Plasmon Emission Research Articles

Mimicking plasmonic nanolaser emission by selective extraction of electromagnetic near-field from photonic microcavity.

Plasmonic nanolasers have attracted significant attention owing to their ability to generate a coherent optical field in the deep subwavelength region, and they exhibit promising applications in integrated photonics, bioimaging and sensing. However, the demonstration of lasing in individual metallic nanoparticles with 3D subwavelength confinement represents a significant challenge and is yet to be realized. Herein, we propose to mimic a plasmonic nanolaser via selective scattering off the evanescent tail of a lasing photonic nanobelt using a single silver nanorod (24 nm × 223 nm). The nanorod acts as an optical antenna that selectively extracts the near-field component along the rod axis. The light output from the silver nanorod mimics the emission of a plasmonic nanolaser in its localized near-field and polarization dependence, except for the lasing wavelength and linewidth, which are inherited from the photonic laser. The realization of localized coherent light sources provides promising nanoscale lighting that shows potential in background-suppressed illumination, biosensing and imaging.

Carrier recombination and plasmonic emission channels in metallic photoluminescence.

We systematically investigate the metallic photoluminescence (MPL) emitted from plasmonic nanoparticles (NPs) upon excitation with ultrafast laser pulses using a scanning confocal optical microscope (SCOM). By comparing the emission spectra of Au NPs of varying dimensions with the corresponding dark-field scattering spectra, indications are found that MPL encompasses two emission channels: the particle plasmons (PPs) and the electron-hole (e-h) pair recombination. The plasmons can be interpreted to play a twofold role: in the excitation process they provide the local field enhancement, and in the emission process they offer extra radiation channels.

Plasmonic metamaterial based unified broadband absorber/near infrared emitter for thermophotovoltaic system based on hexagonally packed tungsten doughnuts

In this paper, we report a simple and effective design of a polarization independent and wide incident angle plasmonic metamaterial based unified broadband absorber and thermal emitter consisting of hexagonally packed tungsten doughnuts (hexa-rings) for thermophotovoltaic system. The proposed design shows more than 85% of absorption over 0.3 to 2.18 μm, that is, over the broad spectral range from the ultraviolet to the near infrared (NIR), and 100% absorption and thermal emission at 2.18 μm. Further, the NIR plasmonic absorption and thermal emission peak is tuned from the spectral range 2.18 to 3 μm for different low bandgap photovoltaic materials by varying the design parameters such as inner and outer ring radius, instead of varying any other design parameters in the proposed design. The possibility of the realization of hexa-doughnut structures through a single-step phase engineered interference lithography technique is also demonstrated through the realization of micro/nanostructure samples over large area.

Spectroscopically forbidden infra-red emission in Au-vertical graphene hybrid nanostructures

Implementation of Au nanoparticles (NPs) is a subject for frontier plasmonic research due to its fascinating optical properties. Herein, the present study deals with plasmonic assisted emission properties of Au NPs-vertical graphene (VG) hybrid nanostructures. The influence of effective polarizability of Au NPs on the surface enhanced Raman scattering and luminescence properties is investigated. In addition, a remarkable infra-red emission in the hybrid nanostructures is observed and interpreted on the basis of intra-band transitions in Au NPs. The flake-like nanoporous VG structure is invoked for the generation of additional confined photons to impart additional momentum and a gradient of confined excitation energy towards initiating the intra-band transitions of Au NPs. Integrating Au plasmonic materials in three-dimensional VG nanostructures enhances the light–matter interactions. The present study provides a new adaptable plasmonic assisted pathway for optoelectronic and sensing applications.

Relation between plasmonic tip emission and electromagnetic enhancement evidenced in tip‐enhanced Raman spectroscopy

AbstractWe report tip‐enhanced Raman spectroscopy measurements of single wall carbon nanotubes deposited on a barium titanate substrate. The tip‐enhanced Raman spectroscopy mappings demonstrate that the evolution of the gold tip enhanced luminescence is strongly correlated with the intensity of the Raman modes from the single wall carbon nanotubes and the substrate. As the tip emission is directly related to the plasmonic properties of the nanoantenna at the apex of the tip, it is possible to compare the frequency and intensity of each vibrational mode with the electromagnetic enhancement model. We find a very good agreement between all these parameters confirming the essential role of the electromagnetic enhancement mechanism in surface enhanced spectroscopy.

Enhanced Light Emission from Plasmonic Nanostructures by Molecules

Interaction between plasmonic nanostructures and molecules is modeled based on the concept of quantized optical cavity for surface enhanced Raman scattering process. We have found that the background emission from plasmonic nanostructures is not constant as speculated ordinarily, it is enhanced accompanying with the molecules Raman scattering. The plasmonic nanostructures not only scatter elastically the energy coupling from the molecules excited states, but also radiate it inelastically as surface plasmon emission partly resulting an enhanced background. According to single nanoparticle experiments, the model reveals that the background fluctuations is mainly due to the induced field of the molecules, which increases the local field felt by the nanostructures that was often overlooked in the past. These findings suggest considering the plasmonic nanostructures and molecules as a hybrid entity to analyze and optimize the surface enhanced spectroscopy.

Plasmon-assisted resonant tunneling in graphene-based heterostructures

We develop a theory of electron tunneling accompanied by carrier-carrier scattering in graphene - insulator - graphene heterostructures. Due to the dynamic screening of Coulomb interaction, the scattering-aided tunneling is resonantly enhanced if the transferred energy and momentum correspond to those of surface plasmons. We reveal the possible experimental manifestations of such plasmon-assisted tunneling in current-voltage curves and plasmon emission spectra of graphene-based tunnel junctions. We find that inelastic current and plasmon emission rates have sharp peaks at voltages providing equal energies, momenta and group velocities of plasmons and interlayer single-particle excitations. The strength of this resonance, which we call plasmaronic resonance, is limited by interlayer twist and plasmon lifetime. The onset of plasmon-assisted tunneling can be also marked by a cusp in the junction $I(V)$-curve at low temperatures, and the threshold voltage for such tunneling weakly depends on carrier density and persists in the presence of interlayer twist.

Carbon nanoflake-nanoparticle interface: A comparative study on structure and photoluminescent properties of carbon nanoflakes synthesized on nanostructured gold and carbon by hot filament CVD

Three dimensional vertically-oriented carbon nanoflakes grown on carbon and gold nanoparticles by the hot filament chemical vapor deposition in CH4 environment demonstrate quite similar structure and composition, but drastically different room temperature photoluminescent properties. The interfacial interactions were asserted to be the main reason for the differences in the optical emission. The mechanisms of highly oriented growth, generation and enhancement of photoluminescence were investigated, and it was demonstrated that the formation of oriented nanoflakes resulted from the stress produced in the carbon layers on carbon and gold nanoparticles. Specifically, deformation of nanoparticles and difference in the expansion rates of carbon layer, gold and carbon nanoparticles are the main causes for the stress formation. The oriented growth of carbon nanoflakes is maintained by the repulsion effect between the carbon nanoflakes due to the net charge produced from the hydrocarbon radicals on the edges of carbon nanoflakes via charge transfer between H and C atoms. The photoluminescence generation of carbon nanoflakes is related to the sp2 carbon clusters on the edges of carbon nanoflakes. Stronger green photoluminescent emission from the carbon nanoflake/gold nanoparticle system than from the carbon nanoflake/carbon nanoparticle system is the result of the intense plasmon emission from gold nanoparticles.

Plasmonic lattice resonance-enhanced light emission from plastic scintillators by periodical Ag nanoparticle arrays

We have demonstrated that periodical arrays of silver nanoparticles can enhance the light emission from a plastic scintillator layer on the surface of a silicon substrate. The enhancement is attributed to surface lattice resonances with a photonic-plasmonic nature. Although the enhancement exhibits directional characteristics for individual wavelengths, the wavelength-integrated enhancement shows a monotonous increase with increasing emission angle. As a result, an overall 1.81-fold wavelength- and angle-integrated enhancement has been obtained. This observation is promising for fundamental and applied research into enhanced luminescent material layers on opaque substrates.

Imaging the dark emission of spasers.

Spasers are a new class of laser devices with cavity sizes free from optical diffraction limit. They are an emergent tool for various applications, including biochemical sensing, superresolution imaging, and on-chip optical communication. According to its original definition, a spaser is a coherent surface plasmon amplifier that does not necessarily generate a radiative photon output. However, to date, spasers have only been studied with scattered photons, and their intrinsic surface plasmon emission is a "dark" emission that is yet to be revealed because of its evanescent nature. We directly image the surface plasmon emission of spasers in spatial, momentum, and frequency spaces simultaneously. We demonstrate a nanowire spaser with a coupling efficiency to plasmonic modes of 74%. This coupling efficiency can approach 100% in theory when the diameter of the nanowire becomes smaller than 50 nm. Our results provide clear evidence of the surface plasmon amplifier nature of spasers and will pave the way for their various applications.

Gap-plasmon of Fe3O4@Ag core-shell nanostructures for highly enhanced fluorescence detection of Rhodamine B

A novel gap-plasmon of Fe3O4@Ag core-shell nanoparticles for surface enhanced fluorescence detection of Rhodamine B (RB) was developed. Fe3O4@Ag core-shell nanostructures with Ag shell and Fe3O4 core were synthetized by self-assembled method with the assistance of 3-mercaptopropyl trimethoxy silane (MPTS). To study the RB fluorescence enhanced by gap-plasmon, the fluorescence properties of RB on the substrates with different nanogap densities were systematically investigated, and the results showed that the fluorescence intensity of RB on Fe3O4@Ag core-shell NPs substrate was much stronger than that on bare glass substrate, and the fluorescence intensity was further improved by using multilayer Fe3O4@Ag core-shell NPs substrate which had higher nanogap density. Different from the mechanism that is based on the maximum overlap of the surface plasmon resonance (SPR) band and emission band, the mechanism of the fluorescence enhancement in our work is based on the localized surface plasmon (LSP) and the gap plasmon near-field coupling with the Fe3O4@Ag core-shell NPs. Besides, the detection limit obtained was as low as 1×10-7 mol/L, and the Fe3O4@Ag core-shell NPs substrate had high selectivity for RB fluorophores. It was demonstrated that the Fe3O4@Ag core-shell NPs substrate had activity, good stability, and selectivity for fluorescence detection of RB. And the detection of RB by the surface plasmon enhanced fluorescence was more convenient and rapid than the traditional detection methods in previous works.

Theory and technology of SPASERs

Spaser is an acronym for surface plasmon amplification by stimulated emission of radiation. A spaser is effectively a nanoscale laser with subwavelength dimensions and a low-Q plasmonic resonator, which sustains its oscillations using stimulated emission of surface plasmons. The concept of stimulated emission to sustain plasmonic oscillations in a resonator was first described by David Bergman and Mark Stockman in 2003. Using a unified notation, we provide an up-to-date literature review of the major developments and latest advances in spaser theory and carry out a systematic exposition of some of the key results useful to understand the operation of spasers. Our presentation covers both semiclassical and quantum-mechanical formulations of spaser models as well as various designs and technologies demonstrated/suggested to illustrate key aspects of this technology. Even though many advances have already been made in spaser technology, there are many hurdles that need to be overcome to bring this technology up to the level of modern laser technology. We take especially great care to highlight the main challenges facing various spaser designs and the limitations of widely used methods and materials. This review is written for both specialists in the field and a general engineering–physics–chemistry readership.

Submolecular Electroluminescence Mapping of Organic Semiconductors.

The electroluminescence of organic films is the central aspect in organic light emitting diodes (OLEDs) and widely used in current display technology. However, its spatial variation on the molecular scale is essentially unexplored. Here, we address this issue by using scanning tunneling microscopy (STM) and present an in-depth study of the electroluminescence from thin C60 films (<10 monolayers) on Ag(111) and Au(111) surfaces. Similar to an OLED, the metal substrate and STM tip inject complementary charge carriers that may recombine within the molecular film; however, the atomically defined charge injection by the tip enables mapping of the local electroluminescence down to the submolecular scale. We show that the radiative recombination in solid C60 is restricted to various structural defects, whose emission characteristics can be addressed individually. The emission fine structure reveals a coupling to Jahn-Teller active vibrational modes of C60, which implies that its parity-forbidden lowest singlet transition becomes locally allowed at the emission centers. At lateral distances of a few nanometers, only a weak emission from tip-induced plasmons is detectable. Their excitation evidences the injection of both charge carrier types and confirms that they are unable to recombine radiatively at positions far from structural defects. Finally, we demonstrate that the molecular orbital pattern visible in electroluminescence maps enables an unambiguous discrimination between the intrinsic radiative recombination of electron-hole pairs in the organic film and the technique-related emission of tip-induced plasmons. This capability is essential to consolidate STM as a tool to explore the light generation from organic films on the nanoscale.

Splashing transients of 2D plasmons launched by swift electrons.

Launching of plasmons by swift electrons has long been used in electron energy-loss spectroscopy (EELS) to investigate the plasmonic properties of ultrathin, or two-dimensional (2D), electron systems. However, the question of how a swift electron generates plasmons in space and time has never been answered. We address this issue by calculating and demonstrating the spatial-temporal dynamics of 2D plasmon generation in graphene. We predict a jet-like rise of excessive charge concentration that delays the generation of 2D plasmons in EELS, exhibiting an analog to the hydrodynamic Rayleigh jet in a splashing phenomenon before the launching of ripples. The photon radiation, analogous to the splashing sound, accompanies the plasmon emission and can be understood as being shaken off by the Rayleigh jet-like charge concentration. Considering this newly revealed process, we argue that previous estimates on the yields of graphene plasmons in EELS need to be reevaluated.

Synthesis and Characterization of Ag Nanoparticles for Orthopaedic applications

Bacterial infections are a leading cause of death for millions of people worldwide, while few antibiotics have been proved effective against multidrug-resistant bacteria. Recently, nanoparticles have been used for the delivery of therapeutic agents to reduce bacterial infections due to their antimicrobial activity and unique mode of action. In our studies, silver nanoparticles (Ag NPs) have been used in order to meddle with associated infections for orthopaedic applications, due to their unique morphology and size. Nanoprecipitation method was used for the development of the NPs, using PVP (polyvinylpyrrolidone) as a reducing agent. Chitosan was used as a stabilizing and a coating agent at different concentrations (0.1%, 0.01% and 0.001%) in order to evaluate the most optimum capped coating. Atomic Force Microscopy (AFM) was the appropriate indicator for the morphological and topography analysis. Results showed that chitosan-capped NPs with 0.01% were found to be the most optimum. Transmittance measurements at plasmon emission at ∼320nm wavelength have showed Ag nanoparticles which were identified due to the sharp absorption peak. Variations of the absolute transmittance values due to the different thickness of the samples confirmed the coating of chitosan in Ag NPs. XRD measurements further took place and successfully have indicated the presence of chitosan in Ag nanoparticles’ surface. Electrospinning System was used for the formation of PCL (poly-ε-caprolactone) scaffolds where Ag NPs were deposited via Electrospraying System. The final scaffolds were then studied with AFM and SEM (Scanning Electron Microscopy) Images. As a conclusion, the fabricated Ag NPs into polymer scaffolds appeared to be a valuable tool with antibacterial properties towards implant-associated orthopedic infections.

Chip-integrated plasmonic cavity-enhanced single nitrogen-vacancy center emission.

High temporal stability and spin dynamics of individual nitrogen-vacancy (NV) centers in diamond crystals make them one of the most promising quantum emitters operating at room temperature. We demonstrate a chip-integrated cavity-coupled emission into propagating surface plasmon polariton (SPP) modes narrowing the NV center's broad emission bandwidth with enhanced coupling efficiency. The cavity resonator consists of two distributed Bragg mirrors that are built at opposite sides of the coupled NV emitter and are integrated with a dielectric-loaded SPP waveguide (DLSPPW), using electron-beam lithography of hydrogen silsesquioxane resist deposited on silver-coated silicon substrates. A quality factor of ∼70 for the cavity (full width at half maximum ∼10 nm) with full tunability of the resonance wavelength is demonstrated. An up to 42-fold decay rate enhancement of the spontaneous emission at the cavity resonance is achieved, indicating high DLSPPW mode confinement.

Plasmons in tunnel-coupled graphene layers: Backward waves with quantum cascade gain

Plasmons in van der Waals heterostructures comprised of graphene and related layered materials demonstrate deep subwavelength confinement and large propagation length. In this letter, we show that graphene-insulator-graphene tunnel structures can serve as plasmonic gain media. The gain stems from the stimulated electron tunneling accompanied by the emission of coherent plasmons under interlayer population inversion. The probability of tunneling with plasmon emission appears to be resonantly large at certain values of frequency and interlayer voltage corresponding to the transitions between electron states with collinear momenta - a feature unique to the linear band structure of graphene. The dispersion of plasmons undergoes a considerable transformation due to the tunneling as well, demonstrating negative group velocity in several frequency ranges.

Efficient plasmonic emission by the quantum Čerenkov effect from hot carriers in graphene.

Graphene plasmons have been found to be an exciting plasmonic platform, thanks to their high field confinement and low phase velocity, motivating contemporary research to revisit established concepts in light–matter interaction. In a conceptual breakthrough over 80 years old, Čerenkov showed how charged particles emit shockwaves of light when moving faster than the phase velocity of light in a medium. To modern eyes, the Čerenkov effect offers a direct and ultrafast energy conversion scheme from charge particles to photons. The requirement for relativistic particles, however, makes Čerenkov emission inaccessible to most nanoscale electronic and photonic devices. Here we show that graphene plasmons provide the means to overcome this limitation through their low phase velocity and high field confinement. The interaction between the charge carriers flowing inside graphene and the plasmons enables a highly efficient two-dimensional Čerenkov emission, giving a versatile, tunable and ultrafast conversion mechanism from electrical signal to plasmonic excitation.

Nonequilibrium plasmon emission drives ultrafast carrier relaxation dynamics in photoexcited graphene

The fast decay of carrier inversion in photoexcited graphene has been attributed to optical phonon emission and Auger recombination. Plasmon emission provides another pathway that, as we show here, drives the carrier relaxation dynamics on ultrafast timescales. In studying the nonequilibrium relaxation dynamics we find that plasmon emission effectively converts inversion into hot carriers, whose energy is then extracted by optical phonon emission. This mechanism not only explains the observed fs-lifetime of inversion but also offers the prospect for atomically thin ultrafast plasmon emitters.

Microscopic analysis of gain spectrum of surface plasmons in graphene

In this paper, microscopic interactions of surface plasmons and carriers in the graphene layer are investigated and based on the second quantization formalism, rate equations of surface plasmons are presented. Plasmonic matrix element for surface plasmon-induced transitions in the graphene is also analytically studied. We have shown TE plasmonic modes, due to vanishing plasmonic matrix elements, cannot be amplified in the graphene layer and amplification is only possible for TM plasmonic modes. Using the rate equation and the plasmonic matrix element, we have investigated emission and absorption spectra of surface plasmons in graphene for thermal equilibrium, optical induced population inversion and carrier-injected inversion regimes in the graphene layer and demonstrated that only interband band processes are involved in the surface plasmon emission. We have shown optical pumping opens a gain window for large wavenumbers and the gain window shifts toward larger wavenumbers by increasing pump energy, while carrier injection provides gain for small wave numbers.