scholarly journals Computational Methods for Light Scattering by Metallic Nanoparticles

2021 ◽  
Author(s):  
◽  
Walter Ross Campbell Somerville
Keyword(s):  
Light Scattering ◽  
Power Series ◽  
Metallic Nanoparticles ◽  
Near Field ◽  
Power Series Expansion ◽  
Primary Source ◽  
Surface Enhanced Raman Spectroscopy ◽  
Metallic Surface ◽  
Correct Result ◽  
Local Shape

<p>The unifying theme of this thesis is that of light scattering by particles, using computational approaches. This contributions here are separated into two main areas. The first consists of examining the behaviour of the extended boundary-condition method and T-matrix method, and providing a modified set of equations to use to calculate the relevant integrals. From this, some linear relations between integrals were found, which hint at the possibility of a more efficient means of performing these calculations. As well as this, the severe numerical problems associated with this method were investigated, and the primary source of these problems was identified in the case of two commonly-used shapes, spheroids and offset spheres. The cause of these numerical problems is that dominant, leading terms in the power series expansion of the integrands integrate identically to zero, but in practice, numerical calculations have insufficient precision to compute this exactly, and the overwhelming errors from this lead to drastically incorrect results. Following this identification, a new formulation of the integrals for spheroids is presented, which allows the much easier treatment of spheroids, approaching the level of ease of calculations for spheres in Mie theory. This formulation replaces some terms in the integrands with modified terms, that do not contain the parts of the power series that cause problems. As these should integrate to zero, we are able to remove them from the integrand without affecting the correct result. The second area of this thesis is concerned with calculations of the near-field for systems of interest in plasmonics, and specifically in surface-enhanced Raman spectroscopy. Here, the enhancement of the electric field in the vicinity of a metallic surface has a large effect on measured signals. The contribution of this thesis is to study the geometric parameters that influence the distribution of the field enhancement at the particle's resonance, specifically focusing on different effects caused by the overall shape of the particle, as opposed to those effects due to the local shape of the particle in regions of high enhancement. It is shown that the overall shape determines the location of the resonance, while the local shape determines how strongly the enhancement is localised. Understanding the factors that influence the enhancement localisation will help in guiding the design of suitable plasmonic substrates.</p>

scholarly journals Computational Methods for Light Scattering by Metallic Nanoparticles

2021 ◽  
Author(s):  
◽  
Walter Ross Campbell Somerville
Keyword(s):  
Light Scattering ◽  
Power Series ◽  
Metallic Nanoparticles ◽  
Near Field ◽  
Power Series Expansion ◽  
Primary Source ◽  
Surface Enhanced Raman Spectroscopy ◽  
Metallic Surface ◽  
Correct Result ◽  
Local Shape

<p>The unifying theme of this thesis is that of light scattering by particles, using computational approaches. This contributions here are separated into two main areas. The first consists of examining the behaviour of the extended boundary-condition method and T-matrix method, and providing a modified set of equations to use to calculate the relevant integrals. From this, some linear relations between integrals were found, which hint at the possibility of a more efficient means of performing these calculations. As well as this, the severe numerical problems associated with this method were investigated, and the primary source of these problems was identified in the case of two commonly-used shapes, spheroids and offset spheres. The cause of these numerical problems is that dominant, leading terms in the power series expansion of the integrands integrate identically to zero, but in practice, numerical calculations have insufficient precision to compute this exactly, and the overwhelming errors from this lead to drastically incorrect results. Following this identification, a new formulation of the integrals for spheroids is presented, which allows the much easier treatment of spheroids, approaching the level of ease of calculations for spheres in Mie theory. This formulation replaces some terms in the integrands with modified terms, that do not contain the parts of the power series that cause problems. As these should integrate to zero, we are able to remove them from the integrand without affecting the correct result. The second area of this thesis is concerned with calculations of the near-field for systems of interest in plasmonics, and specifically in surface-enhanced Raman spectroscopy. Here, the enhancement of the electric field in the vicinity of a metallic surface has a large effect on measured signals. The contribution of this thesis is to study the geometric parameters that influence the distribution of the field enhancement at the particle's resonance, specifically focusing on different effects caused by the overall shape of the particle, as opposed to those effects due to the local shape of the particle in regions of high enhancement. It is shown that the overall shape determines the location of the resonance, while the local shape determines how strongly the enhancement is localised. Understanding the factors that influence the enhancement localisation will help in guiding the design of suitable plasmonic substrates.</p>

scholarly journals Freeform 3D Plasmonic Superstructures

2020 ◽  
Author(s):  
Won-Geun Kim ◽  
Jongmin Lee ◽  
Vasanthan Devaraj ◽  
Minjun Kim ◽  
Hyuk Jeong ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Self Assembly ◽  
Metallic Nanoparticles ◽  
Near Field ◽  
Surface Enhanced Raman Spectroscopy ◽  
Far Field ◽  
Plasmonic Nanoparticle ◽  
Surface Enhanced ◽  
Nanoparticle Clusters ◽  
Surface Enhanced Raman

Abstract Plasmonic nanoparticle clusters promise to support various, unique artificial electromagnetisms at optical frequencies, realizing new concept devices for diverse nanophotonic applications. However, the technological challenges associated with the fabrication of plasmonic clusters with programmed geometry and composition remain unresolved. Here, we present a freeform fabrication of hierarchical plasmonic clusters (HPCs) based on omnidirectional guiding of evaporative self-assembly of gold nanoparticles (AuNPs) with the aid of 3D printing. Our method offers a facile, universal route to shape the multiscale features of HPCs in three-dimensions, leading to versatile manipulation of both far-field and near-field characteristics. Various functional nanomaterials can be effectively coupled to plasmonic modes of the HPCs by simply mixing with AuNP ink. We demonstrate in particular an ultracompact surface-enhanced Raman spectroscopy (SERS) platform to detect M13 viruses and their mutations from femtolitre volume, sub-100pM analytes. This SERS microplatform could pave the way towards simple, innovative detection methods of diverse pathogens, which is in high demand for handling pandemic situations. We expect our method to freely design and realize nanophotonic structures beyond the restrictions of traditional fabrication processes. Plasmonic nanoparticle clusters have attracted great attention due to the unique capability to manipulate electromagnetic fields at the sub-wavelength scale1–5. Ensembles of metallic nanoparticles generate various electromagnetisms at optical frequencies such as artificial magnetism6–10 and Fano-like interference11–13 and a strong field localization in the structure14–16. These unique properties are geometry-dependent and lead to a broad range of applications in sensing16,17, surface-enhanced spectroscopies18–22, nonlinear integrated photonics23,24, and light harvesting25,26. Traditionally, plasmonic clusters with tailored size and geometry are fabricated on substrates by top-down processes such as electron-beam lithography4,5 or focused-ion beam milling27,28. These approaches suffer from low throughput and are generally limited to in-plane fabrication. Alternatively, the self-assembly of colloids has been proposed as a versatile, high-throughput, and cost-effective route. A number of clever methods based on chemical linking (e.g., DNA origami)29–30 and/or convective assembly on lithographically structured templates25,26,31 have been devised to construct 2D or 3D plasmonic clusters. The shape formation, however, is mostly constrained by the thermodynamic impetus and/or template geometry. A significant challenge would be overcome these restrictions and expand structural design freedom in the fabrication of plasmonic cluster architectures with symmetry-breaking geometries. In this work, we develop a freeform, programmable 3D assembly of of hierarchical plasmonic clusters (HPCs). By exploiting micronozzle 3D printing, we demonstrate highly localized, omnidirectional meniscus-guided assembly of metallic nanoparticles, constructing a freestanding HPC with a tailored geometry that can control the far-field character. Our approach also allows versatile manipulation and exploitation of the near-field interaction in the HPC by a facile heterogeneous nanoparticle mixing. We demonstrate that 3D-printed HPCs can be utilized as an ultracompact surface-enhanced Raman spectroscopy (SERS) platform to detect M13 viruses and their mutations from femtolitre volume, sub-100pM analytes.

scholarly journals Light-Scattering Simulations from Spherical Bimetallic Core–Shell Nanoparticles

Micromachines ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 359
Author(s):  
Francesco Ruffino
Keyword(s):  
Optical Properties ◽  
Light Scattering ◽  
Bimetallic Nanoparticles ◽  
Dominant Role ◽  
Scattered Light ◽  
Specific Interaction ◽  
Surface Enhanced Raman Spectroscopy ◽  
Localized Surface Plasmon ◽  
Core Shell ◽  
The Core

Bimetallic nanoparticles show novel electronic, optical, catalytic or photocatalytic properties different from those of monometallic nanoparticles and arising from the combination of the properties related to the presence of two individual metals but also from the synergy between the two metals. In this regard, bimetallic nanoparticles find applications in several technological areas ranging from energy production and storage to sensing. Often, these applications are based on optical properties of the bimetallic nanoparticles, for example, in plasmonic solar cells or in surface-enhanced Raman spectroscopy-based sensors. Hence, in these applications, the specific interaction between the bimetallic nanoparticles and the electromagnetic radiation plays the dominant role: properties as localized surface plasmon resonances and light-scattering efficiency are determined by the structure and shape of the bimetallic nanoparticles. In particular, for example, concerning core-shell bimetallic nanoparticles, the optical properties are strongly affected by the core/shell sizes ratio. On the basis of these considerations, in the present work, the Mie theory is used to analyze the light-scattering properties of bimetallic core–shell spherical nanoparticles (Au/Ag, AuPd, AuPt, CuAg, PdPt). By changing the core and shell sizes, calculations of the intensity of scattered light from these nanoparticles are reported in polar diagrams, and a comparison between the resulting scattering efficiencies is carried out so as to set a general framework useful to design light-scattering-based devices for desired applications.

Study of the mechanism of the light-scattering-mode superresolution near-field structure

2001 ◽  
Author(s):  
Wei Chih Lin ◽  
Jun D. Su ◽  
Ming C. Tsai ◽  
Din Ping Tsai ◽  
Nien H. Lu ◽  
...  
Keyword(s):  
Light Scattering ◽  
Near Field ◽  
Field Structure

scholarly journals All-dielectric chiral-field-enhanced Raman optical activity

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ting-Hui Xiao ◽  
Zhenzhou Cheng ◽  
Zhenyi Luo ◽  
Akihiro Isozaki ◽  
Kotaro Hiramatsu ◽  
...  
Keyword(s):  
Optical Activity ◽  
Metallic Nanoparticles ◽  
Near Field ◽  
Localized Surface Plasmon ◽  
Chiral Field ◽  
Resonance Spectroscopy ◽  
Conformational Structure ◽  
Dark Mode ◽  
Spontaneous Raman Scattering ◽  
Raman Optical Activity

AbstractRaman optical activity (ROA) is effective for studying the conformational structure and behavior of chiral molecules in aqueous solutions and is advantageous over X-ray crystallography and nuclear magnetic resonance spectroscopy in sample preparation and cost performance. However, ROA signals are inherently minuscule; 3–5 orders of magnitude weaker than spontaneous Raman scattering due to the weak chiral light–matter interaction. Localized surface plasmon resonance on metallic nanoparticles has been employed to enhance ROA signals, but suffers from detrimental spectral artifacts due to its photothermal heat generation and inability to efficiently transfer and enhance optical chirality from the far field to the near field. Here we demonstrate all-dielectric chiral-field-enhanced ROA by devising a silicon nanodisk array and exploiting its dark mode to overcome these limitations. Specifically, we use it with pairs of chemical and biological enantiomers to show >100x enhanced chiral light–molecule interaction with negligible artifacts for ROA measurements.

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