Plasmon Excitation Research Articles

Active control of terahertz surface plasmonic wave excitation using electromagnetically induced transparency based graphene metasurfaces.

Surface plasmonic waves (SPWs) that propagate at meta-dielectric interface are a good source of information carrier waves for on-chip photonic devices, where SPW excitation is one key procedure. Recently, controlling SPW excitation using metasurface methods has drawn considerable attention owing to their design flexibility, wherein achieving dynamic control is of great importance. However, most studies in the terahertz regime so far are working in a passive way or only dynamically controllable at the propagation process. In this work, an active design for controlling terahertz SPWs at the excitation process is proposed using graphene metasurfaces based on the manipulation of the electromagnetically induced transparency (EIT) effect. Large modulation depth with controllable SPW excitations is demonstrated. Our method is flexible and promising in achieving more controlling degree of freedom, which can find broadband applications in future integrated devices and systems.

Gold Nanorod/Titanium Dioxide Hybrid Nanoparticles for Plasmon-Enhanced Near-Infrared Photoproduction of Hydroxyl Radicals and Photodynamic Therapy.

Gold nanoparticles, such as nanorods (AuNRs), present exceptionally high absorption cross sections that can be tuned to the near-infrared (NIR), the optimal window for light penetration in biological tissues. This makes them valuable photosensitizers for the treatment of cancer using photothermal therapy, where absorbed light energy is converted into heat. In addition, there is a strong interest in using hot electron carriers generated in AuNRs by NIR irradiation to produce cytotoxic radical oxygen species in order to enhance the efficiency of the phototherapy. Here, we show that hybrid nanoparticles composed of AuNRs with TiO2 deposited at their extremities are efficient sensitizers to produce hydroxyl radical species under NIR irradiation. We attribute this phenomenon to the transfer of hot electrons generated from the plasmon excitation in AuNR to the TiO2 tips, followed by reduction of dioxygen. We then functionalize these hybrid AuNR/TiO2 nanoparticles with block poly(ethylene glycol)-phosphonate polymer ligands to stabilize them in a physiological medium. We finally demonstrate that the photodynamic effect induces cell death upon irradiation with a greater efficiency than the photothermal effect alone.

Plasmon-enhanced circular dichroism spectroscopy of chiral drug solutions.

We investigate the potential of surface plasmon polaritons at noble metal interfaces for surface-enhanced chiroptical sensing of dilute chiral drug solutions with nl volume. The high quality factor of surface plasmon resonances in both Otto and Kretschmann configurations enables the enhancement of circular dichroism differenatial absorption thanks to the large near-field intensity of such plasmonic excitations. Furthermore, the subwavelength confinement of surface plasmon polaritons is key to attain chiroptical sensitivity to small amounts of drug volumes placed around ≃100 nm by the metal surface. Our calculations focus on reparixin, a pharmaceutical molecule currently used in clinical studies for patients with community-acquired pneumonia, including COVID-19 and acute respiratory distress syndrome. Considering realistic dilute solutions of reparixin dissolved in water with concentration ≤5 mg/ml and nl volume, we find a circular-dichroism differential absorption enhancement factor of the order ≃20 and chirality-induced polarization distortion upon surface plasmon polariton excitation. Our results are relevant for the development of innovative chiroptical sensors capable of measuring the enantiomeric imbalance of chiral drug solutions with nl volume.

Enhanced nonlinear optical absorption and optical limiting performance of nanoparticles embedded lanthanum alkali borate glasses bearing holmium ions at off–resonant spectral excitation

Herein, the efficacy of silver nanoparticles on the nonlinear optical features of holmium ions bearing melt–quenched borate–based glasses has been investigated. The silver nanoparticles free holmium doped glass possesses weak nonlinear absorption and high optical limiting threshold in the near–infrared spectral range. It was observed that the nonlinear absorption and optical limiting performance were significantly improved upon co–doping of silver NPs in the lanthanum alkali borate glasses. The linear optical absorption measurements partially confirmed the presence of silver nanoparticles in the prepared glasses. The electron microscopic measurements disclosed the evidence for the formation of spherically shaped silver nanoparticles in the glasses. The nonlinear optical and optical limiting features were ascertained by the open aperture Z–scan technique in off–plasmon excitations by benefitting femtosecond laser pulses fired at kHz repetition rate. The outcomes endorse that the high AgCl loaded lanthanum alkali borate glasses are useful in suppressing the high energy near–infrared laser radiation for the protection of sensitive optical devices (e.g., human eye) from the laser damage.

Plasmonic inhibition of bacterial adhesion on gold-decorated mesoporous zirconium oxide thin films

Preventing bacterial development on surfaces is essential to avoid problems caused by biofouling. Surfaces decorated with gold nanoparticles have been shown to thermally kill bacteria under high-intensity NIR illumination. In this study, we evaluated the colonization by E. coli of nanostructured surfaces composed of mesoporous zirconia thin films, both with and without gold nanoparticles embedded into the pores. We studied the effect of the nanostructure and of low intensity visible light excitation of the gold nanoparticles on the colonization process. We found that neither the zirconia, nor the presence of pores, or even gold nanoparticles affect bacterial adhesion compared to the bare glass substrate. Therefore, mesoporous zirconia thin films are biologically inert scaffolds that enable the construction of robust surfaces containing functional nanoparticles that can affect bacterial growth. When the gold containing surfaces are irradiated with light, bacterial adhesion shows a remarkable 96 ± 4% reduction. Our studies revealed that these surfaces affect early colonization steps, prior to biofilm formation, preventing bacterial adhesion without affecting its viability. In contrast to related systems where plasmonic excitation induces membrane damage due to strong local heating, the membrane integrity is preserved, showing that these surfaces have a different working principle.

THz plasmonics and electronics in germanene nanostrips

Germanene nanostrips (GeNSs) have garnered significant attention in modern semiconductor technology due to their exceptional physical characteristics, positioning them as promising candidates for a wide range of applications. GeNSs exhibit a two-dimensional (buckled) honeycomb-like lattice, which is similar to germanene but with controllable bandgaps. The modeling of GeNSs is essential for developing appropriate synthesis methods as it enables understanding and controlling the growth process of these systems. Indeed, one can adjust the strip width, which in turn can tune the bandgap and plasmonic response of the material to meet specific device requirements. In this study, the objective is to investigate the electronic behavior and THz plasmon features of GeNSs (≥100 nm wide). A semi-analytical model based on the charge-carrier velocity of freestanding germanene is utilized for this purpose. The charge-carrier velocity of freestanding germanene is determined through the GW approximation ( m·s−1). Within the width range of 100 to 500 nm, GeNSs exhibit narrow bandgaps, typically measuring only a few meV. Specifically, upon analysis, it was found that the bandgaps of the investigated GeNSs ranged between 29 and 6 meV. As well, these nanostrips exhibit -like plasmon dispersions, with their connected plasmonic frequency (≤30 THz) capable of being manipulated by varying parameters such as strip width, excitation plasmon angle, and sample quality. These manipulations can lead to frequency variations, either increasing or decreasing, as well as shifts towards larger momentum values. The outcomes of our study serve as a foundational motivation for future experiments, and further confirmation is needed to validate the reported results.

On charged particle dynamics near flat solid surface

The motion of a non-relativistic charged particle near flat solid surface at small sliding angles is examined within the formalism of the effective potential composed by interaction of a particle with surface atoms and excited plasmons. As known, the presence of curvature in a solid surface can result in forming a set of discrete quantum states for a particle in the potential well of interaction with the surface.In this work we demonstrate that, at the glancing to flat-surface motion of fast charged particles, small channeling oscillations can be also observed for some special conditions. It is shown that the effective interaction potential represents a shallow well capable to hold a particle in a bound state. We succeeded to analytically determine the energy levels of a particle in such a potential well, as well as the critical angle for a particle to be trapped, in terms of known critical angle of channeling in crystals and a newly proposed function for simplification.

Screening induced crossover between phonon- and plasmon-mediated pairing in layered superconductors

Two-dimensional (2D) metals can host gapless plasmonic excitations that strongly couple to electrons and thus may significantly affect superconductivity. To investigate the dynamical interplay of the electron–electron and electron–phonon interactions in the theory of 2D superconductivity, we apply a full momentum- and frequency-dependent one-loop theory treating electron–phonon, electron–plasmon, and phonon–plasmon coupling with the same accuracy. We tune the strength of the Coulomb interaction by varying the external screening to the layered superconductor and find three distinct regions. At weak screening, superconductivity is mediated by plasmons. In the opposite limit conventional electron–phonon interactions dominate. In between, we find a suppressed superconducting state. Our results show that even in conventional electron–phonon coupled layered materials, superconductivity can be significantly enhanced by the electron–plasmon coupling in a manner that can be controlled by the external screening.

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.

Transport and Interfacial Injection of d-Band Hot Holes Control Plasmonic Chemistry.

Harnessing nonequilibrium hot carriers from plasmonic metal nanostructures constitutes a vibrant research field with the potential to control photochemical reactions, particularly for solar fuel generation. However, a comprehensive understanding of the interplay of plasmonic hot-carrier-driven processes in metal/semiconducting heterostructures has remained elusive. In this work, we reveal the complex interdependence among plasmon excitation, hot-carrier generation, transport, and interfacial collection in plasmonic photocatalytic devices, uniquely determining the charge injection efficiency at the solid/liquid interface. Measuring the internal quantum efficiency of ultrathin (14-33 nm) single-crystalline plasmonic gold (Au) nanoantenna arrays on titanium dioxide substrates, we find that the performance of the device is limited by hot hole collection at the metal/electrolyte interface. Our solid- and liquid-state experimental approach, combined with ab initio simulations, demonstrates more efficient collection of high-energy d-band holes traveling in the [111] orientation, enhancing oxidation reactions on {111} surfaces. These findings establish new guidelines for optimizing plasmonic photocatalytic systems and optoelectronic devices.

Fabrication of a Novel Co/CoO@Fe2 V4 O13 Composite Catalyst as a Photoanode for Enhanced Photoelectrochemical Water Oxidation.

Herein, the synthesis of a novel composite photocatalyst, Co/CoO@Fe2 V4 O13 , is reported by the deposition of CoO metal oxide nanoparticles on the surface of Fe2 V4 O13 bimetallic oxide. The synthesised photocatalyst exhibited a band gap of roughly 1.8 eV, rendering it responsive to the complete visible light spectrum of the sun, thereby enabling optimal absorption of solar radiation. The Co/CoO@Fe2 V4 O13 composites demonstrated an enhanced photoelectrochemical water oxidation capacity compared to pristine Fe2 V4 O13 when exposed to visible light. The enhanced performance is attributed primarily to the creation of a p-n junction at the interface of Fe2 V4 O13 and Co/CoO, as well as the Z-scheme charge transfer mechanism, which aids in the separation and transfer of photogenerated charge carriers. Light absorption by Co nanoparticles via plasmonic excitation and intra- and inter-band transitions in the composite structure is also likely, resulting in increased composite efficiency. Our findings indicate that Co/CoO@Fe2 V4 O13 composites show promising performance for solar water splitting applications and offer new perspectives for designing effective photocatalysts.

Broad-spectrum light absorption and efficient charge transfer in plasmonic PbS/Cu2-xS/CdS polyhedral heterojunction for improved photothermal/photocatalytic performance

The multidimensional structure, abilities of light-harvesting and charge-transfer, photothermal conversion of semiconductor heterojunction are very important characters for high-performance photocatalysis. However, it remains a challenge to rationally design heterojunction photocatalyst that meets the demand. Herein, plasmonic PbS/Cu2-xS/CdS polyhedral heterojunctions, which Cu2-xS and CdS nanoparticles are deposited on the 24-faceted PbS, are prepared for efficient photothermal-assisted photocatalysis for the first time. Owing to the synergistic effect of plasmonic resonance and bandgap excitations, the ternary hybrids display excellent light absorption ranging from ultraviolet to near-infrared (NIR) region. The unique polyhedral structure and rough surface of the hybrids generate a large surface area, offering abundant active sites for catalytic reaction. Importantly, the different work functions and appropriate band arrangements of the three semiconductors provide a double Z-scheme band structure, which leads to efficient charge transfer and separation driven by built-in electric fields. Moreover, the fast hot electron injection from plasmonic Cu2-xS to PbS and CdS also provides energetic electrons for photocatalysis. As a result, the polyhedral hybrids display efficient photocatalytic H2 activity (24.3 times of pure CdS) under visible light irradiation and a high apparent quantum efficiency under NIR light irradiation. Furthermore, the ternary hybrids show excellent photothermal conversion and photothermal-assisted photocatalysis due to plasmonic heating and nonradiative relaxation. The temperature-dependent photocatalytic tests indicate that the photothermal effect has about 35% enhancement on photocatalysis. This work provides an inspiration to develop new functional materials for the field of solar-driven energy conversion.

Plasmonic effects in the neutralization of slow ions at a metallic surface

AbstractSecondary electron emission is an important process that plays a significant role in several plasma‐related applications. As measuring the secondary electron yield experimentally is very challenging, quantitative modelling of this process to obtain reliable yield data is critical as input for higher‐scale simulations. Here, we build upon our previous work combining density functional theory calculations with a model originally developed by Hagstrum to extend its application to metallic surfaces. As plasmonic effects play a much more important role in the secondary electron emission mechanism for metals, we introduce an approach based on Poisson point processes to include both surface and bulk plasmon excitations to the process. The resulting model is able to reproduce the yield spectra of several available experimental results quite well but requires the introduction of global fitting parameters, which describe the strength of the plasmon interactions. Finally, we use an in‐house developed workflow to calculate the electron yield for a list of elemental surfaces spanning the periodic table to produce an extensive data set for the community and compare our results with more simplified approaches from the literature.

Multiresonant plasmon excitation in slit antennas on metallic and hyperbolic metamaterials.

A comparative study of the optical properties of random and ordered arrays of metallic and hyperbolic slit antennas is presented. The metallic slits are fabricated on Au layers, whereas the hyperbolic ones are fabricated on Au/MgO multilayers. The random arrays show, for both types of antennas, similar slit plasmon resonances whose positions depend on the internal structure of the supporting layer. On the other hand, the spectra of the ordered arrays of the hyperbolic slits present additional resonances related to the excitation of Bloch plasmon polaritons in the hyperbolic layer. By varying the slit length and periodicity, an analysis of the interaction between slit localized resonance and Bloch plasmon polaritons is also presented.

Neutron-activated, plasmonically excitable Fe-Pt-Yb2O3 nanoparticles delivering anti-cancer radiation against human glioblastoma cells

Magnetic nanoparticles can be functionalized in many ways for biomedical applications. Here, we combine four advantageous features in a novel Fe-Pt-Yb2O3 core-shell nanoparticle. (a) The nanoparticles have a size of 10nm allowing them to diffuse through neuronal tissue. (b) The particles are superparamagnetic after synthesis and ferromagnetic after annealing, enabling directional control by magnetic fields, enhance NMRI contrast, and hyperthermia treatment. (c) After neutron-activation of the shell, they carry low-energetic, short half-life β-radiation from 175Yb, 177Yb, and 177Lu. (d) Additionally, the particles can be optically visualized by plasmonic excitation and luminescence. To demonstrate the potential of the particles for cancer treatment, we exposed cultured human glioblastoma cells (LN-18) to non-activated and activated particles to confirm that the particles are internalized, and that the β-radiation of the radioisotopes incorporated in the neutron-activated shell of the nanoparticles kills more than 98% of the LN-18 cancer cells, promising for future anti-cancer applications.

Boosting Wavelength‐Selective Absorption and Photocarrier Collection in NiO/ZnO Transparent Photovoltaic Heterojunctions by Plasmonic Ag Nanowire Top Electrodes

AbstractGlobal climate change has compelled many to rely on photovoltaic (PV) technology to meet the highly demanding energy needs of urban areas. In particular, transparent photovoltaic (TPV) devices can be utilized for building windows, not only supplying electric energy but also improving the overall thermal efficiency of a building. In this work, NiO/ZnO wide‐bandgap oxide TPV heterojunctions are fabricated with Ag nanowire (NW) top electrodes and their PV characteristics are investigated. Special attention is paid to the contributions of surface plasmon (SP) excitation in AgNWs to the PV performance of the TPV device. Light polarized perpendicular to the AgNW axis induces a localized SP resonance in AgNWs at a wavelength of 400 nm, as shown by optical measurements and calculations. The investigation on how the plasmonic AgNWs affect real‐space electric potential distributions and local current‐voltage characteristics of the TPV devices uses Kelvin probe force microscopy and current‐sensing atomic force microscopy, respectively. The spatial redistribution and transport of photogenerated charge carriers strongly depend on the polarization as well as the wavelength of incident light. The results demonstrate that the AgNW‐based top electrodes boost the wavelength‐selective absorption and the effective collection of photocarriers in TPV devices.

Theoretical study of perovskite nano material based surface plasmon resonance biosensor for cancers cell detection

The present study reports screening of cancer cells at the earliest stages using prism coupling-based surface plasmon resonance biosensors in a theoretical manner. The SPR sensors designed on Kretschmann configuration consisting of several layers like silver (Ag) metal, beryllium oxide (BeO) and hetero-structure BlueP/WSe2 layer deposited over BK7 glass prism. For maximum light absorption, a perovskite nano material, barium titanate (BaTiO3) layer is placed between BeO and hetero-structure BlueP/WSe2 to enhance the angular sensitivity. The light of 633 nm wavelength has been used for excitation of surface plasmon at metal dielectric interface. The refractive index of cancer cells lies between 1.360 and 1. 400. The optimized angular sensitivity of 216°/RIU and 360°/RIU for PCI-2 (normal, adrenal gland cancer), 248°/RIU and 254°/RIU for MDA-MB-231(normal, breast cancer cell) as well as 248°/RIU and 254°/RIU for MCF-7 (normal, breast cancer cell) respectively has been obtained. The maximum optimized angular sensitivity for adrenal gland cancer is 360°/RIU on employing perovskite layer. The sensor offers excellent performance parameters and covers wide range of refractive index sensing.

Photoemission Electron Microscopy of Blue and UV Surface Plasmons on Nanostructured Aluminum Films

We image surface plasmons on aluminum surfaces in the ultraviolet and blue spectral range with photoemission electron microscopy (PEEM). Plasmon excitation is mediated by light incident on straight aluminum ridges with subwavelength cross section on flat aluminum films. We observe interference patterns due to light/plasmon interaction, with distinct periodicity and orientation depending on the light in-plane incidence angle with respect to the ridge orientation. From the interference patterns, we deduce the surface plasmon propagation directions and decay lengths. The latter are remarkably high with 2.8 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mu$$\\end{document}m and 8.4 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mu$$\\end{document}m for excitation wavelengths of 273 nm and 410 nm, respectively. Our results extend PEEM imaging of surface plasmons into the ultraviolet region.

Anomalous plasmon coupling and Fano resonance under structured light

Structured light carrying orbital angular momentum (OAM) opens up a new physical dimension for studying light–matter interactions. Despite this, the complex fields created by OAM beams still remain largely unexplored in terms of their effects on surface plasmons. This paper presents a revelation of anomalous plasmon excitations in single particles and plasmon couplings of neighboring nanorods under OAM beams, which are forbidden using non-OAM sources. The plasmon excitation of single nanoparticles is determined both by photon spin angular momentum (SAM) and OAM and influenced by the locations of the nanoparticles. Specifically, when SAM and OAM are equal in magnitude and opposite in direction, a pure plasmon excitation along light propagation direction is achieved. Two plasmon dipoles show end-to-end antibonding coupling and side-by-side bounding coupling, which are the opposite of the typical couplings. Furthermore, we observe Fano resonance with a nanorod dimer: one aligned along light propagation direction acting as the bright mode and the other aligned along the global polarization direction of light acting as the dark mode, which is the opposite of the usual plasmonic Fano resonance. By taking advantage of the unique property of the OAM source, this investigation presents a novel way to control and study surface plasmons, and the research of plasmon behavior with OAM would open new avenues for controlling electromagnetic waves and enriching the spectroscopies with more degrees of freedom.

Nondegenerate two-way edge channels of plasmons in networks

An effective one-dimensional channel is formed at the periphery of a two-dimensional electron gas by electronic edge states. Robust edge states with suppressed dissipation arise from the Landau quantization in a strong magnetic field, and propagation through an edge channel formed by these states is one-way. In general, two-way edge channels rather than one-way ones have more advantages for applications and are the main topic of topological insulators. However, two-way edge channels of these are degenerate in their energies, which causes backscattering and dissipation. Here, we show that excited states in networks composed of capacitively coupled integer quantum Hall systems exhibit macroscopic two-way edge channels with different energies. Theoretical results are derived on the basis of two known effects; each system has plasmonic excitations known as edge magnetoplasmons, and the chirality of each system is diverted only locally by the capacitive interaction between nearest-neighbor systems. Because of the simplicity of the model, various extensions from regular networks to more complicated higher-dimensional networks are possible. The networks provide an ideal platform to test the functionality of plasmonic one-dimensional edge channels and suggest a dynamical model of fractional Quantum Hall systems.