Plasmon-exciton Interaction Research Articles

Copper plasmonics with excitons

We investigate the propagation of surface plasmons (SPPs) in a thin layer of copper surrounded by copper oxide Cu$_2$O. It is shown that particularly strong excitons in Cu$_2$O can have considerable impact on plasmon propagation, providing many opportunities for plasmon-exciton and plasmon-plasmon interactions. It is demonstrated that by the use of sufficiently thin metal layer, one can excite the so-called long range plasmons (LRSPPs) which can overcome the inherently high ohmic losses of Cu as compared to usual plasmonic metals such as silver. Analytical results are confirmed by numerical calculations.

Realization of ZnO microrods and Ag nanoparticles on glass and Si substrates by magnetron sputtering and near band edge photoluminescence enhancement from the exciton-plasmon system

• A dry method of fabrication of Ag nanoparticles and ZnO microrods heterostructure. • Preferential nucleation of Ag nanoparticles in proximities of ZnO microrods. • Seed assisted growth of ZnO microrods at higher gas pressure and shorter duration. • Near-UV (380 nm) emission enhancement possibly due to exciton-plasmon interaction. • Nearly 3-fold enhancement of near band edge photoluminescence from ZnO microrods. This work presents a physical vapour-based fabrication of an exciton-plasmon system via depositions of ZnO microrods (ZnOµRs) and Ag nanoparticles (AgNPs) on glass and p-type Si substrates. Pulsed DC sputtering of ZnO at a relatively higher Ar pressure and varying applied power enables deposition of ZnOµRs on ZnO seed layers. Sputtering of Ag ensures fabrication of AgNP/ZnOμR heterostructure with good adhesion suitable for device realization. Microstructural analyses confirm formations of wurtzite ZnOμRs and f.c.c. AgNPs. AgNPs are observed as isolated clusters due to preferential nucleation in the proximities of ZnOµRs. UV-Vis absorption spectroscopy reveals broad surface plasmon resonance (SPR) of Ag NPs around 538 nm, which experiences a bathochromic shift in AgNP/ZnOμR heterostructure. The photoluminescence (PL) spectra of AgNP/ZnOμR heterostructure suggest a 3-fold enhancement of narrow near band edge (NBE) emission attributed to the exciton-plasmon interaction.

Optical Introduction and Manipulation of Plasmon–Exciton–Trion Coupling in a Si/WS2/Au Nanocavity

Strong plasmon-exciton coupling, which has potential applications in nanophotonics, plasmonics, and quantum electrodynamics, has been successfully demonstrated by using metallic nanocavities and two-dimensional materials. Dynamical control of plasmon-exciton coupling strength, especially by using optical methods, remains a big challenge although it is highly desirable. Here, we report the optical introduction and manipulation of plasmon-exciton-trion coupling realized in a dielectric-metal hybrid nanocavity, which is composed of a silicon (Si) nanoparticle and a thin gold (Au) film, with an embedded tungsten disulfide (WS2) monolayer. We employ scattering and photoluminescence spectra to characterize the coupling strength between plasmons and excitons in Si/WS2/Au nanocavities constructed by using Si nanoparticles with different diameters. We enhance the plasmon-exciton and plasmon-trion coupling strength by injecting excitons and trions into the WS2 monolayer with a 488 nm laser beam. It is revealed that the emission intensities of excitons and trions with respect to the reference WS2 monolayer can be modified through the change in the coupling strength induced by the laser light. Interestingly, the coupling strength between the plasmons and the excitons/trions can be manipulated from weak to strong coupling regime by simply increasing the laser power, which is clearly resolved in the scattering spectra of Si/WS2/Au nanocavities. More importantly, the plasmon-exciton-trion coupling induced by the laser light is confirmed by the energy exchange between excitons and trions. Our findings indicate the possibility for optically manipulating plasmon-exciton interaction and suggest the practical applications of dielectric-metal hybrid nanocavities in nanoscale plasmonic devices.

Photoluminescence Properties of CdSe/ZnS Quantum Dot Donor-Acceptor via Plasmon Coupling of Metal Nanostructures and Application on Photovoltaic Devices.

Hybrid nanostructures composed of quantum dots (QDs) and metal nanoparticles (MNS) have gained immense research interest because of their unique optical properties. In optoelectronic applications, quenching and enhancement in QD photoluminescence (PL) are critical parameters. Herein, gold nanoparticles coating a silica layer decorated with quantum dots (AuNPs@SiO2@QDs) are prepared with diverse SiO2 thickness and QD diameter for investigating the exciton-plasmon interaction. This reveals the charge interaction between QDs and AuNPs@SiO2 resulting from different impacts of the Föster energy-transfer process and plasmon resonance enhancement. The variation in both radiative and nonradiative energy-transfer processes in CdSe/ZnS QDs donor-acceptor pairs clarifies the impact of AuNPs@SiO2. In addition, the hybrid structures are plainly incorporated with silicon solar cells, which activated the improvement in the power conversion efficiency (PCE). With the significant tunability of the PL intensity in the visible and near-infrared regions, this hybrid nanostructure provides potential strategies for developing efficient optoelectronics via facile methods.

Shape Dependency of the Plasmon–Exciton Interaction at the Nanoscale: Interplay between the Plasmon Local Density of States and the Plasmon Decay Rate

Shape Dependency of the Plasmon–Exciton Interaction at the Nanoscale: Interplay between the Plasmon Local Density of States and the Plasmon Decay Rate

Strong Light-Matter Interactions between Gap Plasmons and Two-Dimensional Excitons under Ambient Conditions in a Deterministic Way.

Strong exciton-plasmon interactions between layered two-dimensional (2D) semiconductors and gap plasmons show a great potential to implement cavity quantum electrodynamics under ambient conditions. However, achieving a robust plasmon-exciton coupling with nanocavities is still very challenging, because the layer area is usually small in the conventional approaches. Here, we report on a robust strong exciton-plasmon coupling between the gap mode of a bowtie and the excitons in MoS2 layers with gold-assisted mechanical exfoliation and nondestructive wet transfer techniques for a large-area layer. Due to the ultrasmall mode volume and strong in-plane field, the estimated effective exciton number contributing to the coupling is largely reduced. With a corrected exciton transition dipole moment, the exciton numbers are extracted as being 40 for the case of a single layer and 48 for eight layers. Our work paves the way to realize strong coupling with 2D materials with a small number of excitons at room temperature.

One-donor-two-acceptors coupled energy transfer nanoprobe for recording of viral gene replication in living cells

Highly efficient Förster resonance energy transfer (FRET) is in great request for sensitive and high signal-to-background ratio imaging of biomolecule in cells, which is limited in many simple energy transfer system. Herein we report a sensitive one-donor-two-acceptors (DAA*) nanoprobe for live-cell imaging by assembling quantum dots (QDs) and BHQ-2 loaded gold nanoparticles (AuNPs) through molecular beacon. Both nanometal surface energy transfer (NSET) from QDs to AuNPs through the exciton-plasmon interaction and FRET from QDs to BHQ-2 through the exciton-dipole interaction can synergistically occur, significantly enhancing the energy transfer efficiency. The DAA* nanoprobe with strong photostability was then successfully applied to record the spatiotemporal distribution and dynamics of genomic RNA (gRNA) replication of human respiratory syncytial virus (RSV) in live cells by fluorescence imaging with improved signal-to-background ratio. Furthermore, dark-field microscopic imaging (iDFM) was also used to confirm the fluorescence imaging results after scattering signal amplification of AuNPs in the nanoprobe. This multiple energy transfer strategy with universal applicability for other donor-acceptor system required for higher energy transfer efficiency is promising in long-term bioimaging and biosensing of low-abundance biomolecules.

Plasmon-exciton interaction in two-particle nanostructures under the action of a magnetic field

On the basis of a specially created theoretical model, the luminescence spectra and the rate of nonradiative transmission of energy from the exciton-activated quantum dot (QD) to the composite nanoparticle (NP) in the outer magnetic field, depending on the geometric and polarization parameters of the system, were calculated. In addition to the models of the quasi - homogeneous field of the dipole source, a model is shown in which the approximation of the dipole polarizability of plasmon nanoparticles is produced. In such a model, two types of NP were used: a solid metal particle and a layered particle with a dielectric core and a metal shell. When calculating the induced dipole moment, the NP was taken into account the inhomogeneous nature of the field created by the exciton-containing QD. The competition of radiation and nonradiative channels of decomposition of the excited state of the two-particle complex was taken into account. It is shown that in the spectra of the rate of nonradiative energy transfer from QD to NP, in addition to dipole bands, bands of multipole transitions of a higher order arise.It has been established that when changing the induction of an external magnetic field, there is a transformation of both radiative and nonradiative spectra. Plasmon bands of the speed spectra of non-radiation transfer of energy and luminescence are reduced by amplitude and split into two spectral components, the distance between which increases with increasing the induction of the magnetic field.

Влияние сферической наночастицы с металлической оболочкой на дезактивацию возбужденной квантовой точки

The plasmon-exciton interaction between a spherical nanoparticle with a dielectric core and a metal shell and a quantum dot in the mode of strong or weak confinement has been theoretically investigated. The rate of nonradiative transfer of electron excitation energy from a quantum dot to a nanoparticle and the rate of spontaneous emission of a quantum dot in the presence of a nanoparticle are calculated. It is shown that at the radii of the nanoparticle core, for which the frequency of the plasmon oscillation coincides with the frequency of the electronic transition in the quantum dot, the rates of radiative and nonradiative processes increase sharply. The kinetics of energy exchange between a nanoparticle and a quantum dot has been studied, and the values of the parameters of the system under consideration, at which the kinetics has the character of damped oscillations, have been established.

Luminescence transformation mechanisms of indocyanine green dye in the presence of gold nanorods

Spectral-luminescent manifestations of the plasmon-exciton interaction between gold nanorods (Au NRs) with average length and diameter of 35± 5 nm and 9± 2 nm, passivated by molecules of cetyltrimethylammonium bromide (CTAB) and the indocyanine green dye (ICG) molecules are found. Extinguishing of the ICG luminescence near Au NRs and its buildup are detected at spacial separation of hybrid nanosystem components achieved by a spherical shell of SiO2 with an average thickness of 26±5 nm formed on the Au NRs. The amplification of the luminescence with growth of the dielectric shell is provided due to blocking of steric transformations of ICG polymethine chain when the interaction emerges between the dye and the silicious shell, and the Purcell effect. Keywords: luminescence, indocyanine green, gold nanorods, Purcell effect.

Plasmon–Exciton Coupling Effect on Plasmon Damping

Plasmon decay via the surface or interface is a critical process for practical energy conversion and plasmonic catalysis. However, the relationship between plasmon damping and the coupling between the plasmon and 2D materials is still unclear. The spectral splitting due to plasmon–exciton interaction impedes the conventional single‐particle method to evaluate the plasmon damping rate by spectral linewidth. The interaction between a single gold nanorod and 2D materials using the single‐particle spectroscopy technique assisted with in situ nanomanipulation is investigated. The approach allows to indisputably identify that the plasmon–exciton coupling would induce plasmon damping in the GNR–WSe2 hybrid. It is confirmed that the resonant energy transfer channel dominates the plasmon decay rather than the charge transfer channel in the GNR–graphene hybrid first. The contribution of the charge transfer channel by using thin hBN layers as an intermediate medium to block the charge transfer is excluded. It is also found that the contact layer between the GNR and 2D materials contributes most of the interfacial plasmon damping. These findings contribute to a deep understanding of interfacial excitonic effects on the plasmon and 2D materials hybrid.

Single-particle studies on plasmon enhanced photoluminescence of monolayer MoS2 by gold nanoparticles of different shapes.

Plasmon-exciton interactions between noble metal nanostructures and two-dimensional transition metal dichalcogenides have drawn great interest due to their significantly enhanced optical properties. Plasmon resonance of noble metal nanoparticles and plasmon-exciton interactions are strongly dependent on the particle morphology. Single-particle spectroscopic studies can overcome the ensemble average effects of sample inhomogeneity to unambiguously reveal the effects of the particle morphology. In this work, plasmon modulated emission of MoS2 in various plasmon-MoS2 hybrid structures has been studied on the single-particle level. Gold (Au) nanoantennas of different shapes including nanosphere, nanorod, nanocube, and nanotriangle with similar overall dimensions, which have different sharp tips and contact areas with MoS2, have been chosen to explore the particle shape effects. Different extent of enhancement in photoluminescence (PL) of MoS2 was observed for Au nanoantennas of different shapes. It was found that Au nanotriangles gave the highest enhancement factor, while Au nanospheres gave the lowest enhancement factor. The numerical simulation results show that the dominant contribution arises from an increased quantum yield, while enhanced excitation efficiency just plays a minor role. The quantum yield enhancement is affected by both the sharp tips and contact mode of the Au nanoantenna with MoS2. Polarization of the MoS2 emission was also found to be modulated by the plasmon mode of the Au nanoantenna. These single-particle spectroscopic studies allow us to unambiguously reveal the effects of the particle morphology on plasmon enhanced PL in these nanohybrids to provide a better understanding of the plasmon-exciton interactions.

Electrically Tunable and Dramatically Enhanced Valley-Polarized Emission of Monolayer WS2 at Room Temperature with Plasmonic Archimedes Spiral Nanostructures.

Monolayer transition metal dichalcogenides (TMDs) have intrinsic valley degrees of freedom, making them appealing for exploiting valleytronic applications in information storage and processing. WS2 monolayer possesses two inequivalent valleys in the Brillouin zone, each valley coupling selectively with a circular polarization of light. The degree of valley polarization (DVP) under the excitation of circularly polarized light (CPL) is a parameter that determines the purity of valley polarized photoluminescence (PL) of monolayer WS2 . Here efficient tailoring of valley-polarized PL from monolayer WS2 at room temperature (RT) through surface plasmon-exciton interactions with plasmonic Archimedes spiral (PAS) nanostructures is reported. The DVP of WS2 at RT can be enhanced from <5% to 40% and 50% by using 2 turns (2T) and 4 turns (4T) of PAS, respectively. Further enhancement and control of excitonic valley polarization is demonstrated by electrostatically doping monolayer WS2 . For CPL on WS2 -2TPAS heterostructures, the 40% valley polarization is enhanced to 70% by modulating the carrier doping via a backgate, which may be attributed to the screening of momentum-dependent long-range electron-hole exchange interactions. The manifestation of electrically tunable valley-polarized emission from WS2 -PAS heterostructures presents a new strategy toward harnessing valley excitons for application in ultrathin valleytronic devices.

Visualization of Plasmon–Exciton Interactions by Scanning Near-Field Optical Microscopy

Visualization of Plasmon–Exciton Interactions by Scanning Near-Field Optical Microscopy

Strong coupling effects in a plexciton system of gold nanostars and J-aggregates

Strong exciton–plasmon interaction enables effective control of the photonic properties of hybrid organic–inorganic nanostructures encompassing light absorption, scattering and luminescence. Whereas the manifestations of light-matter interactions in the absorption and scattering are reasonably well understood their relation to the luminescence as well as luminescence properties themselves in strongly coupled plexcitonic hybrids is still largely underexplored especially for a system with a complex mechanism of hybridisation of states. Here we report on investigation of the interaction between localized and hybridized plasmons in gold nanostars and excitons in J-aggregates under ambient conditions. Our findings demonstrate the quality performance of the formed plexciton system with multiple hybridization channels in terms of the parameters of strong coupling, such as Rabi splitting (230 meV), coupling-strength-to-transition energy ratio (0.07), and cooperativity (2.03). The results of time-resolved experiments elucidate the observed enhanced spontaneous emission rate with regard to the Purcell effect, whose value was estimated from the extinction spectra of the strongly coupled plexciton system.

Electronic Exciton-Plasmon Coupling in a Nanocavity Beyond the Electromagnetic Interaction Picture.

The optical response of a system formed by a quantum emitter and a plasmonic gap nanoantenna is theoretically addressed within the frameworks of classical electrodynamics and the time-dependent density functional theory (TDDFT). A fully quantum many-body description of the electron dynamics within TDDFT allows for analyzing the effect of electronic coupling between the emitter and the nanoantenna, usually ignored in classical descriptions of the optical response. We show that the hybridization between the electronic states of the quantum emitter and those of the metallic nanoparticles strongly modifies the energy, the width, and the very existence of the optical resonances of the coupled system. We thus conclude that the application of a quantum many-body treatment that correctly addresses charge-transfer processes between the emitter and the nanoantenna is crucial to address complex electronic processes involving plasmon-exciton interactions directly impacting optoelectronic applications.

Plasmon–Exciton Interactions: Spontaneous Emission and Strong Coupling

AbstractThe extraordinary optical properties of surface plasmons in metal nanostructures provide the possibilities to enhance and accelerate the spontaneous emission, and manipulate the decay and emission processes of quantum emitters. The extremely small mode volume of plasmonic nanocavities also benefits the realization of plasmon–exciton strong coupling. Here, the progress on the study of plasmon modified spontaneous emission and plasmon–exciton strong coupling are reviewed. The fundamentals of surface plasmons and quantum emitters, and the methods for assembling coupling systems of plasmonic nanostructures and quantum emitters are first introduced. Then the major aspects of plasmon modified spontaneous emission, including emission intensity, lifetime, spectral profile, direction, polarization, and energy transfer are reviewed. The coupling of quantum emitters and plasmonic waveguides is then discussed. Next, the developments of strong coupling between plasmonic structures and various quantum emitters are reviewed. Finally a few applications are highlighted followed by conclusions and outlook.

Tuneable interplay of plasmonic and molecular excitations in self-assembled silver - fullerene nanocomposites

Elaboration of functional hybrid nanostructures integrating noble metal nanoparticles (NPs) is an attractive topic in nanoplasmonics prompting unique technologies. Here we report on remarkable plasmonic properties of the self-assembled AgxC60 nanocomposite (NC) films, consisting of dense 3D-assembly of small Ag NPs and supporting C60 medium. Systematic study of optical absorption spectra allowed us to disclose the spectral peculiarities of plasmonic and molecular excitations in the AgxC60 NC films in the broad range of Ag concentrations, 0<x < 30. Analysis of the plasmonic modes evaluated in this study designates intriguing features of the Ag NP plasmonic coupling, which are found to be rather different in the NC films with x<10 and x>15. We found that increase of x in the range of 0<x < 10 results in strong enhancement of the electric dipole plasmon mode, whereas optical spectra of the NC films with x > 15 demonstrate pronounced efficiency of tunnelling charge transfer plasmons. Careful analysis of the detected excitations revealed evident conformity in the x-induced alterations of the plasmonic and excitonic modes as hallmarks of plasmon–exciton interactions. The detected plasmonic effects demonstrate great potential of this metal-organic system in molecular sensing, photocatalysis and optoelectronics.

Programmable DNA Circuits for Flexible and Robust Exciton-Plasmon Interaction-Based Photoelectrochemical Biosensing.

DNA circuits as one of the dynamic nanostructures can be rationally designed and show amazing geometrical complexity and nanoscale accuracy, which are becoming increasingly attractive for DNA entropy-driven amplifier design. Herein, a novel and elegant exciton-plasmon interaction (EPI)-based photoelectrochemical (PEC) biosensor was developed with the assistance of a programmable entropy-driven DNA amplifier and superparamagnetic nanostructures. Low-abundance miRNA-let-7a as a model can efficiently initiate the operation of the entropy-driven DNA amplifier, and the released output DNAs can open the partially hybridized double-stranded DNA anchored on Fe3O4@SiO2 particles. The liberated Au nanoparticles (NPs)-cDNA can completely hybridize with CdSe/ZnS quantum dots (QDs)-cDNA-1 and result in proportionally decreased photocurrent of CdSe/ZnS QDs-cDNA-1. This unique entropy-driven amplification strategy is beneficial for reducing the reversibility of each step reaction, enables the base sequence invariant and the reaction efficiency improvement, and exhibits high thermal stability and specificity as well as flexible design. These features grant the PEC biosensor with ultrasensitivity and high selectivity. Also, instead of solid-liquid interface assembly for conventional EPI-based PEC biosensors, herein, DNA hybridization in the solution phase enables the improved hybridization efficiency and sensitivity. In addition, superparamagnetic Fe3O4@SiO2 particles further ensure the enhancement of the selectivity and reliability of the as-designed PEC biosensor. Particularly, this single-step electrode modification procedure evidently improves the electrode fabrication efficiency, reproducibility, and stability.

Relativity and diversity of strong coupling in coupled plasmon-exciton systems

Strong coupling between quantum emitters and photonic modes, at which the level splitting (LS) of the mixed quantum states occurs, has aroused great interest due to diverse important quantum applications. The spectral Rabi-splitting (SRS) in photon emission or absorption has been extensively used to characterize strong coupling based on the equality assumption by assigning the SRS to LS. Here, we demonstrate that the equality assumption is usually invalid via a unified quantum treatment on the coupled plasmon-exciton system. It is revealed that the strong coupling characterized by the SRS is easily observed from the subsystem with larger decay, manifesting itself in relativity and diversity, which is highly correlated to the dissipative decays of the coupling subsystems. The plasmon-exciton interactions can be classified into the weak coupling, pseudo-, dark-, intermediate- and super-strong coupling regimes. Our work not only enriches the underlying physics of strong light-matter interactions, but also may stimulate further experimental researches in this field.