Metal Nanoparticle Clusters Research Articles

Design and simulation of bifacial perovskite solar cell with high efficiency using cubic plasmonic nanoparticles

Bifacial perovskite solar cells (Bi-PSCs) are gaining attention for their ability to exceed the efficiency limits of traditional single-junction cells by absorbing light from both the front and rear surfaces. This study explores a novel approach to boost the efficiency and stability of Bi-PSCs by integrating clusters of cubic metallic nanoparticles (NPs) within the absorber layer. These plasmonic NPs, embedded in the middle of the absorber layer, significantly enhance light absorption, resulting in substantial improvements in power conversion efficiency for both front and rear irradiation. Our three-dimensional simulations demonstrate that incorporating Ag-based NPs can achieve efficiency enhancements of 29.89 % (from 18 % to 23.39 %) for front irradiation and 29.63 % (from 17.22 % to 22.33 %) for rear irradiation. Ag-based NPs exhibit the most notable efficiency improvement, reaching a short-circuit current of 41.30 mA/cm2 and an efficiency of 35.34 % at an albedo of 0.5. To address potential issues such as corrosion and degradation of the perovskite material, the metallic NPs are encapsulated with a thin dielectric nano-shell of SiO₂. This encapsulation strategy effectively prevents degradation, ensuring the long-term stability of the Bi-PSCs. The results indicate that the use of clusters of cubic metallic NPs, combined with dielectric encapsulation, offers a superior approach to optimizing the performance and stability of Bi-PSCs, providing a more efficient alternative to increasing the absorber layer’s thickness.

Dual-Dewetting Process for Self-Assembled Nanoparticle Clusters in Wafer Scale.

Plasmonic molecules, which are geometrically well-defined plasmonic metal nanoparticle clusters, have attracted significant attention due to their enhancement of light-matter interactions owing to a stronger electric field enhancement than that by single particles. High-resolution lithography techniques provide precise positioning of plasmonic nanoparticles, but their fabrication costs are excessively high. In this study, we propose a lithography-free, self-assembly fabrication method, termed the dual-dewetting process, which allows the control of the size and density of gold nanoparticles. This process involves depositing a gold thin film on a substrate and inducing dewetting through thermal annealing, followed by a second deposition and annealing. The method achieves a uniform distribution of particle size and density, along with increased particle density, across a 6-inch wafer. The superiority of the method is confirmed by a 30-fold increase in the signal intensity of surface-enhanced Raman scattering following the additional dewetting with an 8 nm film, compared to single dewetting alone. Our findings indicate that the dual-dewetting method provides a simple and efficient approach to enable a variety of plasmonic applications through efficient plasmonic molecule large-area fabrication.

Electrical Resistance in a Composite of Ultra-Small Silver Nanoparticles Embedded in Gold Nanostructures: Implications for Interface-Enabled Functionality

Ultrasmall nanoparticles of noble metals, in particular silver (Ag) or gold (Au), have been extensively investigated for their optical, magnetic, chemical, and physical properties, but assembling such structures in an electrically conducting metallic matrix, where the physical dimension of individual nanoparticles plays a decisive role, has remained elusive. This is because true metallic conduction through individual or clusters of metallic nanoparticles is often prevented by tunnel barriers due to surface-protecting ligands, oxidation, etc. By removing the chemical remnants, these challenges have been overcome in a cross-linked nanohybrid assembly made of ultrasmall silver nanoparticles (AgNPs) in an all-metallic matrix of Au. The resulting Ag–Au nanohybrid exhibits metallic behavior where the resistance decreases with decreasing temperature, for all radii (rAg ≫ 1–3 nm) and concentrations of AgNPs (average center-to-center distance between two AgNPs d ≈ 4–6 nm) from room to cryogenic temperatures (≈ 6 K). Strikingly, we observe the electrical resistivity of the hybrid to scale directly with the net surface area of the embedded AgNPs, thereby achieving residual resistivity as high as 40 μΩ.m, which is more than 2 orders of magnitude larger than that of crystalline Au. Our experiment outlines a novel method of designing metals with nanostructured interfaces that can lead to new phenomena and functionality.

The Influence of the Multiple Scattering on the Optical Properties of Ag-poly(p-xylylene) Composite Coating

The creation of composite coatings with assigned optical properties is an important problem of modern science and technology. We have considered the metal-polymer nanocomposites based on poly(p-xylylene), with various concentrations of plasmon components—silver nanoparticles. We have carried out the optical measurements of the reflection, transmission, scattering and absorption coefficients for the manufactured films. We have retrieved the effective optical parameters of the composite coatings. The theoretical estimations based on the scattering and absorption data show that the scattering effectively occurs on the clusters of metal nanoparticles. This significantly influences the optical properties of the composite coating.

Compartmentalized bimetal cluster-poly(aniline) hybrid nanostructures for multiplexed detection of autoantibodies in early diagnosis of rheumatoid arthritis

Multi-compartmentalized, inorganic-organic hybrid nanostructures have been studied in biomedical applications due to their compositional and structural differences in each compartment. The combination of these hybrid nanostructures with metallic nanoparticle clusters would be attractive due to their interparticle plasmonic coupling for photonics-based biosensing. We herein report a new class of compartmentalized bimetal cluster-poly(aniline) hybrid nanostructures (CBCPHNs) for surface-enhanced Raman scattering (SERS)-based, multiplexed detection of autoantibodies in early diagnosis of rheumatoid arthritis (RA). The bimetallic nanoparticle clusters (BNCs) were prepared in a core-shell form by Raman dye-induced aggregation of gold nanoparticles (GNPs) for the core and reduction of silver ions onto GNP nanoclusters for the shell. Subsequently, CBCPHNs were formed by one-directional growth of poly(aniline) via surface-templated polymerization of aniline monomers as well as additional Ag deposition onto BNCs in the presence of a surfactant. The CBCPHNs showed significant electromagnetic field enhancement at both GNP aggregates and Au core-Ag shell gaps of the BNCs, whereas the poly(aniline) counter-compartment served as a biomolecular conjugation site. In addition, we developed a sandwich-type immunoassay platform using these hybrid nanostructures as SERS nanoprobes and magnetic beads (MBs) for early diagnosis of RA in multiplexing. Autoantibodies against cyclic citrullinated peptide (anti-CCP) and rheumatoid factor immunoglobulin M (RF IgM) were simultaneously detected, and quantified measuring SERS signals of sandwich-type immunocomplexes. Multiplexing of anti-CCP and RF IgM was achieved in low concentration ranges, and their limits of detection were 0.68 IU/mL and 0.93 IU/mL, respectively. These hybrid nanostructures with collective functionalities represent potential nanomaterials for multiplexed detection of autoantibodies.

Understanding Time-Dependent Surface-Enhanced Raman Scattering from Gold Nanosphere Aggregates Using Collision Theory

Aggregates or clusters of primary metal nanoparticles in solution are one of the most widely used platforms for surface-enhanced Raman scattering (SERS) measurements because these nanostructures induce strong electric fields or hot spots between nanoparticles and as a result, SERS signals. While SERS signals are observed to vary with time, the impact of cluster formation mechanisms on SERS activity has been less studied. Herein, variations in time-dependent SERS signals from gold nanosphere clusters and aggregates are considered both experimentally and theoretically. An excess of the Raman reporter molecule, 2-naphthalenethiol, is added to induce rapid monolayer formation on the nanoparticles. In this diffusion-limited regime, clusters form as loosely packed fractals and the ligands help control nanoparticle separation distances once clusters form. By systematically varying gold nanosphere concentration and diameter, the reaction kinetics and dynamics associated with cluster formation can be studied. Dynamic light scattering (DLS), localized surface plasmon resonance (LSPR) spectroscopy, and SERS reveal that aggregates form reproducibly in the diffusion-limited regime and follow a self-limiting cluster size model. The rate of cluster formation during this same reaction window is explained using interaction pair potential calculations and collision theory. Diffusion-limited reaction conditions are limited by sedimentation only if sedimentation velocities exceed diffusion velocities of the clusters or via plasmon damping through radiation or scattering losses. These radiative loses are only significant when the extinction magnitude near the excitation wavelength exceeds 1.5. By evaluating these responses as a function of both nanosphere radius and concentration, time-dependent SERS signals are revealed to follow collision theory and be predictable when both nanosphere concentration and size are considered.

Radiative heat transfer between metallic nanoparticle clusters in both near field and far field

Micro-nanoparticle systems have wide applications in thermal science and technology. In dense particulate system, the particle separation distance may be less than the characteristic thermal wavelength and near field effect will be significant and become a key factor to influence thermal radiation transfer in the system. In this study, radiative heat transfer (RHT) between two metallic nanoparticles clusters are explored using many-body radiative heat transfer theory implemented with the coupled electric and magnetic dipole (CEMD) approach, which effectively takes into account the contribution of magnetic polarization of metallic nanoparticles on heat exchange. As the focus, the effects of magnetic polarization and many-body interaction (MBI) on RHT were analyzed. The effects of fractal dimension and relative orientation of the clusters were also analyzed. Results show that the contribution of magnetically polarized eddy-current Joule dissipation dominates the RHT between Ag nanoparticle clusters. If only electric polarization (EP approach) is considered, the heat conductance will be underestimated as compared with the CEMD approach in both near field and far field regime. The effect of MBI on the RHT between Ag nanoparticle clusters is unobvious at room temperature, which is quite different from the SiC nanoparticle clusters. For the latter, MBI tends to suppress RHT significantly. The relative orientation has remarkable effect on radiative heat flux for clusters with lacy structure when the separation distance is in the near field. While for the separation distance in far field, both the relative orientation and the fractal dimension has a weak influence on radiative heat flux. This work will help the understanding of thermal transport in dense particulate system.

Dependent absorption property of nanoparticle clusters: an investigation of the competing effects in the near field.

Noble metal nanoparticle clusters show unique light absorption and catalysis properties, which have been widely used in the application of photocatalysis, optoelectronics, biomedical optics and so on. The absorption cross section of densely packed nanoparticle clusters, which can be enhanced or restricted due to the near field effects needs to be studied thoroughly. In this work, focusing on Au nanoparticle at the localized plasmon resonance wavelength, the effects of monomer diameter D, monomer number N, particle volume fraction Fv and complex refractive index m on the nondimensional absorption cross section η = Cabs,total/(N·Cabs) (normalized by N and the absorption cross section Cabs of a single particle) of densely packed nanoparticle clusters are studied by using the superposition T-matrix method. It is found that the enhancement (η > 1) and restriction (η < 1) mechanisms of the absorption cross section of nanoparticle clusters are determined by two competing factors (i.e. the multiple scattering and shielding effect), and the extent of these two mechanisms is mainly dependent on the monomer size parameter and the monomer number. The effect of the particle volume fraction on the nondimensional absorption cross section of nanoparticle clusters is totally different in different mechanisms. Specifically, the nondimensional absorption cross section peaks at the particle volume fraction of about 50% in the enhancement mechanism (in our calculation: D < 14 nm, N = 100), while in the restriction mechanism it decreases monotonously with increasing particle volume fraction. Moreover, the absorption efficiency of nanoparticle clusters with more absorptive monomer decreases more sharply with increasing particle volume fraction. The complex refractive index of particle shows significant effects on the nondimensional absorption cross section of nanoparticle clusters, and the largest nondimensional absorption cross section of nanoparticle clusters (N = 100) is larger than 8.

Relating the rate of growth of metal nanoparticles to cluster size distribution in electroless deposition.

Electroless deposition on patterned silicon substrates enables the formation of metal nanomaterials with tight control over their size and shape. In the technique, metal ions are transported by diffusion from a solution to the active sites of an autocatalytic substrate where they are reduced as metals upon contact. Here, using diffusion limited aggregation models and numerical simulations, we derived relationships that correlate the cluster size distribution to the total mass of deposited particles. We found that the ratio ξ between the rates of growth of two different metals depends on the ratio γ between the rates of growth of clusters formed by those metals through the linearity law ξ = 14(γ − 1). We then validated the model using experiments. Different from other methods, the model derives k using as input the geometry of metal nanoparticle clusters, decoded by SEM or AFM images of samples, and a known reference.

Near-Infrared-Excitable SERS Measurement Using Magneto-Responsive Metafluids for in Situ Molecular Analysis

Metal nanoparticle clusters are regarded as metamaterials, and dispersions of nanoparticle clusters are regarded as metafluids. Surface-enhanced Raman scattering (SERS) from molecules adsorbed on the nanoparticle clusters is one of the notable properties of metafluids. SERS is expected to permit the realization of single-molecule detection in chemical and biological samples, especially cells and tissues. However, most SERS measurements have been done on substrates; local information on cells and tissues have been hard to obtain. SERS active particles can be used to measure the local information on cells. To analyze biological samples using SERS, the SERS substrate should be excitable in the near-infrared (NIR) region to ensure high transparency in biological tissues. Furthermore, transporting the SERS particles to the desired position is crucial for obtaining high resolution. Sizes of SERS-active particles also affect to the resolutions. In this report, gold nanoparticle clusters based on polymer core–she...

Synthesis and light-induced aggregation of benzoate-stabilized silver nanoparticles

We report the influence of LED light irradiation on the colloids of silver nanoparticles synthesized in the presence of sodium benzoate. Scanning electron and atomic force microscopy measurements showed progressive aggregation and agglomeration of the particles during the irradiation with the light which energy is close to particle plasmon resonance. We consider local heating phenomenon caused due to the plasmon excitation as the main reason for the aggregation of the particles. A specific role of the benzoate and irradiation wavelength in these processes are discussed. This plasmon-induced aggregation opens new opportunities for the creation of metallic nanoparticle clusters.

Infrared photodetectors based on graphene metal nano clusters

Graphene is an outstanding photoconductive material for photodetection because of its wide range absorption spectrum and ultrafast response. It is well understood that by adding metal nanoparticle clusters on graphene layer enhances the absorption, also makes possible to focus on a particular region of the optical spectra via subwavelength plasmonic resonances between nanocluster and graphene substrate.In this article, we have designed an improved structure for gold nonamer nanodisk arrays on graphene as a photodetector to enhance the light absorption for optical communication spectrum. Effects of different structural parameters on absorption spectrum have been investigated, numerically. We have shown that light absorption in graphene-based detectors can be manipulated by tuning cluster size, thickness, inter disks gap distance, graphene position, and the number of graphene layers. By changing the radius of central and peripheral disks, we have shown that the Au nonamer on top of graphene is able to support strong sub- and superradiant plasmon resonances because of its unique geometrical features and a second absorption peak is generated. This additionally generated absorption peak is more suitable for application in 1550 nm nanostructure photodetectors.

PEGylated nanographene-mediated metallic nanoparticle clusters for surface enhanced Raman scattering-based biosensing.

Surface-enhanced Raman scattering (SERS) is an optical spectroscopy technique that can detect a variety of analytes with high sensitivity and selectivity without any labels. Controlled clustering of metallic nanoparticles to prepare a new class of SERS nanotags is crucial for the ultra-sensitive detection of specific biological and chemical moieties because increased plasmonic hotspot junctions produce a greatly enhanced SERS signal. We report herein that controlled clustering of Au nanoparticles (AuNPs) was mediated by PEGylated nano-sized graphene (PNG) and that the PNG-induced AuNP clusters (PNG-AuNPCs) were highly sensitive SERS nanotags with colloidal stability for SERS-based biosensing. The AuNPs labeled with 4-mercaptopyridine as a Raman reporter were surface-modified with 1-aminomethylpyrene for the introduction of hydrophobic moieties, and were non-covalently complexed with PNG via π-π stacking and van der Waals forces. It resulted in the formation of PNG-AuNPCs that increased SERS intensity with an enhancement factor of 1.34 × 1011. The PNG induced a high degree of AuNP clustering by enhancing the non-covalent interactions between them, resulting in increased hotspot junctions at highly localized plasmonic centers. Furthermore, to show that the PNG-AuNPCs would serve as stable, reproducible, and highly sensitive SERS nanotags for biosensing, we formed sandwich-type immunocomplexes composed of the PNG-AuNPCs, immunoglobulin G (IgG) as the antigen, and magnetic beads. We found a linear relationship between SERS intensity and IgG concentration, with a limit of detection lower than 31.0 fM for IgG detection. Thus, the PNG-AuNPCs could be useful as SERS nanotags for highly sensitive SERS-based biosensing applications.

Fine-Tuning of the Magnetic Fano Resonance in Hybrid Oligomers via fs-Laser-Induced Reshaping

Various clusters of metallic or dielectric nanoparticles can exhibit sharp Fano resonances originating from at least two modes interference of different spectral width. However, for practical applications such as biosensing or nonlinear nanophotonics, the fine-tuning of the Fano resonances is generally required. Here, we propose and demonstrate a novel type of hybrid oligomers consisting of asymmetric metal-dielectric (Au/Si) nanoparticles with a sharp Fano resonance in the visible range, which has a predominantly magnetic origin. We demonstrate both numerically and experimentally that such hybrid nanoparticle oligomers allow fine-tuning of the Fano resonance via fs-laser-induced melting of Au nanoparticles at the nanometer scale. We show that the Fano resonance wavelength can be changed by fs-laser reshaping very precisely (within 15 nm) being accompanied by a reconfiguration of its profile.

Quantifying and sorting of gold nanoparticle dimers from complex reaction mixtures using flow cytometry

The formation, characterization, and purification of well-defined stoichiometric clusters of metallic nanoparticles, particularly in the form of dimers or trimers, are important and formidable challenges in nanoscience. Here we show that flow cytometry can be used as a high-throughput method to determine the relative distribution of oligomeric clusters of molecularly linked gold nanoparticles in bulk solution at the single-particle level with good statistics. This unique information would be near impossible to obtain using traditional characterization techniques. The flow cytometric approach is utilized to provide fast feedback for the synthesis optimization of the complex reaction between citrate-stabilized gold nanoparticles and bi-functional molecular wires with dithiocarbamate anchoring groups. Finally, we demonstrate that flow cytometry can be used to significantly increase the proportion of AuNP dimers from an oligomer-rich polydisperse sample by size-selective sorting.

Two-Dimensional Nanoparticle Cluster Formation in Supercritical Fluid CO2.

Supercritical fluid carbon dioxide (sc-CO2) is capable of depositing nanoparticles in small structures of silicon substrates because of its gas-like penetration, liquid-like solvation abilities, and near-zero surface tension. In nanometer-sized shallow wells on silicon surface, formation of two-dimensional (2D) monolayer metal nanoparticle (NP) clusters can be achieved using the sc-CO2 deposition method. Nanoparticles tend to fill nanostructured holes first, and then, if sufficient nanoparticles are available, they will continue to cover the flat areas nearby, unless defects or other surface imperfections are available. In addition, SEM images of two-dimensional gold (Au) nanoparticle clusters formed on a flat silicon surface with two to a dozen or more of the nanoparticles are provided to illustrate the patterns of nanoparticle cluster formation in sc-CO2.

Singular electrostatic energy of nanoparticle clusters.

The binding of clusters of metal nanoparticles is partly electrostatic. We address difficulties in calculating the electrostatic energy when high charging energies limit the total charge to a single quantum, entailing unequal potentials on the particles. We show that the energy at small separation h has a singular logarithmic dependence on h. We derive a general form for this energy in terms of the singular capacitance of two spheres in near contact c(h), together with nonsingular geometric features of the cluster. Using this form, we determine the energies of various clusters, finding that more compact clusters are more stable. These energies are proposed to be significant for metal-semiconductor binary nanoparticle lattices found experimentally. We sketch how these effects should dictate the relative abundances of metal nanoparticle clusters in nonpolar solvents.

"Flash" preparation of strongly coupled metal nanoparticle clusters with sub-nm gaps by Ag+ soldering: toward effective plasmonic tuning of solution-assembled nanomaterials.

Noble metal nanoparticle oligomers are important in applications including plasmonics, catalysis, and molecular sensing. These nanostructural units featuring abundant inter-particle junctions are helpful for a physical/chemical understanding of structure-activity relationships of self-assembled metamaterials. A simple, rapid, and potentially general strategy for the preparation of monodisperse nanoparticle clusters in a homogeneous solution is highly desired for fundamental research toward liquid metamaterials and chemical/biological applications, but this is however very challenging. Here we report an Ag+ soldering strategy to prepare strongly coupled plasmonic (Au) and catalytic (Pt, Au@Pd (Au core with a Pd shell)) nanoparticle clusters almost instantly (<1 min) in a solution without special synthetic efforts, complicated surface decorations, or structure-directing templates. The resulting clusters are isolatable by agarose gel electrophoresis, resulting in mechanically stable products in high purity. The optical extinctions of Au nanodimers (the simplest and most basic form of a coupled structure) exhibit prominent longitudinal plasmonic coupling for nanoparticles down to 13.3 nm in diameter. Theoretical simulations attribute the strong coupling to the existence of a sub-nm gap (c.a. 0.76 nm) between soldered particles, suggesting an ideal (stable, soluble, monodisperse, and weakly passivated) substrate for surface enhanced Raman scattering (SERS) applications.

High performance organic photovoltaics with plasmonic-coupled metal nanoparticle clusters.

Performance enhancement of organic photovoltaics using plasmonic nanoparticles has been limited without interparticle plasmon coupling. We demonstrate high performance organic photovoltaics employing gold nanoparticle clusters with controlled morphology as a plasmonic component. Near-field coupling at the interparticle gaps of nanoparticle clusters gives rise to strong enhancement in localized electromagnetic field, which led to the significant improvement of exciton generation and dissociation in the active layer of organic solar cells. A power conversion efficiency of 9.48% is attained by employing gold nanoparticle clusters at the bottom of the organic active layer. This is one of the highest efficiency values reported thus far for the single active layer organic photovoltaics.

Magnetic-based Fano resonance of hybrid silicon-gold nanocavities in the near-infrared region.

Direct interference between the orthogonal electric and magnetic modes in a hybrid silicon-gold nanocavity is demonstrated to induce a pronounced asymmetric magnetic-based Fano resonance in the total scattering spectrum at near-infrared frequencies. Differing from the previously reported magnetic-based Fano resonances in metal nanoparticle clusters, the narrow discrete mode provided by the silicon magnetic dipole resonance can be directly excited by external illumination, and greatly enhanced electric and magnetic fields are simultaneously obtained at the Fano dip.