Finite-Difference Time-Domain Simulation of Localized Surface Plasmon Resonance Adsorption by Gold Nanoparticles

Tunability of the localized surface plasmon resonance (LSPR) peak position of gold and silver nanoparticle arrays embedded in a liquid crystal cell is investigated in this paper. The extinction spectra are computed using the Finite-Difference Time Domain (FDTD) simulation algorithms. Results show that the LSPR properties exhibit significant dependence on nanoparticle size and shape, array periodicity, and liquid crystal layer thickness. Notably, the LSPR wavelength saturates when the liquid crystal thickness exceeds a critical value. Furthermore, controlled rotation of the liquid crystal optical axis within distinct planes (xoy and xoz) reveals systematic variations in LSPR characteristics. Finally, we identify the key factors governing the LSPR spectral sensitivity of these noble metal nano-arrays.

Noble metal nanoparticles, particularly gold and silver nanoparticles, have garnered significant attention due to their ability to manipulate light at the nanoscale through their localized surface plasmon resonance (LSPR). While their LSPRs below 1100 nm were extensively exploited in a wide range of applications, their potential in the near-infrared (NIR) region, crucial for optical communication and sensing, remains relatively underexplored. One primary reason is likely the limited strategies available to obtain highly stable plasmonic nanoparticles with tailored optical properties in the NIR region. Herein, we synthesized AuAg nanorattles (NRTs) with tailored and narrow plasmonic responses ranging from 1000 to 3000 nm. Additionally, we performed comprehensive characterization, employing advanced electron microscopy and various spectroscopic techniques, coupled with finite difference time domain (FDTD) simulations, to elucidate their optical properties. Notably, we unveiled the main external and internal LSPR modes by combining electron energy-loss spectroscopy (EELS) with surface-enhanced Raman scattering (SERS). Furthermore, we demonstrated through surface-enhanced infrared absorption spectroscopy (SEIRA) that the NRTs can significantly enhance the infrared signals of a model molecule. This study not only reports the synthesis of plasmonic NRTs with tunable LSPRs over the entire NIR range but also demonstrates their potential for NIR sensing and optical communication.

Large range LSPR of KTN@Ag core-shell nanoarray dependent of structure size

Gold nanoparticles (GNPs) exhibit unique optical properties, depending on the particle size, geometrical shape, and medium refractive index and interparticle interactions, etc. Among these optical properties, localized surface plasmon resonance (LSPR) has significant effects on the electromagnetic field around the GNPs. The LSPR-induced electromagnetic field enhancement is beneficial to the surface-enhanced Raman scattering (SERS) and energy transfer processes. This dissertation deals with the effects of LSPR on SERS and energy transfer between CdSe/ZnS quantum dots and GNPs. Specifically, the research aims to gain better understanding of (i) the electromagnetic enhancement induced by charge transfer from GNP to molecules, (ii) the SERS in various shaped gold nanostructures, (iii) the energy transfer from quantum dots (QDs) to GNPs, and (iv) SERS- and energy transfer-based sensing platforms for detection of chemical species and biomolecules.;The SERS of two different types of molecules on GNPs has been investigated. It has been found that the aromatic molecules such as p-mercaptobenzenoic acid (MBA) exhibit stronger SERS activity than the linear-chain molecules such as 3-mercaptopropionic acid (MPA) and L-cysteine (Cys). The difference in the SERS activity is attributed to the distinct electronic structures among these molecules. The electron transfer from GNPs to MBA can occur under laser excitation. The transferred electron can effectively strengthen the electromagnetic field around GNPs, leading to electromagnetic enhancement of SERS.;Furthermore, the SERS in different shaped gold nanostructures (gold nanospheres (GSPs), nanorods (GRDs) and nanostars (GSTs)) has been investigated. GSTs show the highest SERS enhancement. Three-dimensional finite-difference time domain (FDTD) method has been used to simulate the electric field distribution. It is demonstrated that the electric field can be concentrated around two ends of GRDs and these tips of GSTs, and the GSTs show the highest maximum electric field intensity under both excitations of 532 nm and 785 nm. It is suggested that the shape of gold nanostructures governs the SERS difference among GSPs, GRDs and GSTs. In addition, gold malachite green isothiocyanate(MGITC) SiO 2 sandwiched nanostructures have been prepared. SiO2 encapsulation not only improves the colloidal and LSPR stability but also endows excellent reproducibility of SERS signal due to the prevention of MGITC leaking. It is demonstrated that the GST MGITC SiO2 can be used for monitoring of DNA hybridization and for detection of adenosine triphosphate (ATP) with high sensitivity.;Energy transfer between the CdSe/ZnS QDs and GNPs was investigated. The 3 nm GNPs without observable LSPR absorption quench the fluorescence emission of the

This paper describes unique plasmonic characteristics of two dimensional (2D) crystalline sheets composed of homogeneous Ag nanoparticles (AgNPs) fabricated by the Langmuir-Schaefer method at an air-water interface. The localized surface plasmon resonance (LSPR) band of the Ag nanosheet was tuned by changing the interparticle distance of AgNPs via the length of the organic capping molecules. Red shift of the LSPR band of the AgNPs sheet followed an exponential law against the interparticle distance in a similar manner to the previous reports of metal nanodisc pairs. However, the shift was much larger and less dependent on the interparticle separation gap. This phenomenon is reasonably interpreted as the long-range interaction of LSPR in the 2D sheet ('delocalized' LSPR) confirmed by simulation using the finite difference time domain (FDTD) method. The FDTD simulation also revealed additional enhancement of local electric fields on the 2D sheet compared to those on the single or paired particles.

Localized surface plasmon resonance (LSPR) plays a significant role in the fields of photocatalysis and solar cells. It can not only broaden the spectral response range of materials, but also improve the separation probability of photo-generated electron-hole pairs through local field enhancement or hot electron injection. In this article, the LSPR effects of Au/TiO2 composite photocatalyst, with different sizes and shapes, have been simulated by the finite difference time domain (FDTD) method. The variation tendency of the resonance-absorption peaks and the intensity of enhanced local enhanced electric field were systematically compared and emphasized. When the location of Au nanosphere is gradually immersed into the TiO2 substrate, the local enhanced electric field of the boundary is gradually enhanced. When Au nanoshperes are covered by TiO2 at 100 nm depths, the local enhanced electric field intensities reach the maximum value. However, when Au nanorods are loaded on the surface of the TiO2 substrate, the intensity of the corresponding enhanced local enhanced electric field is the maximum. Au nanospheres produce two strong absorption peaks in the visible light region, which are induced by the LSPR effect and interband transitions between Au nanoparticles and the TiO2 substrate. For the LSPR resonance-absorption peaks, the corresponding position is red-shifted by about 100 nm, as the location of Au nanospheres are gradually immersed into the TiO2 substrate. On the other hand, the size change of the Au nanorods do not lead to a similar variation of the LSPR resonance-absorption peaks, except to change the length-diameter ratio. Meanwhile, the LSPR effects are obviously interfered with by the interband transitions between the Au nanorods and TiO2 substrate. At the end of this article, three photo-generated carrier separation mechanisms are proposed. Among them, the existence of direct electron transfer between Au nanoparticles and the TiO2 substrate leads to the enhanced local enhanced electric field at the boundaries, which is favorable for the improvement of photocatalytic performance of TiO2. These findings could explain the underlying mechanism of some experimental observations in published experimental works, and helpful to design highly efficient composite photocatalysts that contain noble metal co-catalyst nanoparticles.

The localized surface plasmon resonance (LSPR) of noble metal nanoparticles (NPs) has become an important research topic in various fields and can be systematically tuned to obtain the desired device performance through the appropriate structural and elemental modifications. In this research, the improved LSPR properties of Pt NPs and diverse configurations and compositions of Ag–Pt bimetallic alloy NPs were demonstrated on sapphire (0001) via the solid-state dewetting (SSD) of Ag–Pt bilayers. A strong and dynamic LSPR response in the ultraviolet (UV) and visible (VIS) regions was demonstrated depending on the elemental composition and surface morphology of the NPs, which is discussed along with finite difference time domain (FDTD) simulations. In comparison, the Ag–Pt NPs exhibited stronger LSPR excitation, whereas the Pt NPs showed a relatively weaker and broader response. Meanwhile, the Pt NPs fabricated in this study still demonstrated a much-enhanced LSPR response compared to previous studies on the solid-state dewetting of pure Pt films due to improvements in configuration, uniformity, and interparticle gaps. Various surface morphologies of NPs, such as connected nanoclusters, elongated NPs, and isolated spherical NPs, were obtained on the basis of alloying, diffusion, Rayleigh instability, and a surface minimization mechanism, which were different from those of pure Ag and Pt NPs in similar growth conditions. Particularly, one-step annealing of an Ag–Pt bilayer yielded Ag–Pt alloy NPs below 600 °C, which subsequently transformed into pure Pt NPs above 650 °C, in which the high diffusivity and high vapor pressure of Ag atoms significantly facilitated the overall growth process of the NPs.

Silver (Ag) nanoparticles (NPs) were deposited on the surface of bulk Nitrogen-Boron co-doped 6H silicon carbide (SiC), and the Ag NPs were observed to induce localized surface plasmons (LSP) resonances on the SiC substrate, which was expected to improve the internal quantum efficiency (IQE) of the emissions of the donor-acceptor pairs of the SiC substrate. Room-temperature measurements of photoluminescence (PL), transmittance and time-resolved photoluminescence (TRPL) were applied to characterize the LSP resonances. Through the finite-difference time-domain (FDTD) simulation of the LSP resonance of an Ag nanoparticle on the SiC substrate, it is predicted that when the diameter of the cross section on the xy plane of the Ag nanoparticle is greater than 225 nm, the LSP starts to enhance the PL intensity. With implementation of a 3rd order exponential decay fitting model to the TRPL results, it is found that the average minority carrier lifetime of the SiC substrate decreased.

Localized surface plasmon resonance (LSPR) biosensors represent a relatively new and hot research topic in biosensing applications. Since the fabrication of LSPR biosensors is time consuming and costly, providing a mathematical model that can predict the LSPR characteristics before any fabrication is on edge. Implementing such a model for the LSPR devices, and then optimally designing the LSPR geometrical parameters for a particular surface enhanced Raman Scattering (SERS) biosensor function is the concept that has not been explored yet. In this paper, a multi layered artificial neural network (ANN) is proposed which produces a mathematical model representing the characteristics of LSPR devices as a function of their physical dimensions for a specific shape of nano-particles. Such a model can be used to identify a LSPR structure that is appropriate for a biosensing application requiring specific LSPR characteristics. The numerical electromagnetic modeling approach of the finite difference time domain (FDTD) method, and the analytical method of electrostatic eigenmode are used to implement the proposed model.

Insight into the localized surface plasmon resonance property of core-satellite nanostructures: Theoretical prediction and experimental validation

Localized surface plasmon resonance (LSPR) has great potential for rapid, dynamic, and high-throughput biochemical sensing. To fabricate LSPR nanostructure, many methods have been developed. However, few of them can achieve stable, low-cost, and large-area production of the metal nanostructure. In this paper, we combined laser interference lithography (LIL) and lift-off process to fabricate a periodic isolated gold nanodisk array on a glass substrate for LSPR biosensing applications. Based on above method, a large-area (~5 mm × 5 mm) and highly uniform nanostructure can be fabricated. The parameter of the nanostructure was determined according to finite-difference time-domain (FDTD) simulation. To perform real-time molecular sensing, the LSPR sensor was attached by a microfluidic channel and placed on a spectroscope. The sensitivity and FoM of the sensor are achieve 238 nm/RIU and 1.66, respectively. In addition, we demonstrated the real-time and multi-point immunoglobulin (IgG) detection. Based on above features, we believe this platform has the potential for point-of-care (POC) applications.

Theoretical calculations for localized surface plasmon resonance effects of Cu/TiO2 nanosphere: Generation, modulation, and application in photocatalysis

Because they possess excellent visible light absorption properties, lead-free colloidal copper-based chalcogenide quantum dots (QDs) have emerged in photoelectronic fields. By means of localized surface plasmonic resonance (LSPR), the absorption properties of QDs can be enhanced. In this paper, we fabricate a lead-free CuInSe2 QD field effect phototransistor (FEpT) by utilizing the LSPR enhancement of Au nanoparticles (NPs). The plasmonic FEpT demonstrates responsivity up to 2.7 μA·W−1 and a specific detectivity of 7×103 Jones at zero bias under illumination by a 532 nm laser, values that are enhanced by approximately 200% more than devices without Au NPs. Particularly, the FEpT exhibits a multi-wavelength response, which is photoresponsive to 405, 532, and 808 nm irradiations, and presents stability and reproducibility in the progress of ON–OFF cycles. Furthermore, the enhancement induced by Au NP LSPR can be interpreted by finite-difference time domain simulations. The low-cost solution-based process and excellent device performance strongly underscore lead-free CuInSe2 QDs as a promising material for self-powered photoelectronic applications, which can be further enhanced by Au NP LSPR.

Enhanced photocatalysis of TiO2 by aluminum plasmonic

Plasmonic core-shell nanoparticles (CSNPs) have been extensively used as SERS active-substrates because their localized surface plasmonic resonance (LSPR) properties and thus the surface enhanced Raman scattering (SERS) activities can be regulated by changing the shell thickness. In this work, we selected Ag@MoS₂ CSNP with 40 nm radius of Ag as core and varied thickness of MoS₂ as shell to investigate the shell-dependent plasmonic behaviors including LSPR and SERS by using finite difference time domain (FDTD) simulations. The LSPR peak of Ag@MoS₂ CSNPs shows a broad red-shifting with an increasing shell thickness from 0 nm to 40 nm, giving rise to that the LSPR peak tunes from visible region (385 nm) to near infrared (NIR) region (1100 nm). The SERS activity of Ag@MoS₂ CSNP, represented by the enhancement of local electrical field (EM), can also be modulated by changing the shell thickness, and the optimal enhancement factor (EF) under 633 nm laser excitation is determined to be 3.54×10⁶ when the shell thickness is 4 nm. The wide-range LSPR tunability of Ag@MoS₂ CSNP provides enormous potential for NIR SERS application and enhanced photocatalytic activity