Plasmonic Sources Research Articles

Highly-efficient electrically-driven localized surface plasmon source enabled by resonant inelastic electron tunneling

On-chip plasmonic circuitry offers a promising route to meet the ever-increasing requirement for device density and data bandwidth in information processing. As the key building block, electrically-driven nanoscale plasmonic sources such as nanoLEDs, nanolasers, and nanojunctions have attracted intense interest in recent years. Among them, surface plasmon (SP) sources based on inelastic electron tunneling (IET) have been demonstrated as an appealing candidate owing to the ultrafast quantum-mechanical tunneling response and great tunability. However, the major barrier to the demonstrated IET-based SP sources is their low SP excitation efficiency due to the fact that elastic tunneling of electrons is much more efficient than inelastic tunneling. Here, we remove this barrier by introducing resonant inelastic electron tunneling (RIET)—follow a recent theoretical proposal—at the visible/near-infrared (NIR) frequencies and demonstrate highly-efficient electrically-driven SP sources. In our system, RIET is supported by a TiN/Al2O3 metallic quantum well (MQW) heterostructure, while monocrystalline silver nanorods (AgNRs) were used for the SP generation (localized surface plasmons (LSPs)). In principle, this RIET approach can push the external quantum efficiency (EQE) close to unity, opening up a new era of SP sources for not only high-performance plasmonic circuitry, but also advanced optical sensing applications.

Compact Plasmonic Distributed-Feedback Lasers as Dark Sources of Surface Plasmon Polaritons.

Plasmonic modes in optical cavities can be amplified through stimulated emission. Using this effect, plasmonic lasers can potentially provide chip-integrated sources of coherent surface plasmon polaritons (SPPs). However, while plasmonic lasers have been experimentally demonstrated, they have not generated propagating plasmons as their primary output signal. Instead, plasmonic lasers typically involve significant emission of free-space photons that are intentionally outcoupled from the cavity by Bragg diffraction or that leak from reflector edges due to uncontrolled scattering. Here, we report a simple cavity design that allows for straightforward extraction of the lasing mode as SPPs while minimizing photon leakage. We achieve plasmonic lasing in 10-μm-long distributed-feedback cavities consisting of a Ag surface periodically patterned with ridges coated by a thin layer of colloidal semiconductor nanoplatelets as the gain material. The diffraction to free-space photons from cavities designed with second-order feedback allows a direct experimental examination of the lasing-mode profile in real- and momentum-space, in good agreement with coupled-wave theory. In contrast, we demonstrate that first-order-feedback cavities remain "dark" above the lasing threshold and the output signal leaves the cavity as propagating SPPs, highlighting the potential of such lasers as on-chip sources of plasmons.

The spontaneous emission performance of a quantum emitter coupled to a hybrid plasmonic waveguide with specified output polarization for on-chip plasmonic single-photon source

Nowadays, most of the on-chip plasmonic single-photon sources emit an unpolarized stream of single photons that demand a subsequent polarizer stage in a practical quantum cryptography system. In this paper, we numerically demonstrated the coupling of the light emitted from a quantum emitter (QE) at 700 nm wavelength to the propagation mode supported by an on-chip hybrid plasmonic waveguide (HPW) polarization rotator. Our results proved that the light emitted is linearly polarized at 0º, 45º/−45º, and 90º with propagation lengths of 5 μm, 3.3 μm, and 3.9 μm, respectively. Moreover, high power-conversion efficiency was obtained from an applied transverse magnetic (TM) mode (0º-polarization) to a transverse electric (TE) (90º-polarization) and a linearly polarized light at 45º/−45º of 97% and a 98%, respectively. Furthermore, we obtained almost a 3-fold enhancement of the total decay rate of the QE with high emission coupling efficiency (β-factor) of 88%, 80%, and 87% to the corresponding waveguide mode for 0º, 45º/−45º, and 90º, respectively. Our work paves the way towards more efficient, compact, and less complicated on-chip plasmonic single-photon sources with a specified output polarization.

Surface Plasmons and Visible Light Iniferter Initiated Polymerization for Nanolocal Functionalization of Mesoporous Separation Layers

Although the technological relevance of mesoporous ceramic polymer hybrid materials is well accepted, missing functionalization concepts enabling 3D nanoscale local control of polymer placement into mesoporous materials, including thin films, and ideally using controlled polymerization techniques limit the application potential. Here, nanolocal functionalization of mesoporous separation layers using controlled, visible light iniferter initiated polymerization allowing responsive polymer functionalization locally limited to the irradiated spot is introduced. Thereby, two visible light sensitive iniferters, s-p-trimethoxysilylbenzyl-S´-dodecyltrithiocarbonate and 4-cyano-4-((dodecylsulfanylthiocarbonyl)sulfanyl)pentanoic acid, are developed for polymer functionalization of mesoporous films in a grafting from and a grafting through approach. 3D nanolocal polymer placement close to the proximity of the plasmonic field source is demonstrated by combining these visible light iniferter initiated polymerizations with optical near field modes, such as localized surface plasmon resonance (LSPR). As the location of the LSPR in mesoporous films can be controlled by placing metal alloy nanoparticles into these films and film thicknesses can be adjusted, this strategy is applied for precise positioning of polymers into mesoporous films with nanolocal control in three dimensions and thus reduces the gap in precision of functional group positioning between technological and biological nanopores.

On the performance of a tunable grating-based high sensitivity unidirectional plasmonic sensor.

Optical biosensing is currently an intensively active research area, with an increasing demand of highly selective, sensitivity-enhanced and low-cost devices where different plasmonic approaches have been developed. In this work we propose a tunable optimized grating-based gold metasurface that can act both as a high sensitivity sensor device (up to 1500 nm/RIU) and as an unidirectional plasmon source. The theory behind surface plasmon polariton generation is recalled to thoroughly understand the influence that every parameter of the grating source has on the performance of the proposed device. The results and conclusions discussed here offer a key step toward the design of biosensors based on excitation of surface plasmons polaritons by grating-based structures or in the process of creating new nanophotonic circuit devices.

Surface Plasmons and Visible Light Iniferter Initiated Polymerization for Nanolocal Functionalization of Mesoporous Separation Layers

AbstractAlthough the technological relevance of mesoporous ceramic polymer hybrid materials is well accepted, missing functionalization concepts enabling 3D nanoscale local control of polymer placement into mesoporous materials, including thin films, and ideally using controlled polymerization techniques limit the application potential. Here, nanolocal functionalization of mesoporous separation layers using controlled, visible light iniferter initiated polymerization allowing responsive polymer functionalization locally limited to the irradiated spot is introduced. Thereby, two visible light sensitive iniferters, s‐p‐trimethoxysilylbenzyl‐S´‐dodecyltrithiocarbonate and 4‐cyano‐4‐((dodecylsulfanylthiocarbonyl)sulfanyl)pentanoic acid, are developed for polymer functionalization of mesoporous films in a grafting from and a grafting through approach. 3D nanolocal polymer placement close to the proximity of the plasmonic field source is demonstrated by combining these visible light iniferter initiated polymerizations with optical near field modes, such as localized surface plasmon resonance (LSPR). As the location of the LSPR in mesoporous films can be controlled by placing metal alloy nanoparticles into these films and film thicknesses can be adjusted, this strategy is applied for precise positioning of polymers into mesoporous films with nanolocal control in three dimensions and thus reduces the gap in precision of functional group positioning between technological and biological nanopores.

Exploiting hyperbolic metamaterial as a substrate for graphene surface plasmonic Cherenkov THz radiation source

In this work, a graphene-dielectric multilayer hyperbolic metamaterial (GHMM) has been analyzed for the generation of THz Cherenkov radiation (CR) from graphene surface plasmonics (GSP), induced by a moving electron bunch. The structure under analysis consists of a graphene-dielectric multilayer HMM in which the top graphene layer is considered as an interface between air and the underlying multilayer as the substrate. The dispersion analysis of the structure shows the existence of bulk-HMM (BH) and non-bulk HMM (NBH)-region in the $$\omega$$ – $$k$$ space. The structure is found to generate intense CR from the GSP, when the operating point of the electron bunch lies in the BH-region, as the bulk states of the HMM substrate allows the efficient transformation of high-k GSP into THz-CR. The proposed structure can be exploited as a potential candidate for the development of low-voltage, electron beam-driven, ultra-tunable, compact graphene plasmonic Cherenkov THz radiation source. Moreover, the application of the principle of utilizing bulk states of HMM for CR generation has also been discussed for black phosphorous (BP), an emerging 2Dmaterial for the THz to infrared (IR) region.

Terahertz Spoof Surface Plasmonic Logic Gates.

SummaryLogic gates are important components in integrated photonic circuitry. Here, a series of logic gates to achieve fundamental logic operations based on linear interference in spoof surface plasmon polariton waveguides are demonstrated at terahertz frequencies. A metasurface-based plasmonic source is adopted to couple free-space terahertz radiation into surface waves, followed by a funnel-shaped metasurface to efficiently couple the surface waves to the waveguides built on a domino structure. A single Mach-Zehnder waveguide interferometer can work as logic gates for four logic functions: AND, NOT, OR, and XOR. By cascading two such interferometers, NAND and NOR operations can also be achieved. Experimental investigations are supported by numerical simulations, and good agreement is obtained. The logic gates have compact sizes and high intensity contrasts for the output “1” and “0” states. More complicated functions can be envisioned and will be of great value for future terahertz integrated computing.

Plasmon-enhanced quantum dots electrochemiluminescence aptasensor for selective and sensitive detection of cardiac troponin I

The development of highly sensitive electrochemiluminescence (ECL) immunosensors by using functional nanoparticles as signal amplifiers is a solution towards sensitive determination of many low concentration disease biomarkers. Herein, a sensitive aptamer-based, sandwich-type surface plasmon enhanced electrochemiluminescence (SPEECL) immunosensor was demonstrated for the detection of cardiac troponin I (cTnI), by means of aptamer conjugated CdS QDs and AuNPs as ECL luminophores and plasmon sources, respectively, in which Tro4 aptamer was used as a capture probe for cTnI and Tro6 aptamer as a detecting probe. The signal of the developed SPEECL system showed ~ 5-fold increment as compared to that of without AuNPs. Using this ECL platform for the detection of cTnI, a linear range and the limit of detection (LOD) were found to be 1 fg/mL - 10 ng/mL and 0.75 fg/mL, respectively.

Terahertz Plasmonic Technology

The terahertz (THz) technology has found applications ranging from astronomical science and earth observation to compact radars, non-destructive testing, chemical analysis, explosive detection, moisture content determination, coating thickness control, film uniformity determination, structural integrity testing wireless covert communications, medical applications (including skin cancer detection), imaging, and concealed weapons detection. Beyond 5G Wi-Fi and Internet of Things (IoT) are the expected killer applications of the THz technology. Plasmonic TeraFETs such as Si CMOS with feature sizes down to 3 nm could enable a dramatic expansion of all these applications. At the FET channel sizes below 100 nm, the physics of the electron transport changes from the collision dominated to the ballistic or quasi-ballistic transport. In the ballistic regime, the electron inertia and the waves of the electron density (plasma waves) determine the high frequency response that extends into the THz range of frequencies. The rectification and instabilities of the plasma waves support a new generation of THz and sub-THz plasmonic devices. The plasmonic electronics technology has a potential become a dominant THz electronics sensing technology when the plasmonic THz sources join the compact, efficient, and fast plasmonic TeraFET THz detectors already demonstrated and being commercialized.

Design and Operation of a Graphene-Based Plasmonic Nano-Antenna Array for Communication in the Terahertz Band

Terahertz (THz)-band (0.1 - 10 THz) communication is envisioned as a key wireless technology to satisfy the need for higher wireless data rates in denser networks. Several ongoing approaches are being considered to overcome the grand challenge of the THz band, i.e., the limited communication distance. Among others, the use of new 2D nanomaterials such as graphene to create novel plasmonic devices that operate directly in the THz range and can be densely packed has been proposed. This paper presents a novel THz plasmonic array architecture which leverages the properties of graphene to greatly simplify its design and operation. Each element of the plasmonic array is an independent front-end, consisting of an on-chip plasmonic source, modulator and antenna. The advantages of this array architecture over conventional array architectures are discussed. The trade-offs in the design of the front-end and the array are exhaustively studied in transmission. The ability to perform continuous dynamic beamforming is presented. A new tailored algorithm is developed for beamforming weight selection. Extensive numerical results are provided to demonstrate the functionality of the array for dynamic beamforming and increased power output.

Design and simulation of a germanium multiple quantum well metal strip nanocavity plasmon laser

In order to achieve electrically pumped plasmon nano lasers, several structures, materials and methods, have been proposed recently. However, there is still a long way to find out a reliable appropriate on-chip plasmon source for commercial plasmonic integrated circuits. In this paper, a new integrated nanocavity plasmon laser is proposed, analyzed and simulated for 1550 nm free-space wavelength. Due to its significant field confinement resulted by the metal strip structure and strong interaction of plasmonic modes with the germanium quantum wells this structure has a remarkable output performance. Purcell factor of this nanocavity is about 291. Using semi-classical rate equations in combination with finite difference time domain (FDTD) cavity mode analysis, the output performance measures are estimated and confirmed with respect to various physical models and simulation tools. Simulation results for this structure which has 0.073 µm2 area show a 2.8 µW output power with 10 µA injection current and about 4.16 mW output power with the threshold pump current of 27 mA, while maintaining its performance in a wide spectral bandwidth about 1.46 THz. It also can be electrically modulated by the pump current up to 5.7 GHz.

Design and analysis of an electrically pumped GaAs quantum dot plasmonic nanolaser

Recently, there is increasing attention to electrically pumped room temperature sub-wavelength plasmon sources because of their various potential applications mainly in the integrated plasmonic field. In this paper, a GaAs/AlGaAs quantum-dot based waveguide integrated plasmonic nanolaser is introduced and theoretically investigated. Using a semi-classical rate equation model, the performance of our nanolaser is studied and its characteristics are presented in detail. The proposed nanolaser has a tiny footprint of 0.068 μm2, room temperature operating condition and monolithic process while having remarkable output performance. The new structure generates 1 mW output power with a 23.6 mA injection current. The threshold pump current of this device is calculated to be about 4.7 mA and at this current level output power is about 198 μW. Also, the proposed device provides a wide spectral bandwidth of about 541 GHz in the threshold pumping rate. The compact cavity design provides significant mode confinement and considerable overlap between the lasing mode and the gain medium. This structure provides a Q factor about 30 and Purcell factor about 66.

Antenna surface plasmon emission by inelastic tunneling

Surface plasmons polaritons are mixed electronic and electromagnetic waves. They have become a workhorse of nanophotonics because plasmonic modes can be confined in space at the nanometer scale and in time at the 10 fs scale. However, in practice, plasmonic modes are often excited using diffraction-limited beams. In order to take full advantage of their potential for sensing and information technology, it is necessary to develop a microscale ultrafast electrical source of surface plasmons. Here, we report the design, fabrication and characterization of nanoantennas to emit surface plasmons by inelastic electron tunneling. The antenna controls the emission spectrum, the emission polarization, and enhances the emission efficiency by more than three orders of magnitude. We introduce a theoretical model of the antenna in good agreement with the results.

Resonant-Like Field Enhancement by Nanoscale Grating-Coupled Propagating Surface Plasmons and Localized Surface Plasmons in the Mid-Infrared Range: Implications for Ultrafast Plasmonic Electron Sources

We investigated electron emission induced by an intense mid-infrared (MIR) field from a nanoscale aluminum-coated grating. The total photoelectron yields clearly show a resonant-like behavior when frustrated diffraction occurs near the Wood anomaly. This result indicates that a strong near field, which is formed by the localized surface plasmons (LSPs) at the ridge of the grating, can be enhanced by resonantly produced propagating surface plasmons (PSPs) owing to the phase matching between the diffracted light and PSPs. The observed photoelectron spectra can be reproduced well by a simple one-dimensional (1D) model of a near field that contains two parameters: the field enhancement factor, α, and the ridge radius, r0. In addition, we show that the resonant-like photoemission was attributed to the interference of the near fields produced by the LSPs and PSPs in the nanoscale grating structure. These results demonstrate that the nanoscale structure is useful for ultrafast plasmonic electron sources.

Cavity quantum electrodynamic analysis of spasing in nanospherical dimers

We present a detailed cavity quantum electrodynamic model of a nanospherical dimer and use it to analyze bright hybrid spasing modes there. Using an approximate numerical scheme, we model the complete spasing system as an open quantum system under the Lindblad dissipator formalism. We show that while in general the longitudinal dimer setups display higher intensity spasing as compared with transverse dimers, the latter actually consistently lead to output with higher coherence. Intriguingly, and somewhat counterintuitively, we find that transverse dimers only reach peak output at an intermediate dimer separation at which field confinement is not the strongest. We show that this is due to low radiative decay rates of transverse dimers with significant dimer gaps. We also find that transverse dimers outperform longitudinal dimers in terms of output intensity in a weakly pumped sparse gain medium made of dimers with relatively large separations. Moreover, in all the configurations considered, we find that the second-order coherence of the spasing output shows a peaked behavior just before the threshold, suggesting that the coherence is a useful indicator of spasing. Even though the scheme we describe is focused on dimers, owing to the generic form of the analysis presented, it can be easily extended to investigate spasing in the bright modes of multiple coupled plasmon sources.

High Purcell Factor Achievement of Notched Cavity Germanium Multiple Quantum Well Plasmon Source

Recently, many researches are reported on using germanium in silicon-based lasers but acquiring this potential for a plasmonic nanolaser may also be important for development of silicon-compatible plasmon sources. In this paper, a custom-shaped nanocavity plasmon source based on highly doped tensile-strained germanium/silicon-germanium multiple quantum well gain medium is introduced and theoretically investigated. We have used a semi-classical macroscopic rate equation model for calculation of the output performance characteristics. Also, modal analysis has been done based on FDTD method. The proposed nanolaser has a tiny footprint of 0.1225 μm2, possible room temperature performance, and fabrication process based on a silicon substrate. The output performance of the nanolaser structure as estimated is noticeable and the calculated results, using some previously reported experimental data and redundant software double checking, show acceptable compatibility. In 1550-nm output wavelength, it provides 15.6 mW output power in the 21-mA threshold current and 600 μW in 1-mA pump current, while maintaining its performance in a wide spectral bandwidth about 2 THz. It also can be electrically modulated by the pump current up to 3 GHz. This remarkable performance is achieved, thanks to the high Purcell factor of the parabolically notched nanocavity of about 700 and its high quality factor of about 58.

In Operando Characterization and Control over Intermittent Light Emission from Molecular Tunnel Junctions via Molecular Backbone Rigidity.

In principle, excitation of surface plasmons by molecular tunnel junctions can be controlled at the molecular level. Stable electrical excitation sources of surface plasmons are therefore desirable. Herein, molecular junctions are reported where tunneling charge carriers excite surface plasmons in the gold bottom electrodes via inelastic tunneling and it is shown that the intermittent light emission (blinking) originates from conformational dynamics of the molecules. The blinking rates, in turn, are controlled by changing the rigidity of the molecular backbone. Power spectral density analysis shows that molecular junctions with flexible aliphatic molecules blink, while junctions with rigid aromatic molecules do not.

Excitation of Propagating Plasmons in a Periodic Graphene Structure by Incident Terahertz Waves

Plasmonic transport is considered as a replacement for electronic transport in low-dimensional systems like field-effect transistors, as plasmons are faster than electrons. Plasmons in graphene are promising for use at THz frequencies, but this research is held back by the primitive state of circuitry for plasmonic devices. This study employs an asymmetric periodic grating to solve the problem of effective excitation of propagating plasmons in graphene. The important role of ``dark'' (weakly radiative) plasmon modes in efficient excitation is revealed. The approach outlined here could help to fill the need for THz plasmon sources, for tomorrow's devices.

A GaAs-based plasmonic source employing a nanoscale vertical cavity

In this paper, a new structure of a vertical cavity plasmonic source is presented. The structure, which is adopted from a metal–semiconductor–metal plasmonic photodetector, contains a gold substrate, n-type GaAs layer, active GaAs layer and p-type GaAs layer, respectively from bottom to up. A subwavelength aperture and metal gratings on both sides of the aperture are placed on the top of the device and act both as a gold clad and as the contact for applying DC bias. The metal gratings are improved by adding SiO2 between metal grooves and semiconductor. Applying voltage bias to p-and n-regions leads to photons generation in the active region. The generated photons in the active region excite a resonant surface plasmonic mode in the nanoscale cavity just below the aperture. One can use light outflowing from the nanoscale aperture, with wavelength of 882 nm, as a source to excite an arbitrary plasmonic guiding structure. The output beam has a suitable concentration so that in a 1000 nm distance from the aperture, still 37% of the power is concentrated in a width of 50 nm which is almost a unique specification among plasmonic sources, so far. The function of the device is validated using finite-difference time-domain numerical algorithm.