<p> The classical theory of plasmonics envisions spherical nanoparticles obeying classical electrodynamics. Modern colloidal synthesis of noble metal nanoparticles, in tandem with emerging methods of nanoparticle assembly, transcends the assumptions of this theory. First, strongly nonspherical particles give rise to optical spectra with complicated orientation dependence. An interpolation method is introduced to connect electrodynamic simulation results, generally carried out at fixed orientations, with experimental optical spectra, such as those of randomly oriented ensembles. Second, the ability to manipulate and arrange multiple spherical particles in solution with optical binding demands efficient calculation of the optical forces giving rise to their preferred geometries. A coupled-dipole model is developed to allow for rapid optical force calculations that predict many of the phenomena seen in the laboratory. Third, the prospect of attaching semiconductor quantum dots to metal nanoparticles in the electromagnetic near-field raises new questions about how the quantum behavior of localized surface plasmons affects the nonlinear optical response of the coupled system. Investigating such questions yields several new predictions about the optical response of plasmon-exciton systems. Under ultrafast pulsed illumination, a reversal of a Fano resonance is predicted, turning a dip into a spike in the pulsed optical spectrum. When two quantum dots are coupled to the same metal nanoparticle, it is found that their individual couplings to a quantized plasmon can give rise to coherence between the quantum dots, in particular a state enriched in an antisymmetric dark excitation that can be prepared with pulsed laser illumination. These theoretical tools and predictions, in addition to providing basic insight into plasmonic systems, will serve to guide further developments in colloidal synthesis, nanoparticle assembly, and optical applications.</p>

<p> Optical rectennas, which are micro-antennas to convert optical-frequency radiation to alternating current combined with ultrahigh-speed diodes to rectify the current, can in principle provide high conversion efficiency solar cells and sensitive detectors. Currently investigated optical rectennas using metal/insulator/metal (MIM) diodes are limited in their RC response time and poor impedance matching between diodes and antennas. A new rectifier, the geometric diode, can overcome these limitations. The thesis work has been to develop geometric diode rectennas, along with improving fabrication processes for MIM diode rectennas. The geometric diode consists of a conducting thin-film, currently graphene, patterned into a geometry that leads to diode behavior. In contrast with MIM diodes that have parallel plate electrodes, the planar structure of the geometric diode provides a low RC time constant, on the order of 10^-15 s, which permits operation at optical frequencies. Fabricated geometric diodes exhibit asymmetric DC current-voltage characteristics that match well with Monte Carlo simulations based on the Drude model. The measured diode responsivity at DC and zero drain-source bias is 0.012 A/W. Since changing the gate voltage changes the graphene charge carrier concentration and can switch the majority charge type, the rectification polarity of the diode can be reversed. Furthermore, the optical rectification at 28 THz has been measured from rectennas formed by coupling geometric diodes with graphene and metal bowtie antennas. The performance of the rectenna IR detector is among the best reported uncooled IR detectors. The noise equivalent power (NEP) of the rectenna detector using geometric diode was measured to be 2.3 nW Hz^-1/2. Further improvement in the diode and antenna design is expected to increase the detector performance by at least a factor of two. Applications for geometric diodes and graphene bowtie antennas include detection of terahertz and optical waves, ultra-high speed electronics, and optical power conversion.</p>

<p> Given a rapidly developing world, the need exists for inexpensive renewable energy alternatives to help avoid drastic climate change. Photovoltaics have the potential to fill the energy needs of the future, but significant cost decreases are necessary for widespread adoption. Semiconductor nanocrystals, also known as quantum dots, are a nascent technology with long term potential to enable inexpensive and high efficiency photovoltaics. When deposited as a film, quantum dots form unique nanocomposites whose electronic and optical properties can be broadly tuned through manipulation of their individual constituents. </p><p> The contents of this thesis explore methods to understand and optimize the optoelectronic properties of PbSe quantum dot films for use in photovoltaic applications. Systematic optimization of photovoltaic performance is demonstrated as a function of nanocrystal size, establishing the potential for utilizing extreme quantum confinement to improve device energetics and alignment. Detailed investigations of the mechanisms of electrical transport are performed, revealing that electronic coupling in quantum dot films is significantly less than often assumed based on optical shifts. A method is proposed to employ extended regions of built-in electrical field, through controlled doping, to sidestep issues of poor transport. To this end, treatments with chemical redox agents are found to effect profound and reversible doping within nanocrystal films, sufficient to enable their use as chemical sensors, but lacking the precision required for optoelectronic applications. Finally, a novel doping method employing "redox buffers" is presented to enact precise, stable, and reversible charge-transfer doping in porous semiconductor films. An example of oxidatively doping PbSe quantum dot thin films is presented, and the future potential for redox buffers in photovoltaic applications is examined.</p>

<p> We have developed novel techniques for manufacturing vesicles with predefined attachments to scaffolds of DNA, and have studied the underlying mechanism(s) of this DNA directed vesicle formation by capturing intermediates. These DNA scaffolds are self-assembled by the origami method, which can use DNA as a programmable building block to form diverse structures: two-dimensional crystals, nanotubes, and three-dimensional wireframe nanopolyhedra [1-5]. </p><p> Nano-templated vesicles are prepared using rigid rings of bundled DNA. Single phosphatidyl ethanolamine (PE) lipids are coupled to these rings first by covalent conjugation with an oligonucleotide (oligo) "anti-handle", then by that oligo's sequence-specific hybridization to one of several (0, 1, 2, ..., 16) single-stranded "handles" on the DNA ring, designed to protrude from its interior. Vesicles are then formed in a solution of these ring complexes, excess phospholipid and detergent as the detergent is dialyzed away over several hours. Micelles preferentially nucleate around the alkyl chain of each PE inside the ring, and their growth during dialysis determines the volume of lipid in the final structures formed. Ring-PE lipid-vesicles bear exactly one ring per vesicle in characteristic transmission electron micrographs, with a size close to the inner diameter of its ring template.</p><p> Chapter 1 provides an overview of the significance and roles of engineering membranes in vitro. Biological membranes are incredibly complex, which in turn makes studying structure and function of membrane protein difficult in the absence of an artificial bilayer. Even more so, current limitations of producing high quality liposomes with reproducible techniques are placing more strain on elucidating the mechanisms of reconstitution. However, the emergence of the field of DNA Origami in 2006 truly revolutionized the limitless abilities to create 2D and 3D structures with function. We took advantage of this field by developing geometries to facilitate membrane growth.</p><p> Chapter 2 reports a new method for templating vesicles with a uniform size and shape using DNA origami rings bearing inner handles facing 0&deg; to the center. DNA origami rings of varying diameters can be designed with functional handles for templating the "Saturn" structure. Once the method was established, rings of varying handle angles were synthesized to determine their effects on the final vesicle structures.</p><p> Chapter 3 explores the parameters that affect the quantity of lipids assembling inside the template. These include ultracentrifugation time, detergent to lipid ratio, and dialysis conditions. In order to elucidate the mechanism of formation of our final templated structures, we performed mechanistic studies on 60-nm rings, systematically varying the initial number of lipid molecules anchored inside each ring. The capture of crucial intermediates: circular thin lipidic membrane, lipid bilayer torus, continuous outer bilayer, and seeded small unilamellar vesicles helped us understand how the vesicles are formed.</p><p> Chapter 4 summarizes the main results of the thesis and provides future prospectives on the potential expansion of DNA origami technology. A handful of new opportunities are presented based on control in the organization of DNA materials. Taking advantage of this machinery and applying it to the central problems in engineering, biology, chemistry, physics, and medicine will allow the field to elevate to the next level with promises of becoming a vital area of research.</p>

<p> Luminescent properties of lanthanide complexes possess unique characteristics that make them good candidates for possible bioimaging agents and have inspired research initiatives to further explore these materials. However, the toxicity of these metals limits their applications as in-vivo bioimaging agents. One solution that eliminates the toxic effects is to encase these lanthanide complexes in silica. This project was designed to probe the variation in the fluorescence properties of a highly luminescent europium (III) complex, utilizing a fluorinated &acirc;-diketonate ligand (thenoyltrifluoroacetone (tta)), upon the substitution of the solvent molecules by various functionalized dipyrido[3,2-a:2',3'-c]phenazine (DPPZ) ligands. A method for covalently attaching, or occluding complexes in silica nanoparticles were also included in the project design. The structure and properties of the functionalized DPPZ ligands and their respective complexes were determined by FT-IR, ¹H-NMR, UV-Vis, and fluorescence spectroscopy techniques. UV excitation of the complexes resulted in red luminescence (~ 614 nm) characteristic of trivalent europium ions. The differences in luminescence properties of the complexes are rationalized in terms of the electronic features of the different functionalized DPPZ ligands. The higher overall quantum yield of the un-functionalized DPPZ complex, Eu(tta)3DPPZ (Q.Y.= 7.68 &plusmn; 0.06 %), and the low overall quantum yield observed for Eu(tta)₃DPPZ-COOEt (Q.Y.= 1.08 &plusmn; 0.05%), Eu(tta)₃DPPZ-Si (Q.Y.= 0.65&plusmn; 0.04%), Eu(tta)₃DPPZ-COOH (Q.Y.= 0.61&plusmn; 0.07 %), Eu(tta)₃DPPZ-CH3 (Q.Y.= 0.59&plusmn;0.02 %) are rationalized in terms of how electron donating or withdrawing groups affect their respective ligand-to-metal energy transfer efficiencies. Eu(tta)₃DPPZ was the only complex to show enhanced luminescent properties capable of potential applications in biomedical imaging.</p>

A first approach to engineering problems in nanosized systems requires a thorough understanding of how physical properties change as size decreases from the macroscale. One important class of properties that can be severely affected by such a downward size shift are transport properties - classical mass, momentum and energy transport. Using atomistic simulation techniques, primarily molecular dynamics, and statistical expressions for diffusion, viscosity, and thermal conductivity formulated in terms of atomistic properties, three case studies of transport in important, nanosized systems are investigated, including confined water systems, silicon-germanium nanos- tructures, and carbon nanostructures. In the first study of confined water systems, diffusion and viscosity are of primary interest, as recent experimental studies have shown notably increased rates of diffusion through nano-confined carbon nanotube structures. In this work, a full treatment of the transport properties is provided in both water clusters and water thin films, both having characteristic size scales under 11 nm. The diffusion, viscosity, and thermal conductivity in the nanosized systems are all shown to be significantly different from bulk water systems, with diffusion and thermal transport increasing and viscosity decreasing. For silicon-germanium nanostructures, the thermal transport properties are exclusively considered, with the problem of interest concerning the control of thermal transport through a strict control on the nanostructure. Quantum dot superlattices are shown to be effective structures for controlling the thermal transport properties, the available range of thermal conductivity using these structures being 0.1-160 W/mK. The final study concerns graphene nanostructures, which in terms of thermal transport have some of the highest thermal conductivities of any available materials. Control of thermal transport properties is again of primary importance, with various physical aspects - defects, shape, and size - being probed in graphene, graphene nano ribbons, carbon nanotubes, and fullerenes to determine their influence on transport; overall, these structures yield a large range of thermal transport, 10-2500 W/mK.

Thesis (Ph. D.)--Tufts University, 2005. / Adviser: David R. Walt. Submitted to the Dept. of Chemistry. Includes bibliographical references. Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009. / Committee Chair: Whetten, Robert; Committee Member: Bottomley, Lawrence; Committee Member: de Heer, Walter; Committee Member: El-Sayed, Mostafa; Committee Member: Fernandez, Facundo; Committee Member: Gordon, Sidney; Committee Member: Leavitt, Andrew; Committee Member: Orlando, Thomas. Part of the SMARTech Electronic Thesis and Dissertation Collection.

<p> An atomic force microscopy beam-like cantilever is combined with an electrical tuning fork to form a shear force probe that is capable of generating an acoustic response from the mesoscopic water layer under ambient conditions while simultaneously monitoring force applied in the normal direction and the electrical response of the tuning fork shear force probe. Two shear force probes were designed and fabricated. A gallium ion beam was used to deposit carbon as a probe material. The carbon probe material was characterized using energy dispersive x-ray spectroscopy and scanning transmission electron microscopy. The probes were experimentally validated by demonstrating the ability to generate and observe acoustic response of the mesoscopic water layer.</p><p>

xvii, 183 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 recent years, nanoscience has evolved from a multidisciplinary research concept to a primary scientific frontier. Rapid technological advancements have led to the development of nanoscale device components, advanced sensors, and novel biomimetic materials. However, potential negative impacts of nanomaterials are sometimes overlooked during the discovery phase of research. The implementation of green chemistry principles can enhance nanoscience by maximizing safety and efficiency while minimizing the environmental and societal impacts of nanomaterials. This dissertation introduces the concept of green nanosynthesis, demonstrating the application of green chemistry to the synthesis of nanornaterials. A comprehensive review of the synthesis of metal nanomaterials is presented, demonstrating how individual green chemistry principles can improve traditional synthetic routes as well as guide the design of new materials. Detailed examples of greener syntheses of functionalized gold nanoparticles with core diameters of 2-10 nm are described in subsequent chapters, beginning with a method for functionalizing citrate-stabilized gold nanoparticles that are desirable for advanced applications. Although citrate-stabilized gold nanoparticles can be easily produced from a classic procedure using mild reagents and benign methods, functionalization via ligand exchange is often unsuccessful. It was discovered that an ill-defined layer comprised of citrate and other ligands interferes with functionalization processes. By removing excess citrate in a manner where overall structure and stability is maintained, gold cores produced by this route are readily functionalized by incoming thiols, affording unprecedented control over surface composition and functionality. A direct route to functional nanomaterials using Bunte salt precursors is discussed next, describing the use of easily synthesized shelf-stable alternatives to thiols in the preparation of water-soluble gold nanoparticles. Control of core size and surface chemistry is demonstrated through simple manipulation of reagent ratios, yielding products similar to those produced by traditional direct syntheses which rely on the use of thiols. The use of functionalized nanoparticles as "building blocks" for more complex structures was demonstrated in self-assembly processes. Cationic gold particles were deposited upon DNA scaffolds to create linear arrays. A discussion of the future outlook of green nanosynthesis concludes this work, identifying immediate challenges and long-term goals. This dissertation contains previously published and co-authored materials. / Adviser: James E. Hutchison