Plasmonic Nanoparticle Arrays Research Articles

Incorporation strategy for organic dyes into gold nanoparticle supercrystals.

Ordered arrays of plasmonic nanoparticles, supercrystals can lead to the formation of plasmon-polaritons. Coupling light emitters with plasmon polaritons might allow the formation of exciton-plasmon polaritons with properties tuneable by the supercrystal design. To construct such optically active materials, the inclusion of emitters is imperative. The addition of organic dyes without affecting the periodic order of the nanocrystals is difficult, as post-formation protocols might dissolve the supercrystals, and pre-formation addition might affect the self-assembly process. Here, we present an exemplary strategy to functionalize gold nanoparticles prior to self-assembly with a cyanine isothiocyanate dye that was obtained by a straightforward reaction of the amine functionalized dye with carbon disulfide. In the second step, the nanoparticles are functionalized with a thiol-terminated polystyrene, which stabilizes the nanoparticles and governs the self-assembly process. The dye can be integrated in a quantitative fashion, and the nanoparticles can be self-assembled into supercrystals. The strategy should be applicable in general for amine functionalized dyes, which is a common modification.

Interplay between gain and loss in arrays of nonlinear plasmonic nanoparticles: toward parametric downconversion and amplification.

With the help of a theoretical model and finite-difference time-domain (FDTD) simulations based on the hydrodynamic-Maxwell model, we examine the effect of difference-frequency generation (DFG) in an array of L-shaped metal nanoparticles (MNPs) characterized by intrinsic plasmonic nonlinearity. The outcomes of the calculations reveal the spectral interplay between gain and loss in the vicinity of the fundamental frequency of the localized surface plasmon resonances. Subsequently, we identify different array thicknesses and pumping regimes facilitating parametric amplification and spontaneous parametric downconversion. Our results suggest that the parametric amplification regime becomes feasible on a scale of hundreds of nanometers and spontaneous parametric downconversion on the scale of tens of nanometers, opening up new exciting opportunities for developing building blocks of photonic metasurfaces.

Topological states in breathing honeycomb plasmonic nanoparticle arrays with in-plane polarized modes

Topological states in breathing honeycomb plasmonic nanoparticle arrays with in-plane polarized modes

Deformation induced evolution of plasmonic responses in polymer grafted nanoparticle thin films.

Multi-functional nanoparticle thin films are being used in various applications ranging from biosensing to photo-voltaics. In this study, we integrate two different numerical approaches to understand the interplay between the mechanical deformation and optical response of polymer grafted plasmonic nanoparticle (PGPN) arrays. Using numerical simulations we examine the deformation of thin films formed by end-functionalised polymer grafted nanoparticles subject to uniaxial elongation. The induced deformation causes the particles in the thin film network to rearrange their positions by two different mechanisms viz. sliding and packing. In sliding, the particles move in the direction of induced deformation. On the other hand, in packing, the particles move in a direction normal to that of the induced deformation. By employing a Green's tensor formulation in polarizable backgrounds for evaluating the optical response of the nanoparticle network, we calculate the evolution of the plasmonic response of the structure as a function of strain. The results indicate that the evolution of plasmonic response closely follows the deformation. In particular, we show that the onset of relative electric field enhancement of the optical response occurs when there is significant rearrangement of the constituent PGPNs in the array. Furthermore, we show that depending on the local packing/sliding and the polarization of the incident light there can be both enhancement and suppression of the SERS response.

Asymmetric Transmission in Diffractive Chiral Metasurfaces Consisting of Nanoantennas

We have studied the asymmetric transmission in diffractive chiral metasurfaces consisting of nanoantennas. The study was made of lattice plasmon modes on the phenomenon of asymmetric transmission in chiral two dimensional arrays of plasmonic nanoparticles. It was demonstrated that asymmetric transmission resulted from contribution of higher order diffracted waves. It was shown that the isolated nanostructures has a fourfold rotational symmetry, the diffractive metasurfaces exhibited asymmetric transmission for normal incidence light within spectral range for which lattice plasmon modes were supported. It was found that lattice plasmon modes played role in enabling symmetric transmission in diffractive chiral metasurfaces. The symmetric transmission mechanism is due to different lattice plasmon mode excitation efficiencies of left circularly polarized and right circularly polarized and right circularly polarized light. The excitation efficiencies are controlled by tailoring the nano particles in plan distribution of scattered light for circularly polarized excitation and its alignment with the inplane diffraction orders of the metasurfaces. The phenomenon for a metasurface composed of an array of a chiral nanoparticles consisting of four nanoantennas. It was shown that the Rayleigh anomaly condition where the asymmetric transmission effect was strongest and metasurfaces supported lattice plasmon modes. It was found that the difference in the inplane scattered intensity varied as a function of the inplane angle around the nanostructure, rotating the nanostructure in the plane of the metasurface. The obtained results found in good agreement with previously obtained results.

Superlattice Surface Lattice Resonances in Plasmonic Nanoparticle Arrays with Patterned Dielectrics.

This paper describes how two-dimensional plasmonic nanoparticle lattices covered with microscale arrays of dielectric patches can show superlattice surface lattice resonances (SLRs). These optical resonances originate from multiscale diffractive coupling that can be controlled by the periodicity and size of the patterned dielectrics. The features in the optical dispersion diagram are similar to those of index-matched microscale arrays of metal nanoparticle lattices, having the same lateral dimensions as the dielectric patches. With an increase in nanoparticle size, superlattice SLRs can also support quadrupole excitations with distinct dispersion diagrams. The tunable optical band structure enabled by patterned dielectrics on plasmonic nanoparticle arrays offers prospects for enhanced nonlinear optics, nanoscale lasing, and engineered parity-time symmetries.

SERS as a Probe of Surface Chemistry Enabled by Surface-Accessible Plasmonic Nanomaterials.

ConspectusWhen the size of materials is reduced, their volume decreases much faster than their surface area, which in the most extreme case leads to 2D nanomaterials which are "all surface". Since atoms at the surface have free energies, electronic states, and mobility which are very different from bulk atoms, nanomaterials that have large surface-to-volume ratios can display remarkable new properties compared to their bulk counterparts. More generally, the surface is where nanomaterials interact with their environment, which in turn places surface chemistry at the heart of catalysis, nanotechnology, and sensing applications. Understanding and utilizing nanosurfaces are not possible without appropriate spectroscopic and microscopic characterization techniques. An emerging technique in this area is surface-enhanced Raman spectroscopy (SERS), which utilizes the interaction between plasmonic nanoparticles and light to enhance the Raman signals of molecules near the nanoparticles' surfaces. SERS has the great advantage that it can provide detailed in situ information on surface orientation and binding between molecules and the nanosurface. A long-standing dilemma that has limited the applications of SERS in surface chemistry studies is the choice between surface-accessibility and plasmonic activity. More specifically, the synthesis of metal nanomaterials with strong plasmonic and SERS-enhancing properties typically involves the use of strongly adsorbing modifier molecules, but these modifiers also passivate the surface of the product material, which prevents the general application of SERS in the analysis of weaker molecule-metal interactions.In this Account, we discuss our efforts in the development of modifier-free synthetic approaches to synthesize surface-accessible, plasmonic nanomaterials for SERS. We start by discussing the definition of "modifiers" and "surface-accessibility", especially in the context of surface chemistry studies in SERS. As a general rule of thumb, the chemical ligands on surface-accessible nanomaterials should be easily displaceable by a wide range of target molecules relevant to potential applications. We then introduce modifier-free approaches for the bottom-up synthesis of colloidal nanoparticles, which are the basic building blocks for nanotechnology. Following this, we introduce modifier-free interfacial self-assembly approaches developed by our group that allow the creation of multidimensional plasmonic nanoparticle arrays from different types of nanoparticle-building blocks. These multidimensional arrays can be further combined with different types of functional materials to form surface-accessible multifunctional hybrid plasmonic materials. Finally, we demonstrate applications for surface-accessible nanomaterials as plasmonic substrates for SERS studies of surface chemistry. Importantly, our studies revealed that the removal of modifiers led to not only significantly enhanced properties but also the observation of new surface chemistry phenomena that had been previously overlooked or misunderstood in the literature. Realizing the current limitations of modifier-based approaches provides new perspectives in manipulating molecule-metal interactions in nanotechnology and can have significant implications in the design and synthesis of the next generation of nanomaterials.

Enhanced Two-Dimensional Exciton Propagation via Strong Light–Matter Coupling with Surface Lattice Plasmons

Exciton–polaritons─hybrid exciton–photon quasi-particles─have enabled exciting long-range coherent transport by taking advantage of the properties of their photonic component. However, most experimental demonstrations of strong coupling have been based on semiconductor Fabry–Pérot microcavities. Here, we report an open and versatile exciton–polariton platform by integrating two-dimensional lead halide perovskites with plasmonic nanoparticle arrays, which support hybridization between excitons and surface lattice resonances in the strong coupling regime. Benefitting from the open architecture, we directly visualized polariton-enhanced exciton transport via angle-dependent transient absorption microscopy measurements. The observed transport enhancement extends into the picosecond timescale, leading to more than 1 order of magnitude improvement of exciton migration, from ∼10 nm to 100s of nanometers. We proposed a polariton-mediated exciton transport model and obtained an average polariton velocity of ∼1 × 106 m/s for states with an ∼40% photonic fraction. These results demonstrate plasmonic particle arrays as a versatile and adaptable cavity to enhance exciton transport.

Effects of "defective" plasmonic metal nanoparticle arrays on the opto-electronic performance of thin-film solar cells: computational study.

This computational study investigates the effects of common defects that occur while fabricating arrays of plasmonic metal nanoparticles (NPs) on the absorbing layer of the solar cells for enhancing their opto-electronic performance. Several "defects" in an array of plasmonic NP arrays on solar cells were studied. The results demonstrated no major changes in the performance of solar cells in the presence of "defective" arrays when compared to a "perfect" array with defect-free NPs. The results indicate that relatively inexpensive techniques may be used to fabricate "defective" plasmonic NP arrays on solar cells and still obtain a significant enhancement in opto-electronic performance.

Basics of the LSPR Sensors for Soft Matter at Interfaces

An important class of localized surface plasmon resonance (LSPR)–based sensors implies the fabrication of an array of plasmonic metal nanoparticles on the support in combination with a thin protective dielectric layer. If needed, this layer can be covered, e.g., by a suitable thin biological layer, e.g., a lipid bilayer with receptors. The attachment of analyte (e.g., protein molecules or vesicles) to such interfaces is tracked via its indirect optical effect on the LSPR-related peak extinction wavelength. Such sensors have been commercialized and are now used to study biological soft matter. The length scale of the local field able in probing analyte around plasmonic nanoparticles is in this case on the order of 20 nm. Conceptually, these LSPR sensors are similar to the SPR sensors which were developed much earlier. Herein, the similarities and differences in the formalisms used to interpret SPR and LSPR measurements are discussed in detail. In particular, the exponential and power-law attenuation functions employed in these formalisms to describe the drop of the field are compared from various perspectives. The applicability of the power-law attenuation function in the context of LSPR is illustrated by using a generic model describing spherically shaped plasmonic metal nanoparticles. This model is also employed to illustrate the sensitivity of LSPR sensors with respect to various quantities. Among more specific results, the available expressions for the signal reduction factor for analyte nanoparticles of various shapes are collected and complemented by new ones. In addition, the equation describing the LSPR signal related to analyte attachment to a rough surface is presented.

Enhanced visible light photocatalytic hydrogen evolution of Ta2O5 nanohoneycomb induced by plasmonic Au nanoparticle array

Polystyrene nanospheres in the sizes of 400, 200, and 100 nm were employed as a template to form hexagonal close-packed Ta2O5 nanohoneycombs (nHCs) by means of solution-based nanosphere lithography. Moreover, Au nanoparticle arrays with various diameters were further deposited on the Ta2O5nHCs to achieve surface plasmon resonance (SPR) and enhance visible-light photocatalytic hydrogen evolution. Finite difference time domain (FDTD) simulation was performed and the result showed that the 100-nm Ta2O5nHCs coupled with smaller Au nanoparticles exhibited more effective localized SPR effect to enclose the Ta2O5 photocatalyst. The photocatalytic hydrogen evolution results were consistent with those of FDTD simulation and photoelectrochemical tests. A concept of effective yield ratio is proposed to explain how the Au nanoparticle size and spacing affect the hydrogen evolution efficiency.

Soft Plasmene Helical Nanostructures

AbstractPlasmene is recently defined as 2D arrays of plasmonic nanoparticles, which could be fabricated by the bottom‐up self‐assembly approach and demonstrated a wide range of applications in sensing, energy harvesting, nanophotonics and encryption. Herein, this work further demonstrates a 3D helical plasmonic nanostructures that can be fabricated from 2D plasmene nanosheet. Inspired by chocolate curls‐making process, a micro‐spatula‐based strategy is developed to selectively scrape substrate‐supported plasmene to free space, which spontaneously folds the plasmene nanosheet into various complex helical nanostructures with controlled dimensions. 3D nanospirals can also be obtained by focus ion beam (FIB)‐based lithography on free‐standing plasmene. Helical plasmene structures are robust, exhibiting elastic mechanical properties and chiral optical response. This methodology represents a versatile fabrication route combining both bottom‐up and top‐down approaches to create soft plasmonic helical structures for potential applications in next‐generation flexible nanophotonic devices.

Exploiting Oriented Field Projectors to Open Topological Gaps in Plasmonic Nanoparticle Arrays.

In the last years there have been multiple proposals in nanophotonics to mimic topological condensed matter systems. However, nanoparticles have degrees of freedom that atoms lack of, like dimensions or shape, which can be exploited to explore topology beyond electronics. Elongated nanoparticles can act like projectors of the electric field in the direction of the major axis. Then, by orienting them in an array the coupling between them can be tuned, allowing to open a gap in an otherwise gapless system. As a proof of the potential of the use of orientation of nanoparticles for topology, we study 1D chains of prolate spheroidal silver nanoparticles. We show that in these arrays spatial modulation of the polarization allows to open gaps, engineer hidden crystalline symmetries and to switch on/off or left/right edge states depending on the polarization of the incident electric field. This opens a path toward exploiting features of nanoparticles for topology to go beyond analogues of condensed matter systems.

Impact of thermal annealing and laser treatment on the morphology and optical responses of mono- and bi-metallic plasmonic honeycomb lattice.

Plasmonic nanoparticle arrays with a specific lattice arrangement can support surface lattice resonances (SLRs). SLR exhibits a sharp spectral peak and finds many applications including optical sensing and plasmonic lasers. To optimize SLR for application, a robust method that allows the mass production of plasmonic nanoparticle arrays with refined particle morphology and well-defined lattice arrangement is required. In this work, we combine nanosphere lithography (NSL) with thermal annealing or nanosecond-pulsed laser treatment to refine plasmonic nanoparticles in a honeycomb lattice. We comparatively study the effects of the two treatment methods on the particle morphology and lattice arrangement of mono (Ag and Pd) and bi-metallic (Ag-Pd) nanoparticle lattices. In general, thermal annealing preserves the lattice arrangement but fairly changes the particle roundness, while laser treatment produces particles with varying morphologies and spatial distribution. We also theoretically and experimentally investigate the optical responses of Ag nanoparticle lattices produced by different treatment methods. The observed difference in spectra can be attributed to the varying particle morphology, which shifts the localized surface plasmon resonance differently, resulting in a significant change in SLR. These findings provide valuable insights for optimizing plasmonic nanoparticle arrays for various applications.

Fabrication of Centimeter-Scale Plasmonic Nanoparticle Arrays with Ultranarrow Surface Lattice Resonances.

Plasmonic surface lattice resonances (SLRs) supported by metallic nanoparticle (NP) arrays show diverse applications including nanolasers, sensors, photocatalysis, and nonlinear optics. However, to rationally fabricate high-quality plasmonic NP arrays with ultranarrow SLR line widths over large areas remains challenging. This article describes a general approach for the efficient fabrication of centimeter-scale inorganic NP arrays with precisely controlled NP size, composition, position, and lattice geometry. This method combines the processes of solvent-assisted soft lithography and in situ site-specific NP growth to reproducibly create many replicates of NP arrays without utilizing cleanroom and specialized equipment. For demonstration, we show that Au NP arrays exhibit ultranarrow SLRs with a line width of 4 nm and a quality factor of 218 toward the theoretical limit.

Plasmonic Array at the Liquid-Liquid Interface: A Dual-Mode Optical Sensing Platform for Multianalytes.

Analyte-triggered nanoparticle (NP) assemblies in bulk colloidal suspension have been extensively utilized in various optical sensors. Nevertheless, the assembling process is still limited by the slow diffusion dynamics of NPs and the low concentration of analytes in trace detections, which hinders further improvement of the sensitivity and repeatability of the sensors. In this work, by functionalizing the gold NPs with specific ligands, we constructed a dual-mode optical sensing platform for multianalytes based on the plasmonic NP array at the liquid-liquid interface. Through emulsification, the NP diffusion kinetics are boosted for several orders, and the NPs are condensed from the bulk aqueous phase to the liquid-liquid interface as a plasmonic array. The as-formed metasurface generates major reflectance and surface-enhanced Raman scattering changes in response to analytes, providing two optical sensing modes. As prototypes, cysteine and glucose are selected as the target molecules, achieving the limit of detection as 193 ± 2 and 297 ± 12 pM, respectively.

Perfect absorption and phase singularities induced by surface lattice resonances for plasmonic nanoparticle array on a metallic film.

The formation of pairs of perfect absorption associated with phase singularities in the parameter space using the hybridized structure constructed with a metallic nanoparticle array and a metallic film is promising to enhance light-mater interactions. However, the localized plasmon resonances of the array possess strong radiative losses, which is an obstacle to improve the performances for many applications. On the contrary with the subwavelength array hybridized structure, this study shows that by enlarging the lattice spacing, the oscillator strength of the nanoparticles can be enhanced with the formation of surface lattice resonance, thereby leading to similar but much narrower pairs of perfect absorption due to the interactions with the Fabry-Pérot cavity modes. Furthermore, when the surface plasmon polariton mode shift to the same spectral range associated with the enlarged lattice spacing, the coupling and mode hybridization with the surface lattice resonance result in an anticrossing in the spectra. Although the resonance coupling does not enter the strong coupling regime, the quality factors (∼ 134) and near-field enhancements (∼ 44) are strongly enhanced for the hybridized resonance modes due to the effectively suppressed radiative losses compared with that of the localized plasmon resonances, which make the hybridized structure useful for the design of functional nanophotonic device such as biosensing, multi-model nanolasing, and high-quality imaging.

Comparative study of a perovskite solar cell using different aperiodic arrangements of plasmonic nanoparticles

In this research work, the optimized Fibonacci, Thue-Mors, and Gaussian-based aperiodic arrays of plasmonic nanoparticles were studied to improve the performance of thin perovskite solar cells. Here, the effect of different types of deterministic aperiodic plasmonic arrays on the optical properties of perovskite absorbers is analyzed. At first, different polytypes of perovskite material consistent (C6H5C2H4NH3)2PbI4, CH3NH3FeI2Br, CH3NH3FeI3, CH3NH3PbBr3, CH3NH3PbCl3, and CH3NH3PbI3 as the active layer of a solar cell were analyzed. The results show that CH3NH3PbI3 has higher absorption spectra than other cases. Then, different types of metals (Ag, Au, Cu, Al) as the form of periodic arrays are simulated and Ag was selected to form our arrays according to the Fibonacci, Thue-Mors, Gaussian, and periodic array arrangement. To form such arrays, 36 nanoparticles per cell were used and the effect of network constant (closest distance between the nanoparticles) was evaluated. Our results confirm that all cases of the Fibonacci, Thue-Mors, and Gaussian arrangement improve the photocurrent, while the photocurrent of the Thue-Mors arrangement is higher than in other cases. These findings reveal that it is possible to improve the performance of perovskite solar cells using a realistic plasmonic array.

Surface lattice resonance in three-dimensional plasmonic arrays fabricated via self-assembly of silica-coated gold nanoparticles

HypothesisThree-dimensional plasmonic nanoparticle arrays in which the nanoparticles are assembled with a certain distance apart are expected to exhibit unique optical properties attributed to surface lattice resonances because of the interactions between the nanoparticle layers. ExperimentsMulti-layered gold nanoparticle arrays were created to experimentally prove surface lattice resonances from three-dimensional arrays. Silica-coated gold nanoparticles were employed as building blocks for the array because the distance between the nanoparticles can be tuned by adjusting the thickness of the silica coating. Employing highly monodisperse building blocks enabled to fabricate both single-layered and multi-layered plasmonic arrays via a confined convective assembly method. FindingsMulti-layering of monodisperse building blocks brought about some additional peaks corresponded to Bragg diffraction of gold nanoparticle periodic array and the interactions between layers in a hexagonal close-packed structure of the nanoparticles, respectively. Most importantly, the multi-layered arrays exhibited a distinctive extinction peak at the same wavelength as that observed from the single-layered array, proving the realization of surface lattice resonances from the three-dimensional plasmonic array.

Second harmonic generation under doubly resonant lattice plasmon excitation.

Second harmonic generation is enhanced at the surface lattice resonance in plasmonic nanoparticle arrays. We carried out a parametric investigation on two-dimensional lattices composed of gold nanobars where the centrosymmetry is broken at oblique incidence. We study the influence of the periodicity, the incidence angle and the direction of the linear input polarization on the second harmonic generation. Excitation of the surface lattice resonance either at the fundamental or second harmonic wavelength, achieved by varying the incidence angle, enhance the conversion efficiency. As a special case, we demonstrate that both the wavelengths can be simultaneously in resonance for a specific period of the lattice. In this double resonant case, maximum second harmonic power is achieved.