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

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

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

Lectin-like bacteriocins from pseudomonas spp. utilise D-rhamnose containing lipopolysaccharide as a cellular receptor

Lectin-like bacteriocins consist of tandem monocot mannose-binding domains and display a genus-specific killing activity. Here we show that pyocin L1, a novel member of this family from Pseudomonas aeruginosa, targets susceptible strains of this species through recognition of the common polysaccharide antigen (CPA) of P. aeruginosa lipopolysaccharide that is predominantly a homopolymer of d-rhamnose. Structural and biophysical analyses show that recognition of CPA occurs through the C-terminal carbohydrate-binding domain of pyocin L1 and that this interaction is a prerequisite for bactericidal activity. Further to this, we show that the previously described lectin-like bacteriocin putidacin L1 shows a similar carbohydrate-binding specificity, indicating that oligosaccharides containing d-rhamnose and not d-mannose, as was previously thought, are the physiologically relevant ligands for this group of bacteriocins. The widespread inclusion of d-rhamnose in the lipopolysaccharide of members of the genus Pseudomonas explains the unusual genus-specific activity of the lectin-like bacteriocins

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

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