Metallic Plasmonic Structures Research Articles

Customized Self-Assembled Gold Nanoparticle-DNA Origami Composite Templates for Shape-Directed Growth of Plasmonic Structures.

The metal plasmonic nanostructure has the optical property of plasmon resonance, which holds great potential for development in nanophotonics, bioelectronics, and molecular detection. However, developing a general and straightforward method to prepare metal plasmonic nanostructures with a controllable size and morphology still poses a challenge. Herein, we proposed a synthesis strategy that utilized a customizable self-assembly template for shape-directed growth of metal structures. We employed gold nanoparticles (AuNPs) as connectors and DNA nanotubes as branches, customizing gold nanoparticle-DNA origami composite nanostructures with different branches by adjusting the assembly ratio between the connectors and branches. Subsequently, various morphologies of plasmonic metal nanostructures were created using this template shape guided strategy, which exhibited enhancement of surface-enhanced Raman scattering (SERS) signals. This strategy provides a new approach for synthesizing metallic nanostructures with multiple morphologies and opens up another possibility for the development of customizable metallic plasmonic structures with broader applications.

Band-stop filter based on metal–insulator-metal hybridized with graphene layer in telecommunication regime

Graphene offers unique properties such that changing the incident energy density of the carriers by gate voltage leads to alteration of the chemical potential that can be used in light manipulation of photonic devices. In this work, we propose a band-stop filter hybrid graphene nanostructure composed of a graphene layer which is added to a metal–insulator–metal plasmonic waveguide structure. We use the finite element method to numerically calculate the light transmission of the graphene-based structure for adjusting chemical potential of graphene. Our calculations show that with constant structural parameters the observed transmission is modified when the chemical potential of graphene changes. Also, the transmission can be filtered in specific wavelength by controlling the chemical potential. The result shows the filtering at lower wavelengths by increasing the chemical potential. Moreover, the performance of this structure for the different channel width and refractive index of insulator is studied.

Trap dynamics of hot electrons in metal–insulator–metal plasmonic structures for ultra-fast optoelectronics

We have calculated the time constants of the electron dynamics in traps in a metal–insulator–metal (MIM) plasmonic structure. Because of electron relaxation in metal, the surface plasmon polaritons decays into hot electrons near the surface of the metal, which facilitates the trap of electrons in the interfacial layer of the dielectric. We have calculated the capture and emission times separately as the electron does not follow the same mechanisms with the capture process when it is emitted from a trap at the metal/oxide interface. We have developed a quasi-two-dimensional treatment that has been modified from a previously used semiconductor/oxide junction by using Bardeen’s function to calculate the capture time. Various parameters including trap’s distance from the interface, temperature, voltage bias, and spectral nature of the hot electrons’ energy distribution influence the interaction between a plasmonic hot electron and a neutral near-interface trap in the capture process. On the one hand, the emission time is independent of the capture time, and it is determined by the tunneling time to the metal depending on the temperature and the energy difference between the trap energy levels (ground and excited states). We have showed that a wide range of capture times from seconds to picoseconds is possible for an interfacial trap at the room temperature due to the spectral energy distribution of hot electrons and dependence of the capture process on the losses in metals. On the other hand, the temperature plays the dominant role in the emission time. For the trap with 250 meV energy difference between its levels, the emission time is in the range of picosecond at room temperature. Therefore, the MIM plasmonic device can respond to a wide range of ac voltage frequencies including the ultra-fast domain. These interesting findings are useful to understand the ac response of the MIM plasmonic devices with applications in integrated photonics and ultra-fast optoelectronics.

Metallic Plasmonic Array Structures: Principles, Fabrications, Properties, and Applications (Adv. Mater. 50/2021)

Metallic Plasmonic Arrays Metallic plasmonic array structures provide a powerful platform to control light–matter interactions and show fascinating, rich, and tunable optical properties through morphology and parameter engineering enabled by nanofabrication. In article number 2007988, Bowen Liu, Bin Ren, and co-workers review light-management mechanisms, fabrication techniques, and applications, such as plasmonic sensing, surface-enhanced spectroscopies, nanolasing, and perfect light absorption, for metallic plasmonic array structures.

Metallic Plasmonic Array Structures: Principles, Fabrications, Properties, and Applications.

The vast development of nanofabrication has spurred recent progress for the manipulation of light down to a region much smaller than the wavelength. Metallic plasmonic array structures are demonstrated to be the most powerful platform to realize controllable light-matter interactions and have found wide applications due to their rich and tunable optical performance through the morphology and parameter engineering. Here, various light-management mechanisms that may exist on metallic plasmonic array structures are described. Then, the typical techniques for fabrication of metallic plasmonic arrays are summarized. Next, some recent applications of plasmonic arrays are reviewed, including plasmonic sensing, surface-enhanced spectroscopies, plasmonic nanolasing, and perfect light absorption. Lastly, the existing challenges and perspectives for metallic plasmonic arrays are discussed. The aim is to provide guidance for future development of metallic plasmonic array structures.

Pole-based analysis of coupled modes in metal–insulator–metal plasmonic structures

A second-order transfer function analysis is performed on plasmonic modes with disparate quality factors. This generalized analysis technique is applied to the coupling of modes in metal–insulator–metal structures in the mid-wave infrared, which are systematically studied, both experimentally and with computational modeling. Coupling between these disparate modes is observed from the asymmetric Fano-like lineshape at the resonant crossings in both finite element method simulations and angle dependent spectra. The pole analysis method applied to both experimental and numerical data allows for extraction of the coupling coefficient for this system and is applicable to other plasmonic and photonic coupled resonances.

Controllable hybridization between localized and delocalized anisotropic borophene plasmons in the near-infrared region.

In this Letter, we theoretically propose a coupled borophene plasmonic system, where an anisotropic localized plasmonic (LP) mode and a delocalized guided plasmonic (DGP) mode can be simultaneously excited. This allows us to manipulate the optical response of the strong LP-DGP coupling with exceptional flexibility in the near-infrared region, which is not possible with the conventional metallic plasmonic structures, and overcomes some shortcomings of coupled structures based on the other 2D materials. Specifically, the spatially LP-DGP coupling can arise when the system is driven into the strong coupling regime; this gives rise to a transparency window which can be well described by a coupled oscillation model. The bandwidth of the window is governed by the coupling strength which can be passively adjusted by the spacer thickness, while the center wavelength and the number of windows can be actively modulated by tuning the borophene electron density and the incident angle.

Optimization of plasmonic metal structures for improving the hydrogen production efficiency of metal-organic frameworks.

The introduction of plasmonic metals of gold (Au) nanoparticles onto metal-organic frameworks (MOFs) has been testified as an efficient approach to boost the H2 evolution ability because the excited Au particles can generate hot electrons that can then be injected into MOFs to inhibit the recombination of charges. Generally, Au particles possess two modes of polarization, which are transverse and longitudinal polarizations. However, which of the two modes is more efficient remains unclear and is yet to be disclosed. Herein, we report a strategy of finely controlling the transverse and longitudinal polarizations by gradually reducing the length, without changing the width of Au rods, and then combining with MOF Pt@MIL-125 to construct Pt@MIL-125/Au Schottky junctions, for investigating the polarization mode effects. The results indicate that with the reduction in the length of Au rods from 67 nm to 38 nm, the transverse polarization will be increased, which can lead to a significant enhancement in the electron-hole separation efficiency and H2 generation activity. When Au is in spherical shape, the transverse polarization effect reaches the highest level, thereby achieving the highest H2 production rate of 265.1 μmol g-1 h, which is 1.6 times more than that of 67 nm Au rods. The enhancement can be attributed to the significant accelerated electron transfer rate induced by transverse polarization and evidenced by ESR analysis. The results indicate that the transverse polarization is more efficient for hot electron injection and highlight that the Au sphere is a more appropriate candidate for producing the maximum SPR effect during photocatalysis.

Graphene Nanoribbon Plasmonic Conveyor Belt Network for Optical Trapping and Transportation of Nanoparticles

Optical tweezers based on metallic plasmonic structures can achieve stable trapping of objects with deep subwavelength dimensions. However, due to the lack of real-time tunability of metallic plasm...

THz Biochemical Sensors: Terahertz Biochemical Molecule‐Specific Sensors (Advanced Optical Materials 3/2020)

The highly sensitive and selective detection of ultrasmall quantities of bio-chemical substances by using sensing chips, including metallic plasmonic structures and terahertz metamaterials, is conceptually shown. Such terahertz metamaterials have been designed to target the specific absorption peaks of the certain bio-chemical samples, where molecular-specific vibration modes exist, and increase the detection sensitivity. For further details see article number 1900662 by Minah Seo and Hyeong-Ryeol Park.

Exciton polaritons based on planar dielectric Si asymmetric nanogratings coupled with J-aggregated dyes film.

Optical cavity polaritons, originated from strong coupling between the excitons in materials and photons in the confined cavities field, have recently emerged as their applications in the high-speed lowpower polaritons devices, low-threshold lasing and so on. However, the traditional exciton polaritons based on metal plasmonic structures or Fabry-Perot cavities suffer from the disadvantages of large intrinsic losses or hard to integrate and nanofabricate. This greatly limits the applications of exciton poalritons. Thus, here we implement a compact low-loss dielectric photonic - organic nanostructure by placing a 2-nm-thick PVA doped with TDBC film on top of a planar Si asymmetric nanogratings to reveal the exciton polaritons modes. We find a distinct anti-crossing dispersion behavior appears with a 117.16 meV Rabi splitting when varying the period of Si nanogratings. Polaritons dispersion and mode anti-crossing behaviors are also observed when considering the independence of the height of Si, width of Si nanowire B, and distance between the two Si nanowires in one period. This work offers an opportunity to realize low-loss novel polaritons applications.

Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy.

In 2010, Tian et al. reported the development of a new, relatively sensitive method of the chemical analysis of various surfaces, including buried interfaces (for example the surfaces of solid samples in a high-pressure gas or a liquid), which makes it possible to analyze various biological samples in situ. They called their method shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). SHINERS spectroscopy is a type of surface-enhanced Raman spectroscopy (SERS) in which an increase in the efficiency of the Raman scattering is induced by plasmonic nanoparticles acting as electromagnetic resonators that locally significantly enhance the electric field of the incident electromagnetic radiation. In the case of SHINERS measurements, the plasmonic nanoparticles are covered by a very thin transparent protective layer (formed, for example, from various oxides such as SiO2, MnO2, TiO2, or organic polymers) that does not significantly damp surface electromagnetic enhancement, but does separate the nanoparticles from direct contact with the probed material and keeps them from agglomerating. Preventing direct contact between the metal plasmonic structures and the analyzed samples is especially important when biological samples are investigated, because direct interaction between the metal nanoparticles and various biological molecules (e.g., peptides) may lead to a change in the structure of those biomolecules. In this mini-review, the state of the art of SHINERS spectroscopy is briefly described.

Response Time of a Plasmonic Distributed Feedback Laser in a Large-Signal Modulation Regime

Lasers with ultrafast response are crucial elements for many optoelectronics applications. The response time of dielectric surface emitting lasers is limited to hundreds of picoseconds, while using metallic plasmonic structures can significantly reduce that time. The authors study the behavior of a plasmonic distributed-feedback laser in the regime of large signal modulation, showing that the response time depends strongly and nonmonotonically on the size of the pump beam. For typical experimental parameters, there is an optimal size of the pump beam for which the response time can be reduced to a picosecond.

Tailoring the electron-phonon interaction with metallic plasmonic structures

The interaction between electrons and phonons governs the intrinsic electrical resistance in semiconductors. We show that large reductions in the strength of the interaction between electrons and phonons in polar semiconductors can be achieved by exploiting strong ‘off-resonance’ screening from two-dimensional plasmonic arrays embedded in a nearby insulating layer. By judicious design of the plasmonic layers, remarkably large enhancements of the carrier mobilities are predicted. Examples for GaN-, MoS2-, and GaAs-based structures are given. Experimental verification of these predicted behaviors could lead to significant improvements in the performance of next-generation electronic devices.

Advances in surface-enhanced optical forces and optical manipulations

The localized surface plasmons in metal nanostructures under optical excitation will lead to near-field localization and enhancement, which have shown important applications in surface enhancement spectroscopy, ultra-sensitive sensing, microfluidic chip, enhanced optical force, etc. The plasmon resonance and the resulting electric field enhancement strongly depend on wavelength and structure geometry. As a result, the optical force will be closely related to the field distribution, that is, the optical force can be used to manipulate and sort plasmonic metal structures. The large near-field enhancement and gradient of metal nanoparticle aggregates can also be used as a " plasmonic tweezer” to manipulate other particles. Furthermore, in the case of changing the incident polarization and even for a new type of structured laser beam, the optical manipulation has a higher degree of freedom. In this review, having briefly introduced the plasmon-enhanced optical force, we focus on the recent advances in the following three aspects: 1) the manipulation of plasmonic nanoparticles by optical tweezer, 2) the manipulation of other particles by plasmonic tweezer, and 3) dependence of plasmonic optical force on the polarization, optical angular momentum, structured light and the structured chirality. Comparing with other topics of plasmon- enhanced light-interactions, there is plenty of room for further developing the plasmon-enhanced optical force and optical manipulation. Several research trends can be foreseen. 1) More precise optical manipulating and sorting of nanoparticles (even sub-nanometer). For example, more sensitive special resonant modes (e.g. Fano resonance) of plasmonic nanostructure can be utilized. For some nanostructures with small feature sizes, especially when the gap size is close to 1 nm, the non-local effect has a certain effect on the plasmon resonance. Therefore, when calculating the optical force in this case, non-local effects and possibly other quantum effects should be considered. 2) Richer laser fields, that is, using various new structured fields and chiral structures provides a higher degree of freedom for the optical forces and optical manipulation. Also, the localized surface plasmons can be combined with propagating surface plasmons. 3) Wider applications of plasmonic optical forces, especially in combination with other effects and even interdiscipline, e.g. enhanced spectroscopy, enhanced single particle chemical reactions, nonlinear optical effects, and photothermal manipulations.

Surface Engineering of Nanomaterials for Photo-Electrochemical Water Splitting.

Photo-electrochemical water splitting represents a green and environmentally friendly method for producing solar hydrogen. Semiconductor nanomaterials with a highly accessible surface area, reduced charge migration distance, and tunable optical and electronic property are regarded as promising electrode materials to carry out this solar-to-hydrogen process. Since most of the photo-electrochemical reactions take place on the electrode surface or near-surface region, rational engineering of the surface structures, physical properties, and chemical nature of photoelectrode materials could fundamentally change their performance. Here, the recent advances in surface engineering methods, including the modification of the nanomaterial surface morphology, crystal facet, defect and doping concentrations, as well as the deposition of a functional overlayer of sensitizers, plasmonic metallic structures, and protective and catalytic materials are highlighted. Each surface engineering method and how it affects the structural features and photo-electrochemical performance of nanomaterials are reviewed and compared. Finally, the current challenges and the opportunities in the field are discussed.

Distributed Bragg Reflectors as Broadband and Large-Area Platforms for Light-Coupling Enhancement in 2D Transition-Metal Dichalcogenides.

Two-dimensional (2D) semiconductors, particularly the direct-gap monolayer transition metal dichalcogenides (TMDs), are currently being developed for various atomically thin optoelectronic devices. However, practical applications are hindered by their low quantum efficiencies in light emissions and absorptions. While photonic cavities and metallic plasmonic structures can significantly enhance the light-matter interactions in TMDs, the narrow spectral resonance and the local hot spots considerably limit the applications when broadband and large area are required. Here, we demonstrate that a properly designed distributed Bragg reflector (DBR) can be an ideal platform for light-coupling enhancement in 2D TMDs. The main idea is based on engineering the amplitude and phase of optical reflection from the DBR to produce optimal substrate-induced interference. We show that the photoluminescence, Raman, and second harmonic generation signals of monolayer WSe2 can be enhanced by a factor of 26, 34, and 58, respectively. The proposed DBR substrates pave the way for developing a range of 2D optoelectronic devices for broadband and large-area applications.

Surface plasmon dispersion in a mid-infrared Ge/Si quantum dot photodetector coupled with a perforated gold metasurface

The photodetection improvement previously observed in mid-infrared (IR) quantum dot photodetectors (QDIPs) coupled with periodic metal metasurfaces is usually attributed to the surface light trapping and confinement due to generation of surface plasmon waves (SPWs). In the present work, a Ge/Si QDIP integrated with a metal plasmonic structure is fabricated to experimentally measure the photoresponse enhancement and verify that this enhancement is caused by the excitation of the mid-IR surface plasmons. A 50 nm-thick gold film perforated with a 1.2 μm-period two-dimensional square array of subwavelength holes is employed as a plasmonic coupler to convert the incident electromagnetic IR radiation into SPWs. Measurements of the polarization and angular dependencies of the photoresponse allow us to determine the dispersion of plasmon modes. We find that experimental dispersion relations agree well with that derived from a computer simulation for fundamental plasmon resonance, which indicates that the photodetection improvement in the mid-IR spectral region is actually caused by the excitations of surface plasmon Bloch waves.

Compact flexible multifrequency splitter based on plasmonic graded metallic grating arc waveguide.

A compact flexible multifrequency splitter based on an arc waveguide constructed of plasmonic metallic grating structures with graded-height T-grooves is proposed and studied. The dispersion curves and cutoff frequencies of the plasmonic grating waveguides with different T-groove metallic grating heights are different. The guided spoof surface plasmonic polariton waves at different frequencies can be localized at dissimilar angles along the graded grating arc waveguide. The output flexibility at an arbitrary groove for different frequencies is realized by introducing an additional symmetrical T-groove structure as an output. The compact four-, seven-, and eight-output frequency splitters demonstrate its flexible multifrequency separation capability at different output angle locations, while the dimensional size of the frequency splitters is not increased. Measurement results at the microwave frequency display excellent agreement with numerical simulation results.

2D Materials-Coated Plasmonic Structures for SERS Applications

Two-dimensional (2D) materials, such as graphene and hexagonal boron nitride, are new kinds of materials that can serve as substrates for surface enhanced Raman spectroscopy (SERS). When combined with traditional metallic plasmonic structures, the hybrid 2D materials/metal SERS platform brings extra benefits, including higher SERS enhancement factors, oxidation protection of the metal surface, and protection of molecules from photo-induced damages. This review paper gives an overview of recent progress in the 2D materials-coated plasmonic structure in SERS application, focusing on the fabrication of the hybrid 2D materials/metal SERS platform and its applications for Raman enhancement.