Extinction Spectra Research Articles

Localized surface plasmon resonance of Ag nanoparticle thin films deposited by direct-current magnetron sputtering

This study investigates the localized surface plasmon resonance (LSPR) of Ag nanoparticle (NP) thin films deposited by magnetron sputtering on an alkaline-free aluminosilicate-glass substrate at a substrate temperature of 600 °C. The equivalent film thickness was controlled to be 5, 10, 20, and 50 nm by adjusting the deposition time. The deposited Ag thin films formed NPs with uniform diameter and spacing for all Ag thicknesses. The NP diameters ranged approximately from 16 to 88 nm, corresponding to the equivalent film thickness. Due to the formation of isolated NPs, all Ag thin films exhibited a singlet LSPR peak in their extinction spectra. The LSPR peak position in the extinction spectra shifted with the refractive index of the environmental solvent media when the Ag NP thin films were immersed in these media. In addition, the insertion of a MgO, Nb2O3, or TiO2 underlayer shifted the LSPR peak position in the extinction spectra according to the refractive index of each underlayer material. A peak shift corresponding to the refractive index of the environmental solvent media was also observed for Ag NP thin films deposited on underlayers. The relatively low sensitivity of the LSPR peak shift to the refractive index of the environmental solvent media suggests that the solvent media only covered the top surface of the Ag NPs distributed on the substrate but did not infiltrate the spaces between them. The results of this study demonstrate the applicability of sputter-deposited Ag NP thin films to solid LSPR devices.

Forward-Scattering and Multiple-Scattering Sources of Errors in UV-Visible Spectroscopy of Microspheres.

Conventional UV-visible spectroscopy instruments measure the extinction spectrum of solutions in a transmission configuration. Because of the finite (nonzero) acceptance angle in detection, errors due to forward scattering and multiple scattering can be introduced when measuring scattering samples. We here experimentally quantify these errors using polystyrene spheres of different sizes for two representative analytical/research UV-visible instruments, one based on a single-beam diode array and the other on a double-beam scanning configuration. The measured spectra for particles larger than 1 μm are shown to differ between the two instruments, even at low concentrations, and also vary with concentration (in contradiction with the Beer-Lambert law). We show that systematic errors in the range of 10-40% are common in such measurements. We propose a model accounting for both forward- and multiple-scattering errors and demonstrate its agreement with our experimental results. This model could reduce systematic errors in measurements of scattering samples by up to 40%.

Synthesis of Chiral Au-Ag Core-Shell Nanoparticles and Their Localized Surface Plasmon Resonance Properties

Noble metal nanoparticles (NPs) such as silver (Ag), and gold (Au) exhibit localized surface plasmon resonance (LSPR) peaks in the visible light region, and their optical properties can be tuned by their size and shape. Advances in colloid chemistry enable the introduction of structural chirality to these plasmonic NPs. LSPRs of chiral metal NPs are responsive to circularly polarized light (CPL), giving them chiroptical properties. For example, Au nanoparticles prepared with L- or D-cysteines as a ligand showed almost the same shape of extinction spectra, but their CD spectra showed opposite peaks in the LSPR wavelength region, depending on the handedness of ligands.[1] Metal nanoparticles having chiral structures are expected to be applied to high-sensitivity chiral sensing. While Au nanoparticles have been extensively explored due to their high chemical stability, chiral Ag nanostructures have not been investigated in spite of the potential for a stronger LSPR-induced electric field. In this study, we report the development of a novel colloidal method to synthesize chiral Au-Ag core-shell nanoparticles via electrochemical deposition of Ag layer onto the surface of pre-synthesized chiral Au nanoparticles.Chiral Au NPs were prepared according to a previous report using L-cysteine as the ligand.[1] Thus-prepared NPs were loaded on a glassy carbon (GC) electrode. A Cu monolayer was deposited on Au NPs by the underpotential deposition (UPD) in an aqueous solution containing 1.0 mmol dm-3 CuSO4. The Cu UPD layer was replaced with Ag through galvanic replacement by immersing the electrode with the Cu-UPD Au NPs in a 10 mmol dm-3 AgNO3 aqueous solution. The amount of Ag deposition on individual Au NPs was controlled by repeating the procedures of Cu UPD and Ag replacement.Cyclic voltammograms were measured on GC electrodes loaded with chiral Au NPs in a CuSO4 solution. With a negative sweep of the electrode potential, a cathodic current peak originating from the Cu UPD was observed at ca. +0.5 V vs. RHE and a current assignable to bulk Cu deposition appeared at the potential more negative than +0.25 V vs. RHE. In contrast, a potential sweep to positive direction generated an anodic current corresponding to the oxidation of the Cu layer. Based on these results, we determined the potential of Cu UPD on chiral Au NPs.The average diameter of chiral Au NPs prepared with L-cysteine was 117 nm, and a twisted surface was confirmed by SEM measurements. Even after three cycles of the above-mentioned Ag deposition procedures, no clear change in the shape of chiral Au NPs was observed. However, the average size of particles increased to 123 nm after these cycles, indicating the deposition of Ag shell layer of ca. 1 nm thickness on Au NPs per cycle. This study successfully demonstrates the preparation of chiral Au-Ag core-shell NPs through electrochemical methods involving Cu UPD on Au NPs and subsequent galvanic replacement with Ag. References (1) K. T. Nam, et al, Nat. Commun, 11, 263 (2020).

A mixing rule for imaginary parts of refractive indices of aerosols or colloids in the Rayleigh regime

A Rayleigh mixing rule that relates the effective imaginary part of the refractive index of a composite medium, such as an aerosol or colloid, to the complex refractive index of the Rayleigh particles is derived using Rayleigh scattering theory. The derivation is simple, straightforward, and only weakly dependent on particle morphology. The Rayleigh mixing rule offers an opportunity to derive the imaginary part of refractive index spectra of Rayleigh particles, suspended in a non-absorbing medium with known refractive index spectrum, from an extinction spectrum of the composite medium. However, for this application, the real refractive index spectrum of the particle must be known reasonably well and the imaginary part must be known well enough to decide between two mathematical solutions for it. The Rayleigh mixing rule is compared with widely used mixing rules (i.e., volume, Maxwell Garnett, and Bruggeman mixing rules) and we show that in the small volume fraction regime both the Maxwell Garnet and Bruggeman mixing rules agree with the Rayleigh mixing rule.

Voltage-induced rearrangement in silver nanoparticles spatial distribution produced by EAFD method and its LSPR optimization

Abstract This paper presents a voltage-induced and thermal annealing rearrangement (VITAR) method based on modified electric field assisted film dissolution method as a flexible and powerful tool for manipulating nanoparticles spatial distribution based on drift and diffusion mechanisms that occur due to external DC voltage and thermal annealing processes. Different samples with various arrangements of external DC voltage and thermal annealing processes have been produced. The extinction and attenuated total reflection (ATR) spectra, as well as atomic force microscope (AFM) images, have been employed to investigate their optical and morphological properties. Four cases with arrangements of DV-Anl, DV-Anl-DV, DV-Anl-IV, and DV-IV-Anl have been studied. The AFM images show that by applying secondary voltage (direct or inverse voltage), it is possible to drift nanoparticles and change its morphology (size and shape) as well as surface and volume distributions. As a result, by applying a secondary direct voltage (in the DV-Anl-DV case), the surface density of nanoparticles decreases due to direct drift force. It is notable that in this case, the extinction peak and ATR depth have not significantly changed. By applying a secondary inverse voltage (in the DV-Anl-IV, and DV-IV-Anl cases), an increase in the surface density of the nanoparticles has been observed. Also, the extinction peak has increased, and the ATR depth has decreased in the DV-Anl-IV case, but in the DV-IV-Anl case, due to the uniform size of surface nanoparticles, the resonance power has shown a significant increase in both extinction and ATR spectra compared to other cases. The resulting changes in extinction and ATR spectra show that by using the VITAR process, the surface structure, morphology and its optical properties can be optimized and this method provides a great opportunity to enhance Localized Surface Plasmon Resonance effects, which can be employed in nano-optical devices.

Extended Monte Carlo modeling for submicron particle size measurement under high light extinction conditions.

The light extinction method (LEM) based on Lambert Beer's law (LB) is widely used to characterize particle size distribution (PSD) in multiphase flow. However, as the optical thickness increases with concentration, the phenomenon of multiple scattering is enhanced, potentially leading to reduced accuracy and a limited application range. In this study, an extended Monte Carlo-based light extinction model (EMC) was developed, which was initially employed to calculate and evaluate the impact of multiple scattering. Subsequently, it was used to predict the extinction spectrum that incorporates multiple scattering effects under varying concentrations. To validate the modeling, a compact setup was constructed to perform a series of experiments on polystyrene and silica dioxide (SiO2) suspensions. A differential evolution algorithm was also implemented for the inversion of PSD based on spectral content, with the incorporation of an improved coefficient matrix that considers multiple scattering effects. In comparison to the linear LB model, the EMC exhibits a markedly enhanced capacity in handling higher particle concentrations and improving measurement accuracy. For a 700 nm PS suspension, the particle size inversion error of the EMC can be kept within 4% (93.86% for the LB model) compared with the nominal value, even with an optical thickness of 5.

Impact of tip curvature and edge rounding on the plasmonic properties of gold nanorods and their silver-coated counterparts.

Colloidal solutions of gold nanorods and silver-coated gold nanorods were prepared. The seeded growth synthesis protocols were improved by adding a flocculation purification step. The resulting populations of pure gold nanorods and Au@Ag core-shell cuboids were characterized by very low dispersion in size and shape. UV-vis-near-infrared absorption measurements were performed on several batches of well-calibrated nano-objects, supported by calculations based on the discrete dipole approximation, allowed to highlight the impact of various morphological features on the optical response. In addition to the well-known effect of the nanorod aspect ratio on the shift of the longitudinal surface plasmon resonance mode, special attention was paid to changing either the rounding of the nanorod end-caps or that of the edges of the coating silver shell. Nanorods and cuboids were modeled as superellipsoids. This approach enabled us to model precisely their complex shapes using just a few simple parameters and analyze the evolution of their extinction spectra as a function of the rounding of their tips and edges. Such nano-objects are widely used for various applications in fields such as biomedical, biosensing, or surface-enhanced Raman spectroscopy, thus making it crucial to precisely assess the impact of each morphological feature for optimizing their performance.

Controlled Etching of Gold Nanorods Within Mesoporous Silica Shells at Mild Conditions

AbstractSurface plasmon resonance of precious metal gold nanorods can be tuned by controlling the aspect ratio, and they find widespread applications in biotechnology, imaging, sensing, optoelectronics, photonics, and catalysis. Here, a method is proposed for the controlled etching of gold nanorods within mesoporous silica shells by using a certain concentration of H2O2 at room temperature. In the experiments, the amount of HCl is varied to adjust the acidity and/or change the amount of H2O2 to control the speed of corrosion, achieving controllable adjustment of the aspect ratio of the gold nanorods. The extinction spectra show that under the action of H2O2 and HCl, the longitudinal plasmonic resonance of the gold nanorods shifted to shorter wavelengths, and the intensity of the longitudinal plasmonic resonance decreased. The more hydrochloric acid or hydrogen peroxide added, the faster the corrosion rate of the gold nanorods, and the faster the blue shift of the longitudinal plasmonic resonance. In addition, the intensity of the extinction spectra at 320 nm increased linearly versus time, which can also be used to monitor the etching process. By corroding gold nanorods to control the plasmonic resonances, gold nanorods can find broader applications.

Analyte-dependent Rabi splitting in solid-state plexcitonic sensors based on plasmonic nanoislands strongly coupled to J-aggregates

A key challenge in the field of plexcitonic quantum devices is the fabrication of solid-state, device-friendly plexcitonic nanostructures using inexpensive and scalable techniques. Lithography-free, bottom-up nanofabrication methods have remained relatively unexplored within the context of plexcitonic coupling. In this work, a plexcitonic system consisting of thermally dewetted plasmonic gold nanoislands (AuNI) coated with a thin film of J-aggregates was investigated. Control over nanoisland size and morphology allowed for a range of plasmon resonances with variable detuning from the exciton. The extinction spectra of the hybrid AuNI/J-aggregate films display clear splitting into upper and lower hybrid resonances, while the dispersion curve shows anti-crossing behavior with an estimated Rabi splitting of 180 eV at zero detuning. As a proof of concept for quantum sensing, the AuNI/J-aggregate hybrid was demonstrated to behave as a plexcitonic sensor for hydrochloric acid vapor analyte. This work highlights the possibility of using thermally dewetted nanoparticles as a platform for high-quality, tunable, cost-effective, and scalable plexcitonic nanostructures for sensing devices and beyond.

Significant tunability and absorptivity of plasmonic NiO-Ni nanoshells dispersed in silica in visible and infrared optical spectra

A theoretical study of the optical properties of new NiO-Ni nanoshells (NSs) with different radii and shell thicknesses dispersed in silica was carried out in a wide range of ultraviolet, visible and infrared optical spectra from 200 nm to 5000 nm. The established remarkable tunability of absorption (extinction) spectrum and the high absorption properties of NiO-Ni NSs in the presented spectral ranges are very interesting for use in various photothermal and laser high-temperature technologies, including applications in light-to-heat conversion, solar thermal energy, laser nanomedicine and others.

Multicolorimetric Sensor Array Based on Silver Metallization of Gold Nanorods for Discriminating Dopaminergic Agents.

Dopaminergic agents are compounds that modulate dopamine-related activity in the brain and peripheral nerves within the pathways on both sides of the blood-brain barrier. Atypical levels of them can precipitate a multitude of neurological disorders, whose timely diagnosis signifies not only stopping the advancement of the illness but also surmounting it. A silver metallized gold nanorod (AuNRs) conditional sensor array, designed to detect dopaminergic agents for assessing nervous system disorders, yielded significant results in simultaneous detection and discrimination of Benserazide (Benz), Levodopa (L-DOPA), and Carbidopa (Carb). The array was composed of two different concentrations of silver ions as sensor elements (SEs), which generated unique signatures indicative of the presence of reductive target analytes, triggered by the incongruent formation of the Au@Ag core-shell, causing visual and fingerprint colorimetric patterns. Generating diverse responses is the key to the functionality of array-based sensing, which facilitated achieving spectral and color variation originating from the blue shift of AuNRs longitudinal localized surface plasmon resonance (LLSPR) in the extinction spectrum. Also, employing a smartphone camera enables clear visual discrimination across an extensive concentration span. Pattern recognition through linear discriminant analysis (LDA) underscored the robust discrimination accuracies of this sensor, along with quantification by means of partial least-squares regression (PLSR), affirming its potential for practical applications. Notably, the array demonstrated high sensitivity in detecting varied concentrations of target analytes, even in commercial drug samples. The sensor responses exhibited a linear correlation with the concentrations of Benz, L-DOPA, and Carb ranging from 1.59 to 100.0, 5.26 to 100.0, and 5.32 to 100.0 μmol L-1, respectively, and the minimum detectable concentrations for Benz, L-DOPA, and Carb were measured at 0.53, 1.75, and 1.77 μmol L-1, respectively. The implemented machine-learning-empowered array-based sensor represents advancements in dopaminergic agent tracing and naked eye detection.

Mellitic Acid-Supported Synthesis of Anisotropic Nanoparticles Used as SERS Substrate.

A method for the synthesis of a new SERS substrate-anisotropic silver nanoparticles using mellitic acid as a new capping agent is presented. The synthesis is free of toxic substances and does not require special temperature or lighting conditions. Moreover, it is fast, easy, and inexpensive. Depending on the concentration of silver ions and nanoparticle seeds, four different colloids were obtained, representing the evolution of nanoparticle growth along different paths from the first common stage. One of the synthesized colloids consists mainly of triangular nanoplates, while the other consists of polyhedral NPs. The analysis of the synthesis process together with the observation of TEM images and UV-vis extinction spectra enabled the proposal of the mechanism of interaction of mellitic acid molecules as the capping agent. The ability of mellitic acid molecules to form a hydrogen bond network, together with a ratio of silver ions to the mellitic acid concentration, turned out to be crucial for determining the shape of the NPs. All obtained colloids strongly enhance the Raman spectra of analyte molecules, thus proving their applicability as efficient new SERS substrates. For the one that enhanced the spectra the most, the detection limit was set at 10-9 M. Using it as a SERS substrate enables the identification of a trace amount of a designer drug, i.e., 4-chloromethcathinone (4-CMC, clephedrone). For the first time, SERS spectra of this substance, illegal in many countries, are presented.

Stability and SERS signal strength of laser-generated gold, silver, and bimetallic nanoparticles at different KCl concentrations

Noble metal nanoparticles, specifically gold and silver, are extensively utilized in sensors, catalysts, surface-enhanced Raman scattering (SERS), and optical-electronic components due to their unique localized surface plasmon resonance (LSPR) properties. The production of these nanoparticles involves various methods, but among the environmentally friendly approaches, laser ablation stands out as it eliminates the need for toxic chemicals during purification. However, nanoparticle aggregation poses a challenge in laser ablation, necessitating the addition of extra materials that contaminate the otherwise clean process. In this study, we investigate the effectiveness of a biocompatible material, potassium chloride (KCl), in preventing particle aggregation. Although salt is known to trigger aggregation, we observed that certain concentrations of KCl can slow down this process. Over an eight-week period, we examined the aggregation rate, extinction behavior, and stability of gold, silver, and hybrid nanoparticles generated in different KCl concentrations. Extinction spectra, SEM images, SERS signal strength, and zeta potential were analyzed. Our results demonstrate that laser ablation in water and salt solutions yields nanoparticles with a spherical shape and a negative zeta potential. Importantly, we identified the optimal concentration of potassium chloride salt that maintains solution stability and SERS signal strength. Adsorbed chloride ions on silver nanoparticles were evidenced by low-frequency SERS band near 242 cm−1. A better understanding of the effect of KCl concentration on the properties of noble metal nanoparticles can lead to improved generation protocols and the development of tailored nanoparticle systems with enhanced stability and SERS activity.

The Potential of Wire Explosion in Nanoparticle Production in Terms of Reproducibility.

Aquasols produced by exploding copper wires represent complex systems in which identifying individual colloidal components poses challenges due to broad and multimodal size distributions and varying shares among oxidation states. To evaluate the reproducibility of copper wire explosion, the size distribution of metallic and oxidized colloidal components within the 10-300 nm diameter range was assessed. Classification of each individual particle into bins according to size and chemical composition was accomplished by reconstructing the recorded optical extinction spectra of three sols produced under identical conditions as the weighted sum of the extinction spectra of individual copper and copper-oxide particles, computed using Mie theory. Our spectrophotometry-based component analysis revealed differences in particle number concentrations of the mainly oxidized nanoparticles, corresponding to deviations observed in the ultraviolet portion of the extinction spectra. Notable uniformity was observed, however, in the number of metallic fine particles, consistent with agreement in spectral features in the visible range. Regarding mass concentration, practically no differences were observed among the three samples, with nano-to-fine ratios of copper particles agreeing within 0.45%. Despite the complex processes during explosion leading to limited reproducibility in the ratio of different copper oxidation states, very good reproducibility (54.2 ± 0.7%) was found when comparing the total copper content of the samples to the mass of the exploded copper wire.

Automation of the <i>Ad Hoc</i> Approach for Derandomization of Proteins: A Tutorial for Undergraduates in Molecular Sciences

Data analysis and manipulation software are vulnerable to user error during data processing and computations take considerable time when handling huge data and multiple repetitive tasks. These problems are usually mitigated by creating an app to repeat any given task reproducibly any number of times. This paper discusses the development of app that systematically automates the <i>ad hoc</i> approach for derandomization of proteins and, or peptides. Thirty second-year undergraduates with little-to-no prior knowledge of computer programming are (were) asked to create this app with modules that sequentially convert spectra from original units to molar extinction and subtract baseline spectrum from the resultant spectra, derandomize the spectra by removing suspected significant unfolded domains from them, concatenate the generated files to a single file in an acceptable format for structural analysis, process our group structural algorithm output files into a user-friendly format to ease data analysis. In addition, they are (were) asked to prepare protein solution, determine its concentration spectroscopically, collect circular dichroism measurements of the protein, derandomize the protein spectra, and determine the secondary structure of the resultant protein spectra with our structure algorithm. The assessment results demonstrated that the students could prepare samples for CD analysis, collect spectra of proteins, and create an app to automate the <i>ad hoc</i> approach. The hands-on activities enable students to acquire knowledge in basic programming and circular dichroism, CD spectroscopy.

Observing Metallic Carriers in Highly Faceted Plasmonic Cd2SnO4 Inverse Spinel Nanocrystals

AbstractCorrelating data from optical, structural, and theoretical methods allows the properties of highly faceted Cd2SnO4 (CTO) inverted spinel plasmonic semiconductor nanocrystals (PSNCs) to be fully evaluated. The use of Sn(II) in the colloidal reaction for CTO results in reproducible octahedral PSNCs with an aspect ratio of 1.30. Correlating extinction spectra with magnetic circular dichroism yields a carrier density (n = 5.19 × 1019 cm−3) and carrier effective mass (m* = 0.022me) respectively. 113Cd and 119Sn solid‐state NMR experiments show clear evidence of metallic‐like carriers in CTO NCs based upon the observation of Knight shifts. These data suggest that carrier formation in CTO arises from Sn antisite occupation of octahedral Cd sites (SnCd). From a broader perspective, the results point to wide‐bandgap spinels as being an important but understudied class of plasmonic PSNCs.

Beyond the Passive Diffusion: Core@Satellite Magneto‐Plasmonic Particles for Rapid and Sensitive Colorimetric Immunosensor Response

AbstractMagneto‐plasmonic particles, comprising gold and iron oxide, exhibit substantial potential for biosensing applications due to their distinct properties. Gold nanoparticles (AuNPs) provide plasmonic features, while iron oxide composites, responsive to an external magnetic field, significantly reduce detection time compared to passive diffusion. This study explores core@satellite magneto‐plasmonic particles (CSMPs), featuring magnetic nanoparticle clusters and numerous satellite‐like AuNPs, to amplify the optical response on a nanostructured gold surface. Using a sandwich scheme, target analytes are detected as hybrid nanoparticles bind to the pre‐immobilized target on the AuNPs surface, inducing changes in the immunosensor's extinction spectrum. Application of an external magnetic field notably enhances biosensor response and sensitivity, reducing assay time from hours to minutes. Leveraging the properties of CSMPs, the immunosensor detects specific immune protein at low concentrations within minutes. CSMPs hold considerable promise for precise and sensitive analyte detection, offering potential applications in rapid testing and mass screening.

Numerical simulations of the optical properties of SiO2@Au core–shell nanoparticles: The effect of geometrical parameters on the tunability and sensitivity of their plasmon response

Based on systematic numerical simulations, the effect of geometrical parameters of SiO2@Au core-shells (nanoshells) on the tunability and sensitivity of their optical response was elucidated. The surface plasmon resonance (SPR) of nanoshells experiences a blueshift-redshift crossover with the increase in shell thickness, and this phenomenon is ascribed to the competition between the two effects, that is, the hybridization effect dominated in the thin shells and the retardation effect dominated in the thick shells. The relative strength of absorption/scattering in the extinction spectra and the relative strength of dipolar/multipolar modes can be selectively tuned by controlling the total volume of nanoshells. The sensitivity of the SPR peak wavelength to the shell thickness is primarily dependent on the core-to-shell ratio; the higher this ratio is, the larger the sensitivity. The tailorable properties of nanoshells make them promising and well-suited platforms in various applications.

Polymer-integrated acoustic graphene plasmon resonator for sensitive detection of CO2 gas

Acoustic graphene plasmons (GPs) exhibit an exceptional density of electromagnetic states within the mid-infrared (MIR) and terahertz frequency ranges, leading to a pronounced near-field amplification and localization at the nanometer scale. This characteristic renders them highly promising for the development of ultra-sensitive plasmon-enhanced MIR sensing and spectroscopic applications. However, the tight spatial confinement inherent to acoustic GPs results in a significant momentum mismatch, which in turn leads to poor coupling efficiency with light in free space. To overcome this limitation, we leverage numerical simulations to show that GPs can act as an intermediary to facilitate efficient excitation of acoustic GPs by incident MIR radiation, achieving an extinction spectrum peak value of approximately 0.9. The proposed gas sensor based on the acoustic GP resonator is composed of pristine, large-area graphene, an array of periodic metal nanocubes, and a slender polyethylenimine (PEI) layer that adsorbs CO2, situated between the nanocubes and the graphene sheet. The sensing performance of the proposed sensor is numerically investigated. It is demonstrated that by incorporating a CO2-absorbing material into the acoustic GPs, we can perform highly sensitive assessments of the absorption bands within the PEI layer upon CO2 adsorption. The observed behavior of the acoustic GPs indicates a weakening and broadening with increasing CO2 concentrations, a phenomenon attributed to the alteration in the permittivity of the PEI in the interstitial layer due to CO2 adsorption. Numerical simulation results indicate that the sensitivity of the proposed hybrid gas sensor can reach up to 0.0183% ppm−1, which offers a remarkable 95-fold enhancement over the gas sensor based on graphene nanoribbons. Our findings underscore the potential of acoustic GP nanoresonators as a transformative platform for ultrasensitive plasmon-enhanced sensing applications, particularly when integrated with various gas adsorption layers or molecular agents.

Возбуждение терагерцовых плазмонных мод в графеновом квадратном микрорезонаторе

We consider a graphene square located in the interface between two half-spaces with different dielectric constants. Using a self-consistent electromagnetic approach based on the integral equation method, we solve the problem of a linearly polarized terahertz electromagnetic wave scattering by the graphene square. The spectra of extinction, absorption, and scattering cross sections reveal the various plasmon modes excitation in graphene square. The properties of the plasmon modes different types are discussed.