Tunable Plasmon Resonance Research Articles

Picometer Scale Photothermal Tuning of Plasmonic Nanocavities and Interfacial Processes.

The ability to precisely tune plasmon resonances is critical for advancing nanophotonic and sensing technologies. In this work, we exploit the photothermal effect to achieve picometer-level tunability of plasmon resonances in nanorod-on-mirror nanocavities, using polyelectrolyte (PE) layers as dielectric spacers. The plasmon-induced thermal response of these soft materials allows real-time adjustment of the nanocavity, unlike stable inorganic spacers like aluminum oxide. Under continuous laser illumination, the PE spacers undergo thickness reduction and phase transitions, leading to significant shifts in plasmon resonances. These shifts are influenced by laser power and initial spacer thickness, which govern near-field enhancement and photothermal effects. It is shown that this precise tuning capability enables the exploration of various photophysical processes, including the excitation of higher-order plasmon modes, optomechanical enhancement of surface-enhanced Raman scattering signals, electron tunneling, molecular diffusion from the nanocavities, and the transition to charge transfer plasmons.

Active infrared tuning of metal–insulator-metal resonances by VO2 thin film

VO2 is a promising phase change material offering a large contrast of electric, thermal, and optical properties when transitioning from semiconductor to metallic phase. Here we show that a hybrid metamaterial obtained by proper combination of a VO2 layer and a nanodisk gold array provides a tunable plasmonic gap resonance in the infrared range. Specifically, we have designed and fabricated a metal–insulator-metal gap resonance by inserting sub-wavelength VO2 film between a flat gold layer and a gold nanodisk resonator array. The resonance of the hybrid metamaterial is centered in the useful 3–5 μm range when VO2 is in its semiconductor state. The experimental study highlights a monotonical spectral tuning of the resonance when increasing temperature up to 50 °C above the room temperature, providing a continuous resonance shift of almost 1 μm in the mid-infrared range. Wavelength range and intensity tunability can be further optimized by modifying the thicknesses of the layers and metamaterial parameters.

Tunability of plasmonic resonances in stratified hyperbolic metamaterials

We numerically and experimentally demonstrate the tunability of plasmonic resonances in the spectral range from 550 nm to 900 nm for type II hyperbolic metamaterials, as a function of their number of layers, period, and filling fraction. The type II hyperbolic metamaterial consisted of stratified periodic arrays of gold and titanium dioxide thin layers on top of a glass substrate. Through numerical and experimental characterization of the totally internally reflected spectra as a function of incidence angle, we show that the tunability of the plasmonic resonance mainly depends on the filling fraction, while the number of layers and the period of the structure only affect the contrast of attenuated reflected spectra. In addition to demonstrating the capability of tuning plasmonic resonances in simplistic stratified mediums, this work contributes to the understanding of light interaction with hyperbolic metamaterials for the improvement of optical devices for sensing applications.

Tunable Plasmon Resonance in Silver Nanodisk-on-Mirror Structures and Scattering Enhancement by Annealing.

In this study, we evaluated the surface plasmon characteristics of periodic silver nanodisk structures fabricated on a dielectric thin-film spacer layer on a Ag mirror substrate (NanoDisk on Mirror: NDoM) through finite difference time domain (FDTD) simulations and experiments involving actual sample fabrication. Through FDTD simulations, it was confirmed that the NDoM structure exhibits two sharp peaks in the visible range, and by adjusting the thickness of the spacer layer and the size of the nanodisk structure, sharp peaks can be obtained across the entire visible range. Additionally, we fabricated the NDoM structure using electron beam lithography (EBL) and experimentally confirmed that the obtained peaks matched the simulation results. Furthermore, we discovered that applying annealing at an appropriate temperature to the fabricated structure enables the adjustment of the resonance peak wavelength and enhances the scattering intensity by approximately five times. This enhancement is believed to result from changes in the shape and size of the nanodisk structure, as well as a reduction in grain boundaries in the metal crystal due to annealing. These results have the potential to contribute to technological advancements in various application fields, such as optical sensing and emission enhancement.

Electric tuning of plasmonic resonances in ultrathin gold nanoribbon arrays

Ultrathin plasmonic nanostructures offer an unparalleled opportunity for the study of light–matter interactions at the nanoscale and realization of compact nanophotonic devices. In this study, we introduce an ultrathin gold nanoribbon array and demonstrate an electric approach to actively tuning its plasmonic resonance, which leveraging the extreme light confinement capability in the ultrathin plasmonic nanostructure and a robust nanoscale electro-optical effect in indium tin oxide. Optimizing the design (to a total thickness as small as 12 nm for a 2-nm-thick gold nanoribbon array), we numerically demonstrate a spectral shift in the plasmonic resonance up to 36 nm along with an approximately 16% change in the transmission at a gate voltage below 1.7 V at the wavelength of 1.47 μm. This work presents progress towards electric tuning of plasmonic resonances in ultrathin metallic nanostructures for various applications including surface-enhanced spectroscopy, spontaneous emission enhancement, and optical modulation.

Tunable plasmonic resonance by photothermal deformation in Ag-SiO2 semi-shell nanostructures and enlargement of the controllable spectral region by UV-curable resin

Tunable plasmonic resonance by photothermal deformation in Ag-SiO2 semi-shell nanostructures and enlargement of the controllable spectral region by UV-curable resin

Synthesis of Structure-Adjustable R-Au/Pt-CdS Nanohybrids with Strong Plasmon Coupling and Improved Photothermal Conversion Performance.

Noble metal nanomaterials with a localized surface plasmon resonance effect exhibit outstanding advantages in areas such as photothermal therapy and photocatalysis. As a unique plasmonic metal nanostructure, gold nanobipyramids have been attracting much interest due to their strong specific local electric field intensity, large optical cross sections, and high refractive index sensitivity. In this study, we propose a novel three-component hetero-nanostructure composed of rough gold nanobipyramids (R-Au NBPs), Pt, and CdS. Initially, purified gold nanobipyramids are regrown to form R-Au NBPs that have a certain degree of roughness. These R-Au NBP substrates with a rough surface provide more hotspots and strengthen the intensity of localized electric fields. Subsequently, Pt and CdS nanoparticles are selectively deposited onto the surface of R-Au NBPs. Pt nanoparticles can provide more active sites. Each component of this hetero-nanostructure directly contacts others, creating multiple electron transfer channels. This novel design allows for tunable localized plasmon resonance wavelengths ranging from the visible to near-infrared regions. These factors contribute to the final superior photothermal conversion performance of the R-Au/Pt-CdS nanohybrids. Under the irradiation of near-infrared light (1064 nm), the photothermal conversion efficiency of R-Au/Pt-CdS reached 38.88%, which is 4.49, 1.5, and 1.22 times higher than that of Au NBPs, R-Au NBPs, and R-Au NBPs/Pt, respectively.

THz Scattering and Tunable Plasmonic Resonances from Graphene‐Coated Gold Nanowires

THz Scattering and Tunable Plasmonic Resonances from Graphene‐Coated Gold Nanowires

Atomic Layer Deposition for Tailoring Tamm Plasmon-Polariton with Ultra-High Accuracy

In this study, we demonstrate the potential capability to control Tamm plasmon-polaritons (TPP) by applying atomic layer deposition (ALD) as a highly precise technique for plasmonic applications. Applications in plasmonics usually require tens of nanometers or less thick layers; thus, ALD is a very suitable technique with monolayer-by-monolayer growth of angstrom resolution. Spectroscopic ellipsometry and polarized reflection intensity identified the TPP resonances in the photonic band gap (PBG) formed by periodically alternating silicon oxide and tantalum oxide layers. The sub-nanometer control of the Al2O3 layer by ALD allows precise tailoring of TPP resonances within a few nanometers of spectral shift. The employing of the ALD method for the fabrication of thin layers with sub-nanometer thickness accuracy in more complex structures proves to be a versatile platform for practical applications where tunable plasmonic resonances of high quality are required.

Optoelectronic tuning of plasmon resonances via optically modulated hot electrons.

Fast optical modulation of nanoplasmonics is fundamental for on-chip integration of all-optical devices. Although various strategies have been proposed for dynamic modulation of surface plasmons, critical issues of device compatibility and extremely low efficiency in the visible spectrum hamper the application of optoplasmonic nanochips. Here we establish an optoplasmonic system based on Au@Cu2-xS hybrid core-shell nanoparticles. The optical excitation of hot electrons and their charge transfer to the semiconductor coating (Cu2-xS) lead to lowered electron density of Au, which results in the red shift of the localized surface plasmon resonance. The hot electrons can also transport through the Cu2-xS layer to the metal substrate, which increases the conductance of the nanogap. As such, the coupled gap plasmon blue-shifts with a magnitude of up to ∼15nm, depending on the excitation power and the thickness of the coatings, which agrees with numerical simulations. All of this optoelectronic tuning process is highly reversible, controllable and fast with a modulated laser beam, which is highly compatible and sufficiently useful for on-chip integration of nanophotonic devices.

Sunlight Driven Reversible and Tunable Plasmon Resonance in 2D Amorphous Molybdenum Oxide

AbstractTwo‐dimensional molybdenum oxide (2D MoO3), as a non‐noble metal semiconductor material, is of particular significance for exploring the localized surface plasmon resonance (LSPR). However, the high excitation energy and the irreversible LSPR performance significantly restrict its practical application. To resolve these challenges, the hydrogen intercalated 2D amorphous MoO3 is investigated, and it can be observed that tunable plasmon resonances in the visible and near‐infrared regions occur. More importantly, the LSPR effect can be triggered by visible light and monochromatic light. For the first time, it is found out that the hydrogen intercalated 2D amorphous MoO3 presents a light‐modulated reversible LSPR effect, and its color can transfer from dark blue under illumination to transparent in light‐off. Additionally, solar energy can be effectively stored in bulk‐amorphous MoO3 materials. Therefore, these findings may provide a new platform to utilize sun power.

Magnetically Responsive Optical Modulation: from Anisotropic Nanostructures to Emerging Applications

AbstractMagnetically responsive optical modulation has emerged as a promising application in various fields such as smart windows, anti‐counterfeiting, and colorimetric sensors, due to its unique advantages in remote and nondestructive control, as well as precise and high‐contrast response. Compared to isotropic counterparts, anisotropic magnetic nanostructures (AMNs) take advantage of the interplay among magnetic dipoles, magnetocrystalline anisotropy, shape anisotropy, and crystal facets to control diverse dimensions of light propagation. By manipulating frequency, amplitude, polarization, and plasmonic resonance, AMNs can provide a variety of functional applications. A comprehensive overview of recent developments in optical modulation based on AMNs with a focus on their emerging applications and design strategies is presented. It starts with a brief introduction of typical AMN building blocks, highlighting various optical modulation modes, including tunable transmission, diffraction, polarization, and plasmonic resonance. The primary focus is to discuss design strategies for various applications, i.e., smart windows, anti‐counterfeiting labels, colorimetric sensors, and multifunctional‐driven devices. It concludes with the challenges and perspectives for magneto‐optical modulation based on anisotropic structures. Overall, this review provides in‐depth insight into building blocks, magnetic modulation strategies, and optical property modulation of AMNs, thereby accelerating practical applications of these structures in functional devices.

Controlling Plasmon Resonance of Gold and Silver Nanoparticle Arrays with Help of Liquid Crystal

The tunability of plasmonic resonances in gold and silver nanosphere arrays on a glass substrate, embedded in a liquid crystal matrix, was explored. The calculations involving the finite element method revealed that the optical properties of these arrays can be modulated by reorienting the liquid crystal. When the liquid crystal director was reoriented between planar and homeotropic configurations in the plane containing the incident wave polarization vector, the plasmonic resonance wavelength shifted within an approximately 100 nm range. A reduced shift of about 40 nm was observed when the reorientation occurred in the plane perpendicular to the polarization. Both metal nanosphere arrays showed notable near-field amplification. Gold achieved up to 18 times the amplification of the incident wave electric field, while silver reached 16 times but showed a remarkable 40 times amplification at the inter-band transition resonance wavelength. This research underscores the potential of using liquid crystal reorientation for controlling the plasmonic lattice resonance in metal nanosphere arrays, opening up new possibilities for adaptable plasmonic devices.

MMP simulation of coupled gold nanoparticles as nanoantennae: Efficient tuning of localized surface plasmon resonances

We study localized surface plasmon excitations on a set of two coupled two-dimensional (2D) gold nanoparticles as a nanoantenna by using the multiple multipoles (MMP) method. We investigate the plasmon spectrum as a function of the nanoparticle's size, the background index of refraction, and the separating gap between the nanoparticles in order to provide proper means to tune the underlying plasmon resonance efficiently. Accurate multiple multipoles (MMP) computations are conducted with precise control over error measures, particularly for configurations of coupled particles with varying inter-particle distances and illumination conditions. Our findings demonstrate that by selecting these parameters carefully, nanoantennae can amplify emitter radiation across a wide range of spectra from ultraviolet to near-infrared. Numerical calculations have revealed that the MMP method is accurate, easy to handle, and efficient even on a low-cost, state-of-the-art PC.

Hybrid graphene-plasmon gratings

Graphene can support surface plasmons with higher confinement, lower propagation loss, and substantially more tunable response compared to usual metal-based plasmonic structures. Interestingly, plasmons in graphene can strongly couple with nanostructures and gratings placed in its vicinity to form new hybrid systems that can provide a platform to investigate more complicated plasmonic phenomena. In this Perspective, an analysis on the excitation of highly confined graphene plasmons and their strong coupling with metallic or dielectric gratings is performed. We emphasize the flexibility in the efficient control of light–matter interaction by these new hybrid systems, benefiting from the interplay between graphene plasmons and other external resonant modes. The hybrid graphene-plasmon grating systems offer unique tunable plasmonic resonances with enhanced field distributions. They exhibit a novel route to realize practical emerging applications, including nonreciprocal devices, plasmonic switches, perfect absorbers, nonlinear structures, photodetectors, and optical sensors.

Thermosensitive Plasmonic Color Enabled by Sodium Metasurface

AbstractActive plasmonic nanostructures have attracted tremendous interest in nanophotonics and metamaterials owing to the dynamically switchable capabilities of plasmonic resonances. In this study, tunable hybrid plasmon resonances (HPR) of sodium metasurfaces through heat‐initiated structural transformation is experimentally demonstrated. A HPR is formed by coupling surface plasmon polaritons (SPP) and gap plasmon resonances (GPR), whose resonant wavelengths are highly sensitive to gaseous nanogaps. By carefully manipulating the thermo‐assisted spin‐coating process and post‐thermal treatment, tuning of the HPR is achieved because of the phase transition between the antidome and nanodome structural profiles of liquid sodium inside the patterned fused silica substrates. Furthermore, the figure of merit of the heat initiated variable structure‐spectrum is demonstrated that is highly dependent on the size of the substrate patterns, based on which temperature‐sensitive plasmonic color and “invisible ink” of sodium metasurfaces are demonstrated. These findings can lead to new solutions for manipulating low‐cost and high‐performance active plasmonic devices.

All dissolvable and transient plasmonic device enabled by nanoimprint lithography

Dissolvable and transient devices are important for environment-friendly disposal and information security. Similar to transient electronic devices, photonic devices use dissolvable metals such as magnesium and zinc to enable tunable plasmonic resonances. However, functional nanostructured substrates made of a common photoresist and a soft substrate are not dissolvable. In this study, we report the large-area, dissolvable polylactic-co-glycolic acid nanostructures formed by nanoimprint lithography and discuss the impact of the imprinting temperatures and ambient conditions on the formed nanostructures. The deposition of a thin layer of metal can yield a quasi-3D plasmonic device, and the choice of zinc metal can result in an all-dissolvable device in water over a few days. Consequently, the transmission spectra of these plasmonic devices could be tuned after placement in water. This strategy yields a truly transient nanophotonic device that can be degraded after performing its function for a specific period.

Flexible tuning of the peak wavelength and intensity of localized surface plasmon resonance by heat treatment of nanodisk structures fabricated by electron beam lithography

We demonstrate that the plasmonic properties of Au nanodisk structures fabricated by an electron beam lithography can be improved by very simple heat treatments, and that the resonance wavelength can be tuned by temperature. With a Ni adhesion layer, the resonance peak increased and blue-shifted due to improvement of metal quality without changing the sizes of nanostructures, while without the adhesion layer, the resonance wavelength can be tuned over a wider wavelength range by intentionally reducing the size of nanostructures through annealing. For Ag nanodisks with the adhesive layer, the plasmon resonance wavelength was blue-shifted due to the size reduction of nanodisks through thermal annealing. Full-color tuning of plasmonic resonance should be possible by controlling the diameter and height of Ag nanodisks under appropriate temperature conditions of heat treatment.

2D Assembly of Atomically Oriented Gold Nanodisks Leads to Tunable Plasmonic Resonance

2D Assembly of Atomically Oriented Gold Nanodisks Leads to Tunable Plasmonic Resonance

Facile Preparation of Monodisperse Silver Nanorods with Tunable Plasmon Resonances in the Near-Infrared Region: Implications for SERS-Based Sensing

The facile synthesis of silver nanorods with uniform size and tunable localized surface plasmon resonances is of great significance for plasmon resonance-related applications, such as surface-enhanced Raman spectroscopy (SERS)-based sensing, biomedical diagnostics, and photothermal therapy. However, improving reproducibility is difficult for nonexpert researchers since general synthesis methods involve multiple steps. Addressing this issue, this work develops a facile, effective synthetic strategy for monodisperse silver nanorods with tunable plasmon resonance in the near-infrared region assisted by in situ monitoring via an optical microfiber in the seed formation stage and surfactant-assisted purification of the final product. The optical microfiber monitoring ensures the formation of monodisperse bipyramid templates, guaranteeing the synthesis of the final product. The surfactant-assisted purification of the final product ensures the monodispersity of the final Ag nanorods. This study provides a flexible and alternative approach for nonexpert researchers and may present an opportunity for solving the reproducibility problem faced by nanomaterial synthesis.