Plasmonic Devices Employing Extreme Light Concentration

The development of integrated electronic and photonic circuits has led to remarkable data processing and transport capabilities that permeate almost every facet of our daily lives. Scaling these devices to smaller and smaller dimensions has enabled faster, more power efficient and inexpensive components but has also brought about a myriad of new challenges. One very important challenge is the growing size mismatch between electronic and photonic components. To overcome this challenge, we will need to develop radically new device technologies that can facilitate information transport between nanoscale components at optical frequencies and form a bridge between the world of nano-electronic and micro-photonics. Plasmonics is an exciting new field of science and technology that aims to exploit the unique optical properties of metallic nanostructures to gain a new level of control over light-matter interactions. The use of nanometallic (plasmonic) structures may help bridge the size gap between the two technologies and enable an increased synergy between chip-scale electronics and photonics. In the first part of this dissertation we analyze the performance of a surface plasmon-polariton all-optical switch that combines the unique physical properties of small molecules and metallic (plasmonic) nanostructures. The switch consists of a pair of gratings defined on an aluminum film coated with a thin layer of photochromic (PC) molecules. The first grating couples a signal beam consisting of free space photons to SPPs that interact effectively with the PC molecules. These molecules can reversibly be switched between transparent and absorbing states using a free space optical pump. In the transparent (signal "on") state, the SPPs freely propagate through the molecular layer, and in the absorbing (signal "off") state, the SPPs are strongly attenuated. The second grating serves to decouple the SPPs back into a free space optical beam, enabling measurement of the modulated signal with a far-field detector. We confirm and quantify the switching behavior of the PC molecules by using a surface plasmon resonance spectroscopy. The quantitative experimental and theoretical analysis of the nonvolatile switching behavior guides the design of future nanoscale optically or electrically pumped optical switches. In the second part of the dissertation we provide a critical assessment of the opportunities for use of plasmonic nanostructures in thin film solar cell technology. Thin-film solar cells have attracted significant attention as they provide a viable pathway towards reduced materials and processing costs. Unfortunately, the materials quality and resulting energy conversion efficiencies of such cells is still limiting their rapid large-scale implementation. The low efficiencies are a direct result of the large mismatch between electronic and photonic length scales in these devices; the absorption depth of light in popular PV semiconductors tends to be longer than the electronic (minority carrier) diffusion length in deposited thin-film materials. As a result, charge extraction from optically thick cells is challenging due to carrier recombination in the bulk of the semiconductor. We discuss how light absorption could be improved in ultra-thin layers of active material making use of large scattering cross sections of plasmonic structures. We present a combined computational-experimental study aimed at optimizing plasmon-enhanced absorption using periodic and non-periodic metal nanostructure arrays.

The title of this book, Plasmonics: Principles and Applications, encompasses theory, technical issues, and practical applications which are of interest for diverse classes of the plasmonics. The book is a collection of the contemporary researches and developments in the area of plasmonics technology. It consists of 21 chapters that focus on interesting topics of modeling and computational methods, plasmonic structures for light transmission, focusing, and guiding, emerging concepts, and applications.

The Finite Difference Time Domain (FDTD) method is an essential tool in modeling inhomogeneous, anisotropic, and dispersive media with random, multilayered, and periodic fundamental (or device) nanostructures due to its features of extreme flexibility and easy implementation. It has led to many new discoveries concerning guided modes in nanoplasmonic waveguides and continues to attract attention from researchers across the globe. Written in a manner that is easily digestible to beginners and useful to seasoned professionals, Computational Nanotechnology Using Finite Difference Time Domain describes the key concepts of the computational FDTD method used in nanotechnology. The book discusses the newest and most popular computational nanotechnologies using the FDTD method, considering their primary benefits. It also predicts future applications of nanotechnology in technical industry by examining the results of interdisciplinary research conducted by world-renowned experts. Complete with case studies, examples, supportive appendices, and FDTD codes accessible via a companion website, Computational Nanotechnology Using Finite Difference Time Domain not only delivers a practical introduction to the use of FDTD in nanotechnology but also serves as a valuable reference for academia and professionals working in the fields of physics, chemistry, biology, medicine, material science, quantum science, electrical and electronic engineering, electromagnetics, photonics, optical science, computer science, mechanical engineering, chemical engineering, and aerospace engineering.

The search for cleaner, cheaper, smaller and more efficient energy technologies has to a large extent been motivated by the development of new materials. The aim of this collection of articles is therefore to focus on what materials-based solutions can offer and show how the rationale design and improvement of their physical and chemical properties can lead to energy-production alternatives that have the potential to compete with existing technologies. In terms of alternative means to generate electricity that utilize renewable energy sources, the most dramatic breakthroughs for both mobile (i.e., transportation) and stationary applications are taking place in the fields of solar and fuel cells. And from an energy-storage perspective, exciting developments can be seen emerging from the fields of rechargeable batteries and hydrogen storage.

Nanophotonics is a newly developing and exciting field, with two main areas of interest: imaging/computer vision and data transport. The technologies developed in the field of nanophotonics have far reaching implications with a wide range of potential applications from faster computing power to medical applications, and "smart" eyeglasses to national security. Integrated Nanophotonic Devices explores one of the key technologies emerging within nanophotonics: that of nano-integrated photonic modulation devices and sensors. The authors introduce the scientific principles of these devices and provide a practical, applications-based approach to recent developments in the design, fabrication and experimentation of integrated photonic modulation circuits. For this second edition, all chapters have been expanded and updated to reflect this rapidly advancing field, and an entirely new chapter has been added to cover liquid crystals integrated with nanostructures. Unlocks the technologies that will turn the rapidly growing research area of nanophotonics into a major area of commercial development, with applications in telecommunications, computing, security, and sensing Nano-integrated photonic modulation devices and sensors are the components that will see nanophotonics moving out of the lab into a new generation of products and services By covering the scientific fundamentals alongside technological applications, the authors open up this important multidisciplinary subject to readers from a range of scientific backgrounds

Intrinsically conducting polymers forms a category of doped conjugated polymers that can conduct electricity. Since their discovery in the late 1970s, they have been widely applied in many fields, ranging from optoelectronic devices to biosensors. The most common type of conducting polymers is poly(3,4-ethylenedioxythiophene), or PEDOT. PEDOT has been popularly used as electrodes for solar cells or light-emitting diodes, as channels for organic electrochemical transistors, and as p-type legs for organic thermoelectric generators. Although many studies have been dedicated to PEDOT-based materials, there has been a lack of a unified model to describe their optical properties across different spectral ranges. In addition, the interesting optical properties of PEDOT-based materials, benefiting from its semi-metallic character, have only been rarely studied and utilized, and could potentially enable new applications. Plasmonics is a research field focusing on interactions between light and metals, such as the noble metals (gold and silver). It has enabled various opportunities in fundamental photonics as well as practical applications, varying from biosensors to colour displays. This thesis explores highly conducting polymers as alternatives to noble metals and as a new type of active plasmonic materials. Despite high degrees of microstructural disorder, conducting polymers can possess electrical conductivity approaching that of poor metals, with particularly high conductivity for PEDOT deposited via vapour phase polymerization (VPP). In this thesis, we systematically studied the optical and structural properties of VPP PEDOT thin films and their nanostructures for plasmonics and other optical applications. We employed ultra-wide spectral range ellipsometry to characterize thin VPP PEDOT films and proposed an anisotropic Drude-Lorentz model to describe their optical conductivity, covering the ultraviolet, visible, infrared, and terahertz ranges. Based on this model, PEDOT doped with tosylate (PEDOT:Tos) presented negative real permittivity in the near infrared range. While this indicated optical metallic character, the material also showed comparably large imaginary permittivity and associated losses. To better understand the VPP process, we carefully examined films with a collection of microstructural and spectroscopic characterization methods and found a vertical layer stratification in these polymer films. We unveiled the cause as related to unbalanced transport of polymerization precursors. By selection of suitable counterions, e.g., trifluoromethane sulfonate (OTf), and optimization of reaction conditions, we were able to obtain PEDOT films with electrical conductivity exceeding 5000 S/cm. In the near infrared range from 1 to 5 µm, these PEDOT:OTf films provided a well-defined plasmonic regime, characterized by negative real permittivity and lower magnitude imaginary component. Using a colloidal lithography-based approach, we managed to fabricate nanodisks of PEDOT:OTf and showed that they exhibited clear plasmonic absorption features. The experimental results matched theoretical calculations and numerical simulations. Benefiting from their mixed ionic-electronic conducting characters, such organic plasmonic materials possess redox-tunable properties that make them promising as tuneable optical nanoantennas for spatiotemporally dynamic systems. Finally, we presented a low-cost and efficient method to create structural colour surfaces and images based on UV-treated PEDOT films on metallic mirrors. The concept generates beautiful and vivid colours through-out the visible range utilizing a synergistic effect of simultaneously modulating polymer absorption and film thickness. The simplicity of the device structure, facile fabrication process, and tunability make this proof-of-concept device a potential candidate for future low-cost backlight-free displays and labels.

Optofluidic devices are of high scientific and industrial interest in chemistry, biology, material science, pharmacy, and medicine. In recent years, they have experienced strong development because of impressive achievements in the synergistic combination of photonics and micro/nanofluidics. Sensing and/or lasing platforms showing unprecedented sensitivities in extremely small analyte volumes, and allowing real-time analysis within a lab-on-a-chip approach, have been developed. They are based on the interaction of fluids with evanescent waves induced at the surface of metallic or photonic structures, on the implementation of microcavities to induce optical resonances in the fluid medium, or on other interactions of the microfluidic systems with light. In this context, a large variety of optofluidic devices has emerged, covering topics such as cell manipulation, microfabrication, water purification, energy production, catalytic reactions, microparticle sorting, micro-imaging, or bio-sensing. Moreover, the integration of these optofluidic devices in larger electro-optic platforms represents a highly valuable improvement towards advanced applications, such as those based on surface plasmon resonances that are already on the market. In this Special Issue, we invited the scientific community working in this rapidly evolving field to publish recent research and/or review papers on these optofluidic devices and their applications.