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 Degree Discipline: Physics
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Electrostatic Effects in III-V Semiconductor Based Metal-optical Nanostructures

Electrostatic Effects in III-V Semiconductor Based Metal-optical Nanostructures

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Date: May 2012
Creator: Gryczynski, Karol Grzegorz
Description: The modification of the band edge or emission energy of semiconductor quantum well light emitters due to image charge induced phenomenon is an emerging field of study. This effect observed in quantum well light emitters is critical for all metal-optics based light emitters including plasmonics, or nanometallic electrode based light emitters. This dissertation presents, for the first time, a systematic study of the image charge effect on semiconductor–metal systems. the necessity of introducing the image charge interactions is demonstrated by experiments and mathematical methods for semiconductor-metal image charge interactions are introduced and developed.
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Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures

Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures

Date: May 2012
Creator: Llopis, Antonio
Description: III-V nitrides have been put to use in a variety of applications including laser diodes for modern DVD devices and for solid-state white lighting. Plasmonics has come to the foreground over the past decade as a means for increasing the internal quantum efficiency (IQE) of devices through resonant interaction with surface plasmons which exist at metal/dielectric interfaces. Increases in emission intensity of an order of magnitude have been previously reported using silver thin-films on InGaN/GaN MQWs. the dependence on resonant interaction between the plasmons and the light emitter limits the applications of plasmonics for light emission. This dissertation presents a new non-resonant mechanism based on electrostatic interaction of carriers with induced image charges in a nearby metallic nanoparticle. Enhancement similar in strength to that of plasmonics is observed, without the restrictions imposed upon resonant interactions. in this work we demonstrate several key features of this new interaction, including intensity-dependent saturation, increase in the radiative recombination lifetime, and strongly inhomogeneous light emission. We also present a model for the interaction based on the aforementioned image charge interactions. Also discussed are results of work done in the course of this research resulting in the development of a novel technique for strain measurement ...
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Modification of Graphene Properties: Electron Induced Reversible Hydrogenation, Oxidative Etching and Layer-by-layer Thinning

Modification of Graphene Properties: Electron Induced Reversible Hydrogenation, Oxidative Etching and Layer-by-layer Thinning

Date: May 2012
Creator: Jones, Jason David
Description: In this dissertation, I present the mechanism of graphene hydrogenation via three different electron sources: scanning electron microscopy, e-beam irradiation and H2 and He plasma irradiation. in each case, hydrogenation occurs due to electron impact fragmentation of adsorbed water vapor from the sample preparation process. in the proposed model, secondary and backscattered electrons generated from incident electron interactions with the underlying silicon substrate are responsible for the dissociation of water vapor. Chemisorbed H species from the dissociation are responsible for converting graphene into hydrogenated graphene, graphane. These results may lead to higher quality graphane films having a larger band gap than currently reported. in addition, the dissertation presents a novel and scalable method of controllably removing single atomic planes from multi-layer graphene using electron irradiation from an intense He plasma under a positive sample bias. As the electronic properties or multi-layer graphene are highly dependent on the number of layers, n, reducing n in certain regions has many benefits. for example, a mask in conjunction with this thinning method could be used for device applications.
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Temporal Properties Of Dynamic Processes On Complex Networks

Temporal Properties Of Dynamic Processes On Complex Networks

Date: December 2011
Creator: Turalska, Malgorzata A.
Description: Many social, biological and technological systems can be viewed as complex networks with a large number of interacting components. However despite recent advancements in network theory, a satisfactory description of dynamic processes arising in such cooperative systems is a subject of ongoing research. In this dissertation the emergence of dynamical complexity in networks of interacting stochastic oscillators is investigated. In particular I demonstrate that networks of two and three state stochastic oscillators present a second-order phase transition with respect to the strength of coupling between individual units. I show that at the critical point fluctuations of the global order parameter are characterized by an inverse-power law distribution and I assess their renewal properties. Additionally, I study the effect that different types of perturbation have on dynamical properties of the model. I discuss the relevance of those observations for the transmission of information between complex systems.
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High Efficiency High Power Blue Laser by Resonant Doubling in PPKTP

High Efficiency High Power Blue Laser by Resonant Doubling in PPKTP

Date: August 2011
Creator: Danekar, Koustubh
Description: I developed a high power blue laser for use in scientific and technical applications (eg. precision spectroscopy, semiconductor inspection, flow cytometry, etc). It is linearly polarized, single longitudinal and single transverse mode, and a convenient fiber coupled continuous wave (cw) laser source. My technique employs external cavity frequency doubling and provides better power and beam quality than commercially available blue diode lasers. I use a fiber Bragg grating (FBG) stabilized infrared (IR) semiconductor laser source with a polarization maintaining (PM) fiber coupled output. Using a custom made optical and mechanical design this output is coupled with a mode matching efficiency of 96% into the doubling cavity. With this carefully designed and optimized cavity, measurements were carried out at various fundamental input powers. A net efficie ncy of 81 % with an output power of 680 mW at 486 nm was obtained using 840 mW of IR input. Also I report an 87.5 % net efficiency in coupling of blue light from servo locked cavity into a single mode PM fiber. Thus I have demonstrated a total fiber to fiber efficiency of 71% can be achieved in our approach using periodically poled potassium titanyl phosphate (PPKTP). To obtain these results, all ...
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The Interactions of Plasma with Low-k Dielectrics: Fundamental Damage and Protection Mechanisms

The Interactions of Plasma with Low-k Dielectrics: Fundamental Damage and Protection Mechanisms

Date: August 2011
Creator: Behera, Swayambhu Prasad
Description: Nanoporous low-k dielectrics are used for integrated circuit interconnects to reduce the propagation delays, and cross talk noise between metal wires as an alternative material for SiO2. These materials, typically organosilicate glass (OSG) films, are exposed to oxygen plasmas during photoresist stripping and related processes which substantially damage the film by abstracting carbon, incorporating O and OH, eventually leading to significantly increased k values. Systematic studies have been performed to understand the oxygen plasma-induced damage mechanisms on different low-k OSG films of various porosity and pore interconnectedness. Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and atomic force microscopy are used to understand the damage kinetics of O radicals, ultraviolet photons and charged species, and possible ways to control the carbon loss from the film. FTIR results demonstrate that O radical present in the plasma is primarily responsible for carbon abstraction and this is governed by diffusion mechanism involving interconnected film nanopores. The loss of carbon from the film can be controlled by closing the pore interconnections, He plasma pretreatment is an effective way to control the damage at longer exposure by closing the connections between the pores.
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Nanoscale Materials Applications: Thermoelectrical, Biological, and Optical Applications with Nanomanipulation Technology

Nanoscale Materials Applications: Thermoelectrical, Biological, and Optical Applications with Nanomanipulation Technology

Date: August 2011
Creator: Lee, Kyung-Min
Description: In a sub-wavelength scale, even approaching to the atomic scale, nanoscale physics shows various novel phenomena. Since it has been named, nanoscience and nanotechnology has been employed to explore and exploit this small scale world. For example, with various functionalized features, nanowire (NW) has been making its leading position in the researches of physics, chemistry, biology, and engineering as a miniaturized building block. Its individual characteristic shows superior and unique features compared with its bulk counterpart. As one part of these research efforts and progresses, and with a part of the fulfillment of degree study, novel methodologies and device structures in nanoscale were devised and developed to show the abilities of high performing thermoelectrical, biological, and optical applications. A single β-SiC NW was characterized for its thermoelectric properties (thermal conductivity, Seebeck coefficient, and figure of merit) to compare with its bulk counterpart. The combined structure of Ag NW and ND was made to exhibit its ability of clear imaging of a fluorescent cell. And a plasmonic nanosture of silver (Ag) nanodot array and a β-SiC NW was fabricated to show a high efficient light harvesting device that allows us to make a better efficient solar cell. Novel nanomanipulation techniques were ...
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Ion Beam Synthesis of Carbon Assisted Nanosystems in Silicon Based Substrates

Ion Beam Synthesis of Carbon Assisted Nanosystems in Silicon Based Substrates

Date: May 2011
Creator: Poudel, Prakash Raj
Description: The systematic study of the formation of β-SiC formed by low energy carbon ion (C-)implantation into Si followed by high temperature annealing is presented. The research is performed to explore the optimal annealing conditions. The formation of crystalline β-SiC is clearly observed in the sample annealed at 1100 °C for a period of 1 hr. Quantitative analysis is performed in the formation of β-SiC by the process of implantation of different carbon ion fluences of 1×1017, 2×1017, 5×1017, and 8×1017 atoms /cm2 at an ion energy of 65 keV into Si. It is observed that the average size of β-SiC crystals decreased and the amount of β-SiC crystals increased with the increase in the implanted fluences when the samples were annealed at 1100°C for 1 hr. However, it is observed that the amount of β-SiC linearly increased with the implanted fluences up to 5×1017 atoms /cm2. Above this fluence the amount of β-SiC appears to saturate. The stability of graphitic C-C bonds at 1100°C limits the growth of SiC precipitates in the sample implanted at a fluence of 8×1017 atoms /cm2 which results in the saturation behavior of SiC formation in the present study. Secondly, the carbon cluster formation process ...
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Thorium and Uranium M-shell X-ray Production Cross Sections for 0.4 – 4.0 MeV Protons, 0.4 - 6.0 MeV Helium Ions, 4.5 – 11.3 MeV Carbon Ions, and 4.5 – 13.5 MeV Oxygen Ions.

Thorium and Uranium M-shell X-ray Production Cross Sections for 0.4 – 4.0 MeV Protons, 0.4 - 6.0 MeV Helium Ions, 4.5 – 11.3 MeV Carbon Ions, and 4.5 – 13.5 MeV Oxygen Ions.

Date: May 2011
Creator: Phinney, Lucas C.
Description: The M-shell x-ray production cross section for thorium and uranium have been determined for protons of energy 0.4 - 4.0 MeV, helium ions of energy 0.4 - 6.0 MeV, carbon ions of energy 4.5 - 11.3 MeV and oxygen ions of energy 4.5 - 13.5 MeV. The total cross sections and the cross sections for individual x-ray peaks in the spectrum, consisting of the following transitions Mz (M4-N2, M5-N3, M4-N3), Ma (M5-N6,7), Mb (M4-N6, M5-O3, M4- O2), and Mg (M4-O3, M5-P3, M3-N4, M3-N5), were compared to the theoretical values determined from the PWBA + OBKN and ECUSAR. The theoretical values for the carbon and oxygen ions were also modified to take into account the effects of multiple ionizations of the target atom by the heavier ions. It is shown that the results of the ECUSAR theory tend to provide better agreement with the experimental data.
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A Determination of the Fine Structure Constant Using Precision Measurements of Helium Fine Structure

A Determination of the Fine Structure Constant Using Precision Measurements of Helium Fine Structure

Date: August 2010
Creator: Smiciklas, Marc
Description: Spectroscopic measurements of the helium atom are performed to high precision using an atomic beam apparatus and electro-optic laser techniques. These measurements, in addition to serving as a test of helium theory, also provide a new determination of the fine structure constant α. An apparatus was designed and built to overcome limitations encountered in a previous experiment. Not only did this allow an improved level of precision but also enabled new consistency checks, including an extremely useful measurement in 3He. I discuss the details of the experimental setup along with the major changes and improvements. A new value for the J = 0 to 2 fine structure interval in the 23P state of 4He is measured to be 31 908 131.25(30) kHz. The 300 Hz precision of this result represents an improvement over previous results by more than a factor of three. Combined with the latest theoretical calculations, this yields a new determination of α with better than 5 ppb uncertainty, α-1 = 137.035 999 55(64).
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