Bowtie Nanoantennas Research Articles

Harnessing surface plasmon polaritons from nanogroove plasmonic lenses to enhance the EM fields around plasmonic nanoantennas

In this paper, we present a device—consisting of a bowtie nanoantenna surrounded by either an asymmetric plasmonic nanogroove or a symmetric plasmonic nanogroove—that allows improved excitation of the bowtie nanoantenna via interaction between the bowtie nanoantenna and the surface plasmon polaritons (SPPs) generated from the nanogrooves. We study the effect of both a linear plasmonic nanogroove as well as a circular plasmonic nanogroove (i.e., a circular nanogroove plasmonic lens) on the EM fields around a bowtie nanoantenna placed at a certain distance from the nanogroove. We show that the electric field enhancement of a bowtie nanoantenna can be significantly improved by the interaction between the bowtie nanoantenna and the SPPs generated from the nanogrooves. We employed FDTD simulations to calculate quantities such as the electric field enhancements and power coupling into SPPs as well as a finite difference eigenmode solution to obtain dispersion relation of the nanogrooves. The geometrical parameters of the symmetric nanogroove and asymmetric nanogroove were optimized to couple maximum light into SPPs. We show that the bowtie nanoantenna surrounded by a single asymmetric nanogroove plasmonic lens produces a SERS electromagnetic enhancement factor (EMEF) of 1010—even when the gap between the arms of the bowtie nanoantenna is as large as 10 nm—which is three orders of magnitude higher than SERS EMEF of a stand-alone bowtie nanoantenna and one order of magnitude higher than the SERS EMEF of a bowtie nanoantenna surrounded by a single symmetric nanogroove plasmonic lens. In addition, the effect of the radius of nanogroove plasmonic lenses is studied. The calculation of collection efficiencies of Raman signal from the proposed nanostructures shows that ∼62% Raman signal can be collected from the bowtie nanoantenna surrounded by a symmetric nanogroove plasmonic lens or an asymmetric nanogroove plasmonic lens (PL) compared to 10% Raman signal collected from only a bowtie nanoantenna on a silica substrate.

Singular dielectricnanolaser with atomic-scale field localization.

Compressing the optical field to the atomic scale opens up possibilities for directly observing individual molecules, offering innovative imaging and research tools for both physical and life sciences. However, the diffraction limit imposes a fundamental constraint on how much the optical field can be compressed, based on the achievable photon momentum1,2. In contrast to dielectric structures, plasmonics offer superior field confinement by coupling the light field with the oscillations of free electrons in metals3-6. Nevertheless, plasmonics suffer from inherent ohmic loss, leading to heat generation, increased power consumption and limitations on the coherence time of plasmonic devices7,8. Here we propose and demonstrate singular dielectric nanolasers showing a mode volume that breaks the optical diffraction limit. Derived from Maxwell's equations, we discover that the electric-field singularity sustained in a dielectric bowtie nanoantenna originates from divergence of momentum. The singular dielectric nanolaser is constructed by integrating a dielectric bowtie nanoantenna into the centre of a twisted lattice nanocavity. The synergistic integration surpasses the diffraction limit, enabling the singular dielectricnanolaser to achieve an ultrasmall mode volume of about 0.0005 λ3 (λ, free-space wavelength), along with an exceptionally small feature size at the 1-nanometre scale. To fabricate the required dielectric bowtie nanoantenna with a single-nanometre gap, we develop a two-step process involving etching and atomic deposition. Our research showcases the ability to achieve atomic-scale field localization in laser devices, paving the way for ultra-precise measurements, super-resolution imaging, ultra-efficient computing and communication, and the exploration of light-matter interactions within the realm of extreme optical field localization.

Bowtie Nanoantenna LSPR Biosensor for Early Prediction of Preeclampsia.

The concentration of the placental circulating factor in early pregnancy is often extremely low, and the traditional prediction method cannot meet the clinical demand for early detection preeclampsia in high-risk gravida. It is of prime importance to seek an ultra-sensitive early prediction method. In this study, finite-different time-domain (FDTD) and Discrete Dipole Approximation (DDA) simulation, and electron beam lithography (EBL) methods were used to develop a bowtie nanoantenna (BNA) with the best field enhancement and maximum coupling efficiency. Bio-modification of the placental circulating factor (sFlt-1, PLGF) to the noble nanoparticles based on the amino coupling method were explored. A BNA LSPR biosensor which can specifically identify the placental circulating factor in preeclampsia was constructed. The BNA LSPR biosensor can detect serum placental circulating factors without toxic labeling. Serum sFlt-1 extinction signal (Δλmax) in the preeclampsia group was higher than that in the normal pregnancy group (14.37 ± 2.56 nm vs. 4.21 ± 1.36 nm), p = 0.008, while the serum PLGF extinction signal in the preeclampsia group was lower than that in the normal pregnancy group (5.36 ± 3.15 nm vs. 11.47 ± 4.92 nm), p = 0.013. The LSPR biosensor detection results were linearly consistent with the ELISA kit. LSPR biosensor based on BNA can identify the serum placental circulating factor of preeclampsia with high sensitivity, without toxic labeling and with simple operation, and it is expected to be an early detection method for preeclampsia.

Optical Tweezing Terahertz Probing for a Single Metal Nanoparticle.

Recently, extensive research has been reported on the detection of metal nanoparticles using terahertz waves, due to their potential for efficient and nondestructive detection of chemical and biological samples without labeling. Resonant terahertz nanoantennas can be used to detect a small amount of molecules whose vibrational modes are in the terahertz frequency range with high sensitivity. However, the positioning of target molecules is critical to obtaining a reasonable signal because the field distribution is inhomogeneous over the antenna structure. Here, we combine an optical tweezing technique and terahertz spectroscopy based on nanoplasmonics, resulting in extensive controllable tweezing and sensitive detection at the same time. We observed optical tweezing of a gold nanoparticle and detected it with terahertz waves by using a single bowtie nanoantenna. Furthermore, the calculations confirm that molecular fingerprinting is possible by using our technique. This study will be a prestep of biomolecular detection using gold nanoparticles in terahertz spectroscopy.

Real-time tracking of coherent oscillations of electrons in a nanodevice by photo-assisted tunnelling

Coherent collective oscillations of electrons excited in metallic nanostructures (localized surface plasmons) can confine incident light to atomic scales and enable strong light-matter interactions, which depend nonlinearly on the local field. Direct sampling of such collective electron oscillations in real-time is crucial to performing petahertz scale optical modulation, control, and readout in a quantum nanodevice. Here, we demonstrate real-time tracking of collective electron oscillations in an Au bowtie nanoantenna, by recording photo-assisted tunnelling currents generated by such oscillations in this quantum nanodevice. The collective electron oscillations show a noninstantaneous response to the driving laser fields with a T2 decay time of nearly 8 femtoseconds. The contributions of linear and nonlinear electron oscillations in the generated tunnelling currents were precisely determined. A phase control of electron oscillations in the nanodevice is illustrated. Functioning in ambient conditions, the excitation, phase control, and read-out of coherent electron oscillations pave the way toward on-chip light-wave electronics in quantum nanodevices.

Surface-enhanced photoluminescence and Raman spectroscopy of single molecule confined in coupled Au bowtie nanoantenna

Optical nanoantennas possess broad applications in the fields of photodetection, environmental science, biosensing and nonlinear optics, owing to their remarkable ability to enhance and confine the optical field at the nanoscale. In this article, we present a theoretical investigation of surface-enhanced photoluminescence spectroscopy for single molecules confined within novel Au bowtie nanoantenna, covering a wavelength range from the visible to near-infrared spectral regions. We employ the finite element method to quantitatively study the optical enhancement properties of the plasmonic field, quantum yield, Raman scattering and fluorescence. Additionally, we systematically examine the contribution of nonlocal dielectric response in the gap mode to the quantum yield, aiming to gain a better understanding of the fluorescence enhancement mechanism. Our results demonstrate that altering the configuration of the nanoantenna has a significant impact on plasmonic sensitivity. The nonlocal dielectric response plays a crucial role in reducing the quantum yield and corresponding fluorescence intensity when the gap distance is less than 3 nm. However, a substantial excitation field can effectively overcome fluorescence quenching and enhance the fluorescence intensity. By optimizing nanoantenna configuration, the maximum enhancement of surface-enhanced Raman can be turned to 9 and 10 magnitude orders in the visible and near-infrared regions, and 3 and 4 magnitude orders for fluorescence enhancement, respectively. The maximum spatial resolutions of 0.8 nm and 1.5 nm for Raman and fluorescence are also achieved, respectively. Our calculated results not only provide theoretical guidance for the design and application of new nanoantennas, but also contribute to expanding the range of surface-enhanced Raman and fluorescence technology from the visible to the near-infrared region.

Performance Evaluation of a Fractal Plasmonic Bowtie Nano-Antenna: Optical and Far-Field Properties

Performance Evaluation of a Fractal Plasmonic Bowtie Nano-Antenna: Optical and Far-Field Properties

Streamlines of the Poynting Vector and Chirality Flux around a Plasmonic Bowtie Nanoantenna.

The streamlines of the energy flux (Poynting vectors) and chirality flux as well as the intensity of the electric field around various plasmonic nanostructures (nanocube, nanocuboid, nanotriangle, hexagonal nanoplate and bowtie nanoantenna) induced by a circularly polarized (CP) or linearly polarized (LP) light were studied theoretically. The boundary element method combined with the method of moment was used to solve a set of surface integral equations, based on the Stratton-Chu formulation, for analyzing the highly distorted electromagnetic (EM) field in the proximity of these nanostructures. We discovered that the winding behavior of these streamlines exhibits versatility for various modes of the surface plasmon resonance of different nanostructures. Recently, using plasmonic nanostructures to facilitate a photochemical reaction has gained significant attention, where the hot carriers (electrons) play important roles. Our findings reveal a connection between the flow pattern of energy flux and the morphology of the photochemical deposition around various plasmonic nanostructures irradiated by a CP light. For example, numerical results exhibit vertically helical streamlines of the Poynting vector around an Au nanocube and transversely twisted-roll streamlines around a nanocuboid. Additionally, the behaviors of the winding energy and chirality fluxes at the gap and corners of a plasmonic bowtie nanoantenna, implying a highly twisted EM field, depend on the polarization of the incident LP light. Our analysis of the streamlines of the Poynting vector and chirality flux offers an insight into the formation of plasmon-enhanced photocatalysis.

Resonance mechanisms of coupled-particle plasmonic nano-antennas to maximize UV fluorescence enhancement of biological molecules

We investigated several geometric parameters such as the height, width and length, and the contribution of different plasmonic modes on the enhancement factors of aluminum (Al) bowtie nano-antennas (BNAs) on tryptophan’s native fluorescence in the ultraviolet (UV) to visible range. The highest fluorescence enhancement was produced by the tallest BNAs. Analysis revealed that, in tall BNAs illuminated at normal incidence, phase retardation amplified quadrupole resonances which were exploited to obtain high excitation enhancement. The optimized oxide-free Al BNA predicted 331 × excitation enhancement, 74 x radiative enhancement, 993 × fluorescence net enhancement and the optimized oxidized Al BNA predicted 128 × excitation enhancement, 142 × radiative enhancement and 461 × fluorescence net enhancement. These enhancement factors are the largest reported for simulated UV plasmonic structures in literature using tryptophan as the model molecule. The effect of length and width on the different plasmonic modes were also studied and explained in depth. An oxide layer dampened the excitation enhancement but has negligible effect on emission enhancements. The numerical study conducted in this manuscript sheds light to light–matter interaction in the UV frequency range.

High performance, single crystal gold bowtie nanoantennas fabricated via epitaxial electroless deposition

Material quality plays a critical role in the performance of nanometer-scale plasmonic structures and represents a significant hurdle to large-scale device integration. Progress has been hindered by the challenges of realizing scalable, high quality, ultrasmooth metal deposition strategies, and by the poor pattern transfer and device fabrication yields characteristic of most metal deposition approaches which yield polycrystalline metal structure. Here we highlight a novel and scalable electrochemical method to deposit ultrasmooth, single-crystal (100) gold and to fabricate a series of bowtie nanoantennas through subtractive nanopatterning. We investigate some of the less well-explored design and performance characteristics of these single-crystal nanoantennas in relation to their polycrystalline counterparts, including pattern transfer and device yield, polarization response, gap-field magnitude, and the ability to model accurately the antenna local field response. Our results underscore the performance advantages of single-crystal nanoscale plasmonic materials and provide insight into their use for large-scale manufacturing of plasmon-based devices. We anticipate that this approach will be broadly useful in applications where local near-fields can enhance light–matter interactions, including for the fabrication of optical sensors, photocatalytic structures, hot carrier-based devices, and nanostructured noble metal architectures targeting nano-attophysics.

Plasmonic metasurface superscatters driven by infrared surface lattice resonances

We have demonstrated that plasmonic metasurfaces composed of arrays of Au bowtie nanoantennas can support an infrared bidirectional superscattering state. This state arises when the nanoantennas are coherently coupled together, forming a surface lattice resonance that efficiently guides the infrared range (1–1.6 μm) of incident broadband white light along the plane of the arrays. This process exhibits strong polarization dependence, offering an “OFF” state where a 90° rotation of the incident light polarization effectively suppresses in-plane scattering from all sides. Stokes parameters analysis is used to study the states of polarization of the scattering, demonstrating transformation into a complete depolarized state. The results emphasize the significant influence of the multipolar modes of these nanoantennas on the interference processes associated with such scattering phenomena, and their potential applications in polarization optical switching and unique beamsplitting.

Plasmonic equi-triangular slot loaded bowtie nano-antenna for quantum optical wireless communication

In this manuscript, the plasmonic equi-triangular slot loaded bowtie aluminium dipole nano-antenna is investigated on a glass substrate for quantum optical wireless communication The optical characteristics of aluminium, such as permittivity and refractive index, are analyzed using the Drude dispersive model, which exhibits the required criteria for plasmonic resonance. A nanocircuit model for bowtie nano-antennas using lumped circuit elements is proposed and validated through CST simulation. The four equi-triangular slot loaded bowtie nanostructures are designed to tune the resonating frequency from 111 THz to 292 THz. Further, detailed investigation of the equi-triangular slot loaded bowtie nano-antenna is performed through the design parameter Tc (thickness) to obtain the optimum characteristics appropriate for quantum optical wireless communication. The proposed single bowtie nano-antenna exhibits a directivity of 7.606 dBi and a field enhancement factor of 289.5 at the resonating frequency of 292 THz.

Guided domino lithography for uniform fabrication of single-digit-nanometer scale plasmonic nanoantenna

Abstract Single-digit-nanometer scale plasmonic nanoantenna platforms are widely used in optical sensors, quantum plasmonics, and other applications. Uniform and reliable fabrications with a single-digit-nanometer resolution are desirable for diverse quantum nanophotonic device applications, but improving the process yield and uniformity of the shape of the nanoantenna over the entire fabrication area remains a challenge. Here we report the guided domino lithography fabrication method for uniform ultra-sharp nanoantenna arrays. We use a collapsing of unstable photoresist nanostructures with a guide structure to uniformly fabricate ultra-sharp bowtie photoresist masks. We directly compare the yields of the conventional and the guided domino lithography under the optimized electron beam exposing and development conditions. Furthermore, we conduct a rigorous analysis to verify the electric field enhancement effect from ultra-sharp bowtie nanoantennas fabricated with different geometry. We believe that guided domino lithography can be a promising solution toward a practical manufacturing method for single-digit-nanometer plasmonic nanoantennas.

Materials for Dielectric Nanotweezers in the Near-Visible Region

Nanotweezers made of dielectric nanoantennas have enabled optical trapping and manipulation of nanoscale objects. Commonly used dielectric materials with a high refractive index, notably silicon (Si), suffer from absorption at visible wavelengths and thus Joule heating of the structure and the trapped object. They are thus normally considered unsuitable for trapping applications in this wavelength range. In this work, dielectric materials with low absorption at 785 nm are studied to minimize Joule heating. We consider a bowtie configuration, which is simulated for four different dielectric materials and optimized for maximum electric field enhancement. The results show a significant electric field enhancement in the bowtie gap, which can act as a “hotspot” for optical trapping and enhancement of Raman scattering of a single nanosphere. We numerically investigate optical trapping of nanospheres and compare the results with an analytical expression. Three nanospheres with different refractive indices are used as examples. We further study the temperature increase and the thermally induced flow around the bowtie nanoantenna to understand if and how the trapping is perturbed by Joule heating. We find that nanoantennas made by Si on a Si substrate, although absorbing, can be used for trapping quantum dots (QDs) and polystyrene (PS) beads. The required input intensities for stable trapping are approximately 10 and 50 mW/μm2, for QDs and PS beads, respectively, inducing temperature increases of ∼1.4 K and ∼7 K, respectively. For transparent materials, the input intensity is the limiting factor, and gallium phosphide (GaP) requires the lowest input intensity due to its high refractive index. However, Si is a far more common and standard material and thus gives a significantly easier fabrication process.

Substrate engineering of plasmonic nanocavity antenna modes.

Plasmonic nanocavities have emerged as a promising platform for next-generation spectroscopy, sensing and photonic quantum information processing technologies, benefiting from a unique confluence of nanoscale compactness and integrability, ultrafast functionality and room-temperature viability. Harnessing their unprecedented optical field confinement and enhancement properties for such diverse application domains, however, demands continued innovation in cavity design and robust strategies for engineering their plasmonic mode characteristics, with the aim of optimizing spatial and spectral matching conditions for strong light-matter interaction involving embedded quantum emitters. Adopting the canonical gold bowtie nanoantenna, we show that the complex refractive index, n + ik, of the substrate material provides additional design flexibility in tailoring the properties of plasmonic nanocavity modes, including their resonance wavelengths, hotspot locations, intracavity field polarization and radiative decay rates. In particular, we predict that highly refractive (n ≥ 4) or highly absorptive (k ≥ 4) substrates provide two complementary approaches to engineering nanocavity modes that are especially desirable for coupling two-dimensional quantum materials, featuring namely an elevated hotspot with a dominantly in-plane polarized near-field, as well as a strongly radiative character. Our study elucidates the benefits and intricacies of a largely unexplored facet of nanocavity mode manipulation, beyond the widely practiced synthetic control over the cavity topology or physical dimensions, and paves the way for plasmonic cavity quantum electrodynamics with two-dimensional excitonic matter.

Enhanced quantum efficiency and Purcell factor of incoherent light-emitting source modulators coupled with nanoantennas: DDA modeling and optimization

Gated tunable materials-based devices have proven efficient structures to dynamically control quantum emitters’ (QEs) photonic density of states. The active permittivity control enabled by these materials allows manipulating the coupling and dissipation of evanescent modes radiated by the QE, hence controlling the emission parameters. In this sense, we propose here the design and optimization of a plasmonic device coupled with nanoantennas capable of dynamically manipulating the QEs’ emission at visible wavelengths using a thin gated doped titanium nitrate layer. We explore the use of metallic cubic and bow-tie antennas and study their unique characteristics related to enhancing the QEs’ emission. For the nanoantenna geometrical parameters optimization, we propose a discrete-dipole-approximation (DDA) method to accurately calculate all the radiation parameters of a QE embedded in a layered medium coupled to a nanoantenna. This technique allows calculating the decay behavior of QEs arbitrarily distributed, which is only feasible with knowledge of the Purcell factor and quantum efficiency mapped for all possible positions, easily achieved with the proposed model. We show that by employing the proposed DDA, the time required for optimizing and building those maps to evaluate the device’s response is drastically reduced (98%) compared to conventional numerical techniques. Using the DDA to optimize the antenna allowed the device’s quantum efficiency to be enhanced from 1.8% (no nanoantenna) to 8% and 10.5% using the cubic and bow-tie nanoantenna, respectively. In addition, the nanoantenna helps decrease the QE lifetime by a factor of approximately 2, allowing faster modulation speeds. Finally, our modeling and findings can be used to pave the way for the design of new gated optical modulators coupled with nanoantennas for applications that require amplitude modulation.

Infrared Thermoelectric Nanoantenna with Maximum Output Voltage Using Grounded and Open‐Ended SiO2

AbstractThe potential of a nanoantenna‐coupled thermocouple to convert untapped infrared (IR) energy from low‐temperature heat sources into direct current (DC) energy has recently gained attention. In a typical nanoantenna with a thermocouple, heat spread at the antenna center leads to a limited temperature difference and lowers the open‐circuit voltage (Voc). Therefore, a membrane or air gap under the antenna has recently been used, but when a massive array is constructed for high DC voltage output, stability and fabrication issues can arise. To solve this, this work utilizes the constructively coupled fields at the antenna center in both vertical and horizontal directions via a grounded and open‐ended substrate and maximizes Voc of the thermoelectric nanoantenna. In the antenna structure, a titanium (Ti)‐based bowtie nanoantenna and nickel (Ni)‐Ti bimetal nano‐thermocouple are used for high Seebeck effect. The thermoelectric bowtie nanoantenna is designed and fabricated on a metal‐backed and open‐ended silicon dioxide (SiO2) substrate with optimum dimensions, demonstrating the maximum Voc of 2.03 µV at λ0 = 10.6 µm which is five times the maximum Voc of 0.4 µV from the state‐of‐the‐art substrate‐mounted thermoelectric nanoantennas. It is expected that the fabricated SiO2‐mounted thermoelectric nanoantenna with the maximum Voc can be used for a high DC output IR‐harvesting massive nanoantenna array.

Bowtie Nanoantenna Coupled Metal-Oxide-Silicon (p-Doped) Diode for 28.3 THz IR Rectification.

Low-temperature waste heat in the infrared (IR) wavelength region offers an opportunity to harvest power from waste energy and requires further investigation in order to find efficient conversion techniques. Although grating-coupled metal-oxide-semiconductor (MOS) diode devices offer efficient conversion from low and moderate-temperature thermal sources, the integration of such diodes with a nanoantenna structure has yet to be explored. We propose a bowtie nanoantenna coupled with a p-doped MOS diode for IR to direct current (DC) conversion without any bias voltage at 28.3 THz. The nanoantenna was designed and optimized to provide maximum field enhancement in a 4 nm-thick oxide layer at the resonant frequency. The device was fabricated following the complementary MOS (CMOS) fabrication process and measured in a custom DC and optical characterization setup using a 10.6 μm wavelength CO2 laser. The results reveal two different types of devices with linear and nonlinear I-V curves having kΩ and MΩ zero-bias resistance, respectively. The linear device generates a micron-level open-circuit voltage (Voc) with clear polarization dependence from the laser input, but the nonlinear case suffers from a weak noise-like signal. Finally, we analyze two types of devices using thermoelectric and tunneling effects and discuss the future direction of nanoantenna-integrated MOS devices for efficient IR harvesters.

Spectral exploration of asymmetric bowtie nanoantennas

Bowtie nanoantennas are nanostructures widely used in the field of optical sensing. At present, most of the bowtie nanoantennas are symmetrical structures. Their spectra are dominated by dipolar plasmonic modes. Usually, asymmetries caused by statistical variation in the nanofabrication process are neglected. In this work we have designed, fabricated and characterized nanostructures with varying degrees of asymmetry. The optical behavior was compared with that of symmetrical structures of corresponding dimensions. This study gives a deeper understanding of how asymmetry affects the optical performance of nanoantennas, and how it can be harnessed to introduce additional degrees of freedom, providing extended design ideas for nanosensors.

Numerical investigation of plasmonic bowtie nanorings with embedded nanoantennas for achieving high SEIRA enhancement factors

This paper presents the numerical investigation of several complex plasmonic nanostructures — bowtie nanoring and crossed-bowtie nanoring nanoantennas with embedded bowtie nanoantennas and crossed-bowtie nanoantennas — for surface enhanced infrared absorption (SEIRA) spectroscopy-based substrates. The proposed nanostructures exhibit substantially large SEIRA enhancement factor (∼8.1 × 105) compared to previously reported enhancement factor values for bowtie nanoantennas or nanoring antennas. The plasmonic properties of the proposed nanostructures have been studied by the numerical evaluation of the near-field electromagnetic enhancement at resonant plasmon mode excitation wavelengths in the mid-IR spectral regime. The highest SEIRA enhancement of ∼8.1 × 105 occurs at a wavelength of ∼6800 nm (6.8 μm). A substantial electric field enhancement as large as ∼375, corresponding to SEIRA EF of ∼1.4 × 105 is noted even when the minimum gaps between the plasmonic nanostructures is as large as 10 nm, which can easily be fabricated using the conventional nanolithography techniques. The occurrence of several electric field hotspots due to the presence of plasmonic nanoantennas embedded inside the nanorings was observed, as the electric fields are enhanced in the vicinity of the plasmonic nanostructures being proposed. The multiple electric field hotspots in the proposed nanostructures can lead to larger average electric field enhancement as well as the average SEIRA enhancement for these substrates. Moreover, by embedding plasmonic nanoantenna structures inside the bowtie nanorings and crossed-bowtie nanorings, large spectral tunability of plasmon resonance wavelengths is achieved in the spectral regime from 4 μm to 8 μm. This is done by varying a larger number of spectral parameters that are present in these complex nanostructures. This paper also reports a novel configuration of crossed-bowtie nanoring plasmonic structure exhibiting less polarization dependence of the SEIRA enhancement factor. This structure also exhibits tunability of hotspot positions when the direction of the polarization of the incident light is rotated. The proposed structures in this paper can be fabricated by the state-of-the-art nanofabrication technologies. The proposed structures could find potential applications in chemical and biological sensing and biochemical detection of analyte molecules.