Support Surface Plasmon Resonances Research Articles

Chiro-plasmon responses of x-shaped titanium nitride (TiN) nanoarrays by numerical simulations

Titanium nitride (TiN) has recently been taken as a potential candidate for plasmonic material, which supports surface plasmon resonances and exhibits excellent thermal stability. In this article, we proposed a novel chiral metamaterial with TiN, which consists of X-shaped TiN nanorods periodically arranged on a glass substrate. Its extinction, circular dichroism (CD) spectra, and g-factors were calculated and regulated by the detailed geometry through numerical simulations using the finite element method to further boost the application of TiN in chiro-plasmonic system. We show that it presents chiral responses both in visible and near infrared (NIR) ranges. Under the optimized geometric parameters and NIR incidence, it predicts ∼4 and 2 fold E-field enhancement and g-factor, respectively, than that of experimental reports of TiN nanohelices. The obtained excellent chiro properties are elucidated well in terms of the obtained superchiral field and charge distributions, whose origin was analyzed by a linear superposition method. Moreover, the influence of dielectric environments is discussed as well. Overall, the findings underscore the potential of TiN as a chiro-plasmonic refractory metamaterial and shed light on the design of alternative chiro-plasmon metamaterials for NIR applications in the future.

Highly sensitive plasmonic biosensor enhanced by perovskite-graphene hybrid configuration

This study theoretically proposes a highly sensitive plasmonic biosensor comprising a silver film, perovskite nanosheets, bi-layer silicon nanosheets, and a graphene overlayer. The introduction of perovskite-graphene hybrid structure can reduce the optical reflectivity of the proposed biosensor configuration so that photons are converted into energy to support surface plasmon resonance (SPR) enhancement. Unlike conventional angular modulation, our proposed biosensor configuration is designed using phase modulation, offering sensitivity enhancements as high as 3 orders of magnitude. Excellent biosensing performances have been examined by optimizing the silver film thickness and the number of perovskite nanosheets. Considering a tiny refractive index change of 0.0012 refractive index unit (RIU) caused by biomolecules adsorption behavior, the optimal plasmonic biosensor configuration of 46-nm silver film–5.7-nm silicon interlayer-1-layer CH3NH3PbI3 perovskite film–0.7-nm silicon interlayer-1-layer graphene can produce the highest detection sensitivity of 1.2314 × 105 degree/RIU. In addition, an excellent linear response in the differential phase can be obtained, as the refractive index variation of the sensing interface can be as low as 10−6 RIU, showing great potential in performing ultrasensitive biosensing.

Tunable multi-narrowband perfect absorber based on graphene and black phosphorus metamaterial

Black phosphorus (BP) and graphene are two-dimensional (2D) metamaterials that support surface plasmon resonance. We propose a tunable mid-infrared multi-narrowband perfect absorber based on graphene and BP metamaterial. Perfect absorption peaks can be explained by the interference of two excited states in the structure. The transfer characteristics of the system are calculated by the coupled mode theory (CMT), and the theoretical calculated results agree well with the finite-difference time-domain (FDTD) numerical simulated ones. The resonant positions of the absorption peaks are affected by the layer spacing. By changing BP carrier density and graphene Fermi level, the dynamic tunable function can be realized, and the absorption performance of the system is not affected within the adjustment range. Meanwhile, the absorption performance of the system is not insensitive to the polarization angle of the incident light, when the polarization angle is less than 30°. The designed system can be applied to a variety of optical devices, including plasma sensors, multi-frequency absorbers, reflectors, switching controllers and filters.

(Invited, Digital Presentation) Enhancement of Magnetic Dipole Transition of Molecules By Silicon Nanoparticle Nanoantenna

A nanoantenna is a nanodevice that manipulates light propagation and enhances light-matter interaction at the nanoscale. Integration of an emitter into a nanoantenna capable of increasing local density of photonic states at the emission wavelength results in the enhanced spontaneous emission rate (Purcell effect). The most widely studied nanoantennas for the Purcell enhancement are plasmonic nanoantennas made from gold or silver nanostructures supporting surface plasmon resonances. In most cases, nanoantennas have been used for the enhancement of electric dipole-allowed transition of a molecule. In addition, recently, nanoantennas capable of enhancing magnetic dipole transition of a molecule are attracting attention. For the magnetic Purcell enhancement, nanoantennas have to have magnetic resonances at the optical frequency. Although it is possible to achieve magnetic resonances at the optical frequency by plasmonic nanostructures, the inherent absorption loss of noble metals limits the magnetic Purcell enhancement. On the other hand, nanoparticles of high refractive index dielectrics inherently have low-loss magnetic-type Mie resonances at the optical frequency, and thus are potentially more attractive as a material to realize large magnetic Purcell enhancement.We have developed spherical nanoparticles of crystalline silicon (Si) having the magnetic dipole (MD) and quadrupole (MQ) Mie resonances at the optical frequency [1]. In this work, to demonstrate the potential of a Si nanoparticle as a nanoantenna for the magnetic Purcell enhancement, we develop a composite nanoparticle, that is, a Si nanosphere decorated with europium ion (Eu3+) complexes, in which magnetic dipole emission of Eu3+ is efficiently coupled to the magnetic Mie modes of the nanosphere [2]. We systematically investigate the light scattering and photoluminescence spectra of the coupled system by means of single particle spectroscopy. The results are shown in Figure 1. By tuning the MQ Mie resonance of a Si nanosphere to the 5D0-7F1 magnetic dipole transition of Eu3+, the branching ratio between the magnetic and electric dipole (5D0-7F2) transitions is enhanced up to 7 times. The observed large magnetic Purcell enhancement offers an opportunity to develop novel fluorophores with enhanced magnetic dipole emission. Furthermore, the enhanced magnetic field of dielectric Mie resonators enhances otherwise very weak absorption due to magnetic dipole transition, and makes direct excitation of triplet states of a molecule possible [3]. Direct excitation of triplet states reduces photon energy necessary for energy conversion and chemical reactions utilizing a triplet state compared to a conventional process involving singlet-singlet excitation and singlet-triplet intersystem crossing.[1] H. Sugimoto, et. al., "Mie Resonator Color Inks of Monodispersed and Perfectly Spherical Crystalline Silicon Nanoparticles" Advanced Optical Materials, 8 (2020) 2000033.[2] H. Sugimoto, and Minoru Fujii, "Magnetic Purcell Enhancement by Magnetic Quadrupole Resonance of Dielectric Nanosphere Antenna", ACS Photonics, 8 (2021) 1794.[3] H. Sugimoto, et. al., "Direct Excitation of Triplet State of Molecule by Enhanced Magnetic Field of Dielectric Metasurfaces", Small, 2021, DOI: 10.1002/smll.202104458.Figure 1: Photoluminescence (red curves) and scattering (black curves) spectra of single Si naosphere-Eu3+ complex composite nanoparticles with different Si nanosphere diameters. The diameters are shown at the right end of the figure. Figure 1

Au-Based Thin-Film Metallic Glasses for Propagating Surface Plasmon Resonance-Based Sensor Applications.

We deposited Au–Cu–Si, an Au-based thin-film metallic glass (TFMG) of ∼50 nm thickness, as the activation layer for propagating surface plasmon resonance (PSPR)-based sensors on a BK7 glass substrate to substitute the commonly used gold layer. The film composition was tuned to yield the maximum Au content (∼65 at %), while the structure remained amorphous. The results showed that the Au-based TFMG could support surface plasmon resonance and gave rise to the extinction in the angle-resolved reflection spectrum. Using deionized water and ethyl alcohol with the refractive index difference of ∼0.03 as the analytes, the angle shift given by Au-based TFMG was 4° compared to 5° given by the Au film. Hence, Au-based TFMG is feasible to be used as the activation layer in PSPR-based sensors. Compared to the Au film, Au-based TFMG has the advantages of being less expensive, lacking grain boundary scattering, better adhesion to the substrate, and higher resistance to scratch and corrosion because of its amorphous structure with excellent mechanical properties.

Periodic Nanohole Arrays with Enhanced Lasing and Spontaneous Emissions for Low-Cost Plasmonic Devices

Periodic arrays of air nanoholes in thin metal films that support surface plasmon resonances can provide an alternative approach for boosting the light–matter interactions at the nanoscale. Nanohole arrays have garnered great interest in recent years for their use in biosensing, light emission enhancement, and spectroscopy. Here, we employ a simple technique to fabricate nanohole arrays and examine their photonic applications including enhanced lasing and spontaneous emission of novel nanomaterials. In contrast to the complicated and most commonly used electron-beam lithography technique, hexagonal arrays of nanoholes are fabricated by using a simple combination of shadowing nanosphere lithography technique and electron-beam deposition. Through spectral and temporal characterizations, it was shown that these arrays offer an enhancement in the lasing emission of an organic dye liquid gain medium with a quality factor above 150 as well as an accelerated decay rate for CdSe quantum dots. The simple fabrication of nanohole arrays together with their excellent optical responses can therefore offer a great potential in the industrialization of plasmonic devices for use in various realms of emerging technologies such as gas sensing, biomedical imaging, and ultrafast on-chip coherent light sources.

High sensitivity plasmonic temperature sensor based on a side-polished photonic crystal fiber

A high sensitivity plasmonic temperature sensor based on a side-polished photonic crystal fiber is proposed in this work. In order to achieve high sensitivity and high stability, the gold layer is coated on the side-polished photonic crystal fiber to support surface plasmon resonance. The mixture of ethanol and chloroform is used as the thermosensitive liquid. The performances of the proposed temperature sensor were investigated by the finite element method (FEM). Simulation results indicate that the sensitivity of the temperature sensor is as high as 7.82 nm/°C. It has good linearity (R 2 = 0.99803), the resolution of 1.1 × 10−3 °C, and the amplitude sensitivity of 0.1008 °C−1. In addition, the sizes of the small air hole and polishing depth have little influence on the sensitivity. Therefore, the proposed sensor shows a high structure tolerance. The excellent performance and high structure tolerance of the sensor make it an appropriate choice for temperature measurement.

Plasmonic biosensor based on excellently absorbable adjustable plasmon-induced transparency in black phosphorus and graphene metamaterials

Both black phosphorus (BP) and graphene metamaterials support surface plasmon resonance that is very sensitive to the local change of dielectric properties in the system. We design a novel BP ribbons and graphene sheet hybrid structures based on tunable mid-infrared plasmon-induced transparency. The destructive interference of two excited state modes in the structure leads to a pronounced induced transparent window, and the excellent absorption of the two channels is obtained. The transmission characteristics of the hybrid structures are theoretical calculation, and the results are in good agreement with the numerical simulation curve. The dynamic adjustment function can be realized by adjusting the carrier density of BP and the Fermi level of graphene, and the excellent absorption performance not affected within the adjustment range. Moreover, we found that the optical phase is rapid flips at the plasmon resonance position. Therefore, a sensing medium layer is added on top of the structure to implement a high-sensitivity plasmonic biosensor. This work may provide potential applications to plasmonic devices based on two-dimensional metamaterial.

Pulsed Laser Ablation Produced Copper Nanoparticles (CUO NPS): The Influence of Time

Copper nanoparticles were synthesized using laser ablation method by the reduction of copper plate in the presence of distilled water. Effects of time as the laser hits on the copper target were increased, the amount of Cu NPs in the distilled water also increased. EDAX confirms the existence of Cu NPs. The metallic nanoparticles have a unique optical property known as Surface Plasmon Resonance (SPR) which can be utilized to enhance the light harvesting performance in many applications. The noble metals of copper have the ability to support surface plasmon resonance which can be used to enhance the efficiency of any device.

Imprint and transfer fabrication of freestanding plasmonic membranes

This paper reports an imprint and transfer approach for the rapid and inexpensive fabrication of the ultra-thin freestanding plasmonic membrane (FPM) that supports surface plasmon resonances. The imprint and transfer fabrication method involves the soft imprint lithography on an ultrathin polymer film, transfer of the perforated polymer film to a supporting frame, subsequent deposition of gold, and final removal of the polymer film. Without using any sophisticated lithography and etching processes, the imprint and transfer method can produce freestanding gold membranes with 2D arrays of submicrometer-sized holes that support plasmonic modes in the mid-wavelength infrared (mid-IR) range. Two FPM devices with an array constant of 4.0 and 2.5 μm have been simulated, fabricated, and measured for their transmittance characteristics. The fabricated FPMs exhibit surface plasmon polariton Bloch mode and extraordinary optical transmission (EOT) with the enhanced local field around the membrane. The effects of membrane thickness and angle dispersion on the FPM were investigated to show the tuning of EOT modes in IR. Furthermore, we demonstrated the refractometric sensing and enhanced IR absorption of the FPM device for its potential in chemical and biomolecule sensing applications.

Structural Stability of Optofluidic Nanostructures in Flow-Through Operation.

Optofluidic sensors based on periodic arrays of subwavelength apertures that support surface plasmon resonance can be employed as both optical sensors and nanofluidic structures. In flow-through operation, the nanoapertures experience pressure differences across the substrate in which they are fabricated, which imposes the risk for structural failure. This work presents an investigation of the deflection and structural stability of nanohole array-based optofluidic sensors operating in flow-through mode. The analysis was approached using experiments, simulations via finite element method, and established theoretical models. The results depict that certain areas of the sensor deflect under pressure, with some regions suffering high mechanical stress. The offset in the deflection values between theoretical models and actual experimental values is overturned when only the effective area of the substrate, of 450 µm, is considered. Experimental, theoretical, and simulation results suggest that the periodic nanostructures can safely operate under trans-membrane pressures of up to 20 psi, which induce deflections of up to ~20 μm.

Plasmon-induced light absorption in mid-infrared based on hexagonal-shape graphene

In this manuscript, we numerically propose the plasmon-induced light absorption based on periodical hexagonal-shape graphene. Under the both TM- and TE-polarization light, the patterned graphene can support surface plasmon resonances (SPRs) and introduce the light absorption in mid-infrared, and the mode properties of SPRs are also studied. Besides, the impacts of geometric parameters, Fermi levels as well as number of layers of graphene on absorption spectrum are thoroughly investigated. Finally, a metal layer is introduced at the bottom of the structure to enhance the absorption. Since such pattern graphene can be naturally grown and shaped due to the atom arrangement of graphene, it has low requirement of optical fabrication, and the supported double SPRs can also provide double-peak absorption. This work can find potential applications such as absorbers, photodetectors and biosensors.

Ultrafast relaxation dynamics of aluminum nanoparticles in solution

Colloidal aluminum nanoparticles (Al NPs) can support surface plasmon resonances spanning ultraviolet to near-infrared wavelengths because of the high electron density of Al metal and the favorable position of its interband transitions. Free-standing colloidal Al particles can be synthesized using a variety of methods and suspended in solution, but there are still few investigations of its ultrafast decay processes. We used transient absorption spectroscopy (TAS) to examine the ultrafast relaxation dynamics of colloidal Al NPs suspended in ethanol. The electron-phonon (e-p) coupling times of Al NPs are equivalent or even longer than the e-p coupling times of Ag nanocubes or Au bipyramids in solution. The prolonged hot-electron transfer in Al NPs is likely due to the presence of the Al2O3 shell, which causes excited charge carrier trapping-detrapping at the metal core-oxide shell interface.

Incorporating Aluminum Plasmonic Nanohemisphere Arrays into Organic Ultraviolet Photodetectors for Improved Photoresponse

Aluminum nanostructures, which support surface plasmon resonances in the UV spectral range, were incorporated into conventional organic UV photodetectors with a structure of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM)/LiF/Al. Nanohemisphere arrays (NHSAs) were imprinted into the top surface of the soft organic active layer, thus transferring the pattern to the subsequently thermally deposited layers of LiF and Al. NHSA-top devices and flat-top control devices were investigated by 3-dimensional finite-difference time-domain (3D-FDTD) electromagnetic simulations. Improved UV active layer absorbance and enhanced electric fields in the nanohemispheric region at the top of the active layer were shown for devices with the NHSA-top. The impact of the NHSA-top was found to be more significant for devices with thin active layers and to gradually decrease with increasin...

SPR-Based Fiber Optic Sensor Using IMO Thin Film: Towards Wide Wavelength Tunability From Visible to NIR

Due to existence of free electrons, conducting metal oxides (CMOs) such as indium molybdenum oxide, can support surface plasmon resonance (SPR) at the interface of CMO and dielectric. This research provides, theoretically, the first implementation of indium molybdenum oxide (IMO) as plasmonic layer in SPR fiber optic sensor. We demonstrate how changing the oxygen contents during IMO layer deposition could tune the operational wavelength of sensing probe in a wide range from visible to NIR which has a great significance in many biological and chemical environmental applications. Moreover, sensitivity and figure of merit of the proposed sensor have been calculated and compared for IMO thin films prepared at different oxygen contents.

Perfect optical absorption with nanostructured metal films: design and experimental demonstration.

Structuring metal surfaces on the nanoscale has been shown to alter their fundamental processes like reflection or absorption by supporting surface plasmon resonances. Here, we propose metal films with subwavelength rectangular nanostructuring that perfectly absorb the incident radiation in the optical regime. The structures are fabricated with low-cost nanoimprint lithography and thus constitute an appealing alternative to elaborate absorber designs with complex meta-atoms or multilayer structuring. We conduct a thorough numerical analysis to gain physical insight on how the key structural parameters affect the optical response and identify the designs leading to broad spectral and angular bandwidths, both of which are highly desirable in practical absorber applications. Subsequently, we fabricate and measure the structures with an FT-IR spectrometer demonstrating very good agreement with theory. Finally, we assess the performance of the proposed structures as sensing devices by quantifying the dependence of the absorption peak frequency position on the superstrate material.

Mapping plasmon-enhanced upconversion fluorescence of Er/Yb-doped nanocrystals near gold nanodisks.

Fluorescence enhancement effects have many potential applications in the domain of biochemical sensors and optoelectronic devices. Here, the emission properties of up-converting nanocrystals near nanostructures that support surface plasmon resonances have been investigated. Gold nanodisks of various diameters were illuminated in the near-infrared (λ = 975 nm) and a single fluorescent nanocrystal glued at the end of an atomic force microscope tip was scanned around them. By detecting its visible fluorescence around each structure, it is found that the highest fluorescence enhancement occurs in a zone that forms a two-lobe pattern near the nanodisks and which corresponds to the map of the near-field intensity calculated at the excitation wavelength. In agreement with numerical simulations, it is also observed that the maximum fluorescence enhancement takes place when the disk diameter is around 200 nm. Surprisingly, this disk size is small when compared to that yielding the highest far-field scattering resonance, which occurs for disks with a diameter of 300-350 nm at the same excitation wavelength. This shift between the near and far-field resonances should be taken into account in the design of structures in systems that use plasmon enhanced fluorescence effects.

Hydrogen peroxide and glucose concentration measurement using optical fiber grating sensors with corrodible plasmonic nanocoatings.

We propose and demonstrate hydrogen peroxide (H2O2) and glucose concentration measurements using a plasmonic optical fiber sensor. The sensor utilizes a tilted fiber Bragg grating (TFBG) written in standard single mode communication fiber. The fiber is over coated with an nm-scale film of silver that supports surface plasmon resonances (SPRs). Such a tilted grating SPR structure provides a high density of narrow spectral resonances (Q-factor about 105) that overlap with the broader absorption band of the surface plasmon waves in the silver film, thereby providing an accurate tool to measure small shifts of the plasmon resonance frequencies. The H2O2 to be detected acts as an oxidant to etch the silver film, which has the effect of gradually decreasing the SPR attenuation. The etching rate of the silver film shows a clear relationship with the H2O2 concentration so that monitoring the progressively increasing attenuation of a selected surface plasmon resonance over a few minutes enables us to measure the H2O2 concentration with a limit of detection of 0.2 μM. Furthermore, the proposed method can be applied to the determination of glucose in human serum for a concentration range from 0 to 12 mM (within the physiological range of 3-8 mM) by monitoring the H2O2 produced by an enzymatic oxidation process. The sensor does not require accurate temperature control because of the inherent temperature insensitivity of TFBG devices referenced to the core mode resonance. A gold mirror coated on the fiber allows the sensor to work in reflection, which will facilitate the integration of the sensor with a hypodermic needle for in vitro measurements. The present study shows that Ag-coated TFBG-SPR can be applied as a promising type of sensing probe for optical detection of H2O2 and glucose detection in human serum.

Revealing the Mechanism of Photoluminescence from Single Gold Nanospheres by Defocused Imaging

The mechanism for the photoluminescence (PL) emission from gold nanoparticles has attracted considerable attention for many years. However, there is an important gap between small nanoclusters (∼2 nm) and larger plasmonic particles (∼50 nm). In this work, using defocused imaging technique, we investigate the PL properties of gold nanospheres (15–20 nm in diameter) on a single-particle level. Photoblinking and photobleaching phenomena are both observed. We notice that although these nanospheres can support surface plasmon resonance at ∼515 nm, they emit at ∼630 nm (excited by 532 nm), which is obviously plasmon-independent. The observed defocused images (DIs) exhibit isotropy first and then either transform into anisotropy or vanish rapidly. Surprisingly, the DIs can change their emission pattern within one single nanosphere during the tracing time. All these PL properties suggest a multiple-dipole-emission model. High-resolution transmission electron microscopy images demonstrate that these nanospheres are polycrystalline containing multiple small crystal domains (∼3 nm). We believe that these small domains divide the particle into different clusters and give rise to the photoblinking behavior and rotary DIs. The presented PL mechanism links gold nanoclusters and single-crystal nanorods, which could be helpful in understanding the origins of photoblinking and the luminescent properties from metallic nanoparticles. In addition, these water-soluble gold nanospheres provide new opportunities for biological labels and light-emitting sources in nanophotonics.

Strong interaction between graphene layer and Fano resonance in terahertz metamaterials

Graphene has emerged as a promising building block in modern optics and optoelectronics due to its novel optical and electrical properties. In the mid-infrared and terahertz (THz) regime, graphene behaves like metals and supports surface plasmon resonances (SPRs). Moreover, the continuously tunable conductivity of graphene enables active SPRs and gives rise to a range of active applications. However, the interaction between graphene and metal-based resonant metamaterials has not been fully understood. In this work, a simulation investigation on the interaction between the graphene layer and THz resonances supported by the two-gap split ring metamaterials is systematically conducted. The simulation results show that the graphene layer can substantially reduce the Fano resonance and even switch it off, while leaving the dipole resonance nearly unaffected, which is well explained with the high conductivity of graphene. With the manipulation of graphene conductivity via altering its Fermi energy or layer number, the amplitude of the Fano resonance can be modulated. The tunable Fano resonance here together with the underlying physical mechanism can be strategically important in designing active metal-graphene hybrid metamaterials. In addition, the ‘sensitivity’ to the graphene layer of the Fano resonance is also highly appreciated in the field of ultrasensitive sensing, where the novel physical mechanism can be employed in sensing other graphene-like two-dimensional materials or biomolecules with the high conductivity.