529 research outputs found
Mark Stockman, the knight of plasmonics
No full textMark Stockman, one of the founding members and pioneers of plasmonics and nanophotonics, passed away at the age of 73 on 11 November 2020 in Atlanta, Georgia, USA. Always at the front row of the conference hall, nodding in agreement or shaking his head in disapproval, Mark will be remembered not only for his breakthrough studies, but also for his passion for science and the uncompromising standards in research that he applied to himself and others. At every conferencesession, the speakers would be nervously waiting, with the audience, for Mark’s insightful questions
Alternative Plasmonic Materials:Beyond Gold and Silver (Adv. Mater. 24/2013)Inside Front Cover
Get PDFBeyond Silver and Gold: Better material buildingblocks are essential in transforming the novel ideas of plasmonics and metamaterials into technologies of the future, as reviewed by Alexandra Boltasseva and co-workers on page 3264. Devices built from tailored materials offer improved performance and new functionalities with applications in sensing, imaging, data storage, novel light sources, energy conversion, quantum optics and others. The cover image depicts a negatively refracting metamaterial device built from novel materials. Image prepared with the help of Dr. Alexander V. Kildishev
Transparent Conducting Oxides for Epsilon-Near-Zero Nanophotonics
No full textEpsilon-near-zero materials are an emerging class of nanophotonic materials which engender electromagnetic field enhancement and small phase variation due to their approximate zero permittivity. These quasi-static fields facilitate a number of unique optical properties such as supercoupling, subwavelength confinement, and enhanced light-matter interactions, which has made epsilon-near-zero media a rapidly expanding field of optical physics. Contemporary methods of realizing a system with zero permittivity rely on microwave cavities/waveguides or complex metal-dielectric metamaterials; however, both techniques require advanced fabrication and their operational wavelength is fixed relative to their geometric and optical parameters. It remains an open and substantial challenge to realize an epsilon-near-zero material at pertinent wavelengths, particularly near- and mid-infrared, with tunable/dynamic properties. The focus of this thesis is the exploration of transparent conducting oxides for the development of epsilon-near-zero nanophotonic phenomena and applications. Transparent conducting oxides have an inherent low permittivity, in addition to simple fabrication and tunable optical properties, making them exceptionally promising. Application of transparent conducting oxide films for highly confined modes, nonlinear/ultrafast optics, and strongly coupled systems are discussed
Engineering the Optical Properties and Temporal Responses of Conducting Oxides and Nitrides for Optically Switchable Metasurfaces
No full textMy dissertation involves the development and characterization of conducting oxides and nitrides and their application in tunable nanophotonics. Tunable nanophotonic devices are those with switchable optical properties. When an external stimulus is applied, the optical response of these devices changes. There are a wide variety of stimuli utilized in optical switching, encompassing electrical, optical, thermal, and mechanical impulses. The optical response controlled can be amplitude, polarization, or phase. In my work, I focused on an optical pulse as the stimulus, and amplitude modulation as the response.Optically induced permittivity change is one of the fastest methods of changing the permittivity of a material and has potential use in optical transistors, beam steering, and especially in photonic time-crystal design. In the first chapter, I investigated how much the optical properties of an emerging conducting oxide, cadmium oxide, can be influenced by using yttrium as a dopant. I also investigated the dominant recombination mechanisms in the doped oxide via pump-probe spectroscopy.In the second section, I investigated the transient permittivities of zinc oxide with a singlepump, broadband probe measurement technique. Designing fast, dynamic metasurfaces generally requires the optical properties of a medium in the photoexcited state. However, a detailed characterization of almost any oxide in its excited state is rare in literature. Most of the previously reported optical characterizations only deal with transient reflectance or transmittance measurements. The few that report the transient permittivity, are limited to a wavelength regime near the epsilon-near-zero (ENZ) point of the materials. Working with undoped zinc oxide, I determined the limits of permittivity modulation with optical pumping. The transient permittivities were used to design and experimentally demonstrate a metasurface for amplitude modulation at specific wavelengths.In the third section, I report one of the first demonstrations of switching time-control in a dynamic metasurface. Different materials have different relaxation dynamics, dictating their response times. What happens when an optical switch is made with two materials with distinctly different dynamics? Using titanium nitride, a material with a nanosecond response time, and aluminum doped zinc oxide, a material with a picosecond response time, I designed a bilayer absorber. The absorber has distinct resonances near the epsilon near zero wavelengths of the individual components. When probed near the resonances, the same absorber shows distinctly different switching speeds. This demonstrates that the same switch can have different speeds depending on the probe wavelength.The techniques developed and the findings from this dissertation work will help better characterize conducting oxides and nitrides, as well as other materials to better design optically switchable devices, and to better characterize the transient optical properties of tunable materials
A Platform for Practical Nanophotonic Systems Nitrides and Oxides for Integrated Optical Devices
No full textThe fields of nanophotonics and metamaterials have revolutionized the way we think of optical space (ϵ,µ), enabling us to engineer the refractive index almost at will, to confine light to the smallest of volumes, as well as to manipulate optical signals with extremely small foot prints and energy requirements. Throughout the past, this field of research has largely been limited to the use of noble metals as plasmonic materials, largely due to the high conductivity (low loss) and wide availability in research institutions. However, the research which follows focuses on the development of two alternative material platforms for nanophotonics: namely the transition metal nitrides and the transparent conducting oxides. Through this research, we have explored the nonlinear optical properties of thin films, demonstrating unique and ultrafast dynamic response, and have designed and realized high performance integrated plasmonic devices. Ultimately, this work aims to demonstrate the impact and potential of alternative plasmonic materials for numerous nanophotonic applications
Making Better Use of Light: Addressing Optical Challenges With Metasurfaces
No full textThe capability of light goes well beyond illumination, yet it is so underused in our lives because the control of light still largely relies on clumsy bulk lenses. Less than 10 years ago, a type of revolutionary devices made of nanometer scale optical elements – metasurfaces – was invented to control the light propagation and its energy dissipation with arbitrary degree of freedom, at unprecedentedly small volumes (although some would argue that the advent of metasurfaces came in the 1990s). Vast diversity of new discoveries has since been made possible, and many more existing applications have seen significant performance enhancement with the aid of metasurfaces.In the scope of this work, I explore the use of a variety of metasurfaces to address several existing real-world challenges: sensing, optical heating, and data storage. Among these, three metasurfaces involve the world’s first two-dimensional material, graphene. I first investigate the graphene plasmonic resonator, which have been shown to be extremely sensitive single-molecule sensors. Graphene also has many intriguing properties in photodetection applications, such as lightweight, ultra-wide detection band, and ultrafast response speed. I have used two different metasurfaces to enhance the intrinsically low responsivity (sensitivity) of graphene photodetectors. Amidst the discussion of graphene photodetectors, I show the characterization result of plasmonic heating of metasurfaces, an essential process of the graphene photo-responsivity enhancement. Lastly, I present a multi-functional metasurface which can be used in optical steganography, encryption, and data storage. The proposed metasurface is compatible with large scale parallel readout, which outperforms current Blu-ray technology in both storage capacity and readout spee
New materials and devices for plasmonics and metamaterial applications
No full textPlasmonics and the recent birth of metamaterials and transformation optics are currently driving the development of a family of novel devices with unprecedented functionalities ranging from subwavelength plasmonic waveguides and optical nanoresonators to superlenses, hyperlenses and light concentrators. However, these devices operating in the optical range suffer from poor performance due to limitations arising from their constituent plasmonic materials. The problems with conventional metals include large losses, very large magnitude of real permittivity, lack of tunability, fabrication and integration issues. On the other hand, alternative plasmonic materials can not only overcome many of these bottlenecks but also, open up possibilities for new devices. This research focuses on oxides- and nitrides-based ceramic materials which can be metal substitutes in the near-IR and visible ranges. Devices such as hyperbolic metamaterials, plasmonic waveguides and resonators, and epsilon-near-zero devices are demonstrated with alternative plasmonic materials
Plasmonic devices based on transparent conducting oxides for near infrared applications
Get PDFIn the past decade, there have been many breakthroughs in the field of plasmonics and nanophotonics that have enabled optical devices with unprecedented functionalities. Even though remarkable demonstration of at photonic devices has been reported, constituent materials are limited to the noble metals such as gold (Au) and silver (Ag) due to their abundance of free electrons which enable the support of plasmon resonances in the visible range. With the strong demand for extension of the optical range of plasmonic applications, it is now a necessity to explore and develop alternative materials which can overcome intrinsic issues of noble metals such as integration challenges, considerable optical losses, and lack of tunability of their optical properties. As most promising alternative to noble metals, transparent conducting oxides (TCOs) have been proposed as a promising new class of plasmonic materials for the IR applications. The main objective of the thesis is to explore the various plasmonic devices based on TCOs in order to evaluate the capabilities of TCOs as alternative metallic component for plasmonic applications. By beginning with a discussion of the general (optical, electrical and morphological) properties of TCOs, we describe the demonstration of devices such as plasmonic resonator for bio-sensing and waveplate metasurfaces. In addition, we study the impact of TCOs to local antenna as epsilon-near-zero (ENZ) substrate. The technological importance of the IR range is apparent and growing, and as plasmonics develops a niche at these frequencies, I believe this study represents a scientific directive toward the quest to bring plasmonics into the IR
Plasmonics for Nanotechnology: Energy Harvesting and Memory Devices
No full textMy dissertation research is in the field of plasmonics. Specifically, my focus is on the use of plasmonics for various applications such as solar energy harvesting and optically addressable magnetic memory devices. Plasmonics is the study of collective oscillations of free electrons in a metal coupled to an electromagnetic field. Such oscillations are characterized by large electromagnetic field intensities confined in nanoscale volumes and are called plasmons. Plasmons can be excited on a thin metal film, in which case they are called surface plasmon polaritons or in nanoscale metallic particles, in which case they are called localized surface plasmon resonances. Researchers have taken advantage of this electromagnetic field enhancement resulting from the excitation of plasmons in metallic structures and demonstrated phenomenon such as plasmon-assisted photocatalysis, plasmon-induced local heating, plasmonenhanced chemical sensing, optical modulators, nanolasers, etc.In the first half of my dissertation, I study the role of plasmonics in hydrogen production from water using solar energy. Hydrogen is believed to be a very viable source of alternative green fuel to meet the growing energy demands of the world. There are significant efforts in government and private sectors worldwide to implement hydrogen fuel cells as the future of the automotive and transportation industry. In this regard, water splitting using solar energy to produce hydrogen is a widely researched topic. It is believed that a Solar-to-Hydrogen (STH) conversion efficiency of 10% is good enough to be considered for practical applications. Iron oxide (α-Fe2O3) or hematite is one of the candidate materials for hydrogen generation by water splitting with a theoretical STH efficiency of about 15%. In this work, I experimentally show that through metallic gold nanostructures we can enhance the water oxidation photocurrent in hematite by two times for above bandgap wavelengths, thereby increasing hydrogen production. Moreover, I also show that gold nanostructures can result in a hematite photocurrent enhancement of six times for below bandgap wavelengths. The latter, I believe, is due to the excitation of plasmons in the gold nanostructures and their subsequent decay into hot holes which are harvested by hematite.The second part of my dissertation involves data storage in magnetic media. Memory devices based on magnetic media have been widely investigated as a compact information storage platform with bit densities exceeding 1Tb/in2. As the size of nanomagnets continue to reduce to achieve higher bit densities, the magnetic fields required to write information in these bits increases. To counter this, the field of heat-assisted magnetic recording (HAMR) was developed where a laser is used to locally heat up a magnet and make it susceptible to smaller magnetic switching fields. About two decades ago, it was realized that a single femtosecond laser pulse can switch magnetic media and therefore could be used to write information in magnetic bits. This field is now known as All-Optical Magnetic Switching (AOMS). My research aims to bring together the two fields of HAMR and AOMS to create optically addressable nanomagnets for information storage. Specifically, I want to show that plasmonic resonators can couple the laser field to nanomagnets more efficiently. This can therefore be used not only to heat the nanomagnets but also switch them with lower optical energy compared to free-standing nanomagnets without any plasmonic resonator. The results of my research show that by coupling metallic resonators, supporting surface plasmons, to nanomagnets, one can reduce the light intensity required for laser induced magnetization reversal
Novel techniques for quasi three-dimensional nanofabrication of Transformation Optics devices
Get PDFCurrent nanofabrication is almost exclusively limited to top-down, two-dimensional techniques. As technology moves more deeply into the nano-scale regime, fabrication of new devices with quasi three-dimensional geometries shows great potential. One excellent example of an emerging field that requires this type of non-conformal 3D fabrication technique is the field of Transformation Optics. This field involves transforming and manipulating the optical space through which light propagates. Arbitrarily manipulating the optical space requires advanced fabrication techniques, which are not possible with current two-dimensional fabrication technologies. One step toward quasi three-dimensional nanofabrication involves employing angled deposition allowing new growth mechanisms, and enabling a new realm of quasi three-dimensional fabrication. Transformation optics also has potential for having a huge impact on one of the most fundamental and impactful aspects of optics - the capability of fully controlling and manipulating the phase of light. For this purpose, dielectric metamaterial arrays can be fabricated, altering the phase of light transmitted through the structures, while maintaining a high transmittance (low reflection). By fabricating these structures with a high-index material (such as silicon), a large gradient in phase can be implemented by adjusting the material\u27s effective filling fraction. Using these dielectric metamaterial arrays, anomalous refraction and focusing is demonstrated in films with thicknesses less than one wavelength
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