Predicting and verifying the tunable optical properties of metal nanostructures is central to designing materials optimized for specific applications. Chemically- deposited nanostructures have been well-studied near the percolation threshold, but at lower surface coverages they exhibit sample-to-sample variations in the optical response. We identify how these variations are driven by the high variability in the particle size distribution in a particular surface coverage range. We then explore film- coupled nanoparticle systems consisting of a silver nanoparticle, thin dielectric spacer layer, and flat silver film, to enable tuning toward the blue and green parts of the spectrum. We use the boundary element method to visualize charge distributions of various resonances. We fabricate samples using thermal evaporation and spin coating methods, and use polarized reflectance spectroscopy to measure their optical response at an ensemble level. We achieve a 532nm resonance for 80nm silver nanoparticles on 13nm PMMA spacers and 100nm silver thin films. The resulting design is a candidate for enhancing fluorescence in a new spectral range. This dissertation includes previously unpublished co-authored material.

This dissertation focused on the applications of self-assembled monolayers (SAMs) technique for the investigation of molecule based electronics, plasmon coupling between CdSe quantum dots and metal nanoparticles (MNPs), and copper ion detection using enhanced emission of CdSe quantum dots (QDs). The SAMs technique provides an approach to establish a robust, two-dimensional and densely packed structure which can be formed on metal or semiconductor surfaces. This allows for the design of molecular assemblies that can be used to understand the details of molecular conduction by employing various electrical testbeds. In this work, the strategy of molecular assemblies was used to pattern metal nanoparticles on GaAs surfaces, thereby furnishing a platform to explore the interactions between QDs and MNPs. The enhanced emission of CdSe QDs by MNPs was then used as a probe for ultrasensitive, cheap, and rapid copper(II) detection. The study is divided into three main facets. The first one aimed at controlling electron transport behavior through porphyrins on surfaces with an eye toward optoelectronic and light harvesting applications. The binding of the porphyrin molecules to Au surfaces, pre-covered with a dodecanethiol matrix, was characterized by FTIR, XPS, AFM, STM, of. This study has shown that the perfluoro coupling group between the porphyrin macrocycle and the thiol tether may provide a means of controlling the tunneling behavior. The second area of this study focused on the design of a simple platform to examine the coupling between metal nanostructures and quantum dot assemblies. Here we demonstrate that by using a patterned array of Au or Ag nanoparticles on GaAs, plasmon enhanced photoluminescence (PL) can be directly measured and quantified by direct scaling of regions with and without metal nanostructures. The third field presented a simple manner for using the enhanced PL of CdSe QDs as a probe for ultrasensitive Cu2+ ion detection and quantitative analysis. The PL of QDs was enhanced by two processes: first, photobrightening of the material, and second, plasmonic enhancement by coupling with Ag nanoprisms. This strong PL leads to a high sensitivity of the QDs over a wide dynamic range for Cu2+ detection, as Cu2+ efficiently quenches the QD emission.

Single particle microscopy and spectroscopy strategies reveal hidden relationships between the surface plasmon resonances (SPRs) and the sizes, shapes, and arrangements of gold nanoparticles (Au NPs). The SPR, the coherent oscillation of the conduction electrons, leads to intense absorption and scattering of light at frequencies satisfying the resonance condition determined by the size, shape, and spacings between NPs. Growing and assembling NPs through wet chemistry yields a diversity of geometries. Together, optical spectroscopy, scanning electron microscopy (SEM), and computational modeling of individual NPs and NP assemblies elucidate the resulting variety of SPRs. Strong coupling of the SPRs in linear assemblies provokes particular interest for tunable structures that will benefit surface enhanced spectroscopies and optical computing. The influence of the constituents and imperfections in such assemblies, which deviate from idealized model systems, must be established one assembly at a time. This thesis demonstrates previously unknown and sensitive relationships between the SPRs and these geometric parameters through systematic single particle experiments of self-assembled ring superstructures, nanorod dimers, individual nanorods populating different size regimes, and short linear chains of Au NPs through single particle spectroscopy. Dark-field scattering of self-assembled ring superstructures of 40 nm Au NPs reveals new plasmon modes that are redshifted from the single NP SPR by hundreds of nanometers, highly polarized along the axis of alignment, and indifferent to irregularities in the NP arrangement. SPRs of Au nanorod dimers, however, are dramatically altered by NP size heterogeneity, reduced symmetry, and metallic contact, consistent with previous studies of small assemblies. Broad band single particle extinction measurements of individual Au nanorods and short chains of 200-1000 nm long demonstrate the importance of the overall dimensions of an NP or an assembly of NPs. Finally, extinction measurements of these chains provide a compelling comparison to chemical polymers via the redshifting of the lowest energy SPR, tolerance to disorder, and the influence of the repeat unit. This result extends already well-defined analogies between plasmonic assemblies and chemical molecules to the ‘plasmonic polymer’. The findings presented in this thesis bring deeper and more detailed understanding to the tunable optical properties of real NP assemblies.

Plasmon coupling is known to cause distance dependent red-shifts of the characteristic plasmon resonance and localize strong electric fields to the gap between individual nanoparticles. These effects form the basis of nanoscale plasmonic sensors designed by creating specic structures of coupled nanoparticles. The simplest of these structures, a nanoparticle dimer, can easily be assembled through molecular self-assembly, resulting in a structure called a plasmon ruler. These plasmon rulers are crucial tools for the measurement of nanoscale distances, but the impact of the molecular linker on the plasmonic response of the coupled system remains insufficiently understood. In this dissertation, plasmons rulers composed of 40 nm gold nanoparticles are utilized to systematically investigate the potential effects of one molecular linker, DNA, on the strength of the plasmon coupling at a variety of interparticle separations. The strength of the plasmon coupling is determined based on the shifting of the plasmon resonance, which, at separations below 2.7 nm, is significantly blue-shifted when compared to expected values from electromagnetic simulations and experiments without DNA linkers. This deviation indicates a reduced charge accumulation on the nanoparticles in the gap region and is ascribed to DNA-mediated charge transfer. Enhancements to the charge transfer capabilities of the DNA were also investigated, through the deposition of interstitial palladium nanocrystals on the DNA linkers. The deposition of these nanocrystals results in a variety of structural changes to the plasmon rulers, associated with blue- and red-shifts of the plasmon resonance relative to electromagnetic simulations without gap material and experimental spectra of structures without molecular or metallic linkers. The relative blue-shift of the resonance results from a variety of scenarios, including short interparticle separations bridged by DNA or palladium nanocrystals, the build-up of palladium nanocrystals within the gap, or the incorporation of discrete palladium nanoparticles in the DNA linkers. The underlying mechanisms of the observed spectral shifts are analyzed. The red-shifted resonances resulted from a significant build-up of palladium nanocrystals in the gap, effectively linking the gold nanoparticles and forming a hybrid nanorod-like structure.

xx, 162 p. ; ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / In this thesis we theoretically and experimentally investigate the subwavelength manipulation of light with nano-scale patterned metallodielectric resonators. By coupling light to surface plasmon excitations, we calculate the modified dispersion relation of the resulting surface plasmon polariton (SPP) modes in two types of subwavelength resonators: (i) closed, spherical micro-resonators with nano-scale metal-dielectic-metal shells; (ii) periodic, metal-dielectric-metal-layered silica surfaces. We show theoretically that with the proper geometric parameters, one can use sub-wavelength structure on spherical surfaces to manipulate the SPP dispersion relation in a highly tunable fashion. A tunable avoided-crossing of plasmonic dispersion bands is found to be the result of the coherent near-field coupling of silver nano-shell SPP modes. By developing our own stable computational algorithms, we calculated the far-field scattering of these metal-dielectric-metal layered micro-resonators. We demonstrate that the near-field interaction of the SPPs leads to a tunable, SPP induced transparency in the composite particle's scattering and extinction cross-sections. Utilizing finite element calculations, periodically-modulated metal-dielectric-metal layers are shown to alter the transmission properties of plasmon enhanced transmission through their support of interior surface plasmon (ISP) modes. Our simulations indicate that, subwavelength silver-silica-silver trilayers coating arrays of silica cylinders support ISP modes analogous to those found in spherical metal-dielectric-metal shells. We examine the coupling between ISP and radiating SPPs, and find the possibility of efficient free-space coupling to ISP modes in planar geometries. Further, the excitation of these ISP modes is found to predicate plasmon enhanced transmission, adding directionality and refined frequency selection. Experimentally, we show that self-assembled monolayers of silica spheres form a novel substrate for tunable plasmonic surfaces. We have developed a deposition method to conformally coat these hexagonal-close-packed substrates with nano-scale silver-polystyrene-silver coatings. We use angle-resolved spectroscopy to study their transmission properties. We have discovered that the presence of the silver-polystyrene-silver layer supports the excitation of ISP modes, and that these excitations significantly alter the plasmon enhanced transmission. Finally, we have discovered that the use of the ordered monolayers as a plasmonic substrate can create a new effect in conjunction with plasmon enhanced transmission: directionally asymmetric transmission. This is demonstrated with optically thick silver coatings evaporated upon onto the ordered sphere monolayers. / Adviser: Miriam Deutsch

Nanoscale structures play a fundamental role in diverse scientific areas, including biology and information technology. It is necessary to develop methods that can observe nanoscale structures and dynamic processes that involve them. Colloidal plasmonic nanoparticles (plasmonic “atoms”) and their clusters (plasmonic “molecules”) are nanoscale objects with remarkable optical properties that provide new opportunities for sensing and imaging on the relevant length and time scales. Many biology questions require optically monitoring of the dynamic behavior of biological systems on single molecule level. In contrast to the commonly used fluorescent probes which have the problem of bleaching, blinking and relatively weak signals, plasmonic probes display superb brightness, persistency and photostability, thus enable long observation time and high temporal and spacial resolutions. When plasmonic atoms are clustered together, their resonances redshift while the intensities increase as a result of plasmon coupling. These optical responses are dependent on the interparticle gaps and the overall geometry, which makes plasmonic molecules capable of detecting biomolecule clustering and measuring nanometer scale distance fluctuations. In this dissertation, individual plasmonic atoms are firstly evaluated as imaging probe and their interactions with lipid membrane are tested on a newly developed on-chip black lipid membrane system. Subsequently, plasmonic dimers (plasmon rulers) prepared through DNA-programmed self-assembly are monitored to detect the mechanical properties of single biopolymers. Measurement of the spring constant of short (tens of nucleotides or base pairs) DNAs is demonstrated through plasmon coupling microscopy. Colloidal plasmonic atoms of various materials, sizes and shapes scatter vivid colors in the full-visible range. Assembling them into plasmonic molecules provides additional degrees of freedom for color manipulation. More importantly, the electric field in the gaps of plasmonic molecules can be enhanced by several orders of magnitude, which is highly desirable in single molecule sensing applications. In this dissertation, the fundamentals of plasmonic coupling are investigated through one-dimensional gold nanosphere chains. Using the directed self-assembly approach, multichromatic color-switchable plasmonic nanopixels composed of plasmonic atoms and molecules of various materials, sizes, shapes and geometries are integrated in one image with nanometer precision, which facilitates the encoding of complex spectral features with high relevance in security tagging and high density optical data storage. / 2017-01-01T00:00:00Z

Film thickness, free carrier concentration and free carrier mobility are critical figures of merit for silicon carbide epitaxial growth. Room temperature Fourier Transform Infrared (FTIR) reflection spectroscopy can estimate these parameters non-destructively and is capable of high-resolution wafer mapping. Commercially available equipment has greatly simplified the application of this technique by coupling a high performance automated spectrometer with model-based data analysis and interpretation based on the personal computer. While powerful numerical techniques run fast and efficient on modern computers, it is essential that low-order, well-conditioned models are needed. The observed reflectance spectrum is the result of reflection and refraction of light at different interfaces due to constructive and destructive interference. The estimation of film thickness and free carrier concentration for single epitaxial layers has been improved by studying the Longitudinal Optical Phonon Plasmon (LPP) coupled modes. However, the addition of multiple layers introduces many degrees of freedom, which complicates parameter extraction. The multiple epitaxial layer stacks studied were intended for Metal Semiconductor Field Effect Transistor (MESFET?s) on both conducting and semi-insulating substrates. The thickness estimation of the n-channel in the MESFET stack on semi-insulating substrate is improved by preconditioning the curve fit for plasma frequency obtained from doping estimation from capacitance voltage profiling or by observing an LPP- peak.

Noble metal nanostructures possess unique properties including large near-field enhancement and strong light scattering and absorption due to their plasmon resonance - the collective coherent oscillation of the metal free electrons in resonance with the electromagnetic field of light. The effect of nanostructure size, shape, composition, and environment on the plasmon resonance frequency and plasmonic enhancement is well known. In this thesis, we describe the effect of inter-particle coupling in assembled plasmonic nanostructures on their radiative and non-radiative properties. When metal nanoparticles assemble, plasmon oscillations of neighboring particles couple, resulting in a shift in the plasmon resonance frequency. Our investigation of plasmon coupling in gold nanorods shows that the coupling between the plasmons is "bonding" in nature when the plasmon oscillations are polarized along the inter-particle axis, whereas an "anti-bonding" interaction results when the polarization is perpendicular. We studied the distance-dependence of plasmon coupling using electrodynamic simulations and experimental plasmon resonances of lithographically fabricated gold nanoparticle pairs with systematically varying inter-particle separations. The strength of plasmon bonding, reflected by the fractional plasmon shift, decays near-exponentially with the inter-particle separation (in units of particle size) according to a universal trend independent of the nanoparticle size, shape, metal type, or medium. From the universal scaling model, we obtain a "plasmon ruler equation" which calculates (in good agreement with the experiments of Alivisatos and Liphardt) the inter-particle separation in a gold nanosphere pair from its plasmon resonance shift, making it applicable to the determination of inter-site distances in biological systems. Universal size-scaling is valid also in the metal nanoshell structure, a nanosphere trimer, and pairs of elongated nanoparticles, thus making it a generalized fundamental model, which is useful in optimizing plasmon coupling for achieving tunable plasmon resonances, enhanced plasmonic sensitivities, and large SERS cross-sections. Ultrafast laser pump-probe studies of non-radiative electronic relaxation in coupled metal nanospheres in aggregates and in gold nanospheres conjugated to thiol SAMs are also reported. We also show that the relative contribution of scattering (radiative) to absorption (non-radiative) part of the plasmon relaxation, respectively useful in optical and photothermal applications, can be increased by increasing the nanostructure size.

La réponse optique de nanoparticules (NPs) de métaux nobles est dominée par une résonance géante diterésonance de plasmon de surface (RPS), très sensible à la taille, la morphologie et l’environnement diélectriquedes NPs. Elle est étudiée sur des NPs individuelles grâce à un dispositif de Spectroscopie à Modulation Spatiale(SMS) permettant d’accéder à leur section efficace d’extinction absolue sur un large domaine spectral (300-900nm) en corrélation avec leur morphologie observée indépendamment par microscopie électronique àtransmission (MET) ou à balayage (MEB).Mon travail de thèse a d’abord consisté à développer un nouveau dispositif afin de mesurer l’extinction et de ladiffusion d’un même nano-objet unique, donnant ainsi accès à des mesures quantitatives de la section efficace dediffusion moyennant une connaissance a priori du diagramme angulaire de répartition de la lumière diffusée.La seconde partie concerne des études optiques (expérimentales et théoriques) et structurales (MET ou MEB) denano-objets exotiques. Tout d’abord, une étude systématique réalisée sur un grand nombre de bipyramides d’orélaborées par voie chimique a montré que leur RPS, située dans le rouge, est extrêmement sensible à leurmorphologie et à leur environnement, ce qui en fait des candidats de choix pour des capteurs biologiques. Parailleurs, l‘émergence d’une RPS induite par couplage plasmonique a été mis en évidence sur des nano-antennesnanolithographiées à base de métaux de transition (Pd, Pt, Cr). Ces résultats ouvrent des perspectivesd’applications nouvelles en élargissant la plasmonique à des métaux aux propriétés chimiques très variées(photo-catalyse, magnéto-optique). / The optical response of noble metal nanoparticles (NPs) are known to be dominated by the Localized SurfacePlasmon Resonance (LSPR), which is highly sensitive to the size of the NPs, their shape and their environment.This optical response can be studied on single nanoparticles thanks to a highly sensitive setup based on theSpatial Modulation Spectroscopy (SMS) which gives access to their absolute extinction cross-section on a widespectral range (300–900 nm). Moreover, the morphology of the same objects studied in optics is characterized bya direct observation in Transmission or Scanning Electron Microscopy (TEM or SEM).In this work, a new setup allowing the measurement of both the extinction and the scattering of a single nanoobjecthas been developed. This technique allows a quantitative measurement of the scattering cross-sectionprovided the angular distribution of the scattered light by the NP is known.The second part is related to experimental and theoretical optical studies and morphological observationsthrough TEM and SEM of exotic nano-objects. First, a systematic study performed on a large number of goldbipyramids, chemically elaborated, has shown that the LSPR located in the red is highly sensitive to theirmorphology and to the environment. Thus, these objects can likely be used as biological sensors. In addition,emergence of a resonance induced by plasmon coupling has been evidenced on lithographed nano-antennasbased on transition metal (Pd, Pt, Cr) for which no LSPR is usually expected. This opens up prospects for novelapplications by extending the field of plasmonics to metals of various chemical properties (photocatalysis,magneto-optics).