Plasmonic polymer nanocomposites contain plasmonic nanoparticles that are dispersed within a polymer. The polymer matrix strongly influences the optical properties of plasmonic nanoparticles. It is imperative to understand the interaction between plasmonic nanoparticles and polymers so that one can develop functional devices using nanocomposites. The utilization of plasmonic nanoparticles as fillers has great potential to transform critical nanotechnologies where light management is crucial, such as refractive index based nanosensors, optical coatings, and light actuated devices. Despite the great potential, effective integration of plasmonic nanoparticles with polymers remains challenging. This dissertation presents i) the effects of dielectric media on the optical properties of plasmonic nanoparticles, ii) the sensing of polymer brush formation on nanoparticles, iii) the fabrication of plasmonic nanocomposite thin-films with controlled optical properties, and iv) the development of electrically conductive membranes for electrostatic speakers. The optical response of plasmonic nanoparticles (referred to as wavelength of localized surface plasmon resonance, λLSPR) is sensitive to changes in refractive index of the medium. The sensitivity (S) plays a critical role in determining the performance of nanoparticles in sensing applications. In this dissertation, I have conducted a systematic study on the sensitivity of plasmonic nanoparticles as a function of various parameters: shape, size, composition, initial plasmonic resonance wavelength, cross-sectional area, and aspect ratio. Among the parameters investigated, aspect ratio (R) is determined to be the key parameter that controls S, following an empirical equation, S = 46.87 R + 109.37. This relationship provides a guideline for selecting fillers in plasmonic polymer nanocomposites, and it predicts the final effect of plasmonic nanoparticles on the optical properties of polymer nanocomposites. Plasmonic nanoparticles are employed to probe polymer grafting on the surfaces of metal nanoparticles. Using ultraviolet-visible (UV-vis) spectroscopy, I have demonstrated the quantification of polymer grafting density on the surface of plasmonic nanoparticles. The λLSPR of plasmonic nanoparticles red-shifts as the polymer concentration near the nanoparticle surface increases. I have investigated the formation of polymer brush by grafting the nanoparticles with thiolated polyethylene glycol (PEG-SH) and revealed the three–regime kinetics in situ. Importantly, this study suggests that a latent regime arises due to fast polymer adsorption and prolonged chain rearrangement on nanoparticle surfaces. When the polymer chains rearrange and chemically tether to the surface, they contract and allow more polymer chains to graft onto the particle surface until saturation. This analytical method provides a new surface probing technique for polymer brush analysis, complementary to conventional methods such as quartz crystal microbalance, atomic force microscope, and microcantilivers. Commercial tinted glass employs expensive metalized films to reduce light transmittance but has limited spectral selectivity. To reduce the cost of metalized films and to improve the spectral selectivity, I have employed plasmonic nanoparticles in polymers to fabricate spectral-selective tinted films. First, I have synthesized two-dimensional (2D) plasmonic silver nanoparticles (AgNPs) using multi-step growth. The nanoparticles have a tunable plasmon resonance and provide spectral selectivity. The multi-step growth forgoes polymeric ligands such as poly(vinylpyrrolidone) (PVP) and solely relies on a small molecule sodium citrate. Briefly, small citrate-capped Ag seeds are first grown into small 2D AgNPs. The small 2D AgNPs are then used to grow large 2D AgNPs via multiple growth steps. The PVP-free method allows for fast synthesis of 2D AgNPs with large sizes and tunable plasmon resonance across the visible and NIR region. The 2D AgNPs are integrated with polymers to produce thin-film plasmonic nanocomposites. By controlling the planar orientation of the 2D AgNPs through layer-by-layer assembly, the polymer nancomposites have achieved reduced light transmittance and enhanced reflectance across the visible and NIR range. In contrast to conventional polymer nanocomposites where the AgNPs are randomly oriented, the thin-film polymer nanocomposites exhibit excellent control over nanoparticle density and hence the optical properties, that is, tunable light transmittance and reflectance across the visible and NIR. Lastly, graphene is used to prepare conductive free-standing polymer thin-films. Graphene, an ultralight weight 2D material with excellent electrical and mechanical properties, has potential for use in thin-film composites essential for photovoltaics, electrostatic speakers, sensors, and touch displays. Current graphene-based composite films contain graphene flakes randomly mixed in a polymer matrix and usually possess poor mechanical and electrical properties. In this dissertation, I have developed thin-film nanocomposites comprised of chemical vapor deposited (CVD) graphene and high-performance polyetherimide (PI). The CVD-grown graphene is polycrystalline, and it cannot be used as a free-standing film. By enforcing the polycrystalline graphene with a thin layer of PI, I have prepared free-standing thin-film composites with a high aspect ratio of 105. Mechanical and electrical property characterization reveals a Young's modulus of 3.33 GPa and a resistance of 200 - 500 Ω across the membrane. A typical spring constant of the membrane is ~387 N/m. Dynamic electromechanical actuation shows that the membrane vibrates at various input frequencies. The polymer/graphene film has excellent acoustic properties, and when used as a speaker membrane, it reduces the electrical power consumption by a factor of 10-100 over the frequency range of 600–10,000 Hz. / Doctor of Philosophy / Nanomaterials such as plasmonic nanoparticles and graphene have optical, electrical, and mechanical properties that are important for light filters, sensors, printing, photovoltaics, touch screens, speakers, and biomedical devices. To fully employ the nanomaterials, a support such as polymer is often required. However, when the nanomaterials and polymers are combined, their optical, electrical, and mechanical properties drastically change. Therefore, it is imperative to understand the interactions between nanomaterials and polymers, as well as the resulting properties. Towards this goal, I have studied the sensitivity of plasmonic nanoparticles in a dielectric media and then utilized the sensitivity to investigate polymer brush formation on nanoparticle surfaces. In addition, I have investigated the integration of plasmonic nanoparticles and graphene with polymers to develop thin-film nanocomposites for window coatings and audio speakers, respectively. Plasmonic nanoparticles can detect trace amounts of chemicals, biomolecules, toxics, warfare agents, and environmental pollutants. Sensitivity is the key criterion that determines the performance of nanoparticles for such applications. Firstly, I have conducted a detailed and comprehensive study of the plasmonic sensitivity as a function of various nanoparticle parameters including shape, size, composition, cross-sectional area, initial plasmonic resonance wavelength, and aspect ratio. I have found that the sensitivity scaled linearly with aspect ratio. The strong dependence of sensitivity on aspect ratio provides insight into designing effective plasmonic sensors. Based on the sensitivity study, I have used plasmonic nanoparticles as sensors to probe and understand the mechanism of polymer brush formation in situ. When the concentration of polymer increases on the nanoparticle surfaces, the optical response of the nanoparticle changes. Through functionalizing the plasmonic nanoparticles with polymers, I have confirmed the three different regimes of polymer brush formation. Plasmonic nanoparticles resonating in the visible and near infrared have a great potential in designing polymer nanocomposites for window coatings. Among different exotic shapes, two-dimensional nanoplates are the most important as their optical properties can be easily tuned across a wide range of wavelengths. However, most of the current methods require polymers, long hours of reaction time, and multiple purification steps. I have developed a new multi-step strategy to synthesize Ag nanoplates which absorb in the range of 500–1660 nm. Utilizing the plasmonic nanoparticles, the spectral-selective plasmonic nanocomposites comprised of polymers and planarly oriented Ag nanoparticles of judiciously selected sizes and compositions were prepared. The plasmonic polymer nanocomposites spectral-selectively reflect, scatter, and filter light of any desired wavelength. The nanocomposites will impact on the tinted glass in modern energy-efficient buildings. The outstanding electrical and mechanical properties of graphene have stirred a large volume of research in the last 15 years. Most graphene-based technologies focus on graphene at the nano or micro scale. To further the practicality of graphene in large devices like audio speakers, large areas and thin films are needed to reduce energy consumption. Graphene on its own cannot be used over large areas due to the inherent defects arising during the growth. Here I present results on combining suspended sheets of single layer graphene with a mechanically strong polymer thin film. The acoustic properties of speakers made of polymer/graphene thin films are similar to those of conventional electrodynamic speakers in modern cellphones. The energy consumption, however, reduces sharply by a factor of 10-100 for the polymer/graphene based speakers. This sharp decrease in energy is attributed to the lightweight, flexibility, and excellent electrical conductivity. Apart from speakers, the membrane designed here also has huge potential in other devices like touch panels, capacitive sensors, and photovoltaics.

Nanometer-scale particles of the noble metals have been used for decades as contrast enhancement agents in electron microscopy. Over the past several years it has been demonstrated that these particles also function as excellent contrast agents for optical imaging techniques. The resonant optical scattering they exhibit enables scattering cross sections that may be many orders of magnitude greater than the analogous efficiency factor for fluorescent dye molecules. Biologically relevant labeling with nanoparticles generally results in aggregates containing a few to several tens of particles. The electrodynamic coupling between particles in these aggregates produces observable shifts in the resonance-scattering spectrum. This dissertation provides a theoretical analysis of the scattering from nanoparticle aggregates. The key objectives are to describe this scattering behavior qualitatively and to provide numerical codes usable for modeling its application to biomedical engineering. Considerations of the lowest-order dipole-dipole coupling lead to simple qualitative predictions of the behavior of the spectral properties of the optical cross sections as they depend on number of particles, inter-particle spacing, and aggregate aspect ratio. More comprehensive analysis using the multiple-particle T-matrix formalism allows the elaboration of more subtle cross-section spectral features depending on the interactions of the electrodynamic collective-modes of the aggregate, of individual-particle modes, and of modes associated with groups of particles within the aggregate sub-structure. In combination these analyses and the supporting numerical code-base provide a unified electrodynamic approach which facilitates interpretation of experimental cross section spectra, guides the design of new biophysical experiments using nanoparticle aggregates, and enables optimal fabrication of nanoparticle structures for biophysical applications. / text

The light-matter interaction in the near-field of high-Q resonators in SOI and SiN platforms is studied. The interactions of high-Q traveling-wave resonators with both resonant and non-resonant nanoparticles are studied and different applications based on this enhanced interactions in near-field such as high-resolution imaging of mode profile of high-Q resonators, label-free sensing, optical trapping, and SERS sensing are investigated. A near-field imaging system for the investigation of the near-field phenomena in the near-field of high-Q resonators is realized. A new technique for high-resolution imaging of the optical modes in high-Q resonators based on the near-field perturbation is developed that enables to achieve a very high resolution (< 10 nm) near-field image. The prospect of the high Q resonators on SOI platform for highly multiplexed label-free sensing and the effect of different phenomena such as the analyte drift and diffusion and the binding kinetics are studied. Also, the possibility of enhancing nanoparticle binding to the sensor surface using optical trapping is investigated and the dynamic of a nanoparticle in the high-Q resonator optical trap is studied. Furthermore, the interaction between a resonant nanoparticle with a high-Q microdisk resonator and its application for SERS sensing is studied. A model for interaction of resonant nanoparticles with high-Q resonators is developed and the optimal parameters for the design of coupled microdisk resonator and a plasmonic nanoparticle are calculated. The possible of resonant plasmonic nanoparticle trapping and alignment in an SiN microdisk resonator optical trap is also shown.

Strong light matter interactions in metallic nanoparticles (NPs), especially those made of noble metals such as Gold and Silver is at the heart of much ongoing research in nanoplasmonics. Individual NPs can support collective excitations (Plasmon’s) of the electron plasma at certain wavelengths, known as the localized surface Plasmon resonance (LSPR) which provides a powerful platform for various sensing, imaging and therapeutic applications. For a collection of NPs their optical properties can be signify cannily different from isolated particles, an effect which originates in the electromagnetic interactions between the localised Plasmon modes. An interesting aspect of such interactions is their strong dependence on the geometry of NP collection and accordingly new optical properties can arise. While this problem has been well considered in one and two dimensions with periodic as well as with random arrays of NPs, three dimensional systems are yet to be fully explored. In particular, there are challenges in the successful de-sign and fabrication of three dimensional (3D) plasmonic metamaterials at optical frequencies. In the work presented in this thesis we present a detail investigation of the theoretical and experimental aspects of plasmonic interactions in two geometrically different three dimensional plasmonic nanostructured systems - a chiral system consisting of achiral plasmonic nanoparticles arranged in a helical geometry and an achiral system consisting of achiral plasmonic nanoparticle arrays stacked vertically into three dimensional geometry. The helical arrangement of achiral plasmonic nanoparticles were realised using a wafer scale technique known as Glancing Angle Deposition (GLAD). The measured chiro-optical response which arises solely from the interactions of the individual achiral plasmonic NPs was found to be one of the largest reported value in the visible. Semi analytical calculation based on couple dipole approximation was able to model the experimental chiro-optical response including all the variabilities present in the experimental system. Various strategies based on antiparticle spacing, oriented elliptical nanoparticles, dielectric constant value of the dielectric template were explored such as to engineer a strong and tunable chiro-optical response. A key point of the experimental system despite the presence of variabilities, was that the measured chiro-optical response showed less than 10 % variability along the sample surface. Additionally we could exploit the strong near held interactions of the plasmonic nanoparticles to achieve a strongly nonlinear circular differential response of two photon photoluminescent from the helically arranged nanoparticles. In addition to these plasmonic chiral systems, our study also includes investigation of light matter interactions in purely dielectric chiral systems of solid and core shell helical geometry. The chiro-optical response was found to be similar for both the systems and depend strongly on their helical geometry. A core-shell helical geometry provides an easy route for tuning the chiro-optical response over the entire visible and near IR range by simply changing the shell thickness as well as shell material. The measured response of the samples was found to be very large and very uniform over the sample surface. Since the material system is based entirely on dielectrics, losses are minimal and hence could possibly serve as an alternative to conventional plasmonic chiro-optical materials. Finally we demonstrated the used of an achiral three dimensional plasmonic nanostructure as a SERS (surface enhance Raman spectroscopy) substrate. The structure consisted of porous 3D metallic NP arrays that are held in place by dielectric rods. For practically important applications, the enhancement factor, as well as the spatial density of the metallic NPs within the laser illumination volume, arranged in a porous 3D array needs to be large, such that any molecule in the vicinity of the metal NP gives rise to an enhanced Raman signal. Having a large number of metallic NPs within the laser illumination volume, increases the probability of a target molecule to come in the vicinity of the metal NPs. This has been achieved in the structures reported here, where high enhancement factor (EF) in conjunction with large surface area available in a three dimensional structure, makes the 3D NP arrays attractive candidates as SERS substrates.

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Noble metal nanoparticles have attracted the attentions of many researchers because of unique plasmonic properties since their discovery and successful preparation. Nanocluster formed by the assembly of noble metal nanoparticles can exhibit plasmonic characteristics beyond those of individual nanoparticles, which can be tuned, to a large extent, by adjusting the size, shape, chemical composition, and arrangement of individual nanoparticles. Usually nanocluster with special ordered structures is called as superstructure, which can be designed for different purposes through various methods. Colloidal assembly as a cost-efficient approach can be widely used for fabrication of plasmonic superstructure in solution media. As an introduction of background, the developments of plasmonic nanoparticles and nanoclusters have been discussed in the aspects of their LSPR properties, surface modification for colloidal assembly, and sensing applications. Both colorimetry and SERS detection based on plasmonic assemblies have been presented as effective sensing methods, which are also the motivations for the main experiments in this thesis. As a proof-of-motivation, the different kinds of thiol-terminated PEG assisted hybrid gold nanoparticles have been applied for the protein colorimetric detections based on the specific interaction between heparin and proteins with different surface affinities. In addition, PEG-assisted core/satellite superstructures with various polymer thickness as SERS platform have been demonstrated for trace sensing of specific target molecules in solution. Especially, the method to differentiate between the radiative and non-radiative contributions of plasmonic superstructure has been proposed using diffuse reflectance spectroscopy, which provides a favorable selection and design of best candidates for specific application scenarios. Finally, the concept of NIR-II SERS using biological transparency window has been introduced including the fundamental requirements, which proposed a future experiment to fabricate suitable superstructures for potential biomedical applications with high penetration depth at low laser powers. Generally speaking, the central focus of this thesis is the effect of polymer modification on the structures and properties of plasmonic superstructure and its sensing application. The main research efforts are divided into three parts: (I) investigate the topological effect of polymer structure parameters on plasmonic properties for colorimetric analytics; (II) investigate the impact of interparticle spacing within the assemblies and polymer dimensions on the SERS activity; (III) investigate the plasmonic properties tailoring of superstructures as well as the contribution of scattering (radiative) and absorption (non-radiative), i.e. light-to-heat conversion, within the ensemble optical response.