Hybrid Nanoantennas Research Articles

Nanoscale Electrically Driven Light Source Based on Hybrid Semiconductor/Metal Nanoantenna.

A micro- or nanosized electrically controlled source of optical radiation is one of the key elements in optoelectronic systems. The phenomenon of light emission via inelastic tunneling (LEIT) of electrons through potential barriers or junctions opens up new possibilities for development of such sources. In this work, we present a simple approach for fabrication of nanoscale electrically driven light sources based on LEIT. We employ STM lithography to locally modify the surface of a Si/Au film stack via heating, which is enabled by a high-density tunnel current. Using the proposed technique, hybrid Si/Au nanoantennas with a minimum diameter of 60 nm were formed. Studying both electronic and optical properties of the obtained nanoantennas, we confirm that the resulting structures can efficiently emit photons in the visible range because of inelastic scattering of electrons. The proposed approach allows for fabrication of nanosized hybrid nanoantennas and studying their properties using STM.

Metal, dielectric and hybrid nanoantennas for enhancing the emission of single quantum dots: A comparative study

The confinement of electromagnetic energy to subwavelength volumes through nanoscale antennas can be used to enhance the spontaneous emission of quantum emitters. With this aim, different configurations of metallic and high refractive index dielectric nanoparticles have been explored. Here, we carry out a comparative analysis of planar metallic, high refractive index dielectric, and hybrid nanoantennas considering three different parameters: the Purcell factor enhancement, radiation efficiency, and directionality properties. We focus our study on different geometries and material combinations of a dimer of cylinders. A dimer made of two gold nanocylinders is the most promising candidate for improving the spontaneous emission. While most previous works have paid attention to the redirection of the scattered emission in the nanoparticle plane, our proposed nanostructure of two large gold cylinders (R=λ/4) emits most of the radiation upwards. This effect is due to the strong quadrupolar electric contribution to the resonant mode. With the aim to further improve the directionality properties, additional silicon nanocylinders are used as directors of the scattered radiation, increasing the directivity by a factor of 2.4 with respect to the gold dimer without directors. All in all, a hybrid structure composed of a gold dimer and silicon nanoparticles is proposed to enhance the spontaneous emission of a single quantum dot and to govern its emission pattern. The results shown in this work could be useful in fluorescence enhancement or in quantum photonics. They are particularly interesting for the development of single-photon sources based on quantum dots and other nanoscale emitters.

(Invited) Energy Transfer in Hybrid Plasmonic Nanostructures

A surface plasmon in a metal nanoparticle is the coherent oscillation of the conduction band electrons leading to both strong absorption and scattering as well as large local electromagnetic fields. Plasmonic nanoparticles therefore have the potential to induce electronic transitions in nearby materials. However, but fast internal relaxation limits the efficiency of such plasmonic mediated processes. In this talk, I will discuss our recent results of a new type of nanomaterial: hybrid nanoantennas comprised of plasmonic nanorods with photoconductive polymer coatings that were grown by photo-electrochemistry. The formation of the conductive polymer shell is selective to the nanorods, while the polymerization is enhanced by photoexcitation. In situ single pareticle dark-field scattering spectroscopy and simulations support an energy transfer mechanism with up to 50% efficiency. These hybrid nanoantennas combine the unmatched light harvesting properties of a plasmonic nanoparticles with the similarly unmatched device processability of polymersl.

Replicable Quasi-Three-Dimensional Plasmonic Nanoantennas for Infrared Bandpass Filtering.

Quasi-three-dimensionally designed metal-dielectric hybrid nanoantennas have provided a unique capability to control light at the nanoscale beyond the diffraction limit, which has enabled powerful optical manipulation techniques. However, the fabrication of these nanoantennas has largely relied on the use of nanolithography techniques that are time- and cost-consuming, impeding their application in wide-ranging use. Herein, we report a versatile methodology enabling the repetitive replication of these nanoantennas from their silicon molds with tailored optical features for infrared bandpass filtering. Comprehensive experimental and computational analyses revealed the underlying mechanism of this methodology and also provided a technical guideline for pragmatic translation into infrared filters in multispectral imaging.

Plasmon Energy Transfer in Hybrid Nanoantennas.

Plasmonic metal nanoparticles exhibit large dipole moments upon photoexcitation and have the potential to induce electronic transitions in nearby materials, but fast internal relaxation has to date limited the spatial range and efficiency of plasmonic mediated processes. In this work, we use photo-electrochemistry to synthesize hybrid nanoantennas comprised of plasmonic nanoparticles with photoconductive polymer coatings. We demonstrate that the formation of the conductive polymer is selective to the nanoparticles and that polymerization is enhanced by photoexcitation. In situ spectroscopy and simulations support a mechanism in which up to 50% efficiency of nonradiative energy transfer is achieved. These hybrid nanoantennas combine the unmatched light-harvesting properties of a plasmonic antenna with the similarly unmatched device processability of a polymer shell.

Hybrid Metal-Dielectric Metasurfaces for Refractive Index Sensing.

Hybrid metal-dielectric nanostructures have recently gained prominence because they combine strong field enhancement of plasmonic metals and the several low-loss radiation channels of dielectric resonators, which are qualities pertaining to the best of both worlds. In this work, an array of such hybrid nanoantennas is successfully fabricated over a large area and utilized for bulk refractive index sensing with a sensitivity of 208 nm/RIU. Each nanoantenna combines a Si cylinder with an Al disk, separated by a SiO2 spacer. Its optical response is analyzed in detail using the multipoles supported by its subparts and their mutual coupling. The nanoantenna is further modified experimentally with an undercut in the SiO2 region to increase the interaction of the electric field with the background medium, which augments the sensitivity to 245 nm/RIU. A detailed multipole analysis of the hybrid nanoantenna supports our experimental findings.

Miniaturizing nanoantennas with hybrid photonic-plasmonic modes for improved metasurfaces.

The increasing interest in manipulating light on scales much smaller than its wavelength has driven intensive research on designing high efficiency optical antennas for near and far field applications. In particular, such nanoantennas serve as the main building block of metasurfaces, which were identified as an emerging technology for their capability in constructing versatile optical and electromagnetic devices. Hence, reducing the antennas' dimensions without compromising on their scattering efficiency is of utmost importance. In this Letter, we show that nanoantennas carved from hybrid plasmonic-dielectric waveguides preserve the unique properties of the hybrid modes, showing stronger confinement and better tunability at a relatively low loss, emanating from the coupling between the dielectric and plasmonic modes. This enables a design of high performance ultrasmall antennas that outperform dielectric and plasmonic nanoantennas at similar dimensions. We demonstrate this capability by simulating the performance of metasurfaces made of ultrasmall hybrid nanoantennas, proven to be superior over their dielectric and plasmonic counterparts. Using such hybrid nanoantennas as unit-cells in metasurfaces holds a great promise for designing new tunable, multifunctional, and low-loss nano-optical materials and applications.

Pure magnetic-quadrupole scattering and efficient second-harmonic generation from plasmon-dielectric hybrid nano-antennas

We theoretically demonstrate that pure magnetic quadrupole (MQ) scattering is achieved via the excitation of anapole modes and Fano resonance in noble metal (Au or Ag) and high refractive index dielectric (AlGaAs) hybrid nano-antennas. In Au-AlGaAs hybrid nano-antennas, electric anapole and magnetic anapole modes are observed, leading to the suppressions of electric and magnetic dipoles. Introducing gain material to AlGaAs nanodisk to increase the strength of electric quadrupole (EQ) Fano resonance leads to the suppression of EQ scattering. Then, ideal MQ scattering is achieved at the wavelength of total scattering cross-section dip. The increase of signal-to-noise ratio of MQ results in the great enhancement of near-field inside AlGaAs nanodisk. Additionally, the strong MQ resonance exhibits great capability for boosting second-harmonic generation by proper mode matching. These findings achieved in subwavelength geometries have important implications for functional metamaterials and nonlinear photonic nanodevices.

Directional Emission from Dielectric Leaky-Wave Nanoantennas.

An important source of innovation in nanophotonics is the idea to scale down known radio wave technologies to the optical regime. One thoroughly investigated example of this approach are metallic nanoantennas which employ plasmonic resonances to couple localized emitters to selected far-field modes. While metals can be treated as perfect conductors in the microwave regime, their response becomes Drude-like at optical frequencies. Thus, plasmonic nanoantennas are inherently lossy. Moreover, their resonant nature requires precise control of the antenna geometry. A promising way to circumvent these problems is the use of broadband nanoantennas made from low-loss dielectric materials. Here, we report on highly directional emission from hybrid dielectric leaky-wave nanoantennas made of Hafnium dioxide nanostructures deposited on a glass substrate. Colloidal semiconductor quantum dots deposited in the nanoantenna feed gap serve as a local light source. The emission patterns of hybrid nanoantennas with different sizes are measured by Fourier imaging. We find for all antenna sizes a highly directional emission, underlining the broadband operation of our design.

Optical tuning of near and far fields form hybrid dimer nanoantennas via laser-induced melting

Hybrid nanophotonics based on metal-dielectric nanostructures unifies the advantages of plasmonics and all-dielectric nanophotonics providing strong localization of light, magnetic optical response and specifically designed scattering properties. Here, we propose a new method for optical properties tuning of hybrid dimer nanoantenas via laser-induced melting at the nanoscale. We demonstrate numerically that near- and farfield properties of a hybrid nanoantenna dramatically changes with fs-laser modification of Au particle. The results lay the groundwork for the fine-tuning of hybrid nanoantennas and can be applied for effective light manipulation at the nanoscale, as well as biomedical and energy applications.

Reflection type metasurface designed for high efficiency vectorial field generation.

We propose a reflection type metal-insulator-metal (MIM) metasurface composed of hybrid nano-antennas for comprehensive spatial engineering of the properties of optical fields. The capability of such structure is illustrated in the design of a device that can be used to produce a radially polarized vectorial beam for optical needle field generation. This device consists of uniformly segmented sectors of high efficiency MIM metasurface. With each of the segment sector functioning as a local quarter-wave-plate (QWP), the device is designed to convert circularly polarized incidence into local linear polarization to create an overall radial polarization with corresponding binary phases and extremely high dynamic range amplitude modulation. The capability of such devices enables the generation of nearly arbitrarily complex optical fields that may find broad applications that transcend disciplinary boundaries.

Multipolar Coupling in Hybrid Metal–Dielectric Metasurfaces

We study functional hybrid metasurfaces consisting of metal–dielectric nanoantennas that direct light from an incident plane wave or from localized light sources into a preferential direction. The directionality is obtained by carefully balancing the multipolar contributions to the scattering response from the constituents of the metasurface. The hybrid nanoantennas are composed of a plasmonic gold nanorod acting as a feed element and a silicon nanodisk acting as a director element. In order to experimentally realize this design, we have developed a two-step electron-beam lithography process in combination with a precision alignment step. The optical response of the fabricated sample is measured and reveals distinct signatures of coupling between the plasmonic and the dielectric nanoantenna elements that ultimately leads to unidirectional radiation of light.

Efficient Collection of Light from Colloidal Quantum Dots with a Hybrid Metal–Dielectric Nanoantenna

We introduce a hybrid metal–dielectric nanoantenna consisting of a metallic bullseye nanostructure and a dielectric waveguide layer, for directing the photon emission of embedded colloidal nanocrystal quantum dots. This structure overcomes the intrinsic losses of plasmonic nanoantennas on one hand and is much more scalable than dielectric nanoantennas on the other. The experimental results demonstrate a very low divergence angle beam, allowing a collection efficiency of 30% of the quantum dot emission into a numerical aperture of 0.55. The experimental results are well reproduced by numerical simulations, which predict a maximal collection efficiency larger than 25% directly into a single mode fiber having a numerical aperture of 0.12 without the need for any additional optics. Such hybrid nanoantennas can significantly improve the performance of quantum dot based devices, from displays to single-photon sources.

Hybrid nanoantennas for directional emission enhancement

Plasmonic and dielectric nanoparticles offer complementary strengths regarding their use as optical antenna elements. While plasmonic nanoparticles are well-known to provide strong decay rate enhancement for localized emitters, all-dielectric nanoparticles can enable high directivity combined with low losses. Here, we suggest a hybrid metal-dielectric nanoantenna consisting of a gold nanorod and a silicon nanodisk, which combines all these advantages. Our numerical analysis reveals a giant enhancement of directional emission together with simultaneously high radiation efficiency (exceeding 70%). The suggested hybrid nanoantenna has a subwavelength footprint, and all parameters and materials are chosen to be compatible with fabrication by two-step electron-beam lithography.