Browsing by Subject "Plasmonics"
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Item Bio-inspired nanophotonics : manipulating light at the nanoscale with plasmonic metamaterials(2013-05) Zhao, Yang, active 21st century; Alù, AndreaMetals interact very differently with light than with radio waves and finite conductivities and losses often limit the way that RF concepts can be directly transferred to higher frequencies. Plasmonic materials are investigated here for various optical applications, since they can interact, confine and focus light at the nanoscale; however, regular plasmonic devices are severely limited by frequency dispersion and absorption, and confined signals cannot travel along plasmonic lines over few wavelengths. For these reasons, novel concepts and materials should be introduced to successfully manipulate and radiate light in the same flexible way we operate at lower frequencies. In line with these efforts, optical metamaterials exploit the resonant wave interaction of collections of plasmonic nanoparticles to produce anomalous light effects, beyond what naturally available in optical materials and in their basic constituents. Still, these concepts are currently limited by a variety of factors, such as: (a) technological challenges in realizing 3-D bulk composites with specific nano-structured patterns; (b) inherent sensitivity to disorder and losses in their realization; (c) not straightforward modeling of their interaction with nearby optical sources. In this study, we develop a novel paradigm to use single-element nanoantennas, and composite nanoantenna arrays forming two-dimensional metasurfaces and three-dimensional metamaterials, to control and manipulate light and its polarization at the nanoscale, which can possibly bypass the abovementioned limitations in terms of design procedure and experimental realization. The final design of some of the metamaterial concepts proposed in this work was inspired by biological species, whose complex structure can exhibit superior functionalities to detect, control and manipulate the polarization state of light for their orientation, signaling and defense. Inspired by these concepts, we theoretically investigate and design metasurfaces and metamaterial models with the help of fully vectorial numerical simulation tools, and we are able to outline the limitations and ultimate conditions under which the average optical surface impedance concept may accurately describe the complex wave interaction with planar plasmonic metasurfaces. We also experimentally explore various technological approaches compatible with these goals, such as the realization of lithographic single-element nanoantenna and nanoantenna arrays with complex circuit loads, periodic arrays of plasmonic nanoparticles or nanoapertures, and stacks of rotated plasmonic metasurfaces. At the conclusion of this effort, we have theoretically analyzed, designed and experimentally realized and characterized the feasibility of using discrete metasurfaces to realize phenomena and performance that are not available in natural materials, oftentimes inspired by the biological world.Item Broadly wavelength-tunable bandpass filters based on long-range surface plasmon-polaritons(2011-12) Lee, Jongwon; Belkin, Mikhail A.; Belkin, Mikhail A.; Alu, AndreaBroad spectral tunability is a desired feature of many photonic and plasmonic components, such as optical filters, semiconductor lasers, and plasmonic materials. Here I show that unique properties of long-range surface plasmon polaritons (LR SPP) allow one to produce optical components with very wide tuning range using small variations in the refractive index of the dielectric cladding material. As a proof-of-concept demonstration, I present operation of LR-SPP-based bandpass optical filters in which a 0.004 variation in the refractive index of the cladding dielectric translates into 210 nm of bandpass tuning at telecom wavelengths. The tuning mechanism proposed here may be used to create monolithic bandpass filters with tuning range spanning over more than an optical octave, compact and widely-tunable diode and quantum cascade laser systems, multi-spectral imagers, and other plasmonic components with broadly-tunable optical response.Item Designs of efficient plasmonic probe for near-field scanning optical microscopy(2012-05) Lee, Youngkyu; Alù, Andrea; Zhang, Xiaojing, Ph. D.We present a novel concept to design apertureless plasmonic probes for near-field scanning optical microscopy (NSOM) with enhanced optical power throughput and near-field confinement. Specifically, we combine unidirectional surface plasmon polariton (SPP) generation along the tip lateral walls with nanofocusing of SPPs through adiabatic propagation towards an apertureless tip. Three probe designs are introduced with different light coupling mechanisms. Optimal design parameters are obtained with 2D analysis and realistic probe geometries with patterned plasmonic surfaces are proposed using the optimized designs. The electromagnetic properties of the designed probes are characterized in the near-field and compared to those of a conventional single-aperture probe with same pyramidal shape. The optimized probes feature enhanced light localization in near-field of tip apex and improved optical throughput. Our ideas effectively combine the resolution of apertureless probes with throughput levels much larger than those available even in aperture-based devices.Item Enhanced solar absorption in thin film photovoltaic cells via embedded silica-coated silver nanoparticles(2015-12) Aminfard, Sam; Ben-Yakar, Adela; Harrison, Richard KThin-film photovoltaic cells are a promising technology that can harvest solar energy at a low cost. The main drawback of this technology is its low efficiency in comparison to conventional photovoltaics. This deficiency is due to poor absorption of long wavelengths in the solar spectrum. Plasmonic nanostructures can be tuned to resonantly interact with these wavelengths in order to enhance a solar cell’s absorption of these wavelengths and improve its efficiency. Historically, the two key factors limiting the success of plasmonically-enhanced photovoltaics have been parasitic absorption of light by the nanoparticle lost to heating, and recombination of charge carriers at the interface of the nanoparticle and the photovoltaic medium. Here we propose that these deficiencies can be overcome by employing nanospheres with a silver core and silica shell. Through experimentation supported by simulations, this thesis outlines how these plasmonic nanostructures can be applied to significantly improve the performance thin-film solar cells through experimentation supported by simulations. The plasmonic enhancement of photovoltaic devices can be studied and optimized computationally; however, highly uniform nanoparticles are necessary to validate these simulations.. The colloidal synthesis of plasmonic nanoparticles can achieve this at a low cost. We present several methods for the synthesis of silver nanoparticles with diameter of 5 to 50 nm and compare the monodispersity and yield of the colloids that they produce. These colloids are then adapted to synthesis processes enabling the formation of silica shells of 2 to 20 nm onto the silver cores. To facilitate the integration of silver-core, silica-shell nanoparticles into semiconductor thin films, we also develop procedures to deposit these nanoparticles onto silicon substrates with precisely-controlled inter-particle spacing. Finally, we experimentally integrate silver-core, silica shell nanoparticles into sub-micron layers of silicon. Absorption measurements reveal that integration of these nanoparticles can nearly double the amount of light absorbed by the silicon. The absorption spectra indicate the strong presence of interference effects within the thin films, which we account for in our simulations. We use the simulations to show how parasitic absorption by the nanoparticle only accounts for a small percentage of the absorption gains that we measure. Therefore, most of the optical absorption happens within the silicon, and would potentially improve the efficiency of a silicon solar cell.Item Fano-resonant plasmonic metamaterials and their applications(2012-08) Wu, Chihhui; Shvets, G.; Shih, Chih-Kang; Demkov, Alex; Li, Xiaoqin; Alu, AndreaManipulating electromagnetic fields with plasmonic nanostructures has attracted researchers from interdisciplinary areas and opened up a wide variety of applications. Despite the intriguing aspect of inducing unusual optical properties such as negative indices and indefinite permittivity and permeability, engineered plasmonic nanostructures are also capable of concentrating electromagnetic waves into a diffraction-unlimited volume, thus induce incredible light-matter interaction. In this dissertation, I’ll discuss about a class of plasmonic structures that exhibit the Fano resonance. The Fano resonance is in principle the interference between two resonant modes of distinct lifetimes. Through the Fano resonance, the electromagnetic energy can be trapped in the so called “dark” mode and induce strong local field enhancement. A variety of Fano resonant nanostructures ranging from periodic planar arrays to simple clusters composed of only two particles are demonstrated in this dissertation. By artificially designing the dimensions of the structures, these Fano-resonant materials can be operated over a broad frequency range (from visible to mid-IR) to target the specific applications of interest. In this dissertation, I’ll show the following research results obtained during my PhD study: (1) the double-continuum Fano resonant materials that can slow down the speed of light over a broad frequency range with little group velocity dispersion. (2) Ultra-sensitive detection and characterization of proteins using the strong light-matter interaction provided by the Fano-reonant asymmetric metamaterials. (3) Metamaterials absorbers with nearly 100 % absorbance, tunable spectral position, expandable bandwidth, and wide angle absorption. These Fano-resonant materials can have profound influences in the areas of optical signal processing, life science, bio-defense, energy harvesting and so on.Item Light manipulation through periodic plasmonic corrugations(2014-05) Lee, Youngkyu; Zhang, Xiaojing, Ph. D.Collective oscillations of free electrons localized in a small volume have drawn a lot of attention for the past decades. These so-called plasmons have special optical properties that can be used in many applications ranging from optical modulators to sensing of small quantities of molecules. Large numbers of extensive plasmonic applications are being based on the capability of light manipulation proposed by the periodic nanostructure and its optical response. By controlling over the way in which plasmonic modes interact with incident radiation, periodic corrugation opens up the possibility of developing new and exciting photonic devices. The goal of doctoral research presented herein is to investigate at a fundamental level of several corrugated metallic structures which may offer effective control of the optical response by coupling radiation to plasmonic modes. By controlling morphologies and material compositions, sophisticatedly engineered nanostructure may allow the coupling of electromagnetic waves into desired spectral/spatial modes in a way that an effective tuning of macroscopic optical properties in desired domain can be achieved. This dissertation is dedicated to answer the following question, if and how one can manipulate the optical responses by use of different nanostructures and various materials. Based on devised analytical models proposed for various corrugated nanostructures, we show that I. spatial and II. spectral manipulation of light can be realized. Specifically, we investigate how the grating array interacts with light. To understand those periodic nanostructures showing inherently dispersive nature, firstly the diffraction of light and accompanying effects are studied with the analytical models and numerical simulation. On this basis, we show the optical response is readily tunable, and efficiently controlled by the morphology and dielectric property of the corrugations. The outline of doctoral research is broadly categorized into (1) theoretical considerations on the topic of plasmonics, (2) specific insight in the analytical model of the various nanostructures, and (3) investigation of the plasmonic properties of the fabricated structures. Lastly, the discussion of outlook to possibilities and future experiments will close the dissertation.Item Localized surface plasmon resonance spectroscopy of gold and silver nanoparticles and plasmon enhanced fluorescence(2011-12) Vokac, Elizabeth Anne; Willets, Katherine A.; Brodbelt, Jennifer S.This thesis presents spectroscopic studies of metallic nanoparticle localized surface plasmons and plasmon enhanced fluorescence. We investigated the dielectric sensitivity of silver nanoprisms to an external electric field and gold nanorods to the formation of a self-assembled surface monolayer. Dark field microscopy was used to image plasmonic scattering from single nanoparticles, and a liquid crystal tunable filter was used to construct corresponding spectra. The plasmon resonances of silver nanoprisms displayed both reversible red shifts and irreversible blue shifts along with drastic intensity changes upon exposure to an applied bias. The plasmon resonances of gold nanorods showed sensitivity to the presence of alkanethiol molecules adhered to the particle surface by a moderate red shift. An increase in the effective external dielectric caused a shift toward longer wavelengths. We imaged plasmon enhanced fluorescence in order to optimize experimental parameters for a developing project that can characterize nanoparticle structure on sub-wavelength dimensions. Preliminary controls were performed to account for the effect of O₂ plasma treatment, solvent and alkanethiol monolayer formation on surface plasmon resonances. We found that O₂ plasma treatment for different time intervals did not result in a plasmon shift compared to untreated nanoparticles exposed to N₂; however when exposed to solvent the surface plasmons of the treated particles shifted five times as far toward the red. Interestingly, the solvent effect only resulted in a plasmon shift when the particles were N₂ dried after solvent incubation. Gold nanorods incubated in ethanol showed no wavelength maximum shift in pure solvent over time, but shifted moderately to the red after incubation in a solution of alkanethiol molecules. Conditions for the plasmon enhanced fluorescence study were optimized using a dye conjugate of the same alkanethiol molecule used previously by formation from solution in a monolayer on the gold nanorod surface. The appropriate synthesis for dye functionalization, molecular concentrations, solvents and optical settings were determined.Item Loss compensation in a plasmonic nanoparticle array(2013-05) Miller, Shannon Marie; Alú, AndreaThe problem of heavy material and radiative losses in plasmonic devices has held back their implementation for compact and high-speed data storage and interconnects. One of the most interesting solutions to this problem currently under exploration is the addition of a gain material in close proximity to the metallic nanostructures for loss compensation. Here the physics of light transport in a nanoparticle array, and the operation of gain media in contact with the structure, are described and analytically modeled. A two-dimensional array of closely spaced gold nanoparticles has been fabricated by focused ion beam milling, and its electromagnetic response in the presence or absence of a dye coating has been simulated in preparation for pump-probe optical testing. The compensation of losses via a fluorophore coating has been proven for the first time in this geometry, for a physically realized sample.Item Manipulating fluorescence dynamics in semiconductor quantum dots and metal nanostructures(2011-12) Ratchford, Daniel Cole; Li, Elaine; Chelikowsky, James; Florin, Ernst-Ludwid; Shvets, Gennady; Vanden Bout, DavidRecent scientific progress has resulted in the development of sophisticated hybrid nanostructures composed of semiconductor and metal nanoparticles. These hybrid structures promise to produce a new generation of nanoscale optoelectronic devices that combine the best attributes of each component material. The optical response of metal nanostructures is dominated by surface plasmon resonances which create large local electromagnetic field enhancements. When coupled to surrounding semiconductor components, the enhanced local fields result in strong absorption/emission, optical gain, and nonlinear effects. Although hybrid nanostructures are poised to be utilized in a variety of applications, serious hurdles for the design of new devices remain. These difficulties largely result from a poor understanding of how the structural components interact at the nanoscale. The interactions strongly depend on the exact composition and geometry of the structure, and therefore, a quantitative comparison between theory and experiment is often difficult to achieve. Colloidal semiconductor quantum dots are strong candidates for integration with metal nanostructures because they have a variety of desirable optical properties, such as tunable emission and long term photostability. However, one potential drawback of colloidal quantum dots is the intermittency in their fluorescence (commonly referred to as “blinking”). Blinking was first observed over a decade ago, yet there is still no complete theory to explain why it occurs. In spite of the lack of a full theoretical explanation, multiple methods have been used to reduce blinking behavior, including modifying quantum dot interfaces and coupling quantum dots with metal nanostructures. This thesis focuses on studying the coupling between colloidal quantum dots and metal nanoparticles in simple model systems. Atomic force microscopy nanomanipulation is used to assemble the hybrid structures with a controlled geometry. The experimental studies report for the first time the modified fluorescence decay, emission intensity, and blinking of a single quantum dot coupled to a single Au nanoparticle. Since the geometry of the structure is known, these studies provide reliable information on the interparticle coupling, and quantitative experimental results are shown to be consistent with classical electrodynamic theories.Item Mechanisms and applications of near-field and far-field enhancement using plasmonic nanoparticles(2012-12) Harrison, Richard K., 1982-; Ben-Yakar, AdelaThe resonant interaction of light with metal nanoparticles can result in extraordinary optical effects in both the near and far fields. Plasmonics, the study of this interaction, has the potential to enhance performance in a wide range of applications, including sensing, photovoltaics, photocatalysis, biomedical imaging, diagnostics, and treatment. However, the mechanisms of plasmonic enhancement often remain poorly understood, limiting the design and effectiveness of plasmonics for advanced applications. This dissertation focuses on evaluating the mechanisms of plasmonic enhancement and distinguishing between near and far field effects using simulations and experimental results. Thorough characterization of metal nanoparticle colloids shows that electromagnetic simulations can be used to accurately predict the optical response of nanoparticles only if the true shapes and size distributions are taken into account. By coupling these optical interaction calculations with heat transfer models, experimental limits for the maximum optical power before nanoparticle melting can be found. These limits are important for plasmonic multiphoton luminescence imaging applications. Subsequently, we demonstrate ultrafast laser plasmonic nanoablation of silicon substrates using gold nanorods to identify the near-field enhancement and mechanism of plasmon-assisted ablation. The experimentally observed shape of the ablation region and reduction of the ablation threshold are compared with simulations to show the importance of the enhanced electromagnetic fields in near-field nanoablation with plasmonic nanoparticles. The targeted use of plasmonic nanoparticles requires narrow size distribution colloids, because wide size distributions result in a blurring and weakening of the optical response. A new synthesis method is presented for the seeded-growth of nearly monodisperse metal nanoparticles ranging from 10 to 100 nm in diameter, both with and without dielectric shells of controlled thickness. This method is used to acquire fine control over the position and width of the plasmonic peak response. We also demonstrate self-assembled sub-monolayers of these particles with controllable concentrations, which is ideal for looking at plasmonic effects in surface and layered geometries. Finally, we present results for the spatial distribution of absorption around plasmonic nanoparticles. We introduce field-based definitions for distinguishing near-field and far-field regions and develop a new set of equations to determine the point-by-point enhanced absorption in a medium around a plasmonic nanoparticle. This set of equations is used to study plasmon-enhanced optical absorption for thin-film photovoltaic cells. Plasmonic nanoparticle systems are identified using simulations and proof-of-concept experiments are used to demonstrate the potential of this approach.Item Molecular beam epitaxial growth of rare-earth compounds for semimetal/semiconductor heterostructure optical devices(2012-05) Crook, Adam Michael; Bank, Seth Robert; Yu, Edward; Cheng, Julien; Zhang, John; Belkin, MikhailHeterostructures of materials with dramatically different properties are exciting for a variety of devices. In particular, the epitaxial integration of metals with semiconductors is promising for low-loss tunnel junctions, embedded Ohmic contacts, high-conductivity spreading layers, as well as optical devices based on the surface plasmons at metal/semiconductor interfaces. This thesis investigates the structural, electrical, and optical properties of compound (III-V) semiconductors employing rare-earth monopnictide (RE-V) nanostructures. Tunnel junctions employing RE-V nanoparticles are developed to enhance current optical devices, and the epitaxial incorporation of RE-V films is discussed for embedded electrical and plasmonic devices. Leveraging the favorable band alignments of RE-V materials in GaAs and GaSb semiconductors, nanoparticle-enhanced tunnel junctions are investigated for applications of wide-bandgap tunnel junctions and lightly-doped tunnel junctions in optical devices. Through optimization of the growth space, ErAs nanoparticle-enhanced GaAs tunnel junctions exhibit conductivity similar to the best reports on the material system. Additionally, GaSb-based tunnel junctions are developed with low p-type doping that could reduce optical loss in the cladding of a 4 μm laser by ~75%. These tunnel junctions have several advantages over competing approaches, including improved thermal stability, precise control over nanoparticle location, and incorporation of a manifold of states at the tunnel junction interface. Investigating the integration of RE-V nanostructures into optical devices revealed important details of the RE-V growth, allowing for quantum wells to be grown within 15nm of an ErAs nanoparticle layer with minimal degradation (i.e. 95% of the peak photoluminescence intensity). This investigation into the MBE growth of ErAs provides the foundation for enhancing optical devices with RE-V nanostructures. Additionally, the improved understanding of ErAs growth leads to development of a method to grow full films of RE-V embedded in III-V materials. The growth method overcomes the mismatch in rotational symmetry of RE-V and III-V materials by seeding film growth with epitaxial nanoparticles, and growing the film through a thin III-V spacer. The growth of RE-V films is promising for both embedded electrical devices as well as a potential path towards realization of plasmonic devices with epitaxially integrated metallic films.Item Nonlinear and wavelength-tunable plasmonic metasurfaces and devices(2014-12) Lee, Jongwon; Belkin, Mikhail A.Wavelength-tunable optical response from solid-state optoelectronic devices is a desired feature for a variety of applications such as spectroscopy, laser emission tuning, and telecommunications. Nonlinear optical response, on the other hand, has an important role in modern photonic functionalities, including efficient frequency conversions, all-optical signal processing, and ultrafast switching. This study presents the development of optical devices with wavelength tunable or nonlinear optical functionality based on plasmonic effects. For the first part of this study, widely wavelength tunable optical bandpass filters based on the unique properties of long-range surface plasmon polaritons (LR SPP) are presented. Planar metal stripe waveguides surrounded by two different cladding layers that have dissimilar refractive index dispersions were used to develop a wide wavelength tuning. The concept was demonstrated using a set of index-matching fluids and over 200nm of wavelength tuning was achieved with only 0.004 of index variation. For practical application of the proposed concept, a thermo-optic polymer was used to develop a widely tunable thermo-optic bandpass filter and over 220 nm of wavelength tuning was achieved with only 8 ºC of temperature variation. Another novel approach to produce a widely wavelength tunable optical response for free-space optical applications involves integrating plasmonic metasurfaces with quantum-electronic engineered semiconductor layers for giant electro-optic effect, which is proposed and experimentally demonstrated in the second part of this study. Coupling of surface plasmon modes formed by plasmonic nanoresonators with Stark tunable intersubband transitions in multi-quantum well structures induced by applying bias voltages through the semiconductor layer was used to develop tunable spectral responses in the mid-infrared range. Experimentally, over 310 nm of spectral peak tuning around 7 μm of wavelength with 10 ns response time was achieved. As the final part of this study, highly nonlinear metasurfaces based on coupling of electromagnetically engineered plasmonic nanoresonators with quantum-engineered intersubband nonlinearities are proposed and experimentally demonstrated. In the proof-of-concept demonstration, an effective nonlinear susceptibility over 50 nm/V was measured and, after further optimization, over 480 nm/V was measured for second harmonic generation under normal incidence. The proposed concept shows that it is possible to engineer virtually any element of the nonlinear susceptibility tensor of the nonlinear metasurface.Item Nonlinear, passive and active inclusions to tailor the wave interaction in metamaterials and metasurfaces(2013-08) Chen, Pai-Yen; Alú, AndreaMetamaterials have experienced a rapid growth of interest over the past few years and new capabilities are being explored to broaden the range of their unique electromagnetic properties for functional devices, including tunable, switchable, and nonlinear properties. In the future, there is the prospect of opening even more exciting applications with metamaterials, not yet imagined and thought not to be possible with currently available techniques. In my dissertation, I discuss several solutions for passive and active metamaterials and metasurfaces, with a particular focus on their potential applications, enabling a new class of metamaterials in the spectral range from radio frequencies (RF) and microwaves, terahertz (THz) to visible light. First, I demonstrate that by loading plasmonic nanoantennas with nonlinear nanoparticles, the nonlinear optical processes, such as multiple wave mixing, high harmonic generation, phase conjugation and optical bistability may be realized at the nanoscale, thanks to the strongly enhanced optical near fields accompanied with the plasmonic resonance. I present here the design, practical realization, and homogenization theory of nonlinear optical metamaterials and metasurfaces formed by optical nanoantenna arrays loaded with nonlinearities. As an extreme case of light manipulation at the "atomic" scale, I also study the collective oscillation of massless Dirac fermions inside grapheme monolayers, in which surface plasmon polaritons are controlled by electrostatic gating. I present how a graphene monolayer may serve as a building block and design paradigm for adaptable, switchable and frequency-configurable THz metamaterials and nanodevices, realizing various functionalities for cloaking, sensing, absorbing, switching, modulating, phasing, filtering, impedance transformation, photomixing and frequency synthesis in the THz spectrum. Last I present various metamaterial designs applied to invisibility cloaks based on the scattering cancellation mechanism enabled by plasmonic materials and passive/active metamaterials and metasurfaces. This cloaking technology may be used for camouflaging, enhancing the sensitivity and signal-to-noise ratio in RF wireless communication and sensor networks. In addition, electrically-small antennas based on the phase compensation effect offered by metamaterials with low or negative material properties are presented, with tailorable modal frequencies, bandwidth, and radiation properties.Item Optical properties and collective modes of plasmonic meta-surfaces(2012-12) Mousavi, Seyyed Hossein; Shvets, G.; Bengtson, Roger; Demkov, Alex; Fink, Manfred; Ling, HaoPlasmonics is an important branch of optics and photonics, focusing on the electromagnetic response of metals or other materials with free carriers. This field has recently experienced a significant expansion due to its importance for applications. Plasmonics has shown great promises in green energies, biosensing, nanolasers, and imaging. The main advantage of plasmonics stems from the existence of unique excitations, referred to as plasmons, representing collective response of the free carriers to the electromagnetic field. While plasmons, both in the bulk and on the surface of the metals, have been known for decades, the recent advances in nano fabrication and material sciences at nano scale have enabled versatile engineering of these modes. Focus of my dissertation is surface plasmons whose properties can be tailored by judiciously nano-patterning metal films and surfaces. Such patterned structures, referred to as metasurfaces, are the main tool to control and boost the light-matter interaction. Appropriately designed metasurfaces provide many-fold electromagnetic energy enhancement on the surface which can be used to amplify numerous surface effects such as SEIRA and nonlinear optical phenomena, facilitate spectroscopy, and enhance absorption of light. In this thesis, I report approaches to shape and engineer the confinement, mode profile, and lifetime of the surface modes. I also investigate how the dielectric environment affects the properties of the modes. The effect of the geometry and topology of the nano patterns on the optical response of metasurfaces is also studied. Finally I study how manipulating symmetries of metasurfaces can be used to tailor polarization state of light and lifetime of the modes using an ultrathin metasurface, instead of bulky traditional optical elements. %The symmetry manipulation results in the plasmonic analogue of Electromagnetically Induced Transparency, a well-known phenomenon in atomic physics. The work summarized in this thesis has brought marked advances in understanding the physics behind the collective surface waves in nano-structured metasurfaces. It paves new avenues for engineering structures with desirable properties. The immediate application of my findings is the compactification of optical elements, and envisioning next-generation plasmonic-based on-chip devices.Item Optical Properties of Plasmonic Zone Plate Lens, SERS-active Substrate and Infrared Dipole Antenna(2010-10-12) Kim, Hyun ChulNowadays plasmonics is rapidly developing areas from fundamental studies to more application driven research. This dissertation contains three different research topics on plasmonics. In the first research topic, by modulating the zone width of a plasmonic zone plate, we demonstrate that a beam focused by a proposed plasmonic zone plate lens can be achieved with higher intensity and smaller spot size than the diffraction-limited conventional zone plate lens. This sub-diffraction focusing capability is attributed to extraordinary optical transmission, which is explained by the complex propagation constant in the zone regions afforded by higher refractive index dielectric layer and surface plasmons. On the other hand, the resulted diffraction efficiency of this device is relatively low. By introducing a metal/dielectric multilayered zone plate, we present higher field enhancement at the focal point. This higher field enhancement originates not only from surface plasmon polaritons-assisted diffraction process along the propagation direction of the incident light (longitude mode), but also from multiple scattering and coupling of surface plasmons along the metal/dielectric interface (transverse mode). In the second research topic, we suggest a novel concept of SERS-active substrate applications. The surface-enhanced Raman scattering enhancement factor supported by gap surface plasmon polaritons is introduced. Due to higher effective refractive index induced by gap surface plasmon polaritons in the spacer region between two metal plates, incident light tends to localize itself mostly in the medium with higher refractive index than its adjacent ones and thereby the lights can confine with larger field enhancement. In the last research topic, we offer a simple structure in which a gold dipole antenna is formed on the SiC substrate. Surface phonon polaritons, counterparts of surface plasmon polaritons in the mid-infrared frequencies, are developed. Due to the synergistic action between the conventional dipole antenna coupling and the resonant excitation of surface phonon polaritons, strong field enhancement in the gap region of dipole antenna is attained. Most of research topics above are expected to find promising applications such as maskless nanolithography, high resolution scanning optical microscopy, optical data storage, optical antenna, SERS-active substrate, bio-molecular sensing and highly sensitive photo-detectors.Item Plasmonic laser nanosurgery(2011-08) Eversole, Daniel Steven; Ben-Yakar, AdelaPlasmonic Laser Nanosurgery (PLN) is a novel photodisruption technique that exploits the large enhancement of ultrafast laser pulses in the near-field of gold nanoparticles for the nanoscale manipulation of biological structures. Excitation of surface plasmons on spherical nanoparticles by pulsed irradiation provides a platform for the confinement of photoactivated processes, while functionalized nanoparticle targeting methods provide the highest level of therapeutic selectivity. In this dissertation, we demonstrate and characterize the in vitro plasmonic optoporation of MDA-MB-468 human epithelial breast cancer cells labeled with plasmonic gold nanoparticles using NIR, femtosecond laser pulses. Using a 10 kDa FITC-Dextran probe dye, we find that the PLN can optoporate nanoparticle-labeled cellular membranes at fluences down to just a few mJ/cm², providing a 50-fold reduction in pulse energy necessary to induce membrane dysfunction as compared with unlabeled cells. Limited membrane dysfunction was found to lead to transient optoporation of cells as a possible transfection method, while more extensive, non-recoverable membrane dysfunction lead to cellular death as a possible plasmonic treatment of malicious cells. In the first regime, we found a maximum optoporation efficiency of approximately 31% ± 5.4% with 2 to 2.5 mW laser light having 80 MHz repetition rate. In the second regime, we were able to necrotically kill greater than 90% of irradiated cells with as little as 5 mW average power. We found that particle aggregation along the cellular surface is crucial for the success of PLN. High particle loadings were required, suggesting that particle aggregates provide large enhancements, leading to reduced PLN threshold energies. We provide experimental evidence suggesting photodisruption with ultra-low energy pulses is directly dependent upon the emission of electrons from the particle surface, which seed the formation of free radicals in the surrounding water. These free radicals mediate membrane dysfunction by polyunsaturated lipid and protein peroxidation.Item Rare-earth monopnictide alloys for tunable, epitaxial metals(2013-08) Krivoy, Erica Michelle; Bank, Seth RobertA variety of benefits motivate the development of epitaxial metals, among which include the ability to design fully integrated layer structures where metallic films and nanostructures can be embedded into the cores of optoelectronic devices. Applications include high-performance tunnel-junctions, epitaxial transparent Ohmic contacts, photomixer material, and thermoelectrics. Additionally, the integration of metallic nanostructures and films into optoelectronic devices has shown potential for improving device performance and functionality through sub-wavelength confinement of plasmonic modes and enhancement of light/matter interactions. The rare-earth monopnictide (RE-V) material system can be integrated epitaxially with conventional zincblende III-V substrates under normal growth conditions, resulting in high-quality, thermodynamically stable interfaces. The RE-V semimetals span a range of optical, electrical, and structural properties, making them ideal for integration into III-V-based optoelectronic devices and applications. In this dissertation, high-quality epitaxial LuAs, LaAs and La(x)Lu(1-x)As films and nanostructures were grown and characterized for their structural, electrical, optical, and plasmonic properties. Through a sweep of alloy film compositions of the RE-V alloy material La(x)Lu(1-x)As, the ability to produce tunable epitaxial metals was demonstrated, with a range of peak transmission spectra from near- to mid-infrared wavelengths, plasmonic response in the mid-infrared, moderate resistivity, and lattice-matching potential to many relevant III-V substrates. Additionally, there is a great deal of interest in developing techniques to produce optoelectronic devices that are not restricted by substrate lattice constant. Many epitaxial approaches have been tried, with moderate success; however, growing low defect-density heteroepitaxial materials with differing crystal structures and highly-mismatched lattice parameters is extremely challenging, and such structures suffer from poor thermal properties and reliability issues. A general approach is needed for thin metamorphic buffer layers with minimal threading dislocations that simultaneously have low thermal resistance for effective heat-sinking and device reliability. An investigation was conducted into the use of RE-V nanostructure superlattices towards the reduction of dislocation density in highly-mismatched III-V systems.Item Tailoring nanoscale metallic heterostructures with novel quantum properties(2013-05) Sanders, Charlotte E.; Shih, Chih-Kang; Raizen, Mark G.Silver (Ag) is an ideal low-loss platform for plasmonic applications, but from a materials standpoint it presents challenges. Development of plasmonic devices based on Ag thin film has been hindered both by the dificulty of fabricating such film and by its fragility out of vacuum. Silver is non-wetting on semiconducting and insulating substrates, but on certain semiconductors and insulators can adopt a metastable atomically at epitaxial film morphology if it is deposited using the "two-step" growth method. This method consists of deposition at low temperature and annealing to room temperature. However, epitaxial Ag is metastable, and dewets out of vacuum. The mechanisms of dewetting in this system remain little understood. The fragility of Ag film presents a particular problem for the engineering of plasmonic devices, which are predicted to have important industrial applications if robust low-loss platforms can be developed. This dissertation presents two sets of experiments. In the first set, scanning probe techniques and low energy electron microscopy have been used to characterize Ag(111) growth and dewetting on two orientations of silicon (Si), Si(111) and Si(100). These studies reveal that multiple mechanisms contribute to Ag film dewetting. Film stability is observed to increase with thickness, and thickness to play a decisive role in determining dewetting processes. A method has been developed to cap Ag film with germanium (Ge) to stabilize it against dewetting. The second set of experiments consists of optical studies that focus on the plasmonic properties of epitaxial Ag film. Because of the problems posed until now by epitaxial Ag growth and stabilization, research and development in the area of plasmonics has been limited to devices based on rough, thermally evaporated Ag film, which is robust and simple to produce. However, plasmonic damping in such film is higher than in epitaxial film. The optical studies presented here establish that Ag film can now be stabilized sufficiently to allow optical probing and device applications out of vacuum. Furthermore, they demonstrate the superiority of epitaxial Ag film relative to thermally evaporated film as a low-loss platform for plasmonic devices spanning the visible and infrared regimes.