Surface Plasmon Coupling Research Articles

Plasmon-Enhanced Ultraviolet Photoluminescence from the Graphene/GaN Nanofilm.

The response of graphene surface plasmon (SP) in ultraviolet (UV) wavelength region and its functional applications on the short wavelength of graphene/semiconductorare both fascinating research areas. Herein, a hybrid structure of graphene/GaN nanofilm was designed and fabricated to investigate the photoluminescence (PL) performance and the coupling dynamics. It is demonstrated that the resonant coupling between graphene SPs and GaN exciton emission is responsible for the substantially enhanced PL from the structure of graphene/GaN nanofilm. The underlying mechanism of the improved PL performance was proposed based on theoretical simulation and experimental characterization. The results are helpful to design new types of optic and photoelectronic devices based on SP coupling in graphene/semiconductor hybrid structures.

Localized and Surface Plasmons Coupling for Ultrasensitive Dopamine Detection by means of SPR‐Based Perylene Bisimide/Au Nanostructures Thin Film

AbstractDopamine (DA) is an important catecholamine neurotransmitter involved in neural and hormonal functions. Neural diseases, as Parkinson's, are connected to a significant lowering of DA concentration to picomolar levels in cerebrospinal fluid. So, in this contribution, a hybrid active layer based on a perylene bisimide (PBI) derivative and multishaped Au nanostructures is proposed for the development of surface plasmon resonance (SPR) dopamine detection system. PBI molecules, transferred as thin film by the dip coating approach, are demonstrated to be able to detect dopamine down to 10–12 m by SPR method. The presence of Au nanostructures promotes an important surface enhanced Raman scattering effect of Raman PBI signals highlighting a strong energetic communication between the two species. In this way, when PBI/Au nanostructures (AuNS) films are deposited by the layer‐by‐layer method and used for DA SPR detection, the sensitivity toward dopamine 10−12 m is doubled. The PBI/AuNS hybrid layer is able to detect picomolar concentration of dopamine, due to the coupling of localized (AuNS) and propagating surface plasmons on SPR slide. In particular, an interfacial coupling among localized surface plasmon resonance on AuNS and the propagating plasmon on Au thin film (of SPR slide) can be promoted.

Silver-Nanowire-Based Localized-Surface-Plasmon-Assisted Transparent Conducting Electrode for High-Efficiency Light-Emitting Diode

Silver nanowire (Ag NWs) networks with high transparency and low resistivity are widely used as promising candidates for the replacement of indium tin oxide (ITO)-based transparent conducting oxides (TCOs) in light-emitting diodes (LEDs). However, LEDs with Ag NW electrodes are less efficient than those with ITO electrodes because of their low electrical properties, such as high contact resistance and strong absorption in the visible region. In this work, we tried to improve the efficiency of LEDs with transparent conducting electrodes of Ag NWs networks via localized surface plasmons (LSPs) by adopting silver nanoparticles. We studied the effect of the thickness of the p-GaN layer on surface plasmon coupling. When a 45 nm thick p-GaN layer was used, the internal quantum efficiency was improved by LSP coupling between a dipole of QW and Ag NW/NP, and the light extraction was improved because the NPs afforded a leakage mode and acted as scattering centers.

Solid-state thermal dewetted silver nanoparticles onto electrochemically grown self-standing vertically aligned ZnO nanorods for three-dimensional plasmonic nanostructures

Three dimensional (3D) plasmonic nanostructures composed of silver nanoparticles decorated ZnO NRs arrays, have been fabricated by a process combining the electrochemical growth of ZnO NRs and further formation of Ag nanoparticles by the solid-state thermal dewetting (SSD) process. The effect of SSD parameters on the morphological, structural and optical properties of the Ag NPs decorated ZnO NRs arrays has been investigated. It is possible to tune the bandgap of the Ag NPs@ZnO nanorods array 3D plasmonic nanostructure by tailoring the Ag nanoparticle sizes, allowing light manipulation at the nanoscale. The silver nanoparticles attached to the ZnO NRs arrays experienced surface plasmonic coupling effect, causing enhancement in the room temperature photoluminescence (PL) UV emission and quenching the corresponding visible light one. An enhancement in the near band edge emission PL intensity of ZnO to the deep level emission PL intensity ratio after Ag NPs decoration of the ZnO nanostructures corresponding to ca. 11 folds has been observed, indicating that the defect emission is obviously suppressed.

Ag-Yb Alloy-Novel Tunable Plasmonic Material

Metals are commonly used in plasmonic devices because of their strong plasmonic property. However, such properties are not easily tuned. For applications such as spatial light modulators and beam steering, tunable plasmonic properties are essential, and neither metals nor other plasmonic materials possess truly tunable plasmonic properties. In this work, we show that the silver alloy silver–ytterbium (Ag-Yb) possesses tunable plasmonic properties; its plasmonic response strength can be adjusted as a function of Yb concentration. Such tunability can be explained in terms of the influence of Yb on bound charge and interaction of its dielectric with the dielectric of Ag. The change in transition characteristics progressively weakens Ag’s plasmonic properties. With a spectral ellipsometric measurement, it was shown that the Ag-Yb alloy thin film retains the properties of Ag with high transmission efficiency. The weakened surface plasmon coupling strength without dramatic change in the coupling wavelengths implies that the tunability of the Ag-Yb alloy is related to its volume ratio. The principle mechanism of the plasmonic change is theoretically explained using a model. This work points to a potential new type of tunable plasmonic material.

FDTD Based Simulation of Light Extraction in OLED using Triangular Band Structure

ABSTRACT In OLED, external light extraction shows very low efficiency due to total internal reflection, metal surface absorption and surface Plasmon coupling. The photonic crystal is a unique platform for controlling or modifying the light propagation and its properties such as transmission and absorption. The band structure of photonic crystal is mainly proposed for suppressing the spontaneous emission of light. In this work, the Finite Difference Time Domain (FDTD) mathematical modelling has been used to analyse the light extraction efficiency in the triangular band structure of OLED displays by measuring the Purcell factor. Due to the rectangular nature of FDTD solver region, it may be necessary to include multiple unit cells in the solver region for the triangular band structure. There is an improvement in the far-field intensity in OLED by optimizing the angular distribution of light through the substrate with the triangular band structure. Hence it can be widely used in ultra-compact optical devices.

Ultra-broadband metamaterial absorbers from long to very long infrared regime

Broadband metamaterials absorbers with high absorption, ultrathin thickness and easy configurations are in great demand for many potential applications. In this paper, we first analyse the coupling resonances in a Ti/Ge/Ti three-layer absorber, which can realise broadband absorption from 8 to 12 μm. Then we experimentally demonstrate two types of absorbers based on the Ti/Ge/Si3N4/Ti configuration. By taking advantage of coupling surface plasmon resonances and intrinsic absorption of lossy material Si3N4, the average absorptions of two types of absorbers achieve almost 95% from 8 to 14 μm (experiment result: 78% from 6.5 to 13.5 μm). In order to expand the absorption bandwidth, we further propose two Ti/Si/SiO2/Ti absorbers which can absorb 92% and 87% of ultra-broadband light in the 14–30 μm and 8–30 μm spectral range, respectively. Our findings establish general and systematic strategies for guiding the design of metamaterial absorbers with excellent broadband absorption and pave the way for enhancing the optical performance in applications of infrared thermal emitters, imaging and photodetectors.

Fiber optic coupled surface plasmon resonance sensor based Ag-TiO2 films for hydrogen detection

We propose and demonstrate the fiber optic Surface Plasmon Resonance (SPR) for hydrogen sensing based on Ag/TiO2 at the telecommunications wavelength of 1550 nm . The sensor using TiO2 as a sensitive layer for hydrogen detection consists of a multilayer film of 45 nm Ag/110 nm TiO2 deposited on the coupling prism substrate. An intensity interrogation SPR with Kretschmann configuration is designed, where SPR phenomenon will occur at the interface of the Ag/TiO2 film, and the hydrogen concentration will be detected by measuring the change in the reflected intensity. The sensitivity of the sensor is optimal at an Ag/TiO2 thickness. Simulation and experimental results demonstrate that the fiber-optic SPR sensor developed provides hydrogen sensing and has a high sensitivity to a hydrogen concentration ranging between 14.7% and 25% Hydrogen in Air, reaching 523nW/%.

Tunable propagation of surface plasmon-phonon polaritons in graphene-hBN metamaterials

We present a detailed study on the tunable propagation derived from the coupled surface plasmon–phonon polaritons (SPPPs) with the effective medium theory (EMT) in graphene-hBN metamaterials (MMs). Four reststrahlen bands (RBs) are observed, two of which mainly come from the hBN and the others originate from the effect of the graphene. The RBs frequency windows can be adjusted by the chemical potential and the filling ratio. An epsilon-near-zero-and-pole(εNZP)hyperbolic metamaterial (HMM) is detected at the precise frequency, chemical potential and filling ratio where the HMM undergoes a completely inversion of anisotropy. We derive the relative dispersion relation and demonstrate that the propagation of SPPP modes can be regulated by modifying the chemical potential. In addition, the tunability of the graphene-hBN MMs also can be improved by changing the thicknesses of the hBN and the number of graphene sheets. The energy-flux density in the graphene-hBN MM seriously deviates from its wave vector and can be localized at a certain depth. Besides, the ghost SPPP modes with the oscillation-attenuation character are observed at some special conditions through checking the distribution of electric fields. The attenuation total reflection (ATR) measurement is established to examine these SPPP modes. The numerical results show that the observation of each SPPP modes requires different conditions dictated by material parameters and the polarization direction of the incident light.

Multiplex Electrochemiluminescence Polarization Assay Based on the Surface Plasmon Coupling Effect of Au NPs and Ag@Au NPs.

A novel multiplex electrochemiluminescence (ECL) polarization assay was developed to detect breast cancer-related genes BRCA1 and BRCA2 simultaneously based on the polarization characteristics of surface plasmon-coupled electrochemiluminescence (SPC-ECL). In this work, boron nitride quantum dots (BN QDs) were used as ECL emitters, and gold nanoparticles (Au NPs) and gold-coated silver nanoparticles (Ag@Au NPs) were employed as surface plasmon materials. The surface plasmon coupling resonance of different metal NPs not only enhanced the ECL intensity but also converted the isotropic emission into directional emission. This study revealed the relation between the structure of metal nanomaterials and SPC-ECL, and a high polarization-resolved sensing system was designed to detect multitarget DNA from 100 aM to 1 nM simultaneously. Polarization-based multiple ECL analysis has broad prospects in related cancer diagnosis and treatment evaluation.

Enhanced Photoluminescence of Gold Nanoparticle‐Quantum Dot Hybrids Confined in Hairy Polymer Nanofibers

AbstractIn the present work, we have studied the influence of gold nanoparticles (AuNPs) on the photoluminescence (PL) behavior of cadmium selenide (CdSe) quantum dots (QDs) confined in spatially separated soft nanoscale cylindrical domains. These cylindrical domains, in the form of hairy core‐shell nanofibers, were fabricated via cooperative self‐assembly of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) block copolymer (BCP) mixed with pre‐synthesized CdSe QDs and AuNPs. The CdSe QDs and AuNPs were simultaneously incorporated in the P4VP cylindrical domains of the self‐assembled BCP structure. It was found that the confinement imposed by the nanometer‐sized cylindrical core resulted in the localization of the CdSe QDs and AuNPs in close proximity. Notably, it was observed that the PL intensity of the CdSe QDs could be manipulated by varying the amount of AuNPs present in the cylinder core. Interestingly, in the presence of a very low fraction of AuNPs, the PL intensity of the CdSe QDs increased compared to the AuNPs‐free system. However, further increase in the fraction of AuNPs led to gradual quenching of the photoluminescence intensity. The PL enhancement and quenching plausibly was due to the interplay between the energy transfer due to surface plasmon coupling and FRET/electron transfer from QDs to the AuNPs. The resulting functional nanofibers could have potential applications in sensing, bioimaging, and optoelectronic devices.

Surface plasmon coupling effects on the förster resonance energy transfer from quantum dot into rhodamine 6G

Rhodamine 6G (R6G) molecules linked CdZnSeS/ZnS green-emitting quantum dots (QDs) are self-assembled onto Ag nanoparticles (NPs) for studying the surface plasmon (SP) coupling effect on the Förster resonance energy transfer (FRET) process from QD into R6G. SP coupling can enhance the emission efficiency of QD such that FRET has to compete with QD emission for transferring energy into R6G. It is found that FRET efficiency is reduced under the SP coupling condition. Although R6G emission efficiency can also be enhanced through SP coupling when it is directly linked onto Ag NP, the enhancement decreases when R6G is linked onto QD and then the QD-R6G complex is self-assembled onto Ag NP. In particular, R6G emission efficiency can be reduced through SP coupling when the number of R6G molecules linked onto a QD is high. A rate-equation model is built for resembling the measured photoluminescence decay profiles and providing us with more detailed explanations for the observed FRET and SP coupling behaviors.

Factors Affecting Surface Plasmon Coupling of Quantum Wells in Nitride-Based LEDs: A Review of the Recent Advances.

Surface plasmon (SP)-enhanced quantum-well (QW) LEDs have proved their potential in replacing conventional lighting devices for their high-performance capabilities in ultraviolet (UV), blue and green spectral ranges. The SP-enhanced QW-LEDs have applications in light emission enhancement, light polarization, color conversion, and speed modulation. The electric field of the plasmonic mode of a metal couples with the exciton energy of QWs in resonance results in efficiency enhancement to several folds. The strength of the SP–QW coupling is mainly influenced by the type of metal used for SP enhancement, the metal nanostructure geometry, and the penetration depth of the SP fringing field in the p-GaN. The use of an appropriate dielectric interlayer between the metal and the p-GaN allows further control over SP resonance with QW emission wavelength. The penetration depth defines the p-GaN thickness and the QW period number for effective SP–QW coupling. The optimization of these parameters is key to achieve high efficiencies in SP-enhanced QW-LEDs for various applications. This review explains the SP enhancement mechanism and the key challenges facing the SP enhancement of QW-LEDs. The main factors that affect the SP–QW coupling have been explained in detail based on recent reports devoted to this field.

Independently tunable double Fano-like resonances arising from the interference coupling of localized surface plasmons with waveguide modes

Research on the classical analogy of asymmetric Fano resonances has gained momentum in recent years, owing to the steep dispersion of the Fano-like profile in classical systems, such as plasmonic nanostructures and metamaterials, which has numerous applications. We studied the double Fano-like resonances arising in a waveguide structure made of a periodic array of gold nanospheres placed on the top surface of an indium tin oxide (ITO) film, which is deposited on a silica substrate. These resonances emanate from the interference coupling between the dipolar surface plasmon mode of the individual gold nanospheres and the zero-order transverse electric (TE) and transverse magnetic (TM) waveguide modes within the ITO film. Increasing the array period of the gold nanospheres or thickness of the ITO film shifted the resonance peaks towards the low-frequency side corresponding to the excitation frequencies of the zero-order TE and TM waveguide modes, which were red-shifted. Additionally, the double Fano-like resonance profiles were approximated using an analytical Fano interference model.

Modulating Near-Field Radiative Heat Transfer through Thin Dirac Semimetal Films

ABSTRACT We propose a thermal modulation structure made of two identical SiO2 slabs coated by Dirac semimetal (DSM) films and separated by a nanoscale vacuum gap. The energy transmission probability reveals that the coupled surface plasmon polaritons (SPPs) between the two DSM films, and the surface phonon polaritons (SPhPs) supported by the SiO2 substrate can vary sensitively with the Fermi level, the degenerate factor of 3D Dirac points and the thickness of the DSM film, thus providing the possibilities for modulating the radiative heat transfer by tuning these parameters. Based on Maxwell’s equations incorporating fluctuational electrodynamics, the effects of these parameters on the heat transfer coefficient and the thermal modulation contrast are numerically analyzed. Under proper parameters, higher modulation contrasts are obtained by continuously tuning the Fermi level from 0.05 eV to 0.3 eV. The obtained results might be helpful in designing a DSM-based thermal modulator with higher modulation contrasts.

Self-assembly 2D plasmonic nanorice film for surface-enhanced Raman spectroscopy* *Project supported by the National Natural Science Foundation of China (Grant No. 11974067), Natural Science Foundation Project of CQ CSTC (Grant Nos. cstc2019jcyj-msxmX0145, cstc2019jcyj-bshX0042, and cstc2019jcyj-msxmX0828), and Sharing Fund of Chongqing University & Large-scale Equipment.

As an ultrasensitive sensing technology, the application of surface enhanced Raman spectroscopy (SERS) is one interesting topic of nano-optics, which has huge application prospectives in plenty of research fields. In recent years, the bottleneck in SERS application could be the fabrication of SERS substrate with excellent enhancement. In this work, a two-dimensional (2D) Ag nanorice film is fabricated by self-assembly method as a SERS substrate. The collected SERS spectra of various molecules on this 2D plasmonic film demonstrate quantitative detection could be performed on this SERS substrate. The experiment data also demonstrate this 2D plasmonic film consisted of anisotropic nanostructures has no obvious SERS polarization dependence. The simulated electric field distribution points out the SERS enhancement comes from the surface plasmon coupling between nanorices. And the SERS signals is dominated by molecules adsorbed at different regions of nanorice surface at various wavelengths, which could be a good near IR SERS substrate for bioanalysis. Our work not only enlarges the surface plasmon properties of metal nanostructure, but also exhibits the good applicationprospect in SERS related fields.

Far UV-enhanced Al mirrors with a Ti seed film.

A Ti seed film is investigated towards improving the far UV reflectance of Al/MgF2 mirrors. Samples were initially coated with a Ti film in half of the area and they were later coated in the full area with an Al film and protected with MgF2. All materials were deposited by evaporation. Samples were prepared with the MgF2 layer deposited either at room temperature (RT) or at 225°C. A 3-nm thick Ti seed film was seen to significantly increase the reflectance of Al/MgF2 mirrors at the well-known reflectance dip centered at ∼160 nm; this was attributed to a reduction of short-range surface roughness at the Al/MgF2 interface, which is responsible for radiation absorption through surface-plasmon (SP) coupling. SP absorption was more efficiently reduced with a Ti seed film on samples fully deposited at RT. A Ti seed film as thin as 1 nm provided the largest SP absorption reduction, and the SP dip was almost completely removed.

DNA-Mediated Au-Au Dimer-Based Surface Plasmon Coupling Electrochemiluminescence Sensor for BRCA1 Gene Detection.

Herein, we constructed a DNA-mediated Au-Au dimer-based surface plasmon coupling electrochemiluminescence (SPC-ECL) sensor. In the SPC-ECL sensing system, graphite phase carbon nitride quantum dots (GCN QDs) worked as an ECL emitter. A DNA rigid chain structure was employed to connect two Au NPs in an equilateral triangle configuration to form the Au-Au dimers. Due to the hot spot effect, the designed Au-Au dimers had a strong electromagnetic field intensity, which can greatly enhance the ECL signal of GCN QDs than a single Au nanoparticle. The gap distance of dimers can be effectively regulated by the DNA length, which resulted in different electromagnetic field intensities. Therefore, the different SPC-ECL amplification effects on the GCN QD signal by Au-Au dimers have been revealed. The maximum ECL signal of GCN QDs can be enhanced fourfold based on the Au-Au dimers with a gap distance of 2 nm. Furthermore, the biosensor showed good analytical performance for the detection of breast cancer susceptibility gene 1 (BRCA1 genes) (1 fM-1 nM) with a detection limit of 0.83 fM. This work provided an effective and precise SPC-ECL sensing mode for the diagnosis and prognosis of breast cancer.

Förster resonance energy transfer in surface plasmon coupled color conversion processes of colloidal quantum dots.

Förster resonance energy transfer (FRET) from a green-emitting quantum dot (GQD) into a red-emitting quantum dot (RQD) is an important mechanism in a multiple-color conversion process, particularly under the surface plasmon (SP) coupling condition for enhancing color conversion efficiency. Here, the dependencies of FRET efficiency on the relative concentrations of GQD and RQD in their mixtures and their surface molecule coatings for controlling surface charges are studied. Also, the SP coupling effects induced by two kinds of Ag nanoparticles on the emission behaviors of GQD and RQD are demonstrated, particularly when FRET is involved in the coupling process. FRET efficiency is reduced under the SP coupling condition. SP coupling can enhance the color conversion efficiency of either GQD or RQD. The combination of SP coupling and FRET can be used for controlling the relative converted light intensities in a multiple-color conversion process.

Coupled localized surface plasmon resonances in periodic arrays of gold nanowires on ion-exchange waveguide technology

Coupled localized surface plasmon resonances (LSPRs) in periodic arrays of metallic nanowires are attractive for use in sensing applications due to their light enhancement and their sensitivity to the surrounding environment. Due to the interwire coupling, they behave as plasmonic waveguides with high wavevector modes that require bulky methods for efficient excitation. In this contribution, we demonstrate the excitation of coupled LSPRs in gold nanowires with photonic modes supported by an optical waveguide made with ion exchange technology. Currently, although weakly-coupled LSPRs are experimentally demonstrated, strongly-coupled LSPRs are only demonstrated numerically due to the challenge represented by the fabrication of a high density nanowire array with current electron beam lithography. Due to their operation across the visible spectrum and its low-loss coupling to standard optical fibers, integrated nanowires on glass waveguides open new perspectives for the development of hybrid photonic-plasmonic integrated optical devices.