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High sensitivity uncooled microbolometers are necessary to meet the needs of the next generation of infrared detectors, which seek low power consumption and production cost without sacrificing performance. Presented here is the design, fabrication, and characterization of a microbolometer with responsivity enhanced by novel highly absorptive coatings. The device utilizes a gold-doped vanadium oxide film in a standard air bridge design. Performance estimations are calculated from current theory, and efforts to maximize signal to noise ratio are shown and evaluated. Most notably, presented are the experimental results and analysis from the integration of two different absorptive coatings: a patterned gold black film and a plasmonic resonant structure. Infrared-absorbing gold black was selectively patterned onto the active surfaces of the detector. Patterning by metal lift-off relies on protection of the fragile gold black with an evaporated oxide, which preserves gold black's near unity absorptance. This patterned gold black also survives the dry-etch removal of the sacrificial polyimide used to fabricate the air-bridge bolometers. Infrared responsivity is improved 70% for mid-wave IR and 22% for long-wave IR. The increase in the thermal time constant caused by the additional mass of gold black is a modest 15%. However, this film is sensitive to thermal processing; experimental results indicate a decrease in absorptance upon device heating. Sub-wavelength resonant structures designed for long-wave infrared (LWIR) absorption have also been investigated. Dispersion of the dielectric refractive index provides for multiple overlapping resonances that span the 8-12 ?m LWIR wavelength band, a broader range than can be achieved using the usual resonance quarter-wave cavity engineered into the air-bridge structures. Experimental measurements show an increase in responsivity of 96% for mid-wave IR and 48% for long-wave IR, while thermal response time only increases by 16% due to the increased heat capacity. The resonant structures are not as susceptible to thermal processing as are the gold black films. This work suggests that plasmonic resonant structures can be an ideal method to improve detector performance for microbolometers.

Nanoscale structures play a fundamental role in diverse scientific areas, including biology and information technology. It is necessary to develop methods that can observe nanoscale structures and dynamic processes that involve them. Colloidal plasmonic nanoparticles (plasmonic “atoms”) and their clusters (plasmonic “molecules”) are nanoscale objects with remarkable optical properties that provide new opportunities for sensing and imaging on the relevant length and time scales. Many biology questions require optically monitoring of the dynamic behavior of biological systems on single molecule level. In contrast to the commonly used fluorescent probes which have the problem of bleaching, blinking and relatively weak signals, plasmonic probes display superb brightness, persistency and photostability, thus enable long observation time and high temporal and spacial resolutions. When plasmonic atoms are clustered together, their resonances redshift while the intensities increase as a result of plasmon coupling. These optical responses are dependent on the interparticle gaps and the overall geometry, which makes plasmonic molecules capable of detecting biomolecule clustering and measuring nanometer scale distance fluctuations. In this dissertation, individual plasmonic atoms are firstly evaluated as imaging probe and their interactions with lipid membrane are tested on a newly developed on-chip black lipid membrane system. Subsequently, plasmonic dimers (plasmon rulers) prepared through DNA-programmed self-assembly are monitored to detect the mechanical properties of single biopolymers. Measurement of the spring constant of short (tens of nucleotides or base pairs) DNAs is demonstrated through plasmon coupling microscopy. Colloidal plasmonic atoms of various materials, sizes and shapes scatter vivid colors in the full-visible range. Assembling them into plasmonic molecules provides additional degrees of freedom for color manipulation. More importantly, the electric field in the gaps of plasmonic molecules can be enhanced by several orders of magnitude, which is highly desirable in single molecule sensing applications. In this dissertation, the fundamentals of plasmonic coupling are investigated through one-dimensional gold nanosphere chains. Using the directed self-assembly approach, multichromatic color-switchable plasmonic nanopixels composed of plasmonic atoms and molecules of various materials, sizes, shapes and geometries are integrated in one image with nanometer precision, which facilitates the encoding of complex spectral features with high relevance in security tagging and high density optical data storage. / 2017-01-01T00:00:00Z

In recent times, plasmonics has been a hallmark in improving optoelectronic device performance as well as in improving sensing. Confining light in dimensions below the diffraction limit and subsequently converting the incident photons into localized charge-density oscillations called localized surface plasmons, optical enhancements of the local fields by many orders of magnitude is possible. This dissertation explores the use of such surface plasmon resonances in core multishell nanostructures and demonstrates the values of such structures in energy harvesting and sensing. Additionally, it also shows the use of emerging plasmonic materials like metal nitrides (TiN, ZrN) instead of traditional plasmonic materials (Au, Ag) in the nanostructure designs. Utilizing the localized surface plasmon resonance (LSPR) in metallic components of core multishell nanowires, calculations of the local density of states as a measure of emission were made using a Green’s function method, while the absorption and scattering were simulated using the Mie formalism. Combining both the absorption and the emission, the quantum efficiency of white LEDs was calculated and the optimal material/dimensions for maximal performance was determined for different phosphor components in a white LED. Additionally, the use of ZrN as a plasmonic cloak for noise cancellation in Si photodetectors is shown and the performance is compared with an Au cloak. Using the developed methodology, it is proved that ZrN cloaks can outperform Au cloaks in a certain region of the visible spectrum, showing the benefit of using such plasmonic systems in place of traditional materials. The fabrication of the different components of the core multishell nanowires is also presented, and in particular, fabrication of ultra-thin (sub-10 nm) plasmonic TiN is achieved. Utilizing plasmon hybridization, a tunable double resonance feature is observed in Au/SiO2/Au core shell shell (CSS) nanoparticles, which have been then demonstrated to improve the photocatalytic performance in hematite. In particular, the double resonance peak allows absorption of light beyond the band gap of hematite and subsequent conversion into photocurrent through hot electron injection. Comparison has been made with Au nanoparticles, and it has been shown that the CSS nanoparticles outperform Au nanoparticles significantly. These CSS nanoparticles have also been used for bioimaging, in particular for Raman spectroscopy, with strong results at high densities of the nanoparticles. Utilizing stronger scattering SiO2/Au Nanoshells, it has been possible to work towards single particle imaging of molecules and demonstration of this phenomenon has been shown here through the use of coherent Raman scattering spectroscopy.

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Nanostructures have potential for use in state-of-the-art applications such as sensing, imaging, therapeutics, drug delivery, and electronics. The ability to fabricate and engineer these nanoscale materials is essential for the continued development of such devices. Because the morphological features of nanomaterials play a key role in determining chemical and physical properties, there is great interest in developing and improving methods capable of controlling their size, shape, and composition. While noble nanoparticles have opened the door to promising applications in fields such as imaging, cancer targeting, photothermal treatment, drug delivery, catalysis and sensing, the synthetic processes required to form these nanoparticles on surfaces are not well-developed. Herein is a detailed account on efforts for adapting established solution-based seed-mediated synthetic protocols to structure in a substrate-based platform. These syntheses start by (i) defining heteroepitaxially oriented nanostructured seeds at site-specific locations using lithographic or directed-assembly techniques, and then (ii) transforming the seeds using either a solution or vapor phase processing route to activate kinetically- or thermodynamically-driven growth modes, to arrive at nanocrystals with complex and useful geometries. The first series of investigations highlight synthesis-routes based on heterogeneous nucleation, where templates serve as nucleation sites for metal atoms arriving in the vapor phase. In the first research direction, the vapor-phase heterogeneous nucleation of Ag on Au was carried out at high temperatures, where the Ag vapor was sourced from a sublimating foil onto adjacent Au templates. This process transformed both the composition and morphology of the initial Au Wulff-shaped nanocrystals to a homogeneous AuAg nanoprism. In the second case, the vapor-phase heterogeneous nucleation of Cu atoms on Au nanocrystal templates was investigated by placing a Cu foil next to Au templates and heating, which caused the Cu atoms from the foil to sublimate from the foil and heterogeneously nucleation on the surface of the immobilized Au seeds. This process caused the composition and morphology of the Au Wulff-shape to transform into a homogeneous AuCu nanotriangle. Lastly, we characterized the morphological features and composition, optical properties, and also the catalytic and photocatalytic performance toward hydrogenation of 4-nitrophenolate. The second series of investigations highlight synthetic routes utilizing competencies of substrate-based techniques with colloidal chemistry. We have demonstrated two substrate-based syntheses yielding bimetallic nanostructures where shape control was achieved through (i) facet-selective capping agents and (ii) additive and subtractive process. In the first case a citrate-based cubic structure has been synthesized in the presence or absence of ascorbic acid and the role of each has been considered in shape control. Reactions were carried out in which Ag+ ions were reduced onto substrate-immobilized Ag, Au, Pd, and Pt seeds. It was discovered that for syntheses lacking ascorbic acid, citrate acts as both the capping and the reducing agent, resulting in a robust nanocube growth mode; however, when ascorbic acid was included in these syntheses, then the growth mode reverted to one that advances the octahedral geometry. The conclusion of these results was that citrate, or one of its oxidation products, selectively caps (100) facets, but where this capability was compromised by ascorbic acid. In the second case, galvanic replacement reactions have been carried out on immobilized cubic and Wulff structures to create the substrate-based nanoshells and nanocages, where the prepositioned templates were chemically transformed into hollow structures. In this novel research, Wulff-shaped templates of Au, Pt, or Pd, formed through the dewetting of ultrathin films, were first transformed into core−shell structures through the reduction of Ag+ ions onto their surface and then further transformed through the galvanic replacement of Ag with Au. Detailed studies were provided highlighting discoveries related to (i) alloying, (ii) dealloying, (iii) hollowing, (iv) crystal structure and (vi) the localized surface plasmon resonance (LSPR). Overall, a series of synthetic strategies based on physical and chemical vapor deposition were devised and validated to achieve novel substrate- based nanomaterials with different shapes and compositions for a variety of applications such as sensing, plasmonics, catalysis, and photocatalysis. The novel research in this dissertation also takes advantage of competencies of substrate-based techniques with colloidal chemistry and, brings this rich and exciting chemistry and its associated functionalities to the substrate surface. / Mechanical Engineering

<p> As the fundamental basic building blocks of photonic circuits, optical waveguide structures play important roles in modem telecommunication and sensing systems. Various structures ranging from the dielectric waveguide utilizing the total internal reflection (TIR) to the more advanced structures based on the surface plasmon polaritions (SPPs) are widely investigated and studied in industrial and research areas. With the fast development of fabrication technologies, more and more complicated structures are predicated to emerge as the requirement of highly integrated photonic circuits. Modeling and simulation methods, as efficient as well as excellent cost performance tools comparing to costly facilities and time-consuming fabrication procedures, are demanded to explore and design the devices and circuits before their finalization. </p> <P> This thesis reports a series of techniques to model two dimensional waveguide structures, including the conventional planar and surface plasmon polariton waveguides. This thesis contains both the methods and their applications to model and investigate the mode and propagation characteristics including the guided waves and the radiative waves. The methods include mode solvers based on fmite difference method (FDM) and complex mode matching method (CMMM), furnished with perfect matching layer (PML) for both guided and radiation modes. Based on the developed techniques, solutions of design of Bragg gratings with deep corrugations are presented; also various surface plasmon polariton (SPPS) grating structures are investigated. </p> / Thesis / Master of Applied Science (MASc)