA9550-15-1-0514. Author contributions: F.H.L.K, D.A.I. and S.N. conceived the idea; E.J.C.D and N.M.R.P. developed the analytical model; S.N., C.P., J.O.,D.E. and D.A.I. fabricated the devices; S.N., R.P.and D.A.I.performed measurements; D.A.I., M.L., I.E., and S.N. performed data analysis; J.Y.H. and J.K. provided h-BN; D.A.I., S.N., E.J.C.D., N.M.R.P, I.E., D.E. and F.H.L.K wrote the manuscript; D.E. and F.K. supervised the project. Competing interests: None of the authors have competing interests.info:eu-repo/semantics/publishedVersio

    Modern Industrial Economics and Competition Policy: Open Problems and Possible Limits

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    Kant sur la musique

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    Music according to Kant in the Critique of Judgement has an ambiguous status in the hierarchy of the fine arts: it is valued highly as a language of the affects, but finds itself at the bottom of the classification due to its lack of durability and of "urbanity". The certainly intuitive musicology of Kant is based on fundamental options: music is above all a matter of sonority, and it is the tonality of sounds that accounts for their quality; pure sound is natural sound, that of the voice. Kant does not discuss the temporality essential to music nor the components of harmony, rhythm or tempo. The musicologist Christian Friedrich Michaelis made use of Kant's conception of music as early as 1795: he showed himself to be more Kantian than Kant himself. This Kantian view can be related to other Kantian philosophical standpoints, in particular in regard to Genius and culture. Finally, the "music of the Kantian text" itself has a very interesting character, and the hypothesis is put forward that the essential components of artefacts and of instruments, of bodies, of the pathemic, of rhythm and of time, all "repressed", reappear in Kant's writing itself (in the dominant isotopy and in the metaphors in his text). (Transl. by J. Dudley).La musique, selon Kant dans la Critique de la faculté déjuger, a un statut ambigu dans l'hiérarchie des beaux-arts: elle est hautement évaluée en tant que langage des affects mais elle se trouve au bas du classement par manque de durabilité et d' «urbanité». La musicologie bien intuitive de Kant repose sur des options de base: la musique est avant tout une affaire de sonorité, et c'est la tonalité des sons qui fait leur qualité; le son pur est un son naturel, celui de la voix. Ni la temporalité essentielle à la musique ni les composantes de l'harmonie, du rythme et du tempo ne sont discutées par Kant. Le musicologue Christian Friedrich Michaelis applique la conception kantienne de la musique déjà en 1795: il se révèle plus kantien que Kant lui-même. Cette conception kantienne peut être mise en relation avec d'autres positions philosophiques de Kant, notamment concernant le Génie et la culture. Finalement, la «musique du texte kantien» lui-même est d'une spécificité bien intéressante, et l'hypothèse est formulée que les composantes essentielles de l'artefact et de l'instrument, du corps, du pathémique, du rythme et du temps, toutes «refoulées», réapparaissent au niveau de l'écriture kantienne elle-même (dans l'isotopie dominante et dans les métaphores de son texte).Parret Herman. Kant sur la musique. In: Revue Philosophique de Louvain. Quatrième série, tome 95, n°1, 1997. pp. 24-43

    [Problematology Confronted With the Faculty of Judgment]

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