Plasmonically active materials have the unique ability to use photons to drive a collective multi-electronic oscillatory response. On the nanoscale, this plasmon response gives rise to absorption features previously unseen in bulk materials. This brilliant optical effect has been seen for centuries; suspensions of metallic nanocrystals have been used as a way to achieve beautiful coloration in glassware and art. The nature of this phenomena has only recently been explained in the last century, however, the physics behind the relaxation of electrons driven by this response, and how to exploit them, still desire elucidation. Here, the energetic pathways of electronic absorption and relaxation in plasmonically-active doped semiconductor nanocrystals are studied using spectroscopic and computational methods. We explore the material-dependent properties of the localized surface plasmon resonance in doped metal-oxide nanoparticles, and how to optimize a material for a desired effect. We find that compared to their metallic counterparts, metal oxide nanoparticles have the unique ability to absorb near-infrared light while elevating their electrons to exceedingly high energies. The intense changes in electronic temperatures result in various optical and thermal changes necessary for applications such as electron transfer, biological phototherapies, and optical switching. Next, observable variations to the material’s extinction profile driven by plasmon excitation, whether absorption or reflectivity, are detected using ultrafast spectroscopic methods. The changes are due to alterations in the nanocrystal’s dielectric function due to heating of its electronic and lattice temperatures. We are able to successfully model the ultrafast response of these materials by determining several material constants, that allows us to predict how different materials will behave under plasmon excitation. Lastly, utilization of these plasmonically-active charge carriers for photocatalytic processes is explored. Knowledge of the physics behind how plasmonically-driven electrons respond to photoexcitation allows us to confidently move forward complexing these semiconductors with organic molecules with the goal of directing electron and/or hole transfer with low-energy photons. We find there is much to explore in this area, as the preliminary data suggests plasmonically-enhanced multiphoton absorption by organic semiconductors. The fundamentals of plasmon resonances in semiconductor nanoparticles is vast, yet current research, including this work, suggests their future as a photoactive material is bright

This book highlights the theoretical foundations of and experimental techniques in photothermal heating and applications involving nanoscale heat generation using gold nanostructures embedded in various media. The experimental techniques presented involve a combination of nanothermometers doped with rare-earth atoms, plasmonic heaters and near-field microscopy. The theoretical foundations are based on the Maxwell’s and heat diffusion equations. In particular, the working principle and application of AlGaN:Er3+ film, Er2O3 nanoparticles and β-NaYF4:Yb3+,Er3+ nanocrystals for nanothermometry based on Er3+ emission are discussed. The relationship between superheated liquid and bubble formation for optically excited nanostructures and the effects of the surrounding medium and solution properties on light absorption and scattering are presented. The application of Er2O3 and β-NaYF4:Yb3+,Er3+ nanocrystals to study the temperature of optically heated gold nanoparticles is also presented. In closing, the book presents a new thermal imaging technique combining near-field microscopy and Er3+ photoluminescence spectroscopy to monitor the photothermal heating and steady-state sub-diffraction local temperature of optically excited gold nanostructures.

Abstract Optical Characterization of Localized Surface Plasmon Resonances in Doped Metal Oxide Nanocrystals by Robert Walker Johns Doctor of Philosophy in Chemistry University of California, Berkeley Professor Tanja Cuk, Co-Chair Professor Delia Milliron, Co-Chair Electronically doped metal oxide nanocrystals exhibit tunable infrared localized surface plasmon resonances (LSPRs). Semiconductors provide an alternative dielectric environment than metallically bonded solids, such as noble metals, for metallic behavior. The ways in which the electronic structure of the semiconductor and of the dopants used to make them metallic hybridize substantially changes the plasmonic behavior. Choice of dopant element, dopant placement within the nanocrystal, and dopant interaction with other defects in the lattice all lead to changes in the observed optical properties of these nanocrystals. Here, the methods for optical characterization of LSPRs in doped metal oxides are discussed with particular attention directed at how undetermined heterogeneous contributions to ensemble measurements lead to misattributing inhomogenous broadening to poor plasmonic performance. Electronic damping in these materials is incredibly low compared to coinage metals, and they tout the added benefit of spectral tuning through chemical composition rather than morphology. The result is a class of materials that can both have their optical response tuned separately from other application relevant factors like nanocrystal size, and yield high performance LSPR for directing far-field radiation to the near-field. Learning that doped metal oxides have high quality factor LSPR was found through the first single nanocrystal measurements of LSPR made in the mid-IR through the use of near-field optics to interrogate these nanocrystals separately. The result was uncovering substantial nanocrystal-to-nanocrystal variation within batches of nanocrystals making ensemble measurements appear to have broad LSPR, while in fact these materials have high quality factors individually. These measurements were enabled by broadband synchrotron based scattering type- scanning near field optical microscopy (s-SNOM). Broadband s-SNOM in the IR can yield the single nanocrystal optical spectrum and dielectric function of an isolated signal nanocrystal when the proper considerations are made to backgrounding signal over such a wide spectral range. The methodology as well as new understanding of the materials learned through this instrumentation advance are outlined. Finally, the lessons learned about the properties of LSPR in doped metal oxides from single nanocrystal measurements are extended to an adaptation of applying Mie theory to the nanocrystal dielectric function in order to assign reasonable dielectric constants to nanocrystals even from ensemble optical measurements over any energy range, not just those obtained from mid-IR s-SNOM. Further, these advances in assigning optical density to an ensembles of doped metal oxide nanocrystals are applied to understanding how energy relaxation out of the LSPRs occurs in these materials through the use of the two-temperature model, using constants obtained from NIR ultrafast transient absorption measurements. The low free carrier concentrations of metal oxide nanocrystals lead to less efficient heat generation as compared to metallic nanocrystals such as Ag. This suggests that metal oxide nanocrystals may be ideal for applications wherein untoward heat generation may disrupt the application’s overall performance, such as solar energy conversion and photonic gating.

Metal-semiconductor nanostructures represent an important new class of materials employed in designing advanced optoelectronic and nanophotonic devices, such as plasmonic nanolasers, plasmon-enhanced light-emitting diodes and solar cells, plasmonic emitters of single photons, and quantum devices operating in infrared and terahertz domains. The combination of surface plasmon resonances in conducting structures, providing strong concentration of an electromagnetic optical field nearby, with sharp optical resonances in semiconductors, which are highly sensitive to external electromagnetic fields, creates a platform to control light on the nanoscale. The design of the composite metal-semiconductor system imposes the consideration of both the plasmonic resonances in metal and the optical transitions in semiconductors - a key issue being their resonant interaction providing a coupling regime. In this book the reader will find descriptions of electrodynamics of conducting structures, quantum physics of semiconductor nanostructures, and guidelines for advanced engineering of metal-semiconductor composites. These constituents form together the physical basics of the metal-semiconductor plasmonics, underlying many effective practical applications. The list of covered topics also includes the review of recent results, such as the achievement of a strong coupling regime, and the preservation of non-classical statistics of photons in plasmonic cavities combined with semiconductor nanostructures.

Semiconductor nanocrystals and metal nanoparticles are the building blocks of the next generation of electronic, optoelectronic, and photonic devices. Covering this rapidly developing and interdisciplinary field, the book examines in detail the physical properties and device applications of semiconductor nanocrystals and metal nanoparticles. It begins with a review of the synthesis and characterization of various semiconductor nanocrystals and metal nanoparticles and goes on to discuss in detail their optical, light emission, and electrical properties. It then illustrates some exciting applications of nanoelectronic devices (memristors and single-electron devices) and optoelectronic devices (UV detectors, quantum dot lasers, and solar cells), as well as other applications (gas sensors and metallic nanopastes for power electronics packaging). Focuses on a new class of materials that exhibit fascinating physical properties and have many exciting device applications. Presents an overview of synthesis strategies and characterization techniques for various semiconductor nanocrystal and metal nanoparticles. Examines in detail the optical/optoelectronic properties, light emission properties, and electrical properties of semiconductor nanocrystals and metal nanoparticles. Reviews applications in nanoelectronic devices, optoelectronic devices, and photonic devices.

The book is focused on the nanoparticle-based modification of micron-size ZnO, TiO2, ZrO2, Al2O3, CeO2, and Y2O3 oxide powders and BaSO4, BaTiZrO3, and LaSrMnO3 solid solutions applied for enamels, paints, construction materials, ceramics, and electric insulators. It presents the results of studies of the grain size distribution, phase composition, structure, optical properties, and physical processes that occur in micropowders modified with ZnO, TiO2, ZrO2, Al2O3, CeO2, Y2O3, SiO2, ZrO2/Y2O3, and Al2O3/CeO2 nanoparticles and subsequently irradiated with accelerated electrons and protons. The text will be helpful to researchers, engineers, structural developers, postgraduates, master’s students, and undergraduate students who study the processes that occur during the synthesis and modification of inorganic powders with nanoparticles of various oxides differing in the size and type of cations, in their mass and charge, and in the size and surface area of nanoparticles per se.

Examines the optical properties of low-dimensional semiconductor structures, a hot research area - for graduate students and researchers.