The high speed transfer of information in materials with dimensions below the sub-diffraction limit is essential for future technological developments. Metallic nanoparticle (NP) waveguides serve a unique role in efficient energy transfer in this size regime. Light may be confined to metallic structures and propagate along the surface of the waveguide via propagating plasmon waves known as surface plasmon polaritons (SPPs). Plasmon propagation of energy in metallic structures is not perfect however and damping losses from the waveguide material lead to a characteristic exponential decay in the plasmon near field intensity. This decay length is known as the propagation length and serves as an excellent metric to compare various waveguide materials and structures to one another at particular excitation wavelengths. This thesis presents recent work in the development of a novel measurement technique termed bleach imaged plasmon propagation (BlIPP). BlIPP uses the photobleaching property of fluorophores and far field fluorescence microscopy to probe the near-field intensity of propagating plasmons and determine the propagation length. The experimental setup, image analysis, conditions, and application of BlIPP are developed within this thesis and an in depth review of the 1-photon photobleaching mechanism is also investigated. The BlIPP method is used to investigate long plasmon propagation lengths along straight chains of tightly packed Au NPs through the coupling of light to sub-radiant propagating modes, where radiative energy losses are suppressed. The findings of this work reveal, experimentally, the importance of small gap distances for the propagation of energy. Complex chain architectures are then explored using BlIPP measurements of tightly packed straight and bent chains of spherical silver NPs. We observe the highly efficient propagation of energy around sharp corners with no additional bending losses. The findings of this thesis demonstrate the advantages and capabilities of using BlIPP propagation length measurement. Further, BlIPP is used to reveal the advantage of coupling light to sub-radiant modes of NP chains, which demonstrate the ability to guide light efficiently across long distances and around complex structures, bringing us a step closer to the goal of applying plasmonic devices and circuitry in ultra compact opto-electronic devices.

This work will describe research directed towards the synthesis of anisotropic gold nanoparticles as well as their functionalization and biological applications. The thesis will begin by describing a new technique for the high-yield synthesis of gold nanorods using hydroquinone as a reducing agent. This addresses important limitations of the traditional nanorod synthesis including low yield of gold ions conversion to metallic form and inability to produce rods with longitudinal surface plasmon peak above 850 nm. The use of hydroquinone was also found to improve the synthesis of gold nanowires via the nanorod-seed mediated procedure developed in our lab. The thesis will next present the synthesis of novel starfruit-shaped nanorods, mesorods, and nanowires using a modified nanorod-seed mediated procedure. The starfruit particles displayed increased activity as surface-enhanced Raman spectroscopy (SERS) substrates as compared to smooth structures. Next, a method for the functionalization of gold nanorods using a cationic thiol, 16-mercaptohexadecyltrimethylammonium bromide (MTAB), will be described. By using this thiol, we were able to demonstrate the complete removal of toxic surfactant from the nanorods and were also able to precisely quantify the grafting density of thiol molecules on the nanorod surface through a combination of several analytical techniques. Finally, this thesis will show that MTAB-functionalized nanorods are nontoxic and can be taken up in extremely high numbers into cancer cells. The thesis will conclude by describing the surprising uptake of larger mesorods and nanowires functionalized with MTAB into cells in high quantities.

Self-assembling peptides have emerged as new nanobiomaterials and received considerable attention in the areas of nanoscience and biomedical engineering. In this category are ionic-complementary peptides, which contain a repeating charge distribution and alternating hydrophobic and hydrophilic residues in the amino acid sequence, leading to the unusual combination of amphiphilicity and ionic complementarity. Although their self-assembled nanostructures have been successfully applied as scaffoldings for tissue engineering, novel materials for regenerative medicine and nanocarriers for drug and gene/siRNA delivery, aspects of the assembly process remain unclear. Since many of these applications involve peptide-modified interfaces and surfaces, a better understanding and control of the peptide assembly on a surface are very crucial for future development of peptide-based applications in nano-biotechnology. This thesis contains two major parts: (i) fundamental study of the assembly of a model ionic-complementary peptide EAK16-II on surfaces and (ii) potential applications of such a peptide in surface modification and nanofabrication. In the fundamental study, EAK16-II assembly on negatively charged mica was first investigated via in-situ Atomic Force Microscopy (AFM). It was found that EAK16-II nanofiber growth on mica is surface-assisted and follows a nucleation and growth mechanism involving two steps: (i) adsorption of nanofibers and fiber clusters (from the bulk solution) on the surface to serve as the seeds and (ii) fiber elongation from the active ends of the seeds. Such a process can be controlled by adjusting the solution pH since it modulates the adsorption of the seeds and the growth rates. Unlike what is observed on mica, EAK16-II formed well-ordered nanofiber patterns with preferential orientations at angles of 60° or 120° to each other on hydrophobic highly ordered pyrolytic graphite (HOPG) surfaces, resembling the crystallographic structure of the graphite. Nanofiber formation on HOPG is also surface-assisted and adopts a nucleation and growth mechanism that can be affected by solution pH. The pH-dependent adsorption of peptides to HOPG is attributed to the resulting changes in peptide hydrophobicity. It was also found that EAK16-II assembly can be induced by the mechanical force of a tapping AFM tip. It occurs when the tip cuts the adsorbed EAK16-II nanofibers into segments that then serve as seeds for new nanofiber growth. This finding allows one to locally grow nanofibers at specific regions of the surface. The tip cutting has been combined with the effect that solution pH has on peptide assembly to develop a new AFM lithography method to fabricate local patterned peptide nanostructures on HOPG. To study the use of EAK16-II for surface modification applications, the wettability and stability of the peptide-modified surfaces were characterized. EAK16-II-modified mica becomes slightly hydrophobic as the water contact angle increases from <10° to 20.3 ± 2.9°. However, the hydrophobicity of the HOPG surface is significantly reduced, as reflected in a contact angle change from 71.2 ± 11.1° to 39.4 ± 4.3°. The EAK16-II-modified mica surface is stable in acidic solution, while the modified HOPG surface is stable in both acidic and alkaline solutions. The peptide-modified HOPG shows potential as a biocompatible electrode for (bio)molecular sensing. The ability of EAK16-II to form nanofibers on surfaces has also promoted research on peptide-based metallic nanowire fabrication. Our approach is to provide EAK16-II with metal ion binding ability by adding a GGH motif to the C-terminus. This new peptide EAK16(II)GGH has been found to form one-dimensional nanofibers while binding to Cu2+ ions. The dimensions of the nanofibers were significantly affected by the nature of the anions (SO42-, Cl- and NO3-) in the copper salt solution. This work demonstrates the potential usage of EAK16-II for nanowire fabrication.

Superconducting nanowire single-photon detectors (SNSPDs) are nanodevices usually made from thin niobium nitride (NbN) films. Operated at liquid helium temperature, they can exhibit high detection efficiency with low dark-counts associated with a fast response time and a low timing jitter. Covering a broad detection range from ultraviolet to mid-infrared, SNSPDs are a very attractive alternative to silicon or gallium arsenide based semiconductor detectors for fiber based telecommunication when single-photon sensitivity and high counting rates are necessary. Efficient packaging and fiber coupling of a SNSPD is in itself a real challenge and is often a limiting factor in reaching high system quantum efficiency. Our approach makes use of a controlled expansion alloy which has been adequately heat treated to enhance its characteristics for cryogenic operation. This insures the integrity of the optical coupling at cryogenic temperatures while done at room temperature. It also provides a good attenuation for electromagnetic interference due to the high relative permeability of the nickel-iron alloy. The small form factor of this pigtailed optical fiber package makes it versatile and could be easily integrated with a commercial cryogen-free system or simply dipped into a standard helium transport Dewar. We report on our theoretical and experimental methodology to evaluate the optical coupling quality and present the optoelectronic characterization of two devices packaged in this way. Electrical simulation is studied to understand the speed limitation factor inherent to these devices and preliminary speed and jitter measurements are reported.

<p>This thesis focuses on the fluctuation in the switching current $I_s$ of superconducting Al nanowires. We discovered that the maximum current which nanowires can support is limited by a single phase slip at low temperature. </p><p>Al superconducting nanowires less than 10 nm wide were fabricated based on a MBE grown InP ridge template in an edge-on geometry. The method utilizes a special substrate featuring a high standing 8nm-wide InP ridge. A thin layer of Al was evaporated on the substrate and Al on the ridge formed nanowires.</p><p>The fluctuation effects starts to dominate in the nanowire due to reduced energy barrier. One of such effects is the phase slip. The phase slip is a topological event, during which the superconducting phase between two superconducting electrodes changes by $2\pi$. The phase slip broadens the normal-superconducting transition. Part of the nanowire becomes normal during the phase slip and forms a normal core. The normal core generates heat and causes the premature switching in superconducting nanowires.</p><p></p><p>The nanowire becomes superconducting below the critical temperature $T_c$. The superconducting-normal transition was studied in the thesis. The transition of nanowires with superconducting leads qualitatively fits the thermally activated phase slip (TAPS) theory. On the other hand, the transition of the nanowires with normal leads showed a resistive tail due to the inverse-proximity effect.</p><p>The nanowire switches from the superconducting state to the normal state as the current is increased. Ideally, the maximum current is set by a pair-breaking mechanism, by which the kinetic energy of quasi-particles exceeds the bonding energy of Cooper pairs. This is called the critical current, $I_c$. In practice, the measured maximum current, called the switching current $I_s$, cannot reach $I_c$ because of the phase slip.</p><p>$I_s$ shows stochasticity due to the phase slip. For the nanowires with superconducting leads, the average $I_s$ approximately follows but falls below $I_c$. The fluctuation in $I_s$ shows non-monotonic behavior, in contrast to other studies. The fluctuation first increases and then decreases rapidly with increasing temperature. The fluctuation behavior is consistent with a scenario where the switch is triggered by a single phase slip at low temperature while by multiple phase slips at higher temperature. Thermal activation of phase slips appears dominant at most temperatures. However, in the thinnest nanowire, the saturation of the fluctuation at low temperature indicates that the phase slips by macroscopic quantum tunneling.</p><p>The superconducting nanowires with normal leads were also studied. One of the distinctive properties of our nanowire (the critical field of 1D nanowire is 10 times larger than that of a 2D superconducting film) allowed us to study the same nanowire with different leads (superconducting or normal). Both the average $I_s$ and the fluctuation in $I_s$ differed qualitatively depending on whether the leads were superconducting or normal. The temperature dependence of the average $I_s$ followed the $I_c$ of the Josephson junction instead of the phenomenological pair-breaking $I_c$. The difference was found to depend on both the temperature (close to $T_c$ or 0) and the length (shorter or longer than the charge imbalance length). Our study also showed that nonlinear current-voltage (IV) curves were observed due to the inverse-proximity effect.</p> / Dissertation

In this study, we used the molecular statics, molecular dynamics, and density function theory to investigate structural, electronic, and mechanical properties of ultra-thin silica nanowires. There are two parts in this study. In the first part, we used basin-hopping method to get different diameters of silica nanowires, nemed 2MR, 2MR-2O, 3MR-3O, 4MR-4O, 5MR-5O, 4MR-3f, 4MR-4f, and 4MR-5f. The various silica nanowires were optimized by density function theory to obtain the projected density of states, Mulliken charge, and electronic density difference, and we also compared this results to £\-quartz. In the second part, the molecular dynamics simulations were performed to investigate deformation behavior of silica nanowires under axial tensile loading at 10K. The Young¡¦s modulus increases when the diameter decreases. We also used angular correlation function to study the mechanical properties and variation of structures.

In this study, the structures of two ultrathin Pd nanowires were predicted by the simulated annealing basin-hopping method (SABH) with the tight-binding potential. The thermal stability of the Pd wires and adsorption, dissociation and diffusion behaviors were further examined by the density functional theory (DFT) calculation and DFT molecular dynamics (DFT-MD) simulation. In terms of thermal stability, these two Pd nanowires are still very stable at temperatures as high as 400 K. The configurations and adsorption energy have been calculated for H atom and H2 molecular adsorption on Pd nanowires. The minimum energy pathways and transition states of H2 molecular dissociation and H atom diffusion process on Pd nanowires were studied by the nudged elastic band (NEB) method. For the dissociation of hydrogen molecules, results show the dissociation is almost barrierless so the dissociation is easy to occur at very low temperatures, and their catalytic reactivity is very similar to the Pd bulk material. The thermal stability of the H atom within these Pd nanowires were also investigated by DFT-MD, with results showing that the H atom can only stay within Pd nanowires at temperatures much lower than room temperature (298 K). This phenomenon is very different from that of H atoms within Pd bulk material or other reported nanomaterials, leading to hydrogen embrittlement. Our results reveal that these two ultrathin Pd nanowires not only possess the same excellent catalytic activity for hydrogen molecules as the bulk Pd materials or other Pd nanomaterials do, but also avoid the hydrogen embrittlement occur.

In recent year, the quantum device has been rapid developed. The quantum conductor has been of great interest for most authors, and one of that is gold nanowire. As the diameter of the gold nanowire is smaller than 2nm, the structure arrangement is affected by surface tensor, and therefore the FCC structure will self assemble to a helical structure. However, the nanowire would be used in quantum devices, therefore, the material property must be understood and investigated. The properties of nanowire would be a significant on development of quantum device in the future. In this study, the molecular dynamics is employed to investigate the mechanical properties of the helical multi-shall gold nanowires and nanowries of the bulk FCC. The stress and strain relationship is obtained form the tensile and compressed tests. In addition, the yielding stress, maximum stress, Young¡¦s modulus, and breaking force can be determined from the tensile test and compressed test. Moreover, the different length/diameter ratio, temperature, and strain rate effects on mechanical properties and deformation behaviors are also investigated. The structure transform from crystalline to non-crystalline is also observed by the variation of radial distribution function (RDF) and angular correlation function (ACF). In this study, the tight-binding many body potential is employed to model the interaction between gold atoms.

Recently extensive efforts have been spent in order to achieve all silicon based photonic devices exploiting the efficient light emission from nanostructured silicon systems. In this thesis, silicon based nanostructures have been investigated for electro-optical and photovoltaic applications. The thesis focused on three application areas of silicon nanostructures: Light emitting diode (LED), light modulation using quantum confined Stark effect (QCSE) and photovoltaic applications. In the context of LED applications, ZnO nanocrystal/silicon heterojunctions were investigated. Contrary to observation of pure ultraviolet photoluminescence (PL) from ZnO nanocrystals that were synthesized through vapor liquid solidification (VLS) method, visible emissions were observed in the electroluminescence (EL) due to defect states of ZnO. The discrepancy between these emissions could be ascribed to both change in excitation mechanisms and the defect formation on ZnO nanocrystals surface during device fabrication steps. EL properties of silicon nanocrystals embedded in SiO2 matrix were also systematically studied with and without Tb doping. Turn-on voltage of the Tb doped LED structures was reduced below 10 V for the first time. Clear observation of QCSE has been demonstrated for the first time in Si nanocrystals embedded in SiO2 through systematic PL measurements under external electric field. Temperature and size dependence of QCSE measurements were consistently supported by our theoretical calculations using linear combination of bulk Bloch bands (LCBB) as the expansion basis. We have managed to modulate the exciton energy as high as 80 meV with field strength below MV/cm. Our study could be a starting point for fabrication of electro-optical modulators in futures for all silicon based photonic applications. In the last part of the thesis, formation kinetics of silicon nanowires arrays using a solution based novel technique called as metal assisted etching (MAE) has been systematically studied over large area silicon wafers. In parametric studies good control over nanowire formation was provided. Silicon nanowires were tested as an antireflective layer for industrial size solar cell applications. It was shown that with further improvements in surface passivation and contact formation, silicon nanowires could be utilized in very efficient silicon solar cells.

Oxide nanowire arrays are playing an important role in energy sciences nowadays, including energy harvesting, energy storage, and power management. By utilizing a wet chemical growth method, we demonstrated the capabilities of synthesizing density controlled vertical ZnO nanowire arrays on a general substrate, optimizing the aspect ratio of the vertical ZnO nanowire arrays guided by a statistical method, epitaxially growing patterned vertical ZnO nanowire arrays on inorganic substrates, epitaxially growing patterned horizontal ZnO nanowire arrays on non-polar ZnO substrates, and the lift-off of the horizontal ZnO nanowire arrays onto general flexible substrates. In addition, single crystalline PbZrxTi1-xO3 (PZT) nanowire arrays were epitaxially grown on conductive and nonconductive substrates by hydrothermal decomposition. Beyond that, based on the as-synthesized ZnO nanowire arrays, we demonstrated multilayered three dimensionally integrated direct current and alternating current nanogenerators. By integrating a ZnO nanowire based nanogenerator with a ZnO nanowire based nanosensor, we demonstrated solely ZnO nanowire based self-powered nanosystems. Also, utilizing a commercial full-wave bridge rectifier, we rectified the alternating output charges of the nanogenerator based on PZT nanowire arrays, and the rectified charges were stored into capacitors, which were later discharged to light up a laser diode (LD). In addition, blue/near-ultraviolet (UV) light emitting diodes (LED) composed of ordered ZnO nanowire arrays on p-GaN wafers were presented.