Plasmon Emission Research Articles

Plasmonic Light Emission by Inelastic Charge Transport in Ultrathin Zinc Oxide/Metal Heterostructures.

Controlling light emission from plasmonic nanojunctions is crucial for developing tunable nanoscale light sources and integrated photonic applications. It requires precise engineering of plasmonic nanocavity electrodes and a detailed understanding of electrically driven light emission. Using scanning tunneling microscopy-induced luminescence (STML), we studied plasmonic light emission from ultrathin ZnO/Ag(111) inside a silver nanocavity. At positive bias, plasmonic luminescence, caused by radiative decay of localized surface plasmons (LSP), is spectrally low-pass filtered by the ZnO layers. The emission of photon energies above the conduction band edge energy (ECB) of ZnO is suppressed, while the spectral distribution below ECB resembles the LSP resonance on Ag(111). This spectral filtering is absent at negative bias and depends on the local electronic structure, as confirmed by spatial STML mapping. Our findings demonstrate that the ZnO conduction band serves as the initial state for plasmonic luminescence driven by inelastic electron transport across the ZnO/Ag(111) interface.

Electrically Driven Deterministic Plasmon Light Sources Based on Arrays of Molecular Tunnel Junctions.

Surface plasmons excited via inelastic tunnelling have led to plasmon light sources with small footprints and ultrafast response speeds, which are favored by integrated optical circuits. Self-assembled monolayers of organic molecules function as highly tunable tunnel barriers with novel functions. However, limited by the low effective contact between the liquid metal electrode and the self-assembled monolayers, it is quite challenging to obtain molecular plasmon light sources with high density and uniform emission. Here, by combining lithographic patterning with a solvent treatment method, we have demonstrated electrically driven deterministic plasmon emission from arrays of molecular tunnel junctions. The solvent treatment could largely improve the effective contact from 9.6% to 48% and simultaneously allow the liquid metal to fill into lithographically patterned micropore structures toward deterministic plasmon emission with desired patterns. Our findings open up new possibilities for tunnel junction-based plasmon light sources, laying the foundation for electrically driven light-emitting metasurfaces.

Upconversion electroluminescence in 2D semiconductors integrated with plasmonic tunnel junctions.

Plasmonic tunnel junctions are a unique electroluminescent system in which light emission occurs via an interplay between tunnelling electrons and plasmonic fields instead of electron-hole recombination as in conventional light-emitting diodes. It was previously shown that placing luminescent molecules in the tunneling pathway of nanoscopic tunnel junctions results in peculiar upconversion electroluminescence where the energy of emitted photons exceeds that of excitation electrons. Here we report the observation of upconversion electroluminescence in macroscopic van der Waals plasmonic tunnel junctions comprising gold and few-layer graphene electrodes separated by a ~2-nm-thick hexagonal boron nitride tunnel barrier and a monolayer semiconductor. We find that the semiconductor ground exciton emission is triggered at excitation electron energies lower than the semiconductor optical gap. Interestingly, this upconversion is reached in devices operating at a low conductance (<10-6 S) and low power density regime (<102 W cm-2), defying explanation through existing proposed mechanisms. By examining the scaling relationship between plasmonic and excitonic emission intensities, we elucidate the role of inelastic electron tunnelling dipoles that induce optically forbidden transitions in the few-layer graphene electrode and ultrafast hot carrier transfer across the van der Waals interface.

Strong enhancement of graphene plasmonic emission by quantum Čerenkov effect in confined structures

Strong enhancement of graphene plasmonic emission by quantum Čerenkov effect in confined structures

Cathodoluminescence and tip-plasmon resonance of Bi2Te3 triangular nanostructures.

Bi2Te3, as a topological insulator, is able to support plasmonic emission in the visible spectral range. Thin Bi2Te3 flakes can be exfoliated directly from a Bi2Te3 crystal, and the shape of Bi2Te3 flakes can be further modified by focused ion beam milling. Therefore, we have designed a Bi2Te3 triangular antenna with distinct tip angles for the application of plasmonic resonance. The plasmonic emission of the Bi2Te3 triangular antenna is excited and investigated by cathodoluminescence in the scanning electron microscope. Enhanced tip plasmons have been observed from distinct tips with angles of 20º, 36º, 54º, 70º, and 90º, respectively. Due to the confinement of geometric boundaries for oscillating charges, the resonant peak position of tip plasmon with a smaller angle has a blue shift. Moreover, the dependence of plasmonic behavior on the excitation position has been discovered as well. This research provides a unique approach to fabricate Bi2Te3 nanostructures and manipulate the corresponding plasmonic properties.

Enabling Localized Surface Plasmon Emission from InGaN/GaN Nano-LEDs Integrated with Ag/SiO2 Nanoparticles

Enabling Localized Surface Plasmon Emission from InGaN/GaN Nano-LEDs Integrated with Ag/SiO₂ Nanoparticles

Energy transfer assisted plasmonic random laser emission from polymer optical fiber

Here, we analyzed the effect of a donor molecule (Rh6G) on the random laser emission of an acceptor molecule (Rh640 perchlorate) coated on the surface of a polymer optical fiber. Due to the energy transfer mechanism, the random lasing threshold of Rh640 perchlorate was found to be reduced in the presence of Rh6G. Also, the emission spectrum of Rh640 perchlorate was blue-shifted with the addition of Rh6G. Meanwhile, there is an enhancement in the lasing threshold of Rh6G in the presence of Rh640 perchlorate. The present study demonstrates that by properly adjusting the concentrations of both donor and acceptor molecules, we can obtain a dual-color random laser emission from polymer optical fiber.

Anharmonicity of Plasmons in Metallic Nanostructures Useful for Metallization of Solar Cells.

Metallic nanoparticles are frequently applied to enhance the efficiency of photovoltaic cells via the plasmonic effect, and they play this role due to the unusual ability of plasmons to transmit energy. The absorption and emission of plasmons, dual in the sense of quantum transitions, in metallic nanoparticles are especially high at the nanoscale of metal confinement, so these particles are almost perfect transmitters of incident photon energy. We show that these unusual properties of plasmons at the nanoscale are linked to the extreme deviation of plasmon oscillations from the conventional harmonic oscillations. In particular, the large damping of plasmons does not terminate their oscillations, even if, for a harmonic oscillator, they result in an overdamped regime.

Electrically Driven Plasmons in Metal-Insulator-Semiconductor Tunnel Junctions: The Role of Silicon Amorphization.

We investigate electrically driven plasmon (EDP) emission in metal-insulator-semiconductor tunnel junctions. We find that amorphization of the silicon crystal at a narrow region near the junction due to the applied voltage plays a critical role in determining the nature of the emission. Furthermore, we suggest that the change in the properties of the insulating layer above a threshold voltage determines the EDP spatial properties, from being spatially uniform when the device is subjected to low voltages, to a spotty pattern peaking at high voltages. We emphasize the role of the high-energy emission as an unambiguous tool for distinguishing between EDP and radiative recombination of electrons and holes in the semiconductor.

Amplified plasmonic emission enhancement of PbS quantum dots via Al-oxide/PMMA heterostructures

We study the impact of Al oxide/Poly(methyl methacrylate) (PMMA) interface on plasmonic emission enhancement of infrared semiconductor quantum dots (QDs). For this, PbS QDs embedded in PMMA matrix are deposited on the top of heterostructures consisting of a Au thin film, a dielectric spacer, and an ultrathin layer of Al oxide. Our results suggest that such structures can support an emission enhancement far more than what can be reached in the cases when the QDs/PMMA films are placed on Au thin film/dielectric spacer directly, i.e. in the absence of the Al oxide. We also demonstrate that Au/Si/Al oxide/PMMA heterostructures can increase the photo-induced fluorescence enhancement of PbS QDs, making them brighter as they are irradiated with a laser field. We discuss these results in terms of combined effects of plasmonic field enhancement (Purcell effect) and the carboxylate anion bonds formed at the Al oxide/PMMA interface.

Ultrafast terahertz transparency boosting in graphene meta-cavities.

As an exceptional nonlinear material, graphene offers versatile appealing properties, such as electro-optic tunability and high electromagnetic field confinement in the terahertz regime, spurring advance in ultrashort pulse formation, photodetectors and plasmonic emission. However, limited by atomic thickness, weak light-matter interaction still limits the development of integrated optical devices based on graphene. Here, an exquisitely designed meta-cavities combined with patterned graphene is used to overcome this challenge and promote THz-graphene interaction via terahertz location oscillation. By using an 800nm pump laser, the local field-induced strong interaction allows sensitive responses to the ultrafast energy transfer from the ultrafast optical pump to graphene electron heat, enabling 46.2% enhancement of terahertz transparency. Such optical modulation of terahertz waves shows ultrafast response in delay less than 10ps. Moreover, thanks to the nature of graphene, the device shows unique potential for electrically dynamic tuning and further bandwidth broadening.

Recombination with plasmon emission in HgTe/CdHgTe multiple quantum well heterostructures

The work is devoted to the theoretical study of the process of recombination of nonequilibrium charge carriers with the emission of plasmons in structures with two and three quantum wells, and also in an infinite number quantum-well structure under conditions of inverse band population. The plasmon spectra in these structures have been calculated. The dependence of the average probability of electron recombination with plasmon emission on the concentration of nonequilibrium carriers for three temperatures has been found. It has been shown that an increase in the number of quantum wells leads to a slight increase in the average recombination probability.

Plasmon emission by interlayer excitons in twisted bilayers: Effect of large plasmonic wavevector components

While the emission of localized plasmons is often treated in the real-space picture, working in wavevector space makes it possible to resolve the contributions of various plasmonic Fourier components. By calculating the rate of plasmon emission by interlayer excitons in twisted ${\mathrm{MoSe}}_{2}/{\mathrm{WSe}}_{2}$ van der Waals heterostructures as a function of plasmon localization, twist angle, and temperature, we show that a much wider range of exciton states can radiate into subwavelength plasmon modes than into free space. Most of the emission in this case takes place via plasmonic Fourier components that exceed the maximum photon wavevector in free space. We demonstrate that this provides an avenue for continued Purcell scaling of the emission rate with mode size. Furthermore, the scaling is well in excess of the Purcell trend for sufficiently large twist angles and strong plasmonic localization.

Plasmon gain in HgTe/CdHgTe multi-quantum-well heterostructures

The work is devoted to the theoretical study of plasmon gain in HgTe/CdHgTe multi-quantum-well heterostructures. The spectra of plasmons and plasmon gain are found in structures with 2–8 quantum wells (QWs) under the condition of inverse band population. A nonmonotonic increase in the plasmon gain with an increase in the number of QWs is shown. The dependence of the threshold concentration of nonequilibrium carriers for stimulated plasmon emission on the number of QWs in structures with 1–8 QWs has been studied.

Enhanced optical chirality with directional emission of Surface Plasmon Polaritons for chiral sensing applications

Chirality is a crucial aspect in life sciences, where systems capable of enhancing the chiroptical properties of molecules are highly demanded. In this work, we present a numerical proof of concept of a novel approach towards chiral sensing, consisting in the measurement of chiroptical properties via the directional emission of Surface Plasmon Polaritons (SPPs) on a metasurface. Based on the enhanced differential absorption between right and left circularly polarized light upon interaction with a metasurface made of high refractive index dielectric unit cells, a polarization-dependent SPP differential emission is obtained. Furthermore, the plasmonic emission direction is entirely dependent on the polarization handedness. Using FDTD numerical methods we report Circular Dichroism signals of around − 6° for the unit cell, with threefold dissymmetry factor enhancements in places accessible to analytes. We believe that this work sets a brand-new branch in chiral sensing towards faster, real-time measurements.

Optical characterization and emission enhancement property of Ag nanomesh structure fabricated by nanosphere lithography

A metal nanomesh structure with regularly arranged nanosized holes has a light transmission property at a certain wavelength region and good conductivity; therefore, it can be applied to the wavelength-selective electrode of optical devices such as organic light-emitting diodes (OLEDs) and solar cells. In this study, Ag nanomesh structures with hole arrays of different sizes and periods were fabricated, and their electrical and optical properties were evaluated. Alq3, a green light-emitting material for OLEDs, was deposited on the fabricated Ag nanomesh, and its transmission, scattering, and photoluminescence (PL) spectra were investigated. The PL intensity of Alq3 was approximately four times higher than that without the Ag nanomesh. Time-resolved PL measurements showed the presence of a short-lived component in all samples with Ag nanomesh, indicating plasmonic emission enhancement. These results indicate that Ag nanomeshes can be applied as plasmonic electrodes in optical devices.

Recombination in gapless HgTe/CdHgTe quantum well heterostructure

Three recombination mechanisms of nonequilibrium carriers in gapless undoped quantum well in HgTe/CdHgTe heterostructure are considered. Dependencies of ensemble-average probability of recombination (inverse of recombination time) on concentration of nonequilibrium carriers for recombination with emission of optical phonons, recombination with emission of two-dimensional plasmons, and radiative recombination have been calculated. Key words: gapless HgTe quantum well, recombination mechanisms of nonequilibrium carriers.

Recombination in gapless HgTe/CdHgTe quantum well heterostructure

Three recombination mechanisms of nonequilibrium carriers in gapless undoped quantum well in HgTe/CdHgTe heterostructure are considered. Dependencies of ensemble-average probability of recombination (inverse of recombination time) on concentration of nonequilibrium carriers for recombination with emission of optical phonons, recombination with emission of two-dimensional plasmons, and radiative recombination have been calculated. Key words: gapless HgTe quantum well, recombination mechanisms of nonequilibrium carriers.

Power dependent surface plasmon coupled emission studies of metal-dielectric-metal planar structure

Surface plasmon coupled emission (SPCE) was demonstrated in Metal-Dielectric-Metal Planar (MDMP) structure by coupling MDMP structure to a hemicylindrical prism by Reverse Kretchmann configuration. Here silver and Fluorescein dye dispersed in polyvinyl Alcohol (PVA) were used as metal and dielectric layers respectively. Due to the combined effect of (1) confinement of photon mode within MDMP structure and (2) excitation of plasmon modes by RK configuration, highly directional and enhanced emission was observed. Dependence of SPCE emissions on input excitation power were studied. Higher dielectric thickness (∼600 nm) shows a better emission efficiency as compared to lower dielectric thickness (∼140 nm). Our simulation results show that a higher field distribution within MDMP structure for dielectric thickness of 600 nm resulting in better surface plasmon emission coupling and hence in better emission efficiency.

Surface Plasmonic Lasing in Micro-Nanostructures of Silicon Excited by using Pulsed Infrared Lasers

Surface plasmon is a possible candidate to break the diffraction limit and open the door for developing nanolasers on silicon chips. A new step in this development involves the choice of the structures and compositions for better surface plasmonic emission. The micro-nanostructures were fabricated by using a nanosecond pulsed laser on silicon surface, in which the surface plasmonic emission is stronger. The group of emission peaks with multiple-longitudinal-mode occurs in the optical gain curve. Interestingly, the quantum energy of surface plasmon with 140[Formula: see text]meV has been measured at first, which is related to the peak interval (about 62[Formula: see text]nm) of longitudinal modes in the surface plasmonic lasing spectra. The surface plasmonic lasing near 865[Formula: see text]nm was observed in the Purcell cavity with Si–Cr–Si layers excited by using pulsed lasers at 1064[Formula: see text]nm. Surface plasmonic structure induced with photons was observed by using the reflection Talbot effect image, in which the mechanism of the surface plasmonic lasing can be explored. The physical model of the surface plasmonic laser has been built on the energy levels of the micro-nanostructures of Si.