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Mechanical Evaluation of Electronic Properties of MaterialsNudo, Nicholas 02 October 2013 (has links)
The present research focuses on the coupling of mechanical and electrical properties of materials and culminates in a direct connection between applied strain to thin-films, thin-film electron binding energy, the energy loss via plastic deformation provided by an indentation, and the substrate resistance. The methods used in this research include X-ray photoelectron spectroscopy (XPS), nanoindentation, digital optical microscopy, and sputter coat deposition.
It is discovered that there is a shift in electron binding energy on the scale of 0.2 eV to 1.4 eV in gold and palladium thin-films sputtered on polyvinylidene fluoride (PVDF) through the application of strain induced by a convex shape. There is a change in the area beneath the load-displacement curve measured via indentation from 5.55 x 10^-10 J to 4.78 x 10^-10 J when the gold-palladium thin-film sputtered on PVDF is changed from the flat arrangement to the convex arrangement. Furthermore, the strain also changed the electrical resistance of aluminum foil, which indicates that the substrate electrical resistance is affected by the induced strain. The internal resistance of a circuit developed for this research changed from 7.76 ohms for flat samples to 8.03 ohms and 8.33 ohms for flat and convex samples, respectively. It is expected that the research can be used to estimate the strain in nanogears and other devices at small length scales.
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Enhanced Flux-Pinning Properties in Superconducting YBa2Cu3O7-δ Thin Films with Nanoengineering MethodsTsai, Chen-Fong 03 October 2013 (has links)
Since the discovery of the high temperature superconductor YBa2Cu3O7-δ (YBCO), with transition temperature (Tc = 77 K), above liquid nitrogen point in 1987 many research projects have been dedicated to enhancing the high field performance of this material for practical applications. The 2nd generation YBCO-based coated conductors are believed to be the most promising approach for commercial applications including power transmission, motors, generators, and high field magnets. With the advances of nanotechnologies, different nanoengineering methods have been demonstrated to enhance the performance of YBCO thin films, include doping with 0-dimensional (0-D) self-assembled nanoparticles, 1-dimensional (1-D) nanorods, and 2-dimensional (2-D) nanolayers. Furthermore, dopants with ferromagnetic properties are also reported to provide enhanced pinning effects by Lorentz force, especially under high-applied magnetic fields. The principle of these methods is to generate high-density defects at the heterogeneous interfaces as artificial pinning centers in an effort to improve the flux-pinning properties. The morphology and dimensions of the nanoinclusions play an important role in pining enhancement. Optimized pinning structures are likely to be located at energetically favorable vortex cores, which form a triangular lattice with dimensions close to the YBCO coherence length ξ (ξab ~ 4 nm; ξc ~ 0.5 nm at 77 K.) However, it is challenging to achieve small dimensional nanodopants in the vapor deposited YBCO thin films. The purpose of this research is to utilize nanoengineering methods to produce optimized pinning structure in YBCO thin films.
In this thesis, we systematically study the effects of different nanoinclusions on the flux-pinning properties of YBCO thin films. The 0-D ferromagnetic Fe2O3 and CoFe2O4 nanoparticles, 2-D CeO2 multilayers, and tunable vertically aligned nanocomposites (VAN) of (Fe2O3)x:(CeO2)1-x and (CoFe2O4)x:(CeO2)1-x systems are introduced into the YBCO matrix as artificial pinning centers. Results suggest that all nanoinclusions showed significant enhancement in the superconducting properties of YBCO. The ferromagnetic pinning centers dominate at high field and low temperature regimes, however, the defect pinning centers dominate at low field and high temperature regimes. The uniquely arranged VAN structure of alternating magnetic and non-magnetic nanophases, which incorporates both high defect density and tunable distribution of magnetic dopants, is believed to be an ideal solution for flux-pinning enhancement.
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Studies of Magnetic Logic DevicesHu, Likun January 2012 (has links)
Magnetic nanoscale devices have shown great promise in both research and industry. Magnetic nanostructures have potential for non-volatile data storage applications, reconfigurable logic devices, biomedical devices and many more.
The S-state magnetic element is one of the promising structures for non-volatile data storage applications and reconfigurable logic devices. It is a single-layer logic element that can be integrated in magnetoresistive structures. We present a detailed micromagnetic analysis of the geometrical parameter space in which the logic operation is carried out. The influence of imperfections, such as sidewall roughness and roundness of the edge is investigated.
Magnetic nanowires are highly attractive materials that has potential for applications in ultrahigh magnetic recording, logic operation devices, and micromagnetic and spintronic sensors. To utilize applications, manipulation and assembly of nanowires into ordered structures is needed. Magnetic self-alignment is a facile technique for assembling nanowires into hierarchical structures. In my thesis, I focus on synthesizing and assembling nickel nanowires. The magnetic behaviour of a single nickel nanowire with 200~nm diameter is investigated in micromagnetic simulations. Nickel nanowires with Au caps at the ends were synthesized by electrochemical deposition into nanopores in alumina templates. One-dimensional alignment, which forms chains and two-dimensional alignment, which forms T-junctions as well as cross-junctions are demonstrated. Attempts to achieve three-dimensional alignment were not successful yet. I will discuss strategies to improve the alignment process.
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DC, Microwave and Optoelectronic Characterization of YBa2Cu3O7-x Nano-Scale Thin Film StructuresMcConkey, Thomas 25 September 2012 (has links)
The nonlinear electrodynamic characteristics and presence of vortex dynamics in pseudo 2-dimensional microbridges make them attractive to design novel passive and active microwave circuits. Before such applications could be feasibly accomplished, a greater understanding of the
the these devices are necessary, by a complete DC, microwave and optoelectronic characterization.
A cryostat design and construction is discussed including the creation of test beds for DC characterization. Coplanar waveguide (CPW) design methodology is presented and used for the creation of CPWs for microwave characterization. Microbridges and meander lines are also embedded into the CPWs for determining the microwave performance of said devices and for
optoelectronic characterizations.
Results are compared against accepted results from theory and simulations, introducing vortices as explanations for device behaviour. Feasibility of these devices as single photon detectors is discussed.
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Solid phase microextraction for in vivo determination of pharmaceuticals in fish and wastewaterTogunde, Oluranti Paul January 2012 (has links)
This thesis describes the development and application of solid phase microextraction (SPME) as a sample preparation technique for in vivo determination of pharmaceutical residues in fish tissue and wastewater. The occurrence, distribution and fate of pharmaceuticals in the environment are a subject of concern across the globe due to the impact they may have on human life and aquatic organisms. To address this challenge from an analytical perspective, a simplified and reliable analytical methodology is required to investigate and determine the concentration (bioconcentration factors) of trace pharmaceutical residue in fish tissue and environmental water samples (exposure). An improved SPME method, coupled with liquid chromatography with tandem mass spectrometry has been developed and applied to both controlled laboratory and field-caged fish exposed to wastewater effluent for quantitative determination of pharmaceutical residue in fish specific tissue.
A new SPME configuration based on C18 thin film (blade) was developed and optimized to improve SPME sensitivity for in vivo determinations of trace pharmaceuticals in live fish. The C18 thin film extraction phase successfully quantified bioconcentrated fluoxetine, venlafaxine, sertraline, paroxetine, and carbamazapine in the dorsal-epaxial muscle of living fish at concentrations ranging from 1.7 to 259 ng/g. The reproducibility of the method in spiked fish muscle was 9-18% RSD with limits of detection and quantification ranging from 0.08 - 0.21 ng/g and 0.09 - 0.64 ng/g (respectively) for the analytes examined. Fish were sampled by in vivo SPME for 30 min to detect pharmaceutical uptake and bioconcentration, with experimental extracts analyzed using liquid chromatography coupled with tandem mass spectrometry.
In addition, a simplified analytical methodology based on SPME was developed and optimized for determination and bioconcentration factor of different classes of pharmaceuticals residues in fish bile. The reproducibility of the method in spiked fish Rainbow Trout bile was 3-7% RSD with limits of detection (LOD) ranging from 0.3 – 1.4 ng/mL for the analytes examined. The field application of SPME sampling was further demonstrated in Fathead Minnow (Pimephales promelas), a small-bodied fish caged upstream and downstream of a local wastewater treatment plant where fluoxetine, atorvastatin, and sertraline were detected in fish bile at the downstream location. Also, a simple automated analytical method using high throughput robotic system was developed for the simultaneous extraction of pharmaceutical compounds detected in surface waters. The proposed method successfully determined concentrations of carbamazepine, fluoxetine, sertraline, and paroxetine in treated effluent at concentrations ranging from 240 - 3820 ng/L with a method detection limit of 2-13 ng/L, and a relative standard deviation of less than 16%. Application of the method was demonstrated using wastewater from pilot-scale municipal treatment plants and environmental water samples from wastewater-dominated reaches of the Grand River (Waterloo, ON).
Finally, 4 and 8-d laboratory exposures were carried out with Rainbow Trout exposed to wastewater effluent collected from pilot scale at Burlington, ON. Additionally, wild fish, White Sucker (Catostomus commersonii) were collected and sampled from Waterloo and Kitchener downstreams containing local municipal effluent. Bioconcentration factors of the selected compounds were determined in both fish muscle and bile samples. The results show that anti-depressant drugs such fluoxetine, sertraline and paroxetine were uptake in the fish muscle and fish bile for both laboratory and field exposure. In summary, exposure of fish to micro-pollutants such as pharmaceuticals may be monitored through the analysis of bile, particularly at low concentration exposure of pharmaceuticals, where the sensitivity of analytical method may be challenged. SPME is a promising simple analytical tool which can potentially be used for monitoring of pharmaceuticals in fish tissue and wastewater.
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In Search of the Holy Grail of Photoelectrochemistry : A Study of Thin Film Electrodes for Solar Hydrogen GenerationLindgren, Torbjörn January 2004 (has links)
Hydrogen is a wanted energy carrier in a future society less dependent of fossil fuels. This thesis investigates the possibilities of using solar energy to convert water into hydrogen and oxygen, so called artificial photosynthesis. Through this work multiple inexpensive and stable thin film semiconductor electrodes have been produced and used as solar energy absorbers and active sites for direct watersplitting in photoelectrochemical cells. The electrodes have mainly been of nanostructured metal oxide character but also nitrides have been studied. Detailed back ground theory on photoelectrochemistry of semiconductors for hydrogen evolution is given in the summary of the thesis. Nanostructured WO3 electrodes with a quantum yield close to unity were designed and photoelectrochemically characterized. Hematite, α-Fe2O3, nanorods were synthesized and characterized for the aim of water oxidation. The morphology of the hematite nanorods was found to be in favor of the traditional isotropic nanostructured electrodes. Moreover, a unique porous nitrogen doped TiO2 material, photoactive in visible light, was obtained by reactive sputtering. The nitrogen doped material has interesting photoelectrochemical properties and is also promising for related applications such as pollution degradation by photocatalysis. Polycrystalline indium nitride, InN, was produced by reactive sputtering. Electrodes of the as prepared InN as well as electrodes annealed in nitrogen were studied for the aim of photooxidation of water. The electrodes studied are interesting candidates as potential watersplitting electrodes in photoelectrochemical cells, even if all had in common that further improvements and optimizations need to be done.
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The Growth And Characterization Of Galium Selenide Thin FilmsColakoglu, Tahir 01 January 2003 (has links) (PDF)
GaSe thin films were deposited by thermal evaporation technique with and
without Cd doping. X-ray analysis showed that the crystallinity increases in (1014) preferred orientation direction with annealing for doped and undoped films. The room temperature conductivity and mobility values of the samples were found to be for doped and undoped films in between 1.3× / 101 - 3.4× / 102 (& / #8486 / -cm)-1, 1.2× / 10-6 - 1.5× / 10-6 (& / #8486 / -cm)-1 and 5.9 & / #8211 / 20.9 (cm2/V.s) (for doped samples only), respectively.
Due to the high resistivity of the undoped samples mobility measurements could not be performed. The dominant conduction mechanisms were determined to be thermionic emission in the high temperature region (250-400 K), tunneling in the range 160-250 K and between 100-150 K variable range hopping mechanism for the
doped films. For the undoped films above 250 K thermionic emission was the
dominant conduction mechanism. Space charge limited currents in parallel and
perpendicular directions of the film surface showed two different localized energy levels with different concentrations for each case, namely, 99.8 meV with concentration 3.5× / 1012 cm-3 and 418.3 meV with the concentration 2.2× / 105 cm-3 for
parallel direction and for perpendicular direction 58.3 meV with concentration
6.2× / 1025 cm-3 and 486.1 meV with concentration 3.3× / 1022 cm-3. Photocurrentillumination
intensity dependences indicated that power exponent of illumination
intensity with values n> / 1 implied two recombination centers exist in studied
samples.
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Investigation Of Inse Thin Film Based DevicesYilmaz, Koray 01 September 2004 (has links) (PDF)
In this study, InSe and CdS thin films were deposited by thermal evaporation method onto glass substrates. Schottky and heterojunction devices were fabricated by deposition of InSe and CdS thin films onto SnO2 coated glass substrates with various top metal contacts such as Ag, Au, In, Al and C. The structural, electrical and optical properties of the films were investigated prior to characterization of the fabricated devices.
The structural properties of the deposited InSe and CdS thin films were examined through SEM and EDXA analysis. XRD and electrical measurements have indicated that undoped InSe thin films deposited on cold substrates were amorphous with p-type conductivity lying in the range of 10-4-10-5 (& / #61527 / .cm)-1 at room temperature. Cd doping and post-depositional annealing effect on the samples were investigated and it was observed that annealing at 100 oC did not show any significant effect on the film properties, whereas the conductivity of the samples increased as the Cd content increases. Temperature dependent I-V and Hall effect measurements have shown that conductivity and carrier concentration increases with increasing absolute temperature while mobility is almost temperature independent in the studied temperature range of 100-430 K.
The structural and electrical analysis on the as-grown CdS thin films have shown that the films were polycrystalline with n-type conductivity. Temperature dependent conductivity and Hall effect measurements have indicated that conductivity, mobility and carrier concentrations increases with increasing temperature. Transmission measurements on the as-grown InSe and CdS films revealed optical band gaps around 1.74 and 2.36 eV, respectively.
Schottky diode structures in the form of TO/p-InSe/Metal were fabricated with a contact area of around 8x10-3 cm2 and characterized. The best rectifying devices obtained with Ag contacts while diodes with Au contacts have shown slight rectification. The ideality factor and barrier height of the best rectifying structure were determined to be 2.0 and 0.7 eV, respectively. Illuminated I-V measurements revealed open-circuit voltages around 300 mV with short circuit current 3.2x10-7 A. High series resistance effect was observed for the structure which was found to be around 588 & / #61527 / . Validity of SCLC mechanism for Schottky structures was also investigated and it was found that the mechanism was related with the bulk of InSe itself.
Heterostructures were obtained in the form of TO/n-CdS/p-InSe/Metal and the devices with Au and C contacts have shown the best photovoltaic response with open circuit voltage around 400 mV and short circuit current 4.9x10-8 A. The ideality factor of the cells was found to be around 2.5. High series resistance effect was also observed for the heterojunction devices and the fill factors were determined to be around 0.4 which explains low efficiencies observed for the devices.
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Investigation Of Structural, Electrical And Optical Properties Of Cu1-xagxinse2 Thin Films As A Function Of X ContentGullu, Hasan Huseyin 01 September 2010 (has links) (PDF)
In this work, we will focus on the quaternary system Cu1-xAgxInSe2 (CAIS) to investigate the effects of silver (Ag) contribution and exchange with copper (Cu) in CuInSe2. This system is located between the ternary semiconducting chalcopyrite compounds CuInSe2 and AgInSe2. These are two most popular materials applied in photovoltaic cells because of their high optical absorption coefficient, which is an important factor for the manufacture of devices, direct energy gap with values Eg ~1.05 and 1.24 eV, respectively, and excellent thermal stabilities in air. As being a quaternary alloy, we expect that Cu1-xAgxInSe2 will show the advantage of a large degree of variation of their properties as a function of the composition, which allows adjusting of the band gap and other properties. We will analyze the behavior of Ag in the structure depending on the annealing and the effects of the Ag exchange to the Cu vacancies in this crystal structure by changing x (Ag content).
The crystals will be characterized structurally by X-ray diffraction (XRD). It will be used to prove crystallinity, determine perfection and lattice parameters depending on composition. Surface morphology and stoichiometry will be examined using scanning electron microscope (SEM) equipped with EDXA. Moreover, electrical properties including the temperature dependent electrical conductivity, and carrier concentrations and mobility extracted from Hall effect measurements, and, optical properties including absorption coefficient, photoconductivity, spectral transmission, and optical band gap have been determined to characterize Cu1-xAgxInSe2 thin films deposited using e-beam evaporation technique.
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Nanoscale Metal Thin Film Dewetting Via Nanosecond Laser Melting: Understanding Instabilities and Materials Transport in Patterned Thin FilmsWu, Yueying 01 December 2011 (has links)
Nanoscale metal thin film dewetting via laser treatment is studied in this dissertation. The purpose is to understand: 1) the spatial and temporal nature of intrinsic instabilities; and 2) mass transportation involved in dewetting pattern evolution in metal thin films as well as in lithographically patterned nanostructures; and finally 3) to explore advanced control of metallic nanostructure fabrication via the confluence of top down nanolithography and pulsed laser induced dewetting. This study includes three sections. In first section, thin film Cu-Ni alloys ranging from 2-8nm were synthesized and laser irradiated. The evolution of the spinodal dewetting process is investigated as a function of the thin film composition which ultimately dictates the size distribution and spacing of the nanoparticles, and the optical measurements of the copper rich alloy nanoparticles revealed characteristic plasmonic peaks. In section two, the dewetting behavior of nanolithographically patterned copper rings on Silicon substrate was studied. The self assembly of the rings into ordered nanoparticle/nanodrop arrays was accomplished via nanosecond pulsed laser heating. The resultant length scale of the 13nm and 7nm thick copper rings was correlated to the competition between transport and instabilities time scales during the liquid lifetime of the melted copper rings. To explore the influence of different substrates with different surface energy, the pulsed laser heated assembly of lithographically patterned copper rings on SiO2 substrate was studied in the last section. The correlated transport and instabilities show modified timescales. It is demonstrated again that the original geometry dictates the instability pathway, which for narrow rings obeys the Rayleigh-Plateau instability and for wider rings are influenced by the thin film instability.
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