Optical Properties Of Metal Nanoparticles Research Articles

Symmetry-breaking-induced off-resonance second-harmonic generation enhancement in asymmetric plasmonic nanoparticle dimers

Abstract The linear and nonlinear optical properties of metallic nanoparticles have attracted considerable experimental and theoretical research interest. To date, most researchers have focused primarily on exploiting their plasmon excitation enhanced near-field and far-field responses and related applications in sensing, imaging, energy harvesting, conversion, and storage. Among numerous plasmonic structures, nanoparticle dimers, being a structurally simple and easy-to-prepare system, hold significant importance in the field of nanoplasmonics. In highly symmetric plasmonic nanostructures, although the odd-order optical nonlinearity of the near-surface region will be improved because of the enhanced near-fields, even-order nonlinear processes such as second-harmonic generation (SHG) will still be quenched and thus optically forbidden. Under this premise, it is imperative to introduce structural symmetry breaking to realize plasmon-enhanced even-order optical nonlinearity. Here, we fabricate a series of nanoparticle dimers each composed of two gold nanospheres with different diameters and subsequently investigate their structural asymmetry dependent linear and nonlinear optical properties. We find that the SHG intensities of gold nanosphere dimers are significantly enhanced by structural asymmetry under off-resonance excitation while the plasmonic near-field enhancement mainly affects SHG under on-resonance excitation. Our results reveal that symmetry breaking will play an indispensable role when designing novel coupled plasmonic nanostructures with enhanced nonlinear optical properties.

Colorimetric detection of aflatoxins B1 and M1 using aptamers and gold and silver nanoparticles

Mycotoxins are small molecules produced by fungi that contaminate crops and cause notable health effects for humans, owing to their inherent toxicity. Aflatoxins are among the most potent mycotoxins, with aflatoxin B1 and M1 being the most concerning. Due to their negative impact on human health and agro-economics, developing cost-effective, rapid, highly sensitive and specific detection tools is urgently needed. Nucleic acid–based synthetic receptors, aptamers, have been successfully selected for aflatoxin with high binding affinity and selectivity, and have been incorporated into a wide array of sensor platforms. By exploiting the optical properties of metallic nanoparticles, aptasensors have been developed to achieve low-cost, rapid, and sensitive tests to detect contaminated foods. Herein, we describe the use of functional nucleic acids, specifically DNA aptamers with metallic nanoparticles such as gold and silver for detecting aflatoxin B1 and M1. This review highlights various aptamer-nanoparticle assay types designed for colorimetric aflatoxin detection (i.e., solution and paper-based) along with their associated detection limits, as well as their strengths and areas for further development.

Engineering Optical Absorption in Late Transition-Metal Nanoparticles by Alloying

Alloying is an increasingly important handle to engineer the optical properties of metal nanoparticles that find applications in, for example, optical metamaterials, nanosensors, and plasmon-enhanced catalysis. One advantage of alloying over traditionally used particle size and shape engineering is that it, in principle, enables tuning of optical properties without a spectral shift of the localized surface plasmon resonance, which is important for applications where a specific spectral band is targeted. A second advantage is that alloying simultaneously enables adjustment of nanoparticle electronic, chemical, mechanical, and light absorption properties. However, a systematic survey of the impact of alloying on light absorption in metal nanoparticles does not exist, despite its key role in applications that include photothermal therapy, plasmonic heat generation, and plasmon catalysis. Therefore, we present here the systematic screening of the light absorption properties of binary late transition-metal alloys composed of Au, Ag, Cu, Pd, and Pt in the visible spectral range, based on a combination of experiments and finite-difference time-domain simulations, and discuss in detail the underlying physics. By studying these 10 alloy systems for 14 different nanoparticle sizes, we find that most nanoparticles experience a maximal absorption efficiency at around 80 nm particle diameter, and that most alloy systems outperform their neat constituents, with integrated absorption enhancement factors of up to 200%. This highlights the untapped potential of alloying for the engineering of light absorption in nanoparticles, and the presented material screening constitutes a resource for the rational selection of alloy systems with tailored absorption properties.

Control of Surface Plasmon Resonance in Silver Nanocubes by CEP-Locked Laser Pulse

Localized surface plasmon resonance (LSPR) of metal nanoparticles has attracted increasing attention in surface-enhanced Raman scattering, chemical and biological sensing applications. In this article, we calculate the optical extinction spectra of a silver nanocube driven by an ultrashort carrier envelope phase (CEP)-locked laser pulse. Five LSPR modes are clearly excited in the optical spectra. We analyze the physical origin of each mode from the charge distribution on different parts of the cubic particle and the dipole and quadrupole excitation features at the LSPR peaks. The charge distribution follows a simple rule that when the charge concentrates from the face to the corners of the cubic particle, the resonant wavelength red-shifts. Then we modulate the LSPR spectra by changing CEP. The results show that CEP has selective plasmon mode excitation functionality and can act as a novel modulation role on LSPR modes. Our work suggests a novel means to regulate LSPR modes and the corresponding optical properties of metal nanoparticles via various freedoms of controlled optical field, which can be useful for optimized applications in chemical and biological sensors, single molecule detection, and so on.

Noble classical and quantum approach to model the optical properties of metallic nanoparticles to enhance the sensitivity of optoplasmonic sensors.

The bright light obtained from the quantum principle has a key role in the construction of optical sensors. Yet, theoretical and experimental work highlights the challenges of overcoming the high cost and low efficiency of such sensors. Therefore, we report a metallic nanoparticle-based metasurface plasmons polariton using quantum and classical models. We have investigated the material properties, absorption cross-section, scattering cross-section, and efficiency of the classical model. By quantizing light–matter interaction, the quantum features of light – degree of squeezing, correlation, and entanglement are quantified numerically and computationally. In addition, we note the penetration depth and propagation length from a hybrid model in order to enhance the optoplasmonic sensor performance for imaging, diagnosing, and early perception of cancer cells with label-free, direct, and real-time detection. Our study findings conclude that the frequency of incident light, size, shape, and type of nanoparticles has a significant impact on the optical properties of metallic nanoparticles and the nonlinear optical properties of metallic nanoparticles are dynamic, enhancing the sensitivity of the optoplasmonic sensor. Moreover, the resulting bright light shows the systematic potential for further medical image processing.

INFLUENCE OF TEMPERATURE DEPENDENCE ON OPTICAL PROPERTIES OF GOLD NANOPARTICLES AND THEIR HEATING, MELTING, AND EVAPORATION BY LASER PULSES

The temperature dependence of refractive indices of metals influences the optical properties of metallic nanoparticles (NPs) during their laser heating. The optical factors of absorption, scattering, and extinction of the laser radiation at a wavelength of ~ 532 nm by gold nanoparticles with radii in the range of 5-100 nm have been calculated for nanoparticle temperatures in the range of 300-1336 K, including nanoparticle melting. Absorption, scattering, and extinction of radiation by nanoparticle are significantly decreased with increasing temperature. The influence of the dependence of gold nanoparticle absorption on its temperature determines the temporal behavior of nanoparticle temperature and the value of the maximal temperature. The decrease of nanoparticle absorption during its laser heating leads to the significant increase of laser fluences (intensities) initiating threshold processes like nanoparticle melting or evaporation upon reaching the maximal temperature at the end of laser action. Accounting for this impact on threshold parameters is important for laser nanotechnology applications.

Electrical conductivity of intermetallic and nanocomposites: A comparative experimental and theoretical study

• Four series of intermetallic and metal nanocomposites were synthesized. • The influence of heat treatment, coinage metal, and ferromagnetic material was investigated. • Electrical conductivity increases with heat treatment temperature and sub-zero temperature. • The electrical conductivity of nanocomposites was higher than IMCs and coinage metals. • Experimental finding was supported by the theoretical (computational) study. In an attempt to find room-temperature superconductors, the electrical conductivity of intermetallic and nanocomposites needs to be explored at room and subzero temperatures by different experimental and theoretical methods. For the same, the intermetallic compounds (IMCs) and nanocomposites (NCs) of ZnO, TiO 2 , Al 2 O 3 , and CuO were synthesized by high-temperature reactive synthesis and Sol-gel techniques, respectively. NCs were annealed at 100, 200, 300, and 400 °C. The NCs were characterized by FESEM, XRD, UV visible, and FTIR methods. The theoretical study (DMol3, CASTEP, Forcite, Reflex, and VAMP) were performed to study the electronic and optical properties of metal nanoparticles. The effect of annealing, the coinage metals, and ferromagnetic material, and decrease in temperature on the electrical conductivity of IMCs and NCs were meticulously investigated. The electrical conductivity of NCs increases with heat treatment temperature (400 °C), and with the decrease in temperature (−70 °C). The addition of α-Fe 2 O 3, and coinage metals does not have a significant effect on the increase in electrical conductivity of NCs. The conductivity of NCs was found higher than IMCs and coinage metals. The synthesized NCs can have a large number of applications in nanowires, nano cables, and quantum dots.

Recent Progress on Metal‐Based Nanomaterials: Fabrications, Optical Properties, and Applications in Ultrafast Photonics

AbstractNanomaterials have demonstrated excellent mechanical, thermal, optical, and electrical properties in various fields, including 1D carbon nanotubes, as well as 2D materials starting from graphene. Metal‐based nanomaterials, mainly divided into metal and metal oxide nanoparticles, also gradually come into the sight of ultrafast photonics applications due to the outstanding optical properties. The optical properties of metal nanoparticles can be enhanced by the interaction between conduction electrons with electric fields that is called surface plasmon resonance. As for metal oxide nanoparticles, optical properties are closely related to bandgap structures. When it comes to transition metal oxides, other phenomena also play important roles in optical absorption such as spin inversion and excitons of iron. Moreover, preparation methods of materials are also crucial for their properties and further applications. Therefore, in this review, commonly used physical and chemical fabrication methods for metal‐based nanomaterials are first introduced. Then the optical properties of typical metal and metal oxide nanoparticles are discussed specifically. In addition, the applications of metal‐based nanomaterials in ultrafast lasers based on mode‐locked and Q‐switched techniques are also summarized. Finally, a summary and outlook toward the synthesis, optical properties, and applications in ultrafast photonics of metal‐based nanomaterials are presented.

Optimized 3D Finite-Difference-Time-Domain Algorithm to Model the Plasmonic Properties of Metal Nanoparticles with Near-Unity Accuracy

The finite difference time domain (FDTD) method is a grid-based, robust, and straightforward method to model the optical properties of metal nanoparticles (MNPs). Modelling accuracy and optical properties can be enhanced by increasing FDTD grid resolution; however, the resolution of the grid size is limited by the memory and computational requirements. In this paper, a 3D optimized FDTD (OFDTD) was designed and developed, which introduced new FDTD approximation terms based on the physical events occurring during the plasmonic oscillations in MNP. The proposed method not only required ~52% less memory than conventional FDTD, but also reduced the calculation requirements by ~9%. The 3D OFDTD method was used to model and obtain the extinction spectrum, localized surface plasmon resonance (LSPR) frequency, and the electric field enhancement factor (EF) for spherical silver nanoparticles (Ag NPs). The model’s predicted results were compared with traditional FDTD as well as experimental results to validate the model. The OFDTD results were found to be in excellent agreement with the experimental results. The EF accuracy was improved by 74% with respect to FDTD simulation, which helped reaching a near-unity OFDTD accuracy of ~99%. The λLSPR discrepancy reduced from 20 nm to 3 nm. The EF peak position discrepancy improved from ±5.5 nm to only ±0.5 nm.

Small and large scale plasmonically enhanced luminescent solar concentrator for photovoltaic applications: modelling, optimisation and sensitivity analysis.

Hybrid 3D Finite difference time domain-Monte Carlo ray tracing (FDTD-MCRT) algorithm has been developed to model and optimise small and large scale plasmonically-enhanced luminescent solar concentrator (pLSC) devices for photovoltaic (PV) applications. The configuration parameters (for example, dimensions, shape, and optical properties of metal nanoparticles, luminescent species, and host material) were used to characterise the probability of optical energy transfer and loss processes, as well as reflection, refraction, absorption, emission enhancement, and total internal reflection (TIR) in the pLSC. The algorithm was validated through modelling of various doping concentrations of CdSe/ZnS quantum dots (QD) and gold nano spheres (Au NS) where ∼50% enhancement in optical conversion efficiency (OCE) was observed for a plasmonic composite of 2 ppm Au NS and 0.008 wt. % QD.

Temperature Dependences of the Optical Properties of Metal Nanoparticles in Various Media

Temperature Dependences of the Optical Properties of Metal Nanoparticles in Various Media

Surface roughness and substrate induced symmetry-breaking: influence on the plasmonic properties of aluminum nanostructure arrays.

The surface topography is known to play an important role on the near- and far-field optical properties of metallic nanoparticles. In particular, aluminum (Al) nanoparticles are commonly fabricated through evaporation techniques, therefore exhibiting elevated surface roughness additionally to their native oxide layer. In this study, the mode-dependent influence of surface roughness on the plasmonic properties sustained by Al nanodisks (NDs) is first numerically investigated using a realistic model taking into account the thin native oxide layer. Due to the symmetry-breaking induced by the supporting dielectric substrate to Al ND, it appears that the roughness affects differently the substrate-induced out-of-plane quadrupolar mode (below 300 nm) and the in-plane dipolar mode sustained by the Al ND. By increasing the top surface roughness of the Al ND, the substrate-induced quadrupolar mode is significantly damped especially in the ultraviolet regime, while the dipolar resonance is broadened and redshifted. The explanation of these effects relies in the decoherence and dissipation of the collective electronic oscillations as a result of the top surface roughness to the different near-field distribution of the out-of-plane quadrupolar mode and in-plane dipolar mode. Moreover, the influences of the diameter of Al ND, dielectric substrate with different refractive index, and the oxidation of Al ND on these two modes are also investigated. Particularly, the quadrupolar mode disappears with surface roughness and oxidation, explaining why this mode is very weak and sometimes barely visible on evaporated Al nanostructures reported in the literature. Finally, these results are experimentally confirmed by characterizing the optical properties of periodic Al ND arrays.

Optical and electrical characterization of organic solar cells obtained using gold and silver metal nanoparticles

Light absorption of metal nanoparticles and charge separation are two major factor for the efficiency improvement in organic solar cells. Metallic nanoparticles may exhibit surface plasmons when exposed to light. This special optical properties of metal nanoparticles make them useful in photonics, electronics and biomedical applications. In this study, gold and silver nanoparticles increased the surface roughness of the active layer. The absorption, SEM, AFM, XRD measurements of 1% ratio gold and silver nanoparticles doped active layers were carried out. Optical band gap of these films was calculated with using absorption measurements. Then, ITO/PEDOT:PSS/P3HT:PCBM:Au/LiF/Al and ITO/PEDOT:PSS/P3HT:PCBM:Ag/LiF /Al organic solar cells were obtained. It was calculated the solar cells parameters such as short -circuit current density (Jsc), open - circuit voltage (Voc), fill factor (FF) and power conversion efficiency (PCE) from current density–voltage (J-V) measurements at the room temperature. The experimental results revealed that the presence of Au and Ag nanoparticles (NPs) in the ITO/PEDOT:PSS/P3HT:PCBM/Al solar cell improved its performance with respect to undoped solar cells. For example, the power conversion efficiency was increased from 2.11% to 2.55% when doping 1 wt% of Au NPs to P3HT:PCBM and to 2.23% when doping of Ag NPs to P3HT:PCBM. This was attributed to increase of the light absorption in the presence of Au and Ag NPs doping. However, the optical band gap of films have not changed significiantly after the NPs doping.

Towards Reducing Computational Costs of Finite Difference Time Domain Algorithm in Plasmonic Optical Properties Modelling of Metal Nanoparticles

Finite difference time domain (FDTD) method is a grid-based, robust and straightforward method to model and study the optical properties of metal nanoparticles (MNPs). However, high computational costs of FDTD including simulation time and memory demand mitigate the interest in this algorithm. In this paper, FDTD algorithm is reviewed and reasons of high computational cost requirement in FDTD are investigated. Computational costs are directly characterised by the resolution and size of FDTD grid (known as Yee grid). High FDTD grid resolution is essentially required in MNPs plasmonic modelling to achieve promising accuracy. This results in increasing the dimension of FDTD operational parameters (stored in FDTD matrices) which increases memory and simulation time required and consumed by the algorithm.

Doping Concentration Tuning and Plasmonic Optical Properties Modelling of Metal Nano Particles Utilizing FDTD Method

Among noble metal nanoparticles (MNPs), plasmonic effect of gold and silver nanoparticles (Au NPs and Ag NPs) is interesting to study due to their high near-field energy. This makes them excellent particles to absorb and scatter incident radiation in optical applications such as coupling them to fluorescent emitters to enhance their radiative decay and emission rate. This paper reviews and studies the methodology required for tuning the doping concentration and modelling plasmonic optical properties of Au NPs and Ag NPs by using finite difference time domain (FDTD) method. The frequency-dependent optical behaviour of MNPs is discussed. Plasmonic optical properties of MNPs can be characterised by their dimension, shape and doping concentration. Dimension and shape of MNPs can be simply defined in FDTD space grid (known as Yee grid). However, tuning MNPs doping concentration is more challenging which is undertaken by changing the spacing between MNPs and lateral boundaries of FDTD Yee grid. This can be vastly useful in Au NPs and Ag NPs optical optimization and applications to estimate plasmonic resonance based on doping concentration of particles.

Graphene nanofl akes and hybrid nanocomposites with gold and silver nanoparticles: optical and thermal properties

New technologies for the preparation of graphene nanofl akes (GNF) with noble metal nanoparticles (NPs), specifi cally Au and Ag, as well as hybrid nanocomposites composed of metal microspheres coated with nanostructures [GNF+metal NPs], were considered. The optical properties of metal nanoparticles, their adsorption characteristics with respect to graphene fl akes, and the thermophysical properties of the obtained functional nanomaterials were studied. The obtained data on dynamic optical absorption and thermal conductivity makes it possible to propose new fi elds of application of graphene materials.

Theoretical Investigation of Plasmonic Properties of Quantum-Sized Silver Nanoparticles

Plasmonic nanoparticles (NPs) like silver (Ag) strongly absorb the incident light and produce enhanced localized electric field at the localized surface plasmon resonance (LSPR) frequency. Enormous theoretical and experimental research has focused on the plasmonic properties of the metallic nanoparticles with sizes greater than 10 nm. However, such studies on smaller sized NPs in the size range of 3 to 10 nm (quantum-sized regime) are sparse. In this size regime, the conduction band of the metal particles discretizes, thus altering plasmon properties of the NPs from classical to the quantum regime. In this study, plasmonic properties of the spherical Ag NPs in size range of 3 to 20 nm were investigated using both quantum and classical modeling to understand the importance of invoking quantum regime to accurately describing their properties in this size regime. Theoretical calculations using standard Mie theory were carried out to monitor the LSPR peak shift and electric field enhancement as a function of the size of the bare plasmonic nanoparticle and the refractive index (RI) of the surrounding medium. Comparisons were made with and without invoking quantum regime. Also, the optical properties of metallic NPs conjugated with a chemical ligand using multi-layered Mie theory were studied, and interesting trends were observed.

Extended Discrete Interaction Model: Plasmonic Excitations of Silver Nanoparticles

We present a new atomistic model for plasmonic excitations and optical properties of metallic nanoparticles, which collectively describes their complete response in terms of fluctuating dipoles and charges that depend on the local environment and on the morphology of the composite nanoparticles. Being atomically dependent, the total optical properties, the complex polarizability, and the plasmonic excitation of a cluster refer to the detailed composition and geometric characteristics of the cluster, making it possible to explore the role of the material, alloy mixing, size, form shape, aspect ratios, and other geometric factors down to the atomic level and making it useful for the design of plasmonic particles with particular strength and field distribution. The model is parameterized from experimental data and, at present, practically implementable for particles up to more than 10 nm (for nanorods even more), thus covering a significant part of the gap between the scales where pure quantum calculations are possible and where pure classical models based on the bulk dielectric constant apply. We utilized the method to both spherical and cubical clusters along with nanorods where we demonstrate both the size, shape, and ratio dependence of plasmonic excitations and connect this to the geometry of the nanoparticles using the plasmon length.

Assembly and Optical Properties of Metal Nanoparticles

In this paper, the deposition and optical properties of charge-stabilized gold nanoparticles on silicon oxide substrates is studied, which have been derivatised with (aminopropyl) triemethoxysilane. Monodispersed charged-stabilized colloidal gold nanoparticles with diameters between 20-150 nm were prepared and their self-assembly and optical properties on silica substrates is studied. Atomic force microscopy (AFM) is employed to investigate the nanoparticle monolayers ex situ. Analysis of AFM images provide evidence that the formation of the colloidal nanoparticle monolayers is governed by random sequential adsorption. The results indicate that the ionic strength of the suspension influences the spatial distribution of the nanoparticles. For all sizes of the Au nanoparticles tested, optical simulations of extinction coefficients made by finite-difference time domain (FDTD) indicate a resonance peak in the range of 510-600 nm wavelength of the visible range of the electromagnetic spectrum. The results indicate a simple and inexpensive approach of assembly of plasmonic nanostructures that can find applications in metamaterials and light waveguides.

Quantum plasmonics of metal nanoparticles

A new theoretical approach is developed that describes quantum optical properties of metal nanoparticles interacting with an electromagnetic field. In the linear regime of interaction, the model treats a metal nanoparticle as a two-level quantum system comprised of the lowest plasmonic Fock states governed by the optical Bloch equations. This approach not only agrees with the classical results, but provides also a direct link to quantum optics and cavity quantum electrodynamics that allows one to predict quantum phenomena not anticipated from a classical description. The new model is applied to the calculations of the radiative relaxation rate in a nanoparticle, the quantum beats in the intensity of radiation from a nanoparticle dimer, and the radiative relaxation rate in both 1D and 2D nanoparticle arrays in close vicinity to a reflective surface.