Plasmonic Crystals Research Articles

Two-dimensional plasmonic biosensing platform: Cellular activity detection under laser stimulation

Combining biosensors with nanoscience provides great advantages such as being label-free and real time, highly sensitive, and small in size, as well as providing a low limit of detection and integration to other systems. That is why plasmonics finds various applications in drug detection, food safety, agriculture, photothermal therapy, etc. In this paper, we have fabricated a two-dimensional plasmonic grating biosensor using a soft lithography technique, which has eliminated some disadvantages of conventional plasmonic structures like expensive fabrication cost, inflexibility, and lack of mass production. On the other hand, we benefited from infrared neural stimulation for regulating membrane depolarization, which was based on photothermal mechanism and provided a contact-free and high spatial/temporal resolution. Eventually, the membrane depolarization of two different cell types of Hep G2 and mesenchymal stem cells cultured on two-dimensional plasmonic structure has been investigated under infrared neural stimulation. After preparing the soft plasmonic crystal, its reflection spectra and respective ellipsometry parameters were analyzed before and after cell culture with/without stimulation (near-infrared immune region ∼1450 nm). By comparing the obtained ellipsometry results for HEP G2 and mesenchymal stem cells, it is observed that the behavior of two cell types with respect to IR stimulation was the same as well as providing us the possibility of distinguishing the level of membrane depolarization under various stimulating frequencies. The strength of this integrated system for membrane depolarization detection has been shown experimentally, which can open new avenues toward neuroplasmonic application in the future.

Controlling Fano resonances using the geometrical phase of light in spatially tailored waveguided plasmonic crystals

Fano resonance exhibiting an asymmetric spectral line shape is a universal phenomenon observed in diverse physical systems. Here we experimentally establish a direct link between the spectral asymmetry parameter and a physically realizable phase factor of interference between a continuum and a discrete mode that leads to Fano resonance. Using a specially designed metamaterial, namely waveguided plasmonic crystal with a spatially varying orientation axis of plasmonic grating, we demonstrate control on the spectral asymmetry of the Fano resonance through changes in the geometric phase of polarized light. In this scenario, the changes in the geometric phase for input left, and right circular polarized light arises due to varying orientation angle of the grating axis. The systematic changes in the geometric phase and the resulting q-parameter of Fano resonance is interpreted by an appropriate theoretical model connecting the two physical entities. The demonstrated control over the spectral line shape of Fano resonance achieved by tailoring geometric phase may open up novel routes for polarization-based photonic applications.

3D Hybrid Plasmonic Photonic Crystals by Colloidal‐Crystal Templating and Hydrogel‐Assisted Conformal Metal Etching

AbstractThe development of efficient colloidal templating methods for nanophotonic structures, leading to 3D synergy of photonic crystal behavior with uniform plasmonic resonances is significant, yet challenging. In this work, uniform Ag or Ni octahedral particles with 3D periodicity derived from dissociation of metallic inverse opals are dispersed in hydrogel by conformal etching. The hydrogel can maintain the position of the dissociated metal particles and does not hinder ion transport during the two‐step cyclic electrochemical process. Bragg peaks from the 3D behavior of the colloidal photonic crystals appear due to the reduced filling fraction of metals and are affected by the existence of localized plasmonic resonance (LSPR). LSPR is supported at frequencies ranging from near‐infrared to near‐ultraviolet due to the geometry of the dissociated metal particles. Dissociation of inverse opals during etching is monitored by examining their morphologies, cycle‐related variations in the electrochemical current density, cycle‐related increases of transmission intensities, and redshifts of the Bragg peak wavelengths due to an increased lattice constant in high pH solutions. Ag plasmonic photonic crystals filled with functional polymethacrylic acid and polyacrylamidophenylboronic acid hydrogels function as pH and glucose sensors. The sensitivity increases when plasmonic resonances affect the Bragg peaks.

Heat capacity and electrical conductivity of plasmon excitations

In this research, we calculate the heat capacity and electrical conductivity of plasmon excitations in an arbitrary degenerate electron gas by using the linearized Schrödinger-Poisson model. It is shown that the large heat capacity of electron fluid such as in metals can be attributed to the collective excitations. These excitations unlike those for low energy fermion excitations dominant at low temperatures follow the Bose-Einstein statistics and contribute significantly at higher temperatures where a significant number of electrons excite to energy levels beyond twice the plasmon energy of electron fluid. The current density and electrical conductivity of plasmon excitations in the current model show unique features for characteristic current-voltage and their temperature dependence. It is found that a single electron fermion excitation model such as the one used in free electron assumption is not appropriate for a full description of electron contribution to the physical properties of metals and plasmas at very high temperatures. The coupled pseudoforce system with a periodic density structure in the presence of a uniform electric field is also considered with appropriate boundary conditions to evaluate the characteristic aspects of collective excitations in a one dimensional plasmonic crystal. The application of the lattice periodicity on the wavefunction and the electrostatic potential results in singularities for the probability current due to plasmon excitations. It is shown that such an effect persists with an arbitrary ion core potential function which obeys the lattice periodicity. The current model clearly demonstrates the importance of collective electronic excitation in the physical properties of electron gas with an arbitrary degree of degeneracy.

Real-Time Surface-Enhanced Raman Scattering Tracking of Adenine–Gold Charge Transfer Complex Formation on Nanocavity-Shaped Plasmonic Crystals

Understanding binding of DNA bases with gold surfaces is crucial for designing reliable tools in biosensing technology and organic-based electronics. Herein, we discuss an application of quasi peri...

Coupling phenomena and collective effects in resonant meta-atoms supporting both plasmonic and (opto-)magnetic functionalities: an overview on properties and applications [Invited

We review both the fundamental aspects and the applications of functional magneto-optic and opto-magnetic metamaterials displaying collective and coupling effects on the nanoscale, where the concepts of optics and magnetism merge to produce unconventional phenomena. The use of magnetic materials instead of the usual noble metals allows for an additional degree of freedom for the control of electromagnetic field properties, as well as it allows light to interact with the spins of the electrons and to actively manipulate the magnetic properties of such nanomaterials. In this context, we explore the concepts of near-field coupling of plasmon modes in magnetic meta-molecules, as well as the effect of excitation of surface lattice resonances in magneto-plasmonic crystals. Moreover, we discuss how these coupling effects can be exploited to artificially enhance optical magnetism in plasmonic meta-molecules and crystals. Finally, we highlight some of the present challenges and provide a perspective on future directions of the research towards photon-driven fast and efficient nanotechnologies bridging magnetism and optics beyond current limits.

Template-Free, Surfactant-Mediated Orientation of Self-Assembled Supercrystals of Metal-Organic Framework Particles.

Mesoscale self-assembly of particles into supercrystals is important for the design of functional materials such as photonic and plasmonic crystals. However, while much progress has been made in self-assembling supercrystals adopting diverse lattices and using different types of particles, controlling their growth orientation on surfaces has received limited success. Most of the latter orientation control has been achieved via templating methods in which lithographic processes are used to form a patterned surface that acts as a template for particle assembly. Herein, a template-free method to self-assemble (111)-, (100)-, and (110)-oriented face-centered cubic supercrystals of the metal-organic framework ZIF-8 particles by adjusting the amount of surfactant (cetyltrimethylammonium bromide) used is described. It is shown that these supercrystals behave as photonic crystals whose properties depend on their growth orientation. This control on the orientation of the supercrystals dictates the orientation of the composing porous particles that might ultimately facilitate pore orientation on surfaces for designing membranes and sensors.

Quantum interference of three dimensional plasmon excitations

In this paper, the quantum interference of plasmon excitations in the presence of charges or multipolar sources/sinks is investigated. The effective Schrödinger-Poisson system for dynamical description of the arbitrary degenerate fermi gas is reduced to a set of coupled linear pseudoforce system, and it is shown that this system admits a general multipolar solution in the 3D Cartesian coordinate. The obtained solution is then used to study well-known problems such as the double and quadruple charge interference effects. The double source interference produces patterns quite reminiscent of that of the double slit interference with the corresponding matter-wavelength matching that of the de Broglie wavelength of the electrons. It is found that the collective electrostatic interactions of quantum electron gas leads to the electrostatic energy depletion around the pole which causes electrostatic polar binding in the electron fluid. The later effect which has also been previously reported in some research seems to be an appropriate description of attractive metallic bindings. The current model is then extended to electronic interference effects in a crystal lattice with the quasiperiodic electronic states. The periodic arrangement of ionic cores in a crystal is shown to produce different density and electrostatic potential patterns for given energy eigenvalues of the fermi gas. Moreover, a generalized expression is obtained for electron probability current in the Schrödinger-Poisson model. The current model may provide a better platform for studying the quantum interference phenomenon in complex environments such as nanocompounds and plasmonic crystals.

Fano resonance of collective excitations in 1D plasmonic crystal

The quantum coupled pseudoforce model with the damping term is used to study the plasmon excitations in a variety of systems. Damped plasmon excitations can be used to model different physical situations such as the plasmon penetration into insulating environments and surface plasmon excitations in semiconductors. The application of the pseudoforce model with damping around a charged Dirac sheet reveals that such pseudoforce system can also be used to model the charge shielding. It is also observed that quantum charge shielding possesses two-tone field-density variations due to both single-particle oscillations and collective electrostatic excitations. The effect of uniform electric field on the damped plasmon excitations is also considered in this paper. We further report new findings concerning the effect of collective quantum excitations which may provide further insight into the theory of bandgap structure in crystals. It is remarked that the presence of charge screening in a periodic lattice can lead to Fano resonance. Finally, a new expression for the charge-particle continuity equation in the presence of shielding effect is presented. Current investigation can have fundamental results for better understanding of the quantum transport phenomenon and optical properties of semiconductors, metallic compounds, nanoclusters, and plasmonic crystals.

Dynamic Plasmon Resonance Tuning for Surface Enhanced Sensing.

We report on fabricating plasmonic nanorod crystals using focused ion beam lithography. We first demonstrate manipulating the profiles of nanorods perpendicularly aligned with the substrate. Then we show accurate control of nanorod outlines can be achieved. We also show that it is feasible to manufacture nanorods obliquely aligned with the substrate. Tunable plasmon resonance can be realized with different tilting angles and geometries. Our approach may find important applications in plasmon-assisted sensing and surface enhanced spectroscopy.

Electrically Tunable Exciton-Plasmon Coupling in a WSe2 Monolayer Embedded in a Plasmonic Crystal Cavity.

We realize a new electroplasmonic switch based upon electrically tunable exciton-plasmon interactions. The device consists of a hexagonal boron nitride (hBN)-encapsulated tungsten diselenide (WSe2) monolayer on top of a single-crystalline silver substrate. The ultrasmooth silver substrate serves a dual role as the medium to support surface plasmon polaritons (SPPs) and the bottom gate electrode to tune the WSe2 exciton energy and brightness through electrostatic doping. To enhance the exciton-plasmon coupling, we implement a plasmonic crystal cavity on top of the hBN/WSe2/hBN/Ag heterostructure with a quality factor reaching 550. The tight confinement of the SPPs in the plasmonic cavity enables strong coupling between excitons and SPPs when the WSe2 exciton absorption is resonant with the cavity mode, leading to a vacuum Rabi splitting of up to 18 meV. This strong coupling can also be switched off with the application of a modest gate voltage that increases the doping density in the monolayer. This demonstration paves the way for new plasmonic modulators and a general device architecture to enhance light-matter interactions between SPPs and various embedded emitters.

Observing vortex polarization singularities at optical band degeneracies

In the momentum space of two-dimensional (2D) periodic photonic systems, the polarization states of radiating Bloch modes on a single band can form vortex polarization singularities. Here, we study vortex polarization singularities at the band degeneracies. We design a quadratic degeneracy in a plasmonic crystal with ${C}_{4v}$ symmetry which, by symmetry breaking, splits into a pair of Dirac points with half vortices. The integer vortex singularity at the quadratic degeneracy and the half one at the Dirac degeneracy are measured using polarization-resolved momentum-space imaging spectroscopy. The complete evolution of the splitting from the integer vortex to a pair of half vortices is observed in experiments.

Quasinormal mode solvers for resonators with dispersive materials.

Optical resonators are widely used in modern photonics. Their spectral response and temporal dynamics are fundamentally driven by their natural resonances, the so-called quasinormal modes (QNMs), with complex frequencies. For optical resonators made of dispersive materials, the QNM computation requires solving a nonlinear eigenvalue problem. This raises a difficulty that is only scarcely documented in the literature. We review our recent efforts for implementing efficient and accurate QNM solvers for computing and normalizing the QNMs of micro- and nanoresonators made of highly dispersive materials. We benchmark several methods for three geometries, a two-dimensional plasmonic crystal, a two-dimensional metal grating, and a three-dimensional nanopatch antenna on a metal substrate, with the perspective to elaborate standards for the computation of resonance modes.

Metal-coated microsphere monolayers as surface plasmon resonance sensors operating in both transmission and reflection modes

Metal-coated microsphere monolayers (MCM) are a class of plasmonic crystals consisting of noble metal films over arrays of self-assembled colloidal microspheres. Despite their ease of fabrication and tunable plasmonic response, their optical sensing potential has been scarcely explored. Here, silver coated polystyrene sphere monolayers are proposed as surface plasmon resonance sensors capable of functioning in both transmission (T) and reflection (R) readout modes. An original and key point is the use of ~200 nm colloids, smaller than in MCM studied before. It allowed us to reveal a previously unobserved, additional/secondary Enhanced Optical Transmission band, which can be exploited in sensing, with higher sensitivity than the better-known main transmission band. The reflection configuration however, is almost an order of magnitude more efficient for sensing than the transmission one. We also evidenced a strong impact of the adsorbate location on the metal surface on the sensing efficiency. Electric field distribution analysis is performed to explain these results. Proof-of-concept experiments on the detection of 11-MUA molecular monolayers, performed in both readout modes, confirm the behaviors observed through FDTD simulations. Results in this paper can serve as guidelines for designing optimized sensors based on metal-coated colloidal monolayers, and more generally for plasmonic sensors based on metal nanostructured films.

Nano-optical elements for surface plasmon waves: (50th anniversary of the Institute of Spectroscopy, Russian Academy of Sciences)

The main results obtained recently at the Laboratory of Laser Spectroscopy, Institute of Spectroscopy of the Russian Academy of Sciences in researching and developing various 2D optical elements for surface plasmon waves and their characterization using near- and far-field methods are presented. They include an optical medium for plasmon waves, a plasmon interferometer, a parabolic mirror for focusing plasmon waves, a dielectrically loaded plasmon-polariton waveguide, a plasmon nanolaser based on a plasmonic crystal, and a plasmon sensor of fluorescent biomarkers. lenses, mirrors, detectors, interferometers, waveguides, and lasers. We show that state-of-the-art techniques for the development of plasmon optics elements, which are based on utilizing single-crystal ultrahigh quality metal surfaces, enable us to come closer to the theoretically predicted characteristics of these elements.

Surface states ensured by a synthetic Weyl point in one-dimensional plasmonic dielectric crystals with broken inversion symmetry

Weyl points, i.e., peculiar nodal degenerate points in three-dimensional reciprocal space, carry topological charges, therefore giving rise to many intriguing phenomena including topologically protected surface states and chiral anomaly. More importantly, the concept of the Weyl point can be applied in systems with reduced geometrical dimensionality by means of synthetic dimension. Such generalized synthetic Weyl points therefore provide a versatile platform to explore the Weyl-point physics in one or two-dimensional structures. In this work, we study the synthetic Weyl points in one-dimensional plasmonic-dielectric crystals with broken inversion symmetry and further demonstrate that the synthetic Weyl points can ensure the emergence of topological interface states. Instead of using the Zak phase, the emergence of a Weyl point in synthetic space is helpful to understand the underlying physics and the topological properties of the interface states in one-dimensional crystals with broken inversion symmetry. Due to the opposite sign of the surface impedance for plasmonic and dielectric cover medium, the surface states demonstrate distinct properties and locate in separated parameter space regions. Our results show that the synthetic Weyl point provides a potential approach for studying novel electromagnetic modes and facilitates the formation of topologically protected interface states in systems with reduced geometrical dimensions.

State-of-the-art plasmonic crystals for molecules fluorescence detection

We propose a method of measuring low concentrations of fluorescent molecules located in a small volume of a liquid solvent (about 5 μl) based on the Ebbesen effect of the extraordinary transmission (EOT) of light through a state-of-the-art plasmonic crystal formed by a nanohole array perforated in the ultra-high-quality Ag film. In the method, the EOT effect is realized at the fluorescence wavelength of the detected molecules with a low transmission of light at the absorption wavelength. This approach enables the realization of high level sensor sensitivity approaching a sensitivity level of single molecules counting sensors, owing to the suppression of the sensor substrate’s inevitable parasitic luminescence. The proposed method was successfully demonstrated by detection an ultra-low concentration of Cy-5 fluorescent markers in a dimethyl sulfoxide solution corresponding to less than 1000 molecules in the sensor detection volume.

Tunable Valley Polarized Plasmon-Exciton Polaritons in Two-Dimensional Semiconductors.

Monolayers of transition-metal dicalcogenides have emerged as two-dimensional semiconductors with direct bandgaps at degenerate but inequivalent electronic "valleys", supporting distinct excitons that can be selectively excited by polarized light. These valley-addressable excitons, when strongly coupled with optical resonances, lead to the formation of half-light half-matter quasiparticles, known as polaritons. Here we report self-assembled plasmonic crystals that support tungsten disulfide monolayers, in which the strong coupling of semiconductor excitons and plasmon lattice modes results in a Rabi splitting of ∼160 meV in transmission spectra as well as valley-polarized photoluminescence at room temperature. More importantly we find that one can flexibly tune the degree of valley polarization by changing either the emission angle or the excitation angle of the pump beam. Our results provide a platform that allows the detection, control, and processing of optical spin and valley information at the nanoscale under ambient conditions.

Symmetry Breaking in Oligomer Surface Plasmon Lattice Resonances.

We describe a novel plasmonic-mode engineering, enabled by the structural symmetry of a plasmonic crystal with a metallic oligomer as unit cell. We show how the oligomer symmetry can tailor the scattering directions to spatially overlap with the diffractive orders directions of a plasmonic array. Applied to the color generation field, the presented approach enables the challenging achievement of a broad spectrum of angle-dependent colors since smooth and continuous generation of transmitted vibrant colors, covering both the cyan-magenta-yellow and the red-green-blue color spaces, is demonstrated by scattering angle- and polarization-dependent optical response. The addition of a symmetry driven level of control multiplies the possibility of optical information storage, being of potential interest for secured optical information encoding but also for nanophotonic applications, from demultiplexers or signal processing devices to on-chip optical nanocircuitry.

Pseudo-resonance and energy band gaps in plasmonic crystals

In this paper, using the generalized coupled pseudoforce model with driving elements, we develop a method to study the plasmon excitations and energy band structure in a plasmonic crystal. It is shown that the presence of the periodic ion core potential leads to a pseudo-resonance condition in the plasmon wavefunction and electrostatic potential profiles, quite analogous to the frequency resonance, leading to the gap formation in the energy dispersion profiles. It is found that the dual length scale character of plasmon excitations leads to the occurrence of a critical value of ac = 2πλp for the lattice constant (λp being the plasmon wavelength) above and below which the energy band structure of plasmonic crystals becomes substantially different. It is also found that energy bandgap positions of the parabolic free electron energy dispersion relation are slightly higher compared to those of the plasmon excitations. The wavefunction and electrostatic potential solution for a one dimensional plasmonic lattice with a generalized periodic potential are also derived in this research. Current development helps us to illuminate the basic properties of the collective quantum phenomenon in many physical contexts by appropriately incorporating the collective effect in the root level and can have a wide range of applications in developments of the rapidly growing fields of nano-technology, nano-electronics, and plasmonics.