Intraband and intersubband many-body effects in the nonlinear optical response of single-wall carbon nanotubes

International audienceWe report on the nonlinear optical response of a mono-chiral sample of (6,5) single-wall carbon nanotubes by means of broad-band two-color pump-probe spectroscopy with selective excitation of the S11 excitons. By using a moment analysis of the transient spectra, we show that all the nonlinear features can be accurately accounted for by elementary deformations of the linear absorption spectrum. The photo-generation of S11 excitons induces a broadening and a blue shift of both the S11 and S22 excitonic transitions. In contrast, only the S11 transition shows a reduction of oscillator strength, ruling out population up-conversion. These nonlinear signatures result from many-body effects, including phase-space filling, wave-function renormalization and exciton collisions. This framework is sufficient to interpret the magnitude of the observed nonlinearities and stress the importance of intersubband exciton interactions. Remarkably, we show that these intersubband interactions have the same magnitude as the intraband ones and bring the major contribution to the photo-bleaching of the S22 excitonic transition upon S11 excitation through energy shift and broadening

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

Experimental evidence of a mechanical coupling between layers in an individual double-walled carbon nanotube

We perform transmission electron microscopy, electron diffraction, and Raman scattering experiments on an individual suspended double-walled carbon nanotube (DWCNT). The first two techniques allow the unambiguous determination of the DWCNT structure: (12,8)@(16,14). However, the low-frequency features in the Raman spectra cannot be connected to the derived layer diameters d by means of the 1/d power law, widely used for the diameter dependence of the radial-breathing mode of single-walled nanotubes. We discuss this disagreement in terms of mechanical coupling between the layers of the DWCNT, which results in collective vibrational modes. Theoretical predictions for the breathing-like modes of the DWCNT, originating from the radial-breathing modes of the layers, are in a very good agreement with the observed Raman spectra. Moreover, the mechanical coupling qualitatively explains the observation of Raman lines of breathing-like modes, whenever only one of the layers is in resonance with the laser energy.This work has been done in the framework of the GDR-E No 2756 “Science and Application of the Nanotubes-NANO-E”. The authors acknowledge financial support from ANR Excitubes, TRAIN2 network, and French Russian PICS No. 4818. V.N.P. acknowledges financial support from University of Montpellier 2.Peer reviewe

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

Synthesis and structural properties of polymer/carbon nanotube composite materials obtained by functionalization of nanotubes surface

International audienceComposite materials made with polymer and carbon nanotubes (CNTs) are expected to have enhanced mechanical, thermal and electrical properties, due to extraordinary properties exhibited by carbon nanotubes themselves. However due to their insolubility in common solvents, homogeneous dispersion of CNTs in polymer matrix remains challenging. One way to overcome the problem is to functionalize their surface. In our work we used functionalization not only to modify solubility of nanotubes, but also to make covalent links between nanotubes surface and polymer by chemical reaction. Two kind of polymers have been used – thermoset (epoxy) and thermoplastic (PEEK) – and functionalization has been followed using different characterization techniques such as XRD, FT Raman, TEM, XPS and NEXAFS. Then mechanical and electrical tests have been performed. A functionalization method has been successfully applied to functionalize carbon nanotubes surface, then to graft polymer chains like SPEEK, making a composite material with covalent bond between the nanotubes and the polymer. Grafting has been evidenced using spectroscopy techniques such as NEXAFS, XPS or FT Raman. Nevertheless shaping of the PEEK/SPEEK-MWNTs composite sample in order to make mechanical or electrical measurements remains extremely difficult and so far no satisfying method has been found. However mechanical and electrical properties have been enhanced when mixing epoxy resin with functionalized carbon nanotubes. In particular it has been shown that conductivity increases drastically when nanotubes weight fraction increases

Nanoscale investigation of Si nanoribbon growth on Ag(110)

International audienceWe present a nanoscale investigation by means of scanning tunneling microscopy of Si nanostructure growth on the anisotropic silver (110) surface, in the submonolayer range. Four types of Si nanostructures are studied statistically as a function of the substrate temperature in the range 300 K to 500 K: isolated single-and double nanoribbons, which differ only by a factor of two in their width, and their respective bi-dimensional counterparts in the self-assembly regime. Our observations highlight different growth regimes controlled by kinetics. Below 320 K, the Si adatoms diffuse along the easy [11 0] direction, forming essentially isolated single nanoribbons randomly distributed on the silver terraces. At higher temperatures, transverse diffusion along the [001] direction is activated and a competition between the growth of self-assembled single nanoribbons and isolated double nanoribbons is observed. Above 440 K, a transition from one-to two-dimensional double nanoribbon growth is evidenced. At 490 K, the Si deposition results in the formation of massively self-assembled double nanoribbons. Based on Arrhenius analyses, activation barriers are found to be (125 + 15) meV and (210 + 20) meV for the formation of isolated Si nanoribbons and self-assembled Si double nanoribbons, respectively. Our results allow for a better understanding of the kinetic limiting processes which determine the submonolayer morphology and illustrate the role played by the missing row reconstruction of the Ag(110) surface in the formation of extended Si nanoribbon arrays.

Physical properties of epoxy filled carbon nanotubes composites.

Composite materials made with polymer and carbon nanotubes (CNTs) are expected to have enhanced mechanical, thermal and electrical properties, due to extraordinary properties exhibited by carbon nanotubes themselves. However due to their insolubility in common solvents, homogeneous dispersion of CNTs in polymer matrix remains challenging. One way to overcome the problem is to functionalize their surface. In our work we used functionalization not only to modify solubility of nanotubes, but also to make covalent links between nanotubes surface and polymer by chemical reaction. Two kind of polymers have been used - thermoset (epoxy) and thermoplastic (PEEK) - and functionalization has been followed using different characterization techniques such as XRD, FT Raman, TEM, XPS and NEXAFS. Then mechanical and electrical tests have been performed

Graphene and related 2D materials: An overview of the Raman studies

International audienceA After a brief overview of the discovery and the Raman study of new forms of carbons (intercalated graphite, carbon fiber, fullerenes, carbon nanotubes), the invaluable contribution of late Professor M. Dresselhaus is noted and the 10 reviews and 10 contributions collected to present a picture of the present Raman investigations of graphene and related 2D materials (such as black phosphorus, MoS2) are presented. Methods for numbering the graphene layers, the effects of external perturbations (temperature, pressure, doping and magnetic field) on the phonons of graphene, characterization of the chemical and structural properties of graphene at the nanoscale level by tip-enhanced Raman spectroscopy (TERS), surface enhanced Raman spectroscopy (SERS) and hyperspectral imaging, and applications combining graphene and Raman spectroscopy are addressed

Sulfonated poly (ether ether ketone) chains grafted on carbon nanotubes surface

http://www.iwepnm.org/2008/International audienceAmong many extraordinary properties, Carbon nanotubes (CNTs) have a very high Young modulus, generally reported with a value of ~ 1 TPa, making this kind of material even stronger than diamond and carbon fiber. Moreover their very light weight makes them first choice materials for mechanical reinforcement of polymer matrices. Most of previous studies using CNTs deal with so-called physical mixing, meaning that there is no strong link between polymer and nanotube surface, resulting in a relatively poor enhancement of the composite Young's modulus. In our study, we first investigated the functionalization of multi-walled carbon nanotubes (MWNTs) surface by sulfonated poly (ether ether ketone) (SPEEK) chains using a direct attachment reaction, PEEK being known as a very promising polymer especially in aerospace field for its particularly high glass transition and melting temperature, compared with most of polymer material. MWNTs were oxidized by a nitric acid treatment to generate carboxyl groups on their surface, which then react with sulfonated groups of SPEEK using hexane diamine as an interlinking molecule. Characterization of covalent functionalization of MWNTs by SPEEK macromolecules was obtained by electron microscopy, infra-red spectroscopy and near-edge X-ray absorption fine structure spectroscopy (NEXAFS) at O K-edge. Mechanical properties of the MWNT-SPEEK composite material have to be tested to quantify the enhancement of Young's modulu