Plasmonic Nanorod Arrays Research Articles

Random lasers with controlled emission modes by colloidal semiconductor quantum dots coupled to plasmonic nanorod arrays

Random lasers based on scattering for light amplification have gained extensive attention due to their simple structures. Colloidal semiconductor quantum dots (CSQDs) are excellent candidates as active media for random lasing. However, achieving CSQDs-based random lasers is challenging because the non-radiative Auger recombination produces a remarkable carrier loss. Here, we report random lasers with low thresholds based on the CSQDs coupled to the plasmonic nanorod arrays. The random lasers result from the enhancing excitation and emission rates of the CSQDs through plasmon resonance energy transfer induced by the spectral overlap between the resonant cavity modes of the plasmonic nanorod arrays and the excitons of the CSQDs, which reduces the carrier loss and establishes the optical gain in the CSQDs. Moreover, the incoherent and coherent emission modes can be controlled by varying the filling configurations (i.e., full-filling and partial-filling) of the plasmonic nanorods embedded in anodic aluminum oxide templates. Consequently, the incoherent random laser with a threshold of 19.3 μJ/mm2 and coherent random lasers with a threshold of 13.5 μJ/mm2 are performed, respectively. The proposed system provides a feasible method for low-threshold CSQDs-based random lasers with controlled emission modes, showing a promising avenue for potential applications.

Red and green plasmonic-induced random laser in two-dimensional square array onto glass substrate

Red and green lasers are preferred with a multi-layered 2D structure onto a curved glass substrate (clock glass), a charge-coupled camera device (CCD) as a seal, and a gold nanostructure with rhodamine dye. For this purpose, a layer of Kapton tape was attached to the CCD by applying pressure to get a two-dimensional structure and transfer onto the glass, then the gold nanostructure was covered inside that glass substance. To achieve random laser beams of multiple wavelengths, this two-sided curved glass substrate was coated with rhodamine dye. The sample was pumped by a nanosecond green laser. Lasers from band-edge lattice plasmons were collected into arrays of plasmonic nanorods in a homogeneous environment by a spectrophotometer. Our results revealed emission peaks for red and green wavelengths with the lowest value of the laser threshold.

One-Dimensional CdS/Carbon/Au Plasmonic Nanoarray Photoanodes via In Situ Reduction-Graphitization Approach toward Efficient Solar Hydrogen Evolution.

Photoelectrochemical (PEC) hydrogen evolution has been acknowledged as a promising "green" technique to convert solar energy into clean chemical fuel. Photoanodes play a key role in determining the performance of PEC systems, spurring numerous efforts to develop advanced materials as well as structures to improve the photoconversion efficiency. In this work, we report the rational design of a plasmonic hierarchical nanorod array, composed of oriented one-dimensional (1D) CdS nanorods decorated with a uniformly wrapped graphite-like carbon (CPDA) layer and Au nanoparticles (Au NPs), as highly efficient photoanode materials. An interfacial in situ reduction-graphitization method has been conducted to prepare the CdS/CPDA/Au nanoarchitecture, where polydopamine (PDA) coating was used as a C source and a reductant. The CdS/CPDA/Au nanoarray photoanode demonstrates superior photoconversion efficiency with a photocurrent density of 8.74 mA/cm2 and an IPCE value (480 nm) of 30.2% (at 1.23 V vs RHE), under simulated sunlight irradiation, which are 12.7 and 13.5 times higher than pristine CdS. The significant enhancement of PEC performance is mainly benefited from the increase of the entire quantum yield and efficiency due to the formation of a Schottky rectifier, localized surface plasmon resonance (LSPR)-enhanced light absorption, and promoted hot-electron injection from interlayered graphene-like carbon. More importantly, thanks to the inhibited charge carrier recombination process and transferred oxidation reaction sites, the fabricated CdS/CPDA/Au photoelectrode exhibits lengthened electron lifetimes and better photostability, illustrating its wonderful potential for future PEC application.

Two-dimensional plasmonic multilayer as an efficient tool for low power random lasing applications

Multi wavelength lasing is desired in two-dimensional flexible plexcitonic nanostructures through surface lattice plasmon amplification. For this purpose, gold nano-rods covered by the gold dispersed Rhodamine B was used as the first gain media. Then, the spacer layer by Poly-Vinyl-Pyrrolidone polymer was implemented to enhance the total internal reflection between polydimethylsiloxane substrate and this polymer. Finally, it was coated by methylene Blue dye with three different gold concentrations as the second gain media. To achieve multi-wavelength random laser, these three layers pumped by nanosecond green laser and the lasing were collected by spectrometer due to band-edge lattice plasmons in the arrays of plasmonic nano rods in a homogeneous environment. Based on the results, narrow emission peaks were emerged with a full width at half maximum less than 2 nm for every wavelength region, and threshold lasing reduced to the minimum value, along with the maximum emission intensity of multi-wavelength region.

Ultrahigh surface sensitivity of deposited gold nanorod arrays for nanoplasmonic biosensing

The biosensing performance of plasmonic nanostructures critically depends on detecting changes in the local refractive index near the sensor surface, which is referred to as surface sensitivity. For biosensing applications at solid-liquid interfaces, recent efforts to boost surface sensitivity have narrowly focused on laterally isotropic nanostructures, while there is an outstanding need to explore laterally anisotropic nanostructures such as nanorods that have distinct plasmonic properties. Herein, we report the development of plasmonic gold nanorod (AuNR) arrays that exhibit ultrahigh surface sensitivity to detect various classes of biomacromolecular interactions with superior biosensing performance. A colloidal deposition strategy was devised to fabricate AuNR-coated glass substrates, along with experimental measurements and analytical calculations to investigate how nanorod dimensions and local dielectric environment affect plasmonic properties. To validate the sensing concept, real-time biosensing experiments involving protein adsorption and peptide-induced vesicle rupture were conducted and revealed that rationally tuning nanorod dimensions could yield AuNR arrays with the highest reported degree of surface sensitivity compared to a wide range of plasmonic nanostructures tested in past studies. We discuss plasmonic factors that contribute to this ultrahigh surface sensitivity and the measurement capabilities developed in this study are broadly extendable to a wide range of biosensing applications.

Light emitting polymers in two dimensional plasmonic multi wavelength random laser

Red, Green and Blue Multi wavelength lasing is desired in two dimensional flexible plasmonic multi-layer structure based on light emitting polymers and gold nanostructure. For this purpose, gold nano-structure is covered by three different light emitting polymers with poly-vinyl-pyrolydone as spacer layers. To achieve multi-wavelengths random laser, these six layers are coated over the poly-dimethyl siloxane substrate by main surface roughness and the sample is pumped by nanosecond green laser. The lasing due to band-edge lattice plasmons in arrays of plasmonic nano rods in a homogeneous environment is collected by spectrometer. Our results show emission peaks for every wavelength region with the minimum value of threshold lasing and the maximum of emission intensity.

Enhancing Vibrational Light-Matter Coupling Strength beyond the Molecular Concentration Limit Using Plasmonic Arrays.

Vibrational strong coupling is emerging as a promising tool to modify molecular properties by making use of hybrid light–matter states known as polaritons. Fabry–Perot cavities filled with organic molecules are typically used, and the molecular concentration limits the maximum reachable coupling strength. Developing methods to increase the coupling strength beyond the molecular concentration limit are highly desirable. In this Letter, we investigate the effect of adding a gold nanorod array into a cavity containing pure organic molecules using FT-IR microscopy and numerical modeling. Incorporation of the plasmonic nanorod array that acts as artificial molecules leads to an order of magnitude increase in the total coupling strength for the cavity with matching resonant frequency filled with organic molecules. Additionally, we observe a significant narrowing of the plasmon line width inside the cavity. We anticipate that these results will be a step forward in exploring vibropolaritonic chemistry and may be used in plasmon based biosensors.

Interaction between plasmonic silver nanorod arrays and nanosecond pulsed laser

Plasmonic metamaterials have recently received increasing attention due to their favorable optical and electrical properties. The physics of the interaction between plasmonic metamaterials and lasers are rich and open opportunities for applications, such as sensing, imaging and photovoltaics. Here, we investigate the mechanism of the interaction between Ag nanorod arrays and nanosecond (ns) pulsed laser. The experimental results show that ns laser pulses significantly improve the crystallinity of the Ag nanorod arrays. Meanwhile, the laser evaporates some of the Ag into the air. This work paves the way for future high-performance plasmonic meta-devices.

Plasmonic tunable Ag-coated gold nanorod arrays as reusable SERS substrates for multiplexed antibiotics detection.

Antibiotic contaminants in aqueous media pose a serious threat to human and ecological environments. Therefore, it is necessary to develop robust strategies to detect antibiotic residues. For this purpose, a self-assembly and in situ electrochemical reduction method is utilized to tailor silver nanoparticles (AgNPs)-coated GNRs (AgNPs/GNRs) large-scale vertical arrays. These AgNPs/GNRs arrays exhibit outstanding surface-enhanced Raman scattering (SERS) activities because of abundant Raman hot-spots among the adjacent AgNPs and GNRs, but also excellent stability and reproducibility due to the close-packed arrayed nanostructure. These remarkable features validate this arrayed substrate for high-sensitivity 4-aminothiophenol analysis with a detection limit of 0.35 pM and self-cleaning via electrochemical stripping of the adsorbed analytes and AgNPs from the GNRs arrays, therefore realizing renewable SERS applications. Moreover, the distinct SERS performance of AgNPs/GNRs arrays is verified via the analysis of multiplexed antibiotics at tens of picomolar level and no apparent changes of SERS activities are observed when recyclability is explored. The result demonstrates that the proposed AgNPs/GNRs arrays provide a novel strategy for avoiding conventional, disposable SERS substrates, as well as expanding SERS applications for simultaneous sensing and stripping of environmental contaminants.

Plasmonic nanorod array for effective photothermal therapy in hyperthermia

Gold nanorod arrays inside nanopores enhance the longitudinal absorption intensities and the hyperthermia cancer cell killing under photothermal laser exposures.

Acoustofluidics-Assisted Fluorescence-SERS Bimodal Biosensors.

Acoustofluidics, the fusion of acoustics and microfluidic techniques, has recently seen increased research attention across multiple disciplines due in part to its capabilities in contactless, biocompatible, and precise manipulation of micro-/nano-objects. Herein, a bimodal signal amplification platform which relies on acoustofluidics-induced enrichment of nanoparticles is introduced. The dual-function biosensor can perform sensitive immunofluorescent or surface-enhanced Raman spectroscopy (SERS) detection. The platform functions by using surface acoustic waves to concentrate nanoparticles at either the center or perimeter of a glass capillary; the concentration location is adjusted simply by varying the input frequency. The immunofluorescence assay is achieved by concentrating fluorescent analytes and functionalized nanoparticles at the center of the microchannel, thereby improving the visibility of the fluorescent output. By modifying the inner wall of the glass capillary with plasmonic Ag nanoparticle-deposited ZnO nanorod arrays and focusing analytes toward the perimeter of the microchannel, SERS sensing using the same device setup is achieved. Nanosized exosomes are used as a proof-of-concept to validate the performance of the acoustofluidic bimodal biosensor. With its sample-enrichment functionality, bimodal sensing, short processing time, and minute sample consumption, the acoustofluidic chip holds great potential for the development of lab-on-a-chip based analysis systems in many real-world applications.

Ultrastrong coupling between nanoparticle plasmons and cavity photons at ambient conditions

Ultrastrong coupling is a distinct regime of electromagnetic interaction that enables a rich variety of intriguing physical phenomena. Traditionally, this regime has been reached by coupling intersubband transitions of multiple quantum wells, superconducting artificial atoms, or two-dimensional electron gases to microcavity resonators. However, employing these platforms requires demanding experimental conditions such as cryogenic temperatures, strong magnetic fields, and high vacuum. Here, we use a plasmonic nanorod array positioned at the antinode of a resonant optical Fabry-Pérot microcavity to reach the ultrastrong coupling (USC) regime at ambient conditions and without the use of magnetic fields. From optical measurements we extract the value of the interaction strength over the transition energy as high as g/ω ~ 0.55, deep in the USC regime, while the nanorod array occupies only ∼4% of the cavity volume. Moreover, by comparing the resonant energies of the coupled and uncoupled systems, we indirectly observe up to ∼10% modification of the ground-state energy, which is a hallmark of USC. Our results suggest that plasmon-microcavity polaritons are a promising platform for room-temperature USC realizations in the optical and infrared ranges, and may lead to the long-sought direct visualization of the vacuum energy modification.

Coupling between plasmonic nanohole array and nanorod array: the emerging of a new extraordinary optical transmission mode and epsilon-near-zero property

The compound Ag nanohole structures with an Ag nanorod in the middle of an Ag nanohole are investigated by finite-difference-time-domain calculations. The structure shows strong polarization-dependent optical properties. A new extraordinary optical transmission (EOT) mode is observed when the polarization direction is aligned with the long axis of the nanorods, and its resonance wavelength red-shifts exponentially with the nanorod length. Around this resonance wavelength, the real part of the effective permittivity also becomes zero, demonstrating the epsilon-near-zero (ENZ) property. The new EOT mode is found to be the result of the enhanced local radiation of the nanorods as well as the electromagnetic coupling to the nanoholes to produce the enhanced transmission. The tunable resonance wavelength, EOT, strong near-field enhancement, and ENZ properties make the structure ideal for many potential applications, such as ultrathin optical filter, polarizers, surface-enhanced spectroscopies, etc.

High-performance UV surface photodetector based on plasmonic Ni nanoparticles-decorated hexagonal-faceted ZnO nanorod arrays architecture

We report the photoresponse performance of plasmonic nickel (Ni) nanoparticles (NPs)-decorated ZnO NR arrays-based ultraviolet (UV) surface photodetectors. The ZnO NR arrays were grown on the Si substrate by the facile hydrothermal method, followed by Ni NP decoration on the surface by pulsed laser deposition (PLD) technique. Raman analyses reveal that the grown ZnO NR arrays are in hexagonal wurtzite structure. The field emission scanning electron microscopy (FE-SEM) shows that the grown ZnO NR arrays are vertically aligned, hexagonal faceted, and uniformly distributed on the Si substrate. The 14-fold enhancement in the UV emission upon Ni NP decoration implies the near-field coupling of surface plasmons (SPs) of Ni NPs with the excitons of ZnO NRs. The linear increase in current with the applied voltage indicates good Ohmic contacts between the ZnO NR arrays and the Ag electrodes. The transient photo-response measurements were performed for every twenty seconds (20 s) ON/OFF time and for nine cycles to study its response speed, stability, and repeatability of the photodetectors. The improved photo-response of the Ni NP-decorated ZnO NR arrays is attributed to the near-field coupling of Ni NPs with the underlying ZnO NRs. The decoration of plasmonic Ni NPs provides better optical pathway for the incident light and transfers its hot electrons to the conduction band of ZnO NR arrays gives rise the improved photoresponse.

A Plasmonic Painter's Method of Color Mixing for a Continuous Red-Green-Blue Palette.

The ability of mixing colors with remarkable results had long been exclusive to the talents of master painters. By finely combining colors in different amounts on the palette, intuitively, they obtain smooth gradients with any given color. Creating such smooth color variations through scattering by the structural patterning of a surface, as opposed to color pigments, has long remained a challenge. Here, we borrow from the painter's approach and demonstrate color mixing generated by an optical metasurface. We propose a single-layer plasmonic color pixel and a method for nanophotonic structural color mixing based on the additive red-green-blue (RGB) color model. The color pixels consist of plasmonic nanorod arrays that generate vivid primary colors and enable independent control of color brightness without affecting chromaticity by simply varying geometric in-plane parameters. By interleaving different nanorod arrays, we combine up to three primary colors on a single pixel. Based on this, two- and three-color mixing is demonstrated, enabling the continuous coverage of a plasmonic RGB color gamut and yielding a palette with a virtually unlimited number of colors. With this multiresonant color pixel, we show the photorealistic printing of color and monochrome images at the nanoscale, with ultrasmooth transitions in color and brightness. Our color-mixing approach can be applied to a broad range of scatterer designs and materials and has the potential to be used for multiwavelength color filters and dynamic photorealistic displays.

Enhancement of photocurrent in THz photoconductive antenna by a gold nanorod array

In this article, a novel THz photoconductive antenna (THz-PCA) is proposed which is composed of a conventional THz-PCA integrated with a plasmonic nanorod array to enhance surface absorption and boost the THz wave generation. It is shown that by carefully matching the plasmon resonance wavelength of the designed plasmonic structure to the incoming laser light wavelength (λ=780 nm), it is possible to obtain a nearly perfect absorption. Specifically, light absorption inside the LT-GaAs substrate at is increased to more than 96 % which is considerably improved relative to approximately 60 % of light absorption in the conventional structure. Moreover, the designed plasmonic structure provides light absorption and photo-carrier generation mostly at the surface of the GaAs substrate which is highly beneficial due to the fact that surface charge carriers have the minimum travel distance to the antenna terminals resulting in lowest recombination probabilities. The proposed structure is numerically investigated by solving Maxwell’s equations for electromagnetic response along with the charge carrier continuity and Poisson’s equations for electrical response. For the Au nanorod array with a pitch of Λ=0.8 μm and nanorod radius of r=120 nm, photocurrent shows an improvement of nearly 250 % due to the surface absorption enhancement discussed above.

Miniaturized Metalens Based Optical Tweezers on Liquid Crystal Droplets for Lab-on-a-Chip Optical Motors

Surfaces covered with layers of ultrathin nanoantenna structures—so called metasurfaces have recently been proven capable of completely controlling phase of light. Metalenses have emerged from the advance in the development of metasurfaces providing a new basis for recasting traditional lenses into thin, planar optical components capable of focusing light. The lens made of arrays of plasmonic gold nanorods were fabricated on a glass substrate by using electron beam lithography. A 1064 nm laser was used to create a high intensity circularly polarized light focal spot through metalens of focal length 800 µm, N.A. = 0.6 fabricated based on Pancharatnam-Berry phase principle. We demonstrated that optical rotation of birefringent nematic liquid crystal droplets trapped in the laser beam was possible through this metalens. The rotation of birefringent droplets convinced that the optical trap possesses strong enough angular momentum of light from radiation of each nanostructure acting like a local half waveplate and introducing an orientation-dependent phase to light. Here, we show the success in creating a miniaturized and robust metalens based optical tweezers system capable of rotating liquid crystals droplets to imitate an optical motor for future lab-on-a-chip applications.

Self-Rolled Multilayer Metasurfaces

Multilayer metasurfaces (MLMs) represent a versatile type of three-dimensional optical metamaterials that could enable ultra-thin and multi-functional photonic components. Herein we demonstrate an approach to readily fabricate MLMs exploiting a thin film self-rolling technique. As opposed to standard layer-by-layer approaches, all the metasurfaces are defined within a single nanopatterning step, significantly reducing fabrication time and costs. We realize two MLMs platforms relying on widely used nanopatterning techniques, namely focused ion-beam and electron-beam lithographies. A first example are MLMs comprised of nanohole patterns structured into metal-dielectric seed bilayers. The second platform is comprised of vertical stacks of angled plasmonic nanorod arrays separated by thin dielectric layers. Such angled MLMs exhibit a selective response to circularly polarized light, in agreement with previous works relying on layer-by-layer processes. Our approach can pave the way for the efficient prototyping of novel MLMs, such as devices with varying number of layers and configurations that can be fabricated on a single chip.

Generalized tensor FDTD method for sloped dispersive interfaces and thin sheets.

We present a modified formulation of the Finite-Difference Time-Domain (FDTD) technique that facilitates the accurate modeling of curved plasmonic interfaces. These interfaces appear in structures of interest for the design of optical metamaterials, such as arrays of plasmonic nanorods. Our approach uses the standard rectangular FDTD mesh and tensor effective permittivities for the interface cells, implicitly enforcing field boundary conditions, and is readily applicable to thin curved dispersive layers. We demonstrate the accuracy and effectiveness of our approach with the periodic analysis of a silver nanorod array and the computation of scattering parameters from a thin dispersive ring in a waveguide.

Magneto-optical effects in hyperbolic metamaterials.

Highly anisotropic metal-dielectric structures reveal unique dispersion properties providing new optical effects. Here we study experimentally linear optical and magneto-optical response of arrays of plasmonic gold nanorods and similar structures complemented by a thin nickel film. We show that both types of structures reveal distinct optical features expected for hyperbolic media and associated with the epsilon-near-zero (ENZ) and epsilon-near-pole (ENP) points. In the case of Ni-containing nanocomposites, we observe linear magneto-optical effects in transmission through the structure, increasing in the vicinity of these points. This observation reveals an important role of the local field enhancement in a hyperbolic medium associated with ENZ and ENP dispersion points in the appearance of magneto-optical activity of magnetic hyperbolic metamaterials.