Plasmon Emission Research Articles

Directional and enhanced spontaneous emission with a corrugated metal probe.

A three-dimensional corrugated metal tapered probe with surface corrugated gratings at the tip apex is proposed and investigated theoretically, which leads to an obvious emission beaming effect of spontaneous emission from a single emitter near the probe. In contrast with conventional apertureless metal probes, where only the enhancement of an optical near-field is concerned, the corrugated probe is able to manipulate local excitation intensity and far-field emission direction simultaneously. The angular emission from a single dipole source, being placed close to the corrugated probe, falls into a cone with a maximum directivity angle of ±11.6°, which improves the collection efficiency 25-fold. Such a probe simultaneously increases the localized field intensity to about twice as strong as the conventional bare tip. In addition, the radiation pattern is sensitive to the working wavelength and the dipole to tip-apex separation. These findings make a promising route to the development of plasmonic spontaneous emission manipulation based on corrugated tapered antenna-for instance, tip-enhanced spectroscopy, single-molecule sensing, and single-photon source.

Near-Field Imaging of Surface Plasmon Polaritons Excited by Chains of Gold Nanodiscs

We present a study of the near-field pattern created by chains of gold nanodiscs situated on a gold thin film and illuminated at oblique incidence. Each disc generates surface plasmon polaritons that propagate on the gold surface. The created waves interfere between them and with the illuminating beam. We observed that when the discs are separated by a distance smaller than the half wavelength, the chain behaves like a continuous ridge. When the discs separation increases, a complex periodic pattern appears and extends up to several wavelengths from the chain. For some specific separation distances, a directional emission of surface plasmon is also observed. The experimental results are in good agreement with numerical simulations performed by considering each disk as an independent dipole-like surface plasmon source.

Single-Nanocrystal Photoluminescence Spectroscopy Studies of Plasmon-Multiexciton Interactions at Low Temperature.

Using thick-shell or "giant" CdSe/CdS nanocrystal quantum dots (g-NQDs), characterized by strongly suppressed Auger recombination, we studied the influence of plasmonic interactions on multiexciton emission. Specifically, we assessed the separate effects of plasmonic absorption and plasmonic emission enhancement by a systematic analysis of the pump fluence dependence of low-temperature photoluminescence (low-T PL) derived from individual CdSe/CdS g-NQDs deposited on nanoroughened silver films. Our study reveals that (1) the multiexciton (MX) emissions in g-NQD coupled to silver films were enhanced not only through the creation of more excitons via enhancement of absorption but also through the direct modification of the competition between the radiative and nonradiative recombination processes of MXs; (2) strong enhancement in absorption is not necessary for strong multiexciton emission; and (3) the emission of MXs can become stronger with the increase of multiexciton order. We also exploited the strong enhancement of MX emission to perform second-order photon correlation and cross-correlation experiments using very low pump fluences and observed a strong photon bunching that decays with increasing pump fluence.

SiC and GaAs emitters as selective terahertz radiation sources

Two types of electrically heated THz radiation emitters: (1) the Globar-SiC (black body), and (2) the highly doped GaAs plate, are considered as selective high-power terahertz (THz) radiation sources. The spectrum of the new type GaAs emitter in the 9–15 THz frequency range is determined by oscillations of free electron plasma and coupled plasmon–phonons. The thermally stimulated resonant emission of surface plasmon–phonon polaritons is experimentally observed. The radiative modes of coupled surface plasmon–phonon polaritons in the n + -GaAs plate are identified.

Impact of photoinduced processes on the plasmonic enhancement of colloidal quantum dot emission

ABSTRACTWe study the mutual effects of photoinduced processes (irradiation effects) and plasmonic emission enhancement in close-packed CdSe/ZnS colloidal quantum dots in the vicinity of gold metallic nanoparticles with two significantly different size distributions. For this we examine the impact of the heat generated by the metallic nanoparticles, the strength of plasmonic field enhancement, and the rate of energy transfer from the quantum dots to metallic nanoparticles in the presence of a laser field with low and moderate intensities. Our results show that the interplay between the photophysics of the quantum dots and their plasmonic emission enhancement is significantly pronounced when the metallic nanoparticles are large. In such a case we observed large suppression of photoinduced fluorescence enhancement (PFE). For smaller metallic nanoparticles the results suggest mostly an overall time-independent suppression of the quantum dots’ emission with no significant impact on PFE.

Metal nanoparticle plasmons operating within a quantum lifetime

We investigate the dynamics of a plasmonic oscillation over a metal nanoparticle when it is strongly coupled to a quantum emitter (e.g. quantum dot, molecule). We simulate the density matrix evolution for a simple model, a coupled classical-quantum oscillators system. We show that the lifetime of the plasmonic oscillations can be increased several orders of magnitude, up to the decay time of the quantum emitter. This effect shows itself as the narrowing of the plasmon emission band in the spaser (surface plasmon amplification by the stimulated emission of radiation) experiment [Nature, 2009, 460, 1110], where a gold nanoparticle interacts with the surrounding molecules. Enhancement of the plasmonic excitation lifetime enables stimulated emission to overcome the spontaneous one. The enhancement occurs due to the emergence of a phenomenon analogous to electromagnetically induced transparency (EIT). The effect can find applications in many areas of nanoscale physics, such as in quantum information with plasmons and in increasing solar cell efficiency.

Plasmonic Sensing via Photoluminescence of Individual Gold Nanorod

Label-free plasmonic sensors based on localized surface plasmon resonances of nanostructured noble metal materials usually transduce optical refractive index changes occurring in the vicinity of the nanostructures by optical scattering or by extinction. We demonstrate in experiments that the photoluminescence of plasmonic nanoparticles can also be employed to detect biological molecule binding events efficiently. Photoluminescence probably due to plasmon emission of a single gold nanorod presents a similar resonance peak and resembles the response to a refractive index change observed by scattering. The well-known biotin–streptavidin binding assay was detected successfully using the photoluminescence of an individual isolated nanorod. The localized surface plasmon resonances’ responses by scattering in situ with the same nanorod and control experiments were also performed to verify the sensing process. The results evidence that a nanoscale plasmonic sensor can also be archived effectively through the phot...

Modulation of nanocavity plasmonic emission by local molecular states of C_60 on Au(111)

We investigate the modulation of C60 monolayers on the nanocavity plasmonic (NCP) emission on Au(111) by tunneling electron excitation from a scanning tunneling microscope (STM) tip. STM induced luminescence spectra show not only suppressed emission, but also significant redshift of NCP emission bands on the C60 molecules relative to the bare metal surface. The redshift, together with the bias- and coverage-dependent emission feature, indicates that the C60 molecules act beyond a pure dielectric spacer, their electronic states are heavily involved in the inelastic tunneling process for plasmonic emission. A modified quantum cutoff relation is proposed to explain qualitatively the observed emission feature at both bias polarities. We also demonstrate molecularly resolved optical contrast on the C60 monolayer and discuss the contrast mechanism briefly.

Nanowire-based plasmonic waveguides and devices for integrated nanophotonic circuits

AbstractThe fast development of plasmonics have greatly advanced our understanding to the abundant phenomena related to surface plamon polaritons (SPPs) and improved our ability to manipulate light at the nanometer scale. With tightly confined local field, SPPs can be transmitted in waveguides of subwavelength dimensions. Nanophotonic circuits built with plasmonic elements can be scaled down to dimensions compatible with semiconductor-based nanoelectronic circuits, which provides a potential solution for the next-generation information technology. Different structures have been explored as plasmonic waveguides for potential integration applications. This review is focused on metallic nanowire waveguides and functional components in nanowire networks. We reviewed recent progress in research about plasmon generation, emission direction and polarization, group velocity, loss and propagation length, and the near-field distribution revealed by quantum dot fluorescence imaging. Electrical generation and detection of SPPs moves towards the building of plasmonic circuits, where bulky external light sources and detectors may be omitted. The coupling between metal nanowires and emitters is important for tailoring light-matter interactions, and for various potential applications. In multi-nanowire structures, plasmon signal control and processing are introduced. The working principles of these nanowire-based devices, which are based on the control to the near field distributions, will become the design rule for nanophotonic circuits with higher complexity for optical signal processing. The recent developments in hybrid photonic-plasmonic waveguides and devices are promising for making devices with unprecedented performance.

Quantum theory of dipole nanolasers

We generalize the semiclassical model of the dipole nanolaser (DNL) based on the Heisenberg–Langevin approach, taking into account spontaneous emission of plasmons into the generation mode, nonlinearity of generation, and noises. We find a “thresholdless” smooth transition from the spontaneous emission to the stimulated emission and the threshold conditions for such a transition and determine the spectrum of generation and its linewidth. We show that, in spite of the very low quality of the DNL generation mode, the linewidth of a DNL with many M ∼ 104 − 105 emitters decreases, with the pump increase, to quite small values ~ 10−2 of the width 2Γ2 of the lasing transition at modest pump rates, about 30 times larger that the decay rate of the emitter upper lasing state. This fact confirms the practical possibilities of realizing DNLs with narrow-line stimulated emission. Otherwise, the linewidth of DNLs with small M ∼ 1 number of emitters is larger than 2Γ2 and increases with the pump rate. In addition our results on DNLs can be applied to other lasers, such as nanolasers, microlasers, and LEDs for lighting, also with a low-quality cavity and strong spontaneous emission into the generation mode.

Plasmonic properties and device in nanostructures

In this article, we reviewed new designs for plasmonic nanostructure and its nanofocusing, coupling, resonance, and waveguide characterizations. With in-plane Fresnel zone plates, a 15 times field enhancement was achieved for the plasmonic nanofocusing. Plasmonic antennas placed at both ends of a single nanowire, consisting of a nanooptical circuit, was successfully realized in an enhanced plasmon coupling and emission. Plasmonic Fano resonance was also observed in a single sliced Ag nanodisk with the structure symmetry breaking. A hybrid plasmonic waveguide with a CdS nanoribbon placed on Ag surface showed an excellent mode confinement and energy low dissipation. More potential applications based on these plasmonic configurations are also discussed in this article.

Plasmon Emission Quantum Yield of Single Gold Nanorods as a Function of Aspect Ratio

We report on the one-photon photoluminescence of gold nanorods with different aspect ratios. We measured photoluminescence and scattering spectra from 82 gold nanorods using single-particle spectroscopy. We found that the emission and scattering spectra closely resemble each other independent of the nanorod aspect ratio. We assign the photoluminescence to the radiative decay of the longitudinal surface plasmon generated after fast interconversion from excited electron-hole pairs that were initially created by 532 nm excitation. The emission intensity was converted to the quantum yield and was found to approximately exponentially decrease as the energy difference between the excitation and emission wavelength increased for gold nanorods with plasmon resonances between 600 and 800 nm. We compare this plasmon emission to its molecular analogue, fluorescence.

Fano Interference between Localized Plasmons and Interface Reflections

Layers of subwavelength metal nanostructures that support localized surface plasmon resonances are of broad interest in applied nanotechnology, for example, in optical sensor development and solar energy harvesting devices. We measured specular reflection spectra as a function of incidence angle for two-dimensional layers of gold nanodisks on glass and found highly asymmetric line-shapes and a spectral red-shift of up to 0.2 eV, or 10% of the plasmon resonance energy, as the angle changed from normal toward grazing incidence. This dramatic angular dispersion is the result of a tunable Fano interference between the spectrally narrow plasmon emission and a "white" continuum caused by the interface reflection. The data are found to be in excellent agreement with predictions based on a theory for Fresnel reflection coefficients of an interface with subwavelength inclusions. The theory can also be used to derive analytical expressions for the Fano parameters.

Preface

The unique success story of semiconductor physics and technology relies on the ability to highly integrate micro- and nanometer sized functional units on a single chip. Within the last few years single nanostructures, e.g., individual and coupled pairs of quantum dots and single molecules moved more and more into the focus of many research groups to study the exciting physics and to exploit their tremendous potential for device applications. The full advantage of their superior properties can be utilized if a controlled positioning or growth of the nanostructure inside a more complex device structure can be realized, thereby defining precise coupling between the microscopic nanostructure and the macroscopic periphery. single-photon sources coupled quantum-dot gates single quantum-dot tunneling diodes. electroluminescence of single electrically-driven molecules at room temperature controlling quantum-dot emission by integration of semiconductor nanomembranes onto piezoelectric actuators controlled coupling of individual self-assembled quantum dots to plasmonic nanoantennas quantum light emission of two lateral tunnel-coupled (In,Ga)As/GaAs quantum dots controlled by a tunable static electric field realization of vertically stacked and laterally ordered InP and InAs quantum dots for quantum gate applications development of site-controlled SiGe islands on patterned Si(001) and realization of tunneling diodes ultrafast transient reflection spectroscopy of a single self-assembled GaAs quantum dot. We hope that this collection of ideas and results of controlled positioning of single nanostructures stimulates many fascinating experiments and clever applications of quantum objects. We wish to thank all people involved in the research group for their excellent work, the DFG for the financial support and Wiley for the opportunity to publish this volume. On behalf of all applicants being funded by DFG over the years, M. Lippitz and P. Michler Stuttgart, March 2012

Extraordinary Surface Plasmon Coupled Emission Using Core/Shell Gold Nanorods

Plasmon-coupled fluorescence from Au nanorods with fluorophore-doped silica shells has been studied. Besides the ordinary emission of the fluorophore at 590 nm, an extra emission peak was found on the normally weak fluorescence tail at the surface plasmon resonance (SPR) of the Au nanorods around 750 nm. It provides clear evidence of the plasmonic emission. Our experiment results suggest that the linear absorption coefficient of fluorophores was strongly enhanced around the SPR wavelength and the plasmonic emission at 750 nm was created by the resonance energy transfer from the excited fluorophores to SPRs. The energy transfer rate was estimated to be 5.22 ns–1, and the total quantum yield of the sample was 1.5 times that of the free fluorophore molecules in aqueous solutions. This study supports that strong fluorescence at desired wavelength can be engineered by fluorophore–plasmon coupling.

Particular features of a Vavilov-Cherenkov-like phenomenon with emission of surface plasmons

We consider a phenomenon of the Vavilov-Cherenkov type that can be observed in a space with a metal-dielectric boundary that well reflects light. An electron that initially uniformly moves at a constant velocity near this boundary creates surface plasmon-polaritons the phase velocity of which is lower than the electron velocity. The momentum of a photon in the created plasmon-polariton is calculated. This momentum may be almost as high as the doubled initial electron momentum. The velocity of the electron that created the photon in the plasmon-polariton may also become almost zero. We show that, at a nonzero temperature, this process has a nonzero probability.

Electroluminescence of single CdSe nanocrystals induced by scanning tunneling microscope

Electroluminescence intensity of single CdSe nanocrystals (NCs) excited by the tunnel current of a scanning tunneling microscope (STM) was measured. Samples with NCs do not exhibit plasmon emission. This enables one to measure pure emission from a single NC. Electroluminescence, measured in time, differs considerably from that of photoluminescence in similar NCs. This difference in temporal behavior results from the difference in physical conditions of experiments on photo- and electroluminescence.

Plasmon Singularities from Metal Nanoparticles in Active Media: Influence of Particle Shape on the Gain Threshold

Localized surface plasmon singularities from metal nanoparticles in active media are investigated on the basis of classic linear electrodynamics. It is found that the gain threshold is inversely proportional to the shape factor of the particle. When relating this phenomenon to the plasmonic field-enhanced emission from gain units, we show that the maximum electric field around spheroidal particles impacts upon the gain threshold via a two-exponential decay function. Our results provide a way to reduce the gain requirement in metal nanoparticle-based spaser or random laser systems.

Optical Bifunctionality of Europium-Complexed Luminescent Graphene Nanosheets

Graphene is an intriguing two-dimensional material, which could be modified for achieving tunable properties with many applications. Photoluminescence of graphene due to plasmonic emission is well-known, however, attempts to develop strong luminescent graphene have been difficult. Synthesis of a graphene-based material with a dual optical functionality, namely quenching the fluorescence of organic dyes while maintaining its own self-luminescence, is an interesting and challenging proposition. Here, we demonstrate this optical bifunctionality in a lattice-modified luminescent graphene, where europium(III) cations are complexed with graphene through oxygen functionalities. After excitation at 314 nm, a hypersensitive red emission is observed at 614 and 618 nm showing the complexation of europium(III) with graphene. We demonstrate dual functionality of this graphene by the quenching of luminescence of Rhodamine-B while displaying its own hypersensitive red emission. The decay lifetime observed through the time-resolved spectroscopy confirms its potential for applications in biosensing as well as optoelectronics.

Fluctuations of electroluminescence intensity of single CdSe nanocrystals excited by scanning tunneling microscope current

Electroluminescence from single CdSe nanocrystals (NCs) excited by tunneling current of scanning tunneling microscope (STM) has been measured. Two types of samples with low and high concentration of CdSe NCs deposited on the gold substrate have been prepared. Both types of samples had no plasmon emission. It enabled one to detect pure electroluminescence from single CdSe NCs. Samples with low concentration of NCs exhibit an intensive short-term luminescence of NCs for several seconds. Samples with high concentration of NCs exhibit a weak fluctuating long-term luminescence for thousand seconds. Fluctuations of NC electroluminescence differ considerably from those detected recently in photoluminescence of CdSe NCs embedded in polymer films. The difference in fluctuations results from the difference in physical conditions existing in electro- and photoluminescence. The distribution of photons w(N, T) emitted in time interval T has been found from statistical treating of fluctuating luminescence. Due to weakness of the pure signal, we paid a special attention to allowing for photomultiplier tube noise while treating these fluctuations. The photon distribution in pure signal is one of super-Poisson type, i.e. it is broader than Poisson distribution. A dynamical model for an absorber–emitter excited by tunneling current of STM has been offered. The model takes into account the thermal drift of STM tip.