Hybrid Plasmonic Nanostructures Research Articles

Quantum plasmon excitations in gold-fullerene mixture films

Controllable access to the hybrid plasmonic nanostructures built of small metal nanoparticles and organic spacer offers a tempting set of electronic excitations, which proper handling promises valuable applications and bright fundamental prospect. Here, we report on remarkable plasmonic properties of the AuxC60 hybrid nanostructures formed through self-assembling the depositing mixture of metal and fullerene. Using optical absorption spectra, we demonstrate establishing of quantum plasmon (QP) excitations upon the controllable increase of spatial density and size of the Au clusters formed in the films. Detection of two plasmonic modes evidences the QP hybridization enabling by nm-scaled proximity of the neighboured Au clusters. Variation of the QP mode parameters with gradual decrease of the inter-cluster spacing ΔL to the sub-nanometre scale driven by the Au concentration in the film x allowed us to evidence the quantum tunnelling regime in the QP hybridization launching at ΔL ≈ 0.9 nm. The later result designates an important role of the C60 molecules, separating the Au clusters, in design of plasmonic and transport properties of the hybrid films. The obtained results represent the self-assembled AuxC60 nanocomposites as the promising plasmonic materials with potential for application in nanoplasmonics, nanoelectronics, and nanomedicine.

Reduced graphene oxide nanosheets modified with plasmonic gold-based hybrid nanostructures and with magnetite (Fe3O4) nanoparticles for cyclic voltammetric determination of arsenic(III).

The authors have fabricated reduced graphene oxide nanosheets (rGO) supported with Fe3O4 nanoparticles and Ag/Au hollow nanoshells. The material was placed on a glassy carbon electrode which is shown to enable highly sensitive determination of As(III) which is first preconcentrated from solution at a potential of -0.35V (versus Ag/AgCl) for 100s. The electrode, typically operated at a working potential as low as 0.06V, has a linear response in the 0.1 to 20ppb As(III) concentration range and a 0.01ppb detection limit. The electrochemical sensitivity is 52μAppb-1. The high sensitivity is assumed to be the result of various synergistic effects. The method was applied to ultratrace (0.1ppt) determination of As(III) in real water samples. Graphical abstract The hybrid displays a wide linear response in the 0.1 to 20ppb As(III) concentration range and a 0.01ppb detection limit. The high sensitivity is attributed to various synergistic effects. The method was applied to ultratrace determination of As(III) in real water samples.

Sensitive, reproducible, and stable 3D plasmonic hybrids with bilayer WS2 as nanospacer for SERS analysis.

The highly enhanced local electromagnetic field occurring through nanometer gap between the plamonic nanostructures provides the dominant contribution in surface enhancement Raman scattering (SERS) enhancement. Thence, we designed the remarkable SERS platform (AuNPs/WS2@AuNPs hybrids) by introducing bilayer WS2 film as the precise nanospacer. Bilayer WS2 film can realize the facile and tight combination with AuNPs via the thermal decomposition approach. Dense three-dimension (3D) hot spots provided by this hybrid plasmonic nanostructures are responsible for the extremely satisfying SERS performances. Using rhodamine 6G (R6G) as the probe molecules, the AuNPs/WS2@AuNPs hybrids perform the excellent sensitivity with the minimum detectable concentration as low as 10-11 M. Uniform and reproducible SERS signals illustrate that the synthesized SERS hybrids perform the splendid spot-to-spot reproducibility (RSD~5.4%) and substrate-to-substrate reproducibility (RSD~5.7%). The stability of AuNPs and the protection of WS2 film endow this hybrid plasmonic nanostructures with the brilliant anti-oxidation stability. Moreover, the enhanced electric field distribution simulated with the COMSOL software proves the remarkable SERS performance in theory. Therefore, AuNPs/WS2@AuNPs substrate not only widens the SERS research filed of WS2, but also shows vast potential as excellent SERS sensor for practical applicability.

3D Hybrid Plasmonic Nanostructures with Dense Hot Spots Using Monolayer MoS2 as Sub‐Nanometer Spacer

AbstractHere, 3D hybrid plasmonic nanostructures using monolayer MoS2 as sub‐nanometer spacer with high density hot spots are fabricated. For the 3D hybrid assemblies, the hot spots exist not only on the 0.65 nm thick MoS2 gap regions between large and small nanoparticles (NP) but also between small and small NP. The high‐density hot spots induce prominently enhanced optical absorption, huge surface enhanced Raman scattering effect, excellent reproducibility, and ultralow limit of detection. Besides, the obvious electron transfer between MoS2 and metal NP is also found in the 3D hybrid assemblies indicating the strong interactions between MoS2 and Au or Ag. Combined with the long‐term stability, the 3D hybrid assemblies should perform excellent in plasmon‐enhanced sensor and photocatalysis applications.

(Invited) Controlling Energy Flow in Plasmonic Photocatalysis through the Design of Hybrid Plasmonic Nanostructures

It has been shown that photo-excitation of plasmonic metal nanoparticles (Au, Ag, and Cu) can induce direct photo-chemical reactions on the nanoparticles. However, the widespread application of this technology in catalysis has been limited by the relatively poor chemical reactivity of noble metal surfaces. In this presentation, we present our recent work in which we conceptualized and designed hybrid nanostructures in which a plasmonic metal harvests the energy of visible light photons and selectively channels that energy into catalytically active centers on the nanostructure. To accomplish this, we developed a synthetic protocol to deposit a few monolayers of Pt onto plasmonic Ag nanocubes. This model system allows us to conclusively separate the optical and catalytic functions of the hybrid nanomaterial and analyze the interaction between the two functions. Through experimental and theoretical studies of the optical properties of these nanostructures, we show that the flow of energy is strongly biased towards absorption (i.e. excitation of energetic charge carriers) in the thin Pt shell. We demonstrate the utility of these nanostructures for photo-catalytic chemical reactions in the preferential oxidation of CO in excess H2. The reactor studies conclusively show that photo-excitation of these nanostructures results in photo-chemical reactions on the Pt surface. We describe the fundamental physical reasons for the observed directed flow of energy and discuss how these discoveries impact the field of plasmonic catalysis. U. Aslam, S. Chavez, S. Linic, Nature Nanotechnology, 2017 (10.1038/nnano.2017.131)C Boerigter, R Campana, M Morabito, S Linic, Nature communications, 7, 2016C. Boerigter, U Aslam, S Linic, ACS Nano 10 (6), 6108-6115, 2016S. Linic, U Aslam, C Boerigter, M Morabito, Nature Materials 14 (6), 567-576Andiappan, S. Linic Science, 339, 1590, 2013D. B. Ingram, S. Linic, JACS, 133, 5202, 2011Suljo Linic, Phillip Christopher and David B., Nature Materials, 10, 911, 2011.P. Christopher, H. Xin, S. Linic, Nature Chemistry, 3, 467, 2011.P. Christopher, H. Xin, M. Andiappan, S. Linic, Nature Materials, 11, 1044, 2012.

Plasmonic properties of an Ag@Ag2Mo2O7 hybrid nanostructure easily designed by solid-state photodeposition from very thin Ag2Mo2O7 nanowires

A novel Ag@Ag2Mo2O7 plasmonic hybrid nanostructure was designed by a solid state photodeposition method from very thin Ag2Mo2O7 nanowires. The nanocomposite was demonstrated as an efficient SERS-active material by using the molecular probe 2,2′-bipyridine.

Hybrid plasmonic nanostructures based on controlled integration of MoS2 flakes on metallic nanoholes.

Here, we propose an easy and robust strategy for the versatile preparation of hybrid plasmonic nanopores by means of controlled deposition of single flakes of MoS2 directly on top of metallic holes. The device is realized on silicon nitride membranes and can be further refined by TEM or FIB milling to achieve the passing of molecules or nanometric particles through a pore. Importantly, we show that the plasmonic enhancement provided by the nanohole is strongly accumulated in the 2D nanopore, thus representing an ideal system for single-molecule sensing and sequencing in a flow-through configuration. Here, we also demonstrate that the prepared 2D material can be decorated with metallic nanoparticles that can couple their resonance with the nanopore resonance to further enhance the electromagnetic field confinement at the nanoscale level. This method can be applied to any gold nanopore with a high level of reproducibility and parallelization; hence, it can pave the way to the next generation of solid-state nanopores with plasmonic functionalities. Moreover, the controlled/ordered integration of 2D materials on plasmonic nanostructures opens a pathway towards new investigation of the following: enhanced light emission; strong coupling from plasmonic hybrid structures; hot electron generation; and sensors in general based on 2D materials.

Plasmon Enhancement of Triplet Exciton Diffusion Revealed by Nanoscale Imaging of Photochemical Fluorescence Upconversion

Photon upconversion based on the process of triplet–triplet annihilation in a system of organic donor and acceptor molecules has been attracting increasing attention because it can potentially lead to improved efficiency of light energy conversion devices working under sunlight irradiation. Here we aim to gain insight into the effect of localized plasmons of metal nanostructures on the individual photophysical steps involved in the upconversion mechanism. We present an optical microscopy study of the photophysical properties of plasmonic hybrid nanostructures composed of silver nanowires combined with an upconversion system consisting of platinum octaethylporphyrin donor molecules and 9,10-diphenylanthracene acceptor molecules dispersed in poly(methyl methacrylate) thin film. Using an image-splitting technique, we simultaneously record upconversion and phosphorescence microscopy images and analyze the results to decouple the individual photophysical events. In addition to moderate intensity enhancement on...

Facile One-Pot Synthesis of Highly Stable Graphene–Ag0 Hybrid Nanostructures with Enhanced Optical Properties

We report a facile one pot approach to synthesize graphene-Ag0 hybrid plasmonic nanostructures exhibiting superior optical properties. The Ag nanoparticles (NPs) (average particle size ~25 nm) are found to be highly stabilized within the graphene matrix probably due to the favorable d-π interaction among the vacant d-orbitals of Ag0 and the π-electrons cloud of graphene moiety. Transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) have been performed to characterize the hybrid nanostructures. The synergistic effect of plasmonic Ag and graphene in the hybrid nanostructures results enhanced Raman and photoluminescence (PL) in the visible wavelength (~520 nm). Non-linear absorption (NLA) property in femtosecond regime has been studied for this hybrid nanostructure. It is also observed that the two photon absorption (TPA) coefficient of this hybrid increases from 0.0127 cm/GW to 0.0155 cm/GW when the pulse energy is increa...

Plasmonic Dual‐Enhancement and Precise Color Tuning of Gold Nanorod@SiO2 Coupled Core–Shell–Shell Upconversion Nanocrystals

The last decade has witnessed the remarkable research progress of lanthanide‐doped upconversion nanocrystals (UCNCs) at the forefront of promising applications. However, the future development and application of UCNCs are constrained greatly by their underlying shortcomings such as significant nonradiative processes, low quantum efficiency, and single emission colors. Here a hybrid plasmonic upconversion nanostructure consisting of a GNR@SiO2 coupled with NaGdF4:Yb3+,Nd3+@NaGdF4:Yb3+,Er3+@NaGdF4 core–shell–shell UCNCs is rationally designed and fabricated, which exhibits strongly enhanced UC fluorescence (up to 20 folds) and flexibly tunable UC colors. The experimental findings show that controlling the SiO2 spacer thickness enables readily manipulating the intensity ratio of the Er3+ red, green, and blue emissions, thereby allowing us to achieve the emission color tuning from pale yellow to green upon excitation at 808 nm. Electrodynamic simulations reveal that the tunable UC colors are due to the interplay of plasmon‐mediated simultaneous excitation and emission enhancements in the Er3+ green emission yet only excitation enhancement in the blue and red emissions. The results not only provide an upfront experimental design for constructing hybrid plasmonic UC nanostructures with high efficiency and color tunability, but also deepen the understanding of the interaction mechanism between the Er3+ emissions and plasmon resonances in such complex hybrid nanostructure.

Unique role of non-mercapto groups in thiol-pinning-mediated Ag growth on Au nanoparticles

Owing to the strong affinity of thiols to Au and Ag, they are often employed to modify the surfaces of nanoparticles (NPs). Recently, these strong ligand-interface interactions have been employed to control NP growth, and this technique has emerged as a unique modulation strategy for creating unconventional plasmonic hybrid nanostructures. In these systems, the roles of the non-mercapto components of the thiol molecules and their structures are still unknown. Therefore, we herein present our investigation into this phenomenon. Primary amino (–NH2) groups in thiols are found to play a key role in regulating growth kinetics, i.e., in accelerating Ag deposition on Au NPs. The–NH2 groups are thought to bring Ag ions to the particle surface by coordinating to them, and thereby assist their reduction. The effect of molecular structure is non-trivial and thus provides the possibility of selective thiol detection. Based on the dependence of kinetic modulation on the non-mercapto components and molecular structures of molecules, we demonstrate the highly sensitive and specific detection of cysteine (limit of detection: 6 nM) in a mixture of 19 natural amino acids based on Ag growth on Au nanospheres. In addition, based on this modulation effect, we reveal the entrapping of chiral thiols within the growth layer through their plasmonic circular dichroism (PCD) responses. We believe that thiol-based growth regulation has great potential for creating plasmonic nanostructures with novel functionalities.

Modulation and enhancement of optical absorption of graphene-loaded plasmonic hybrid nanostructures in visible and near-infrared regions

Modulation and enhancement of the optical absorption of graphene-loaded plasmonic hybrid nanostructures is one of the important challenges for applications of graphene in advanced nanoelectronic and nanophotonic devices. In this paper, we study systematically the modulation and enhancement of optical absorption of the metal (Au)/graphene/dielectric/metal (Au) (MGDM) structure in visible and near-infrared regions. We find that the absorption intensity of the MGDM structure is significantly enhanced and is about three times higher than the absorption intensity of the traditional metal (Au)/graphene/dielectric (MGD) structure. Next, the dependence of the absorption spectra of the MGDM structure on the parameters of it, the refractive index of the external environment, the refractive index of the dielectric layer, and the graphene Fermi energy is studied. Results show there are optimal parameters of the MGDM structure for maximum absorbance of it. The absorption spectra of the MGDM structure are very sensitive to the refractive index of the external environment and the refractive index of the dielectric layer. Active modulation of the absorption spectra of the MGDM structure is realized by changing the graphene Fermi energy, and the modulation depth can be as high as 27.5%. Finally, the multi-peaks and the broad bandwidth phenomenon of the absorption spectra can be realized by forming a multi-MGDM structure. This study provides a promising platform for the application of graphene in photodetectors, tunable optical modulators, photovoltaic cells, and other plasmonic modulation devices.

Plasmonic Materials: 3D Aluminum Hybrid Plasmonic Nanostructures with Large Areas of Dense Hot Spots and Long‐Term Stability (Adv. Funct. Mater. 10/2017)

Plasmonic Materials: 3D Aluminum Hybrid Plasmonic Nanostructures with Large Areas of Dense Hot Spots and Long‐Term Stability (Adv. Funct. Mater. 10/2017)

Tailoring the field enhancement in Fano-resonant nanoantennas for improved optical bistability

The influence of Fano resonances on the nonlinear response of hybrid plasmonic nanostructures, i.e., nanoantennas loaded with a nonlinear optical material, is theoretically investigated using the combination of a surface integral equation method and an analytical model. The results demonstrate that a suitable design of the field enhancement enables the observation of optical bistability for incident conditions that would be impossible for a bare nanoantenna. This study provides new insights into the possibilities offered by Fano resonances to control the nonlinear response of hybrid plasmonic systems.

3D Aluminum Hybrid Plasmonic Nanostructures with Large Areas of Dense Hot Spots and Long‐Term Stability

Plasmonic materials possessing dense hot spots with high field enhancement over a large area are highly desirable for ultrasensitive biochemical sensing and efficient solar energy conversion; particularly those based on low‐cost noncoinage metals with high natural abundance are of considerable practical significance. Here, 3D aluminum hybrid nanostructures (3D‐Al‐HNSs) with high density of plasmonic hot spots across a large scale are fabricated via a highly efficient and scalable nonlithographic method, i.e., millisecond‐laser‐direct‐writing in liquid nitrogen. The nanosized alumina interlayer induces intense and dual plasmonic resonance couplings between adjacent Al nanoparticles with bimodal size distribution within each of the hybrid assemblies, leading to remarkably elevated localized electric fields (or hot spots) accessible to the analytes or reactants. The 3D‐stacked nanostructure substantially raises the hot spot density, giving rise to plasmon‐enhanced light harvesting from deep UV to the visible, strong enhancement of Raman signals, and a very low limit of detection outperforming reported Al nanostructures, and even comparable to the noble metals. Combined with the long‐term stability and good reproducibility, the 3D‐Al‐HNSs hold promise as a robust low‐cost plasmonic material for applications in plasmon‐enhanced spectroscopic sensing and light harvesting.

Selective turn-on and modulation of resonant energy transfer in single plasmonic hybrid nanostructures.

Förster resonant energy transfer (FRET) is a nonradiative process by which the energy of light absorbed by a donor molecule is transferred to an acceptor molecule over a distance of several nanometers. FRET plays a crucial role in photosynthesis and nature-inspired artificial light-harvesting systems that are being explored for use in energy conversion applications. Localized plasmons of metal nanoparticles can potentially lead to a significant increase of FRET efficiency and effective donor-acceptor distance. Here, we prepare hybrid nanostructures composed of a gold nanorod and donor and acceptor molecules covalently attached to its surface, and study them on the level of a single nanoparticle by simultaneous dark-field scattering, fluorescence imaging and spectroscopy. The single-particle approach enables selective excitation of the longitudinal plasmon of the gold nanorod by polarization of the excitation light. The emission intensity of the acceptor molecules can be controllably and reversibly modulated over a wide range by the polarization angle, thus enabling a selective turn-on of the FRET process and control over the emission color of the hybrid nanostructure. Numerical simulations show that the interactions of the donor and acceptor molecules with the plasmon lead to an increase of the energy transfer efficiency by a factor of ∼65. These findings represent the concept of a novel colour switching approach and could pave the way for innovative applications in optoelectronics and nanophotonics.

Plasmonic enhancement and polarization dependence of nonlinear upconversion emissions from single gold nanorod@SiO2@CaF2:Yb3+,Er3+ hybrid core\u2013shell\u2013satellite nanostructures

Lanthanide-doped upconversion nanocrystals (UCNCs) have recently become an attractive nonlinear fluorescence material for use in bioimaging because of their tunable spectral characteristics and exceptional photostability. Plasmonic materials are often introduced into the vicinity of UCNCs to increase their emission intensity by means of enlarging the absorption cross-section and accelerating the radiative decay rate. Moreover, plasmonic nanostructures (e.g., gold nanorods, GNRs) can also influence the polarization state of the UC fluorescence—an effect that is of fundamental importance for fluorescence polarization-based imaging methods yet has not been discussed previously. To study this effect, we synthesized GNR@SiO2@CaF2:Yb3+,Er3+ hybrid core–shell–satellite nanostructures with precise control over the thickness of the SiO2 shell. We evaluated the shell thickness-dependent plasmonic enhancement of the emission intensity in ensemble and studied the plasmonic modulation of the emission polarization at the single-particle level. The hybrid plasmonic UC nanostructures with an optimal shell thickness exhibit an improved bioimaging performance compared with bare UCNCs, and we observed a polarized nature of the light at both UC emission bands, which stems from the relationship between the excitation polarization and GNR orientation. We used electrodynamic simulations combined with Förster resonance energy transfer theory to fully explain the observed effect. Our results provide extensive insights into how the coherent interaction between the emission dipoles of UCNCs and the plasmonic dipoles of the GNR determines the emission polarization state in various situations and thus open the way to the accurate control of the UC emission anisotropy for a wide range of bioimaging and biosensing applications.

3D Cross-Point Plasmonic Nanoarchitectures Containing Dense and Regular Hot Spots for Surface-Enhanced Raman Spectroscopy Analysis.

3D stacking of plasmonic nanostructures is achieved using a solvent-assisted nanotransfer printing (S-nTP) technique to provide extremely dense and regular hot spot arrays for highly sensitive surface-enhanced Raman spectroscopy (SERS) analysis. Moreover, hybrid plasmonic nanostructures obtained by printing the nanowires on a continuous metal film or graphene surface show significantly intensified SERS signals due to vertical plasmonic coupling.

Structural, Optical and Plasmonic Properties of Ag-TiO2 Hybrid Plasmonic Nanostructures with Enhanced Photocatalytic Activity

Hybrid plasmonic nanostructures consisting of Ag nanoparticles decorated TiO2 nanorods with highly enhanced photocatalytic activity were synthesized by a facile wet chemical method. The structural, optical, plasmonic and photocatalytic properties of the synthesized Ag-TiO2 hybrid nanostructures were well characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), Raman spectroscopy, photoluminescence spectroscopy (PL) and UV-visible absorption spectroscopy. The photocatalytic activities of the as-synthesized Ag-TiO2 hybrid nanostructures were evaluated by studying sun light-driven photocatalytic degradation of methylene blue (MB) and methyl orange (MO) dyes in water. The results showed that Ag-TiO2 hybrid nanostructures exhibit highly enhanced photocatalytic activity towards degradation of MB and MO dyes and the photocatalytic efficiency increased with increase in Ag nanoparticle loading. The mechanism underlying the highly enhanced photocatalytic activity of Ag-TiO2 nanohybrids is proposed. We attribute the observed enhanced photocatalytic activity of Ag-TiO2 hybrid nanostructures to the efficient separation of photogenerated charge carriers in TiO2 due to the electron scavenging action of Ag nanoparticles and the improved sun light utilization by the plasmonic nanohybrids originating from the surface plasmon resonance (SPR) absorption of Ag nanoparticles.

Site-controlled InAs quantum dot chains coupled to surface plasmons

Plasmonic hybrid nanostructures are material combinations where the plasmonic metal structure enables optical field confinement, while the other ingredients provide additional functionality, such as emission, absorption, or optical nonlinearity. In particular, epitaxial InAs quantum dots (QDs) embedded in a single-crystal GaAs matrix are highly efficient quantum emitters that can be integrated as plasmonic–semiconductor hybrids to realize various on-chip functions. In this Letter, we demonstrate QD–plasmon coupling in a hybrid structure consisting of site-controlled InAs/GaAs quantum dot chains (QDCs) in the proximity of an Ag film. The optical properties of the QDC–plasmon system are investigated using a cleaved-edge photoluminescence (PL) geometry, which allows us to probe the vertical and horizontal polarizations of the PL emission. We demonstrate plasmonic enhancement of both PL decay rate and vertical polarization of the PL emission with decreasing separation of the QDCs and the Ag film. The ability to couple site-controlled InAs QDCs with surface plasmons is a significant step toward exploitation of high-quality epitaxial quantum dots as gain or loss compensation in subwavelength plasmonic metal structures, such as waveguide networks, quantum plasmonic structures, and metamaterials.