Evaluating Plasmonic Transport in Current-carrying Silver Nanowires

Plasmonics is an emerging technology capable of simultaneously transporting a plasmonic signal and an electronic signal on the same information ...

CEMES, CNRS-UPR 8011

Self-assembly of porphyrin nanotapes in the presence of alkoxysilane reaction solutions produces hybrid nanofilaments consisting of an optically responsive J-aggregate core encased within an ultrathin shell of amorphous silica.

Template-directed synthesis of silica-coated J-aggregate nanotapes.

Biomolecular interactions are used to programme the assembly of multi-layer, multi-functional CNT-based conjugates.

Programmed assembly of multi-layered protein/nanoparticle-carbon nanotube conjugates.

Extended branched networks of single-nanoparticle chains have recently been self-assembled from colloidal suspensions. In particular, gold nanoparticle linear chains and complex chain networks have revealed unique signatures of plasmon modes in their extinction spectra. In this Letter, we investigate theoretically their near-field optical properties and show that a real space mapping of these modes can be achieved with a photon scanning tunneling microscope setup. A distinct subwavelength patterning of the optical near-field gives rise to well-resolved photon scanning tunneling microscope images that can be used to identify the network segments able to efficiently carry optical energy.

Theoretical near-field optical properties of branched plasmonic nanoparticle networks.

In this Letter, the phenomena and parameters governing the nanoscale dispensing of liquid through an apertured atomic force microscope probe milled by focused ion beam lithography are characterized in detail. We show that the size of deposited droplets can be reproducibly defined by controlling the aperture size on the probe and the surface energies of both tip outer wall and substrate surface. On the basis of these findings, tips with aperture diameter as small as 35 nm enabled the deposition of regular arrays of nanodroplets with diameter down to 70 nm on an alkylamine-modified surface. The fine control of droplet volumes down to a few tens of zeptoliters (10(-21)L) provides a unique tool for creating devices and probing the fundamentals of wetting at the nanometer scale.

Control of droplet size in liquid nanodispensing.

DNA-driven assembly of mesoporous silica/gold satellite nanostructures.

Diatoms, shells, bones and teeth are exquisite examples of well-defined structures, arranged from nanometre to macroscopic length scale, produced by natural biomineralization using organic templates to control the growth of the inorganic phase. Although strategies mimicking Nature have partially succeeded in synthesizing human-designed bio-inorganic composite materials, our limited understanding of fundamental mechanisms has so far kept the level of hierarchical complexity found in biological organisms out of the chemists' reach. In this letter, we report on the synthesis of unprecedented double-walled silica nanotubes with monodisperse diameters that self-organize into highly ordered centimetre-sized fibres. A unique synergistic growth mechanism is elucidated by the combination of light and electron microscopy, synchrotron X-ray diffuse scattering and Raman spectroscopy. Following this growth mechanism, macroscopic bundles of nanotubules result from the kinetic cross-coupling of two molecular processes: a dynamical supramolecular self-assembly and a stabilizing silica mineralization. The feedback actions between the template growth and the inorganic deposition are driven by a mutual electrostatic neutralization. This 'dynamical template' concept can be further generalized as a rational preparation scheme for materials with well-defined multiscale architectures and also as a fundamental mechanism for growth processes in biological systems.

Hierarchical architectures by synergy between dynamical template self-assembly and biomineralization.

Nanosheets or nanoclusters of aminopropyl-functionalized magnesium phyllosilicate (AMP) were prepared in water by exfoliation and used as structural building blocks for the preparation of DNA-based hybrid nanostructures in the form of ordered mesolamellar nanocomposites or highly elongated nanowires, respectively. The former consisted of alternating layers of single sheets of AMP interspaced with intercalated monolayers of intact double-stranded DNA molecules of relatively short length ( approximately 700 base pairs) that were accessible to small molecules such as ethidium bromide. In contrast, the nanowires comprised isolated micrometer-long molecules of lambda-DNA or plasmid DNA that were sheathed in an ultrathin organoclay layer and which were either protected from or remained accessible to endonuclease-mediated clipping depending on the extent of biomolecule wrapping. Both types of hybrid nanostructures showed a marked increase in the DNA melting (denaturation) temperature, indicating significant thermal stabilization of the confined biomolecules. Our results suggest that nanoscale building blocks derived from organically modified inorganic clays could be useful agents for enhancing the chemical, thermal, and mechanical stability of isolated molecules or ensembles of DNA. Such constructs should have increased potential as functional components in bionanotechnology and nonviral gene transfection.

Novel bioinorganic nanostructures based on mesolamellar intercalation or single-molecule wrapping of DNA using organoclay building blocks.

We present a time-resolved study of the evaporation in air of minuscule sessile droplets deposited by nanodispensing techniques. Highly sensitive nanomechanical resonators are designed to monitor in time the mass variation of evaporating liquid droplets. The precision of the measurement setup enables the study of droplets with diameters in the 1 mum range, which correspond to volumes of femtoliters and smaller, 9 orders of magnitude smaller than most of presently published data. Experimental data are compared with macroscopic models.

Evaporation of femtoliter sessile droplets monitored with nanomechanical mass sensors.

Side-gated transport in focused-ion-beam-fabricated multilayered graphene nanoribbons.

A dynamic nanostencil system based on a movable atomic force microscopy (AFM) cantilever-borne mask has been developed in ultrahigh vacuum environment. This system is conceived to offer an outstanding nanopatterning capability of nanometer precision as well as in situ AFM characterization with a large scanning range. Evaporation experiments in both static and dynamic mode have been performed successfully on this system, and some crucial technical problems of stencilling technique such as resolution and clogging are investigated. As an important application of molecular electronics, a method to fabricate and connect nanoscale structures with microelectrodes by accurately combining it with static stenciling is presented.

Development of UHV dynamic nanostencil for surface patterning.

We report on recent progress in the production and the deposition on surfaces of dielectric materials of self-assembled metallic nanoparticle systems able to organize into branched networks. We emphasize the interest of these new objects for tailoring novel near-field optical properties that could be the basis for optical energy transport in systems of extremely reduced sizes. The experimental optical spectra of such chain networks in solution can be very well reproduced by applying the coupled-dipole approximation scheme. In this paper, we apply this method to investigate the near-field optical properties of self-assembled plasmonic nanoparticle networks deposited on transparent surfaces.

Processing and near-field optical properties of self-assembled plasmonic nanoparticle networks.

Nanofabrication by molecular self-assembly involves the design of molecules and self-assembly strategies so that shape and chemical complementarities drive the units to organize spontaneously into the desired structures. The power of self-assembly makes it the ubiquitous strategy of living organized matter and provides a powerful tool to chemists. However, a challenging issue in the self-assembly of complex supramolecular structures is to understand how kinetically efficient pathways emerge from the multitude of possible transition states and routes. Unfortunately, very few systems provide an intelligible structure and formation mechanism on which new models can be developed. Here, we elucidate the molecular and supramolecular self-assembly mechanism of synthetic octapeptide into nanotubes in equilibrium conditions. Their complex hierarchical self-assembly has recently been described at the mesoscopic level, and we show now that this system uniquely exhibits three assembly stages and three intermediates: (i) a peptide dimer is evidenced by both analytical centrifugation and NMR translational diffusion experiments; (ii) an open ribbon and (iii) an unstable helical ribbon are both visualized by transmission electron microscopy and characterized by small angle X-ray scattering. Interestingly, the structural features of two stable intermediates are related to the final nanotube organization as they set, respectively, the nanotube wall thickness and the final wall curvature radius. We propose that a specific self-assembly pathway is selected by the existence of such preorganized and stable intermediates so that a unique final molecular organization is kinetically favored. Our findings suggests that the rational design of oligopeptides can encode both molecular- and macro-scale morphological characteristics of their higher-order assemblies, thus opening the way to ultrahigh resolution peptide scaffold engineering.

Elucidation of the self-assembly pathway of lanreotide octapeptide into beta-sheet nanotubes: role of two stable intermediates.

We demonstrate a universal approach to assemble gold nanoparticles (AuNPs) into ordered robust nanostructures. Colloidal AuNPs are partially coated by thiol-containing ligands and then destabilised into anisotropic superstructures. In situ polymerization of the surface attached ligands produces enveloped nanoparticle networks with retained nanoplasmonic properties and enhanced stability.

Ligand-mediated self-assembly of polymer-enveloped gold nanoparticle chains and networks.

Using dual-plane leakage radiation microscopy, we investigate plasmon propagation in individual penta-twinned crystalline silver nanowires. By measuring the wavevector content of the light emitted in the substrate, we unambiguously determine the effective index and the losses of the mode propagating in these structures. The experimental results, in particular, the unexpectedly low effective index, reveal the direct influence of the nanowire crystallinity and pentagonal structure on the observed plasmon modes. By analogy with molecular orbitals of similar symmetry, the plasmon modes are also determined numerically in good agreement with the observed values. We further investigate the effect of wire geometry (length, diameter) on the effective index and propagation loss. Our results show that, beyond dissipation concerns, the morphological and structural control obtained in crystalline colloidal plasmonic nanostructures can be exploited to finely tune their optical properties.

Imaging symmetry-selected corner plasmon modes in penta-twinned crystalline Ag nanowires.

Self-assembled plasmonic nanoparticle networks (PNN) composed of chains of 12 nm diameter crystalline gold nanoparticles exhibit a longitudinally coupled plasmon mode centered at 700 nm. We have exploited this longitudinal absorption band to efficiently confine light fields and concentrate heat sources in the close vicinity of these plasmonic chain networks. The mapping of the two phenomena on the same superstructures was performed by combining two-photon luminescence and fluorescence polarization anisotropy imaging techniques. Besides the light and heat concentration, we show experimentally that the planar spatial distribution of optical field intensity can be simply modulated by controlling the linear polarization of the incident optical excitation. On the contrary, the heat production, which is obtained here by exciting the structures within the optically transparent window of biological tissues, is evenly spread over the entire PNN. This contrasts with the usual case of localized heating in continuous nanowires, thus opening opportunities for these networks in light-induced hyperthermia applications. Furthermore, we propose a unified theoretical framework to account for both the nonlinear optical and thermal near-fields around PNN. The associated numerical simulations, based on a Green's function formalism, are in excellent agreement with the experimental images. This formalism therefore provides a versatile tool for the accurate engineering of optical and thermodynamical properties of complex plasmonic colloidal architectures.

Plasmonic nanoparticle networks for light and heat concentration.

Surface plasmon (SP) technologies exploit the spectral and spatial properties of collective electronic oscillations in noble metals placed in an incident optical field. Yet the SP local density of states (LDOS), which rule the energy transducing phenomena between the SP and the electromagnetic field, is much less exploited. Here, we use two-photon luminescence (TPL) microscopy to reveal the SP-LDOS in thin single-crystalline triangular gold nanoprisms produced by a quantitative one-pot synthesis at room temperature. Variations of the polarization and the wavelength of the incident light redistribute the TPL intensity into two-dimensional plasmonic resonator patterns that are faithfully reproduced by theoretical simulations. We demonstrate that experimental TPL maps can be considered as the convolution of the SP-LDOS with the diffraction-limited Gaussian light beam. Finally, the SP modal distribution is tuned by the spatial coupling of nanoprisms, thus allowing a new modal design of plasmonic information processing devices.

Erik Dujardin

CEMES, CNRS-UPR 8011

Evaluating Plasmonic Transport in Current-carrying Silver Nanowires