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Title: Selective electro-magnetic absorbers based on metal-dielectric-metal thin-film cavities.
Creator: Nath, Janardan, Peale, Robert, Ishigami, Masa, Chernyak, Leonid, Vodopyanov, Konstantin, University of Central Florida
Abstract / Description: Efficient absorption of light is required for a large number of applications such as thermo-photovoltaics,thermal imaging, bio-sensing, thermal emitters, astronomy, and stealth technology. Strong light absorbers found in nature with high intrinsic losses such as carbon black, metal-black, and carbon nano-tubes etc. are bulky, not design-tunable and are hard to pattern for micro- and nano- devices. We developed thin-film, high performance absorbers in the visible, near-, mid-, long-wave - and...
Show moreEfficient absorption of light is required for a large number of applications such as thermo-photovoltaics,thermal imaging, bio-sensing, thermal emitters, astronomy, and stealth technology. Strong light absorbers found in nature with high intrinsic losses such as carbon black, metal-black, and carbon nano-tubes etc. are bulky, not design-tunable and are hard to pattern for micro- and nano- devices. We developed thin-film, high performance absorbers in the visible, near-, mid-, long-wave - and far-IR region based on a 3 layer metal-dielectric-metal (MDM) structure.We fabricated a 3-layerMDMabsorber with large band-widths in the visible and near IR spectral range without any lithographic patterning. This was the first demonstration in the optical range of the Salisbury Screen, which was originally invented for radar absorption. A Fabry-Perotcavity model depending on the thickness of the dielectric, but also the effective permittivity of the semi-transparent top metal gives calculated spectra that agree well with experiment.Secondly, we fabricated long-wave IR and far-IR MDM absorbers comprising surface patterns of periodic metal squares on the dielectric layer. Strong absorption in multiple bands were obtained, and these depended weakly on polarization and angle of incidence. Though such absorbers had been extensively studied by electrodynamic simulations and experiment in the visible to far- R regions, there existed no analytic model that could accurately predict the wavelengths of the multiple resonances. We developed a theoretical model for these absorbers based on standingwave resonances, which accurately predicts resonance wavelengths for experiment and simulation for the first time. Unlike metamaterial theories our model does not depend on the periodicity of the squares but only on their lateral dimension and the thickness of the dielectric. This feature is confirmed by synchrotron-based IR spectral imaging microscopy of single isolated squares.
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Date Issued: 2015
Identifier: CFE0005851, ucf:50907
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005851

Title: Comparison Of Casimir , Elastic, Electrostatic Forces For A Micro-Cantilever.
Creator: Alhasan, Ammar, Peale, Robert, Del Barco, Enrique, Chow, Lee, University of Central Florida
Abstract / Description: Casimir force is a cause of stiction (adhesion) between metal surfaces in Micro-Electro Mechanical Systems (MEMS). Casimir Force depends strongly on the separation of the two surfaces and the contact area. This thesis reviews the theory and prior experimental demonstrations of the Casimir force. Then the Casimir attractive force is calculated for a particular MEMS cantilever device, in which the metal cantilever tip is required to repeatedly touch and release from a metal tip pad on the...
Show moreCasimir force is a cause of stiction (adhesion) between metal surfaces in Micro-Electro Mechanical Systems (MEMS). Casimir Force depends strongly on the separation of the two surfaces and the contact area. This thesis reviews the theory and prior experimental demonstrations of the Casimir force. Then the Casimir attractive force is calculated for a particular MEMS cantilever device, in which the metal cantilever tip is required to repeatedly touch and release from a metal tip pad on the substrate surface in response to a periodic driving electrostatic force. The elastic force due to the bending of the cantilever support arms is also a consideration in the device operation. The three forces are calculated analytically and compared as a function of cantilever tip height. Calculation of the electrostatic force uses coefficients of capacitance and electrostatic induction determined numerically by the finite element method, including the effect of permittivity for the structural oxide. A condition on the tip area to allow electrostatic release of the tip from the surface against Casimir sticking and elastic restoring forces is established.
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Date Issued: 2014
Identifier: CFE0005123, ucf:50713
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005123

Title: IMPACT OF GAMMA-IRRADIATION ON THE CHARACTERISTICS OF III-N/GaN BASED HIGH ELECTRON MOBILITY TRANSISTORS.
Creator: Yadav, Anupama, Flitsiyan, Elena, Chernyak, Leonid, Peale, Robert, Richie, Samuel, University of Central Florida
Abstract / Description: In this study, the fundamental properties of AlGaN/GaN based High Electron Mobility Transistors (HEMTs) have been investigated in order to optimize their performance in radiation harsh environment. AlGaN/GaN HEMTs were irradiated with 60Co gamma-rays to doses up to 1000 Gy, and the effects of irradiation on the devices' transport and optical properties were analyzed. Understanding the radiation affects in HEMTs devices, on carrier transport, recombination rates and traps creation play a...
Show moreIn this study, the fundamental properties of AlGaN/GaN based High Electron Mobility Transistors (HEMTs) have been investigated in order to optimize their performance in radiation harsh environment. AlGaN/GaN HEMTs were irradiated with 60Co gamma-rays to doses up to 1000 Gy, and the effects of irradiation on the devices' transport and optical properties were analyzed. Understanding the radiation affects in HEMTs devices, on carrier transport, recombination rates and traps creation play a significant role in development and design of radiation resistant semiconductor components for different applications. Electrical testing combined with temperature dependent Electron Beam Induced Current (EBIC) that we used in our investigations, provided critical information on defects induced in the material because of gamma-irradiation. It was shown that low dose (below ~250 Gy) and high doses (above ~250 Gy) of gamma-irradiation affects the AlGaN/GaN HEMTs due to different mechanisms. For low doses of gamma-irradiation, the improvement in minority carrier diffusion length is likely associated with the irradiation-induced growing lifetime of the non-equilibrium carriers. However, with the increased dose of irradiation (above ~ 250 Gy), the concentration of point defects, such as nitrogen vacancies, as well as the complexes involving native defects increases which results in the non-equilibrium carrier scattering. The impact of defect scattering is more pronounced at higher radiation, which leads to the degradation in the mobility and therefore the diffusion length. In addition for each device under investigation, the temperature dependent minority carrier diffusion length measurements were carried out. These measurements allowed the extraction of the activation energy for the temperature-induced enhancement of the minority carrier transport, which (activation energy) bears a signature of defect levels involved the carrier recombination process. Comparing the activation energy before and after gamma-irradiation identified the radiation-induced defect levels and their dependences. To complement EBIC measurements, spatially resolved Cathodoluminescence (CL) measurements were carried out at variable temperatures. Similar to the EBIC measurements, CL probing before and after the gamma-irradiation allowed the identification of possible defect levels generated as a result of gamma-bombardment. The observed decrease in the CL peak intensity after gamma-irradiation provides the direct evidence of the decrease in the number of recombination events. Based on the findings, the decay in the near-band-edge intensity after low-dose of gamma-irradiation (below ~250 Gy) was explained as a consequence of increased non-equilibrium carrier lifetime. For high doses (above ~250 Gy), decay in the CL intensity was observed to be related to the reduction in the mobility of charge carriers. The results of EBIC are correlated with the CL measurements in order to demonstrate that same underlying process is responsible for the changes induced by the gamma-irradiation. DC current-voltage measurements were also conducted on the transistors to assess the impact of gamma-irradiation on transfer, gate and drain characteristics. Exposure of AlGaN/GaN HEMTs to high dose of 60Co gamma-irradiation (above ~ 250 Gy) resulted in significant device degradation. Gamma-rays doses up to 1000 Gy are shown to result in positive shift in threshold voltage, a reduction in the drain current and transconductance due to increased trapping of carriers and dispersion of charge. In addition, a significant increase in the gate leakage current was observed in both forward and reverse directions after irradiation. Post-irradiation annealing at relatively low temperature was shown to restore the minority carrier transport as well as the electrical characteristics of the devices. The level of recovery of gamma-irradiated devices after annealing treatment depends on the dose of the irradiation. The devices that show most recovery for a particular annealing temperature are those exposed to the low doses of gamma-irradiation, while those exposed to the highest doses results in no recovery of performance. The latter fact indicates that a higher device annealing temperature is needed for larger doses of gamma-irradiation.
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Date Issued: 2016
Identifier: CFE0006424, ucf:51458
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006424

Title: Growth and doping of MoS2 thin films for electronic and optoelectronic applications.
Creator: Abouelkhair, Hussain, Peale, Robert, Kaden, William, Stolbov, Sergey, Coffey, Kevin, University of Central Florida
Abstract / Description: MoS2 high absorption coefficient, high mobility, mechanical flexibility, and chemical inertness is very promising for many electronic and optoelectronic applications. The growth of high-quality MoS2 by a scalable and doping compatible method is still lacking. Therefore, the suitable dopants for MoS2 are not fully explored yet. This dissertation consists mainly of four main studies. The first study is on the growth of MoS2 thin films by atmospheric pressure chemical vapor deposition. Scanning...
Show moreMoS2 high absorption coefficient, high mobility, mechanical flexibility, and chemical inertness is very promising for many electronic and optoelectronic applications. The growth of high-quality MoS2 by a scalable and doping compatible method is still lacking. Therefore, the suitable dopants for MoS2 are not fully explored yet. This dissertation consists mainly of four main studies. The first study is on the growth of MoS2 thin films by atmospheric pressure chemical vapor deposition. Scanning electron microscope images revealed the growth of microdomes of MoS2 on top of a smooth MoS2 film. These microdomes are very promising as a broadband omnidirectional light trap for light harvesting applications. The second study is on the growth of MoS2 thin films by low pressure chemical vapor deposition (LPCVD). Control of sulfur vapor flow is essential for the growth of a pure phase of MoS2. Turning off sulfur vapor flow during the cooling cycle at 700 (&)#186;C leads to the growth of highly textured MoS2 with a Hall mobility of 20 cm2/Vs. The third study was on the growth of Ti-doped MoS2 thin films by LPCVD. The successful doping was confirmed by Hall effect measurement and secondary ion mass spectrometry (SIMS). Different growth temperatures from 1000 to 700 ? were studied. Ti act as a donor in MoS2. The fourth study is on fluorine-doped SnO2 (FTO) which has many technological applications including solar cells and transistors. FTO was grown by an aqueous-spray-based method. The main objective was to compare the actual against the nominal concentration of fluorine using SIMS. The concentration of fluorine in the grown films is lower than the concentration of fluorine in the aqueous solution.?
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Date Issued: 2017
Identifier: CFE0006847, ucf:51767
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006847

Title: Optical Parity Time Metasurface Structures.
Creator: El Halawany, Ahmed, Christodoulides, Demetrios, Rahman, Talat, Peale, Robert, Likamwa, Patrick, University of Central Florida
Abstract / Description: In the last few years, optics has witnessed the emergence of two fields namely metasurfaces and parity-time (PT) symmetry. Optical metasurfaces are engineered structures that provide unique responses to electromagnetic waves, absent in natural materials. Optical metasurfaces are known for their reduced dimensionality i.e. subwavelength and consequently lower losses are anticipated. The other paradigm is the PT symmetric materials, also known as photonic synthetic matter. PT symmetry has...
Show moreIn the last few years, optics has witnessed the emergence of two fields namely metasurfaces and parity-time (PT) symmetry. Optical metasurfaces are engineered structures that provide unique responses to electromagnetic waves, absent in natural materials. Optical metasurfaces are known for their reduced dimensionality i.e. subwavelength and consequently lower losses are anticipated. The other paradigm is the PT symmetric materials, also known as photonic synthetic matter. PT symmetry has emerged from quantum mechanics when a new class of non-Hermitian Hamiltonian quantum systems was highlighted to have real eigenvalues, hence eradicating Hermiticity of the Hamiltonian as an essential condition to the existence of real eigenvalues.The first half of the thesis is focused on the experimental and numerical realization of PT symmetric metasurfaces. A systematic methodology is developed to implement this class of metasurfaces in both one-dimensional and two-dimensional geometries. In two dimensional systems, PT symmetry can be established by employing either H-like diffractive elements or diatomic oblique Bravais lattices. It is shown that the passive PT symmetric metasurfaces can be utilized to appropriately engineer the resulting far-field characteristics. Such PT-symmetric structures are capable of eliminating diffraction orders in specific directions, while maintaining or even enhancing the remaining orders. Later, it is shown a first ever attempt of PT metasurface fabricated on a flexible polymer (polyimide) substrate. The studied PT metasurface exhibits the ability to direct light, i.e. Poynting vector in a desired direction. Herein, the light scattered from the fabricated device in the undesired direction is attenuated by at least an order of magnitude. The proposed PT symmetric metasurface is essentially diatomic Honeycomb Bravais lattice, where both the passive and lossy elements exist side by side on each site separated by 50 nm. The unidirectionality of the studied metasurface is not limited to a single wavelength, on the contrary, it is observed to be effective on the entire visible band (400 (-) 600 nm). The PT symmetric meatsurface is also fabricated on a high strength substrate; sapphire (Al2O3). An excellent agreement between the experimental and numerical (COMSOL) results is found for both substrates. Customized modifications to the current design can open avenues to study the unidirectionality of metasurfaces to different optical bands, for example IR.The second part of the thesis deals with the theoretical modeling of the dynamics of an electron that gets trapped by means of decoherence and quantum interference in the central quantum dot (QD) of a semiconductor nanoring (NR) made of five QDs, between 100 and 300 K. The electron's dynamics is described by a master equation with a Hamiltonian based on the tight-binding model, taking into account electron(-)LO phonon interaction. Based on this configuration, the probability to trap an electron with no decoherence is almost 27%. In contrast, the probability to trap an electron with decoherence is 70% at 100 K, 63% at 200 K and 58% at 300 K. Our model provides a novel method of trapping an electron at room temperature.This setup is then used to propose a theoretical model for an electrically driven single photon source operating at high temperatures. It is shown that the decoherence, which is usually the main obstacle for operating single photon sources at high temperatures, ensures an efficient operation of the presented electrically driven single photon source at high temperatures. The single-photon source is driven by a single electron source attached to a heterostructure semiconductor nanoring. The electron's dynamics in the nanoring and the subsequent recombination with the hole is described by the generalized master equation with a Hamiltonian based on tight-binding model, taking into account the electron-LO phonon interaction. As a result of decoherence, an almost 100% single photon emission with a strong antibunching behavior i.e. g(2)(0) (<)(<) 1 at high temperature up to 300 K is achieved.
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Date Issued: 2016
Identifier: CFE0006454, ucf:51421
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006454

Title: Vanadium Oxide Microbolometers with Patterned Gold Black or Plasmonic Resonant Absorbers.
Creator: Smith, Evan, Peale, Robert, Khondaker, Saiful, Dove, Adrienne, Boreman, Glenn, University of Central Florida
Abstract / Description: 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...
Show moreHigh 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.
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Date Issued: 2015
Identifier: CFE0006004, ucf:51026
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006004

Title: Pulsed Tm-Fiber Laser for Mid-IR Generation.
Creator: Kadwani, Pankaj, Richardson, Martin, Abouraddy, Ayman, Schulzgen, Axel, Peale, Robert, University of Central Florida
Abstract / Description: Thulium fiber lasers have attracted interest based on their long emission wavelength and large bandwidth (~1.8 (-) 2.1 (&)#181;m) relative to more established ytterbium and erbium fiber lasers. In addition, Tm:fiber lasers offer the potential for high efficiencies (~60 %) and high output power levels both in cw as well as pulsed regimes. These attributes are useful particularly in applications such as remote sensing, materials processing and mid-infrared generation. This dissertation...
Show moreThulium fiber lasers have attracted interest based on their long emission wavelength and large bandwidth (~1.8 (-) 2.1 (&)#181;m) relative to more established ytterbium and erbium fiber lasers. In addition, Tm:fiber lasers offer the potential for high efficiencies (~60 %) and high output power levels both in cw as well as pulsed regimes. These attributes are useful particularly in applications such as remote sensing, materials processing and mid-infrared generation. This dissertation describes the development of novel nanosecond pulsed thulium fiber laser systems with record high peak power levels in order to pump nonlinear mid-infrared generation. The peak power scaling in thulium fiber lasers requires new fiber designs with ultra large mode field area (MFA). Two different classes of prototype thulium doped photonic crystal fibers (PCF) were investigated for high peak power generation. The first prototype is a flexible-PCF with 50 ?m core diameter, and the second is a rod-type PCF with 80 ?m diameter core. A robust single stage master oscillator power amplifier (MOPA) source based on flexible-PCF was developed. This source provided narrow linewidth, tunable wavelength, variable pulse duration, high peak power, and high energy nanosecond pulses. The PCF-rod was implemented as a second stage power amplifier. This system generated a record level of ~1 MW peak power output with 6.4 ns pulse-duration at 1 kHz repetition rate. This thulium doped PCF based MOPA system is a state of the art laser source providing high quality nanosecond pulses. The single stage MOPA system was successfully implemented to pump a zinc germanium phosphide (ZGP) crystal in an optical parametric oscillator (OPO) cavity to generate 3 - 5 (&)#181;m wavelengths. The MOPA source was also used to demonstrate backside machining in silicon wafer. The PCF based laser system demonstrated an order of magnitude increase in the peak power achievable in nanosecond thulium doped fiber laser systems, and further scaling appears possible. Further increases in the peak power will enable additional capabilities for mid-IR generation and associated applications.
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Date Issued: 2013
Identifier: CFE0005100, ucf:50739
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005100

Title: On-Chip Optical Stabilization of High-Speed Mode-locked Quantum Dot Lasers for Next Generation Optical Networks.
Creator: Ardey, Abhijeet, Delfyett, Peter, Chow, Lee, Peale, Robert, Likamwa, Patrick, University of Central Florida
Abstract / Description: Monolithic passively mode-locked colliding pulse semiconductor lasers generating pico- to sub-picosecond terahertz optical pulse trains are promising sources for future applications in ultra-high speed data transmission systems and optical measurements. However, in the absence of external synchronization, these passively mode-locked lasers suffer from large amplitude and timing jitter instabilities resulting in broad comb linewidths, which precludes many applications in the field of coherent...
Show moreMonolithic passively mode-locked colliding pulse semiconductor lasers generating pico- to sub-picosecond terahertz optical pulse trains are promising sources for future applications in ultra-high speed data transmission systems and optical measurements. However, in the absence of external synchronization, these passively mode-locked lasers suffer from large amplitude and timing jitter instabilities resulting in broad comb linewidths, which precludes many applications in the field of coherent communications and signal processing where a much narrower frequency line set is needed. In this dissertation, a novel quantum dot based coupled cavity laser is presented, where for the first time, four-wave mixing (FWM) in the monolithically integrated saturable absorber is used to injection lock a monolithic colliding pulse mode-locked (CPM) laser with a mode-locked high-Q ring laser. Starting with a passively mode-locked master ring laser, a stable 30 GHz optical pulse train is generated with more than 10 dB reduction in the RF noise level at 20 MHz offset and close to 3-times reduction in the average optical linewidth of the injection locked CPM slave laser. The FWM process is subsequently verified experimentally and conclusively shown to be the primary mechanism responsible for the observed injection locking. Other linear scattering effects are found to be negligible, as predicted in the orthogonal waveguide configuration. The novel injection locking technique is further exploited by employing optical hybrid mode-locking and increasing the Q of the master ring cavity, to realize an improved stabilization architecture. Dramatic reduction is shown with more than 14-times reduction in the photodetected beat linewidth and almost 5-times reduction in the optical linewidth of the injection locked slave laser with generation of close to transform limited pulses at ~ 30 GHz. These results demonstrate the effectiveness of the novel injection locking technique for an all-on-chip stability transfer and provides a new way of stabilizing monolithic optical pulse sources for applications in future high speed optical networks.
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Date Issued: 2014
Identifier: CFE0005299, ucf:50518
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005299

Title: Nonlinear integrated photonics on silicon and gallium arsenide substrates.
Creator: Ma, Jichi, Fathpour, Sasan, Hagan, David, Li, Guifang, Peale, Robert, University of Central Florida
Abstract / Description: Silicon photonics is nowadays a mature technology and is on the verge of becoming a blossoming industry. Silicon photonics has also been pursued as a platform for integrated nonlinear optics based on Raman and Kerr effects. In recent years, more futuristic directions have been pursued by various groups. For instance, the realm of silicon photonics has been expanded beyond the well-established near-infrared wavelengths and into the mid-infrared (3 (-) 5 (&)#181;m). In this wavelength range,...
Show moreSilicon photonics is nowadays a mature technology and is on the verge of becoming a blossoming industry. Silicon photonics has also been pursued as a platform for integrated nonlinear optics based on Raman and Kerr effects. In recent years, more futuristic directions have been pursued by various groups. For instance, the realm of silicon photonics has been expanded beyond the well-established near-infrared wavelengths and into the mid-infrared (3 (-) 5 (&)#181;m). In this wavelength range, the omnipresent hurdle of nonlinear silicon photonics in the telecommunication band, i.e., nonlinear losses due to two-photon absorption, is inherently nonexistent. With the lack of efficient light-emission capability and second-order optical nonlinearity in silicon, heterogeneous integration with other material systems has been another direction pursued. Finally, several approaches have been proposed and demonstrated to address the energy efficiency of silicon photonic devices in the near-infrared wavelength range. In this dissertation, theoretical and experimental works are conducted to extend applications of integrated photonics into mid-infrared wavelengths based on silicon, demonstrate heterogeneous integration of tantalum pentoxide and lithium niobate photonics on silicon substrates, and study two-photon photovoltaic effect in gallium arsenide and plasmonic-enhanced structures.Specifically, performance and noise properties of nonlinear silicon photonic devices, such as Raman lasers and optical parametric amplifiers, based on novel and reliable waveguide technologies are studied. Both near-infrared and mid-infrared nonlinear silicon devices have been studied for comparison. Novel tantalum-pentoxide- and lithium-niobate-on-silicon platforms are developed for compact microring resonators and Mach-Zehnder modulators. Third- and second-harmonic generations are theoretical studied based on these two platforms, respectively. Also, the two-photon photovoltaic effect is studied in gallium arsenide waveguides for the first time. The effect, which was first demonstrated in silicon, is the nonlinear equivalent of the photovoltaic effect of solar cells and offers a viable solution for achieving energy-efficient photonic devices. The measured power efficiency achieved in gallium arsenide is higher than that in silicon and even higher efficiency is theoretically predicted with optimized designs. Finally, plasmonic-enhanced photovoltaic power converters, based on the two-photon photovoltaic effect in silicon using subwavelength apertures in metallic films, are proposed and theoretically studied.
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Date Issued: 2014
Identifier: CFE0005373, ucf:50441
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005373

Title: Electronic transport properties of carbon nanotubes: the impact of atomic charged impurities.
Creator: Tsuchikawa, Ryuichi, Ishigami, Masa, Mucciolo, Eduardo, Peale, Robert, Masunov, Artem, University of Central Florida
Abstract / Description: Even changing one atom in nanoscale materials is expected to alter their properties due to their small physical sizes. Such sensitivity can be utilized to modify materials' properties from bottom up and is essential for the utility of nanoscale materials. As such, the impact of extrinsic atomic adsorbates was measured on pristine graphene and a network of carbon nanotubes using atomic hydrogen, cesium atoms, and dye molecules. In order to further quantify such an atomic influence, the...
Show moreEven changing one atom in nanoscale materials is expected to alter their properties due to their small physical sizes. Such sensitivity can be utilized to modify materials' properties from bottom up and is essential for the utility of nanoscale materials. As such, the impact of extrinsic atomic adsorbates was measured on pristine graphene and a network of carbon nanotubes using atomic hydrogen, cesium atoms, and dye molecules. In order to further quantify such an atomic influence, the resistance induced by a single potassium atom on metallic and semiconducting carbon nanotubes was measured for the first time. Carbon nanotubes are sensitive to adsorbates due to their high surface-to-volume ratio. The resistance arising from the presence of extrinsic impurity atoms depends on the types of nanotubes. Metallic carbon nanotubes are resilient to a long-ranged, Coulomb-like potential, whereas semiconducting carbon nanotubes are susceptible to these impurities. The difference in the scattering strength originates from the chirality of carbon nanotubes, which defines their unique electronic properties. This difference had not directly measured experimentally because of the issue of contact resistance, the difficulty of chirality identification, and the uncertainty in the number of impurity atoms introduced on carbon nanotubes.We synthesized atomically clean, long ((>)100 ?m) carbon nanotubes, and their chirality was identified by Rayleigh scattering spectroscopy. We introduced potassium atoms on the nanotubes to impose a long-range, Coulomb potential and measured the change in resistivity, excluding the contact resistance, by plotting the resistance as a function of the carbon nanotube length. The flux of potassium atoms coming onto the nanotubes was monitored by quartz crystal microbalance, and the scattering strength of a single potassium atom was deduced from the change in resistivity and the density of potassium atoms on the nanotubes. We found that the scattering strength of potassium atoms on semiconducting nanotubes depends on the charge carrier type (holes or electrons). Metallic nanotubes were found to be less affected by the presence of potassium atoms than semiconducting nanotubes, but the scattering strength showed a large dependence on Fermi energy. These experimental results were compared to theoretical simulations, and we found a good agreement with the experiments. Our findings provide crucial information for the application of carbon nanotubes for electronic devices, such as transistors and sensors.
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Date Issued: 2015
Identifier: CFE0005729, ucf:50078
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005729

Title: Detecting and Characterizing Exoplanets: The GJ 436 and HD 149026 Systems.
Creator: Stevenson, Kevin, Harrington, Joseph, Peale, Robert, Fernandez, Yanga, Deming, Drake, University of Central Florida
Abstract / Description: This dissertation investigates two stellar systems known to contain extrasolar planets. It is comprised of five chapters that are readily divided into three independent but related analyses. Chapter 1 reports on the analysis of low signal-to-noise secondary-eclipse observations of the Neptune-sized exoplanet GJ 436b using the Spitzer Space Telescope in multiple infrared channels. The measured wavelength-dependent eclipse depths provide constraints on the planet's dayside atmospheric...
Show moreThis dissertation investigates two stellar systems known to contain extrasolar planets. It is comprised of five chapters that are readily divided into three independent but related analyses. Chapter 1 reports on the analysis of low signal-to-noise secondary-eclipse observations of the Neptune-sized exoplanet GJ 436b using the Spitzer Space Telescope in multiple infrared channels. The measured wavelength-dependent eclipse depths provide constraints on the planet's dayside atmospheric composition and thermal profile. The analysis indicates that GJ 436b's atmosphere is abundant in carbon monoxide and deficient in methane relative to thermochemical equilibrium models for the predicted hydrogen-dominated atmosphere.Chapter 2 discusses the techniques used to analyze GJ 436b, introduces the Least Asymmetry centering method and compares its effectiveness to two existing techniques, and describes the functions used to model Spitzer's position- and time-dependent systematics. Additionally, it includes best-fit parameters with uncertainties, histograms of the free parameters, and correlation plots between free parameters.Chapter 3 reports on the analysis of eleven HD 149026b secondary-eclipse observations at five Spitzer wavelengths plus three primary-transit observations at 8.0 microns. Chemical-equilibrium models find no indication of a temperature inversion in the dayside atmosphere of HD 149026b. The best-fit model favors large amounts of CO and CO2, moderate heat redistribution (f = 0.5), and a strongly enhanced metallicity. These analyses use BiLinearly-Interpolated Subpixel Sensitivity (BLISS) mapping and parameter orthogonalization. The former is a new technique to model two position-dependent systematics, intrapixel variability and pixelation. The latter is a technique that accelerates the convergence of Markov chains that employ the Metropolis random walk sampler.Chapter 4 reports on the detection of GJ 436c, a 0.65 +/- 0.04 Earth-radii exoplanet transiting a nearby M-dwarf star with a period of 1.365862 +/- 8x10^{-6} days. It also presents evidence for a similarly sized exoplanet candidate (currently labeled UCF-1.02) orbiting the same star with an undetermined period. Assuming an Earth-like density of 5.515 g/cm^{3}, GJ 436c has a predicted mass of 0.28 Earth-masses (2.6 Mars-masses) and a surface gravity of 0.65 g (where g is the gravity on Earth). Its weak gravitational field and close proximity to its host star imply that GJ 436c is unlikely to have retained its original atmosphere; however, a transient atmosphere is possible if recent impacts or tidal heating were to supply volatiles to the surface. Chapter 5 presents numerical simulations of the GJ 436 system using the Mercury N-body integrator and detailed calculations used to constrain the atmospheric composition of the sub-Earth-sized planet GJ 436c. The simulations find a ~35-year periodic trend in the osculating elements wherein GJ 436c's eccentricity varies between 0 and 0.21, its peak-to-trough inclination amplitude is 3.2 degrees, and transit-timing variations range from +/-200 to +/-3 minutes.
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Date Issued: 2012
Identifier: CFE0004640, ucf:49889
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004640

Title: Photonic Filtering for Applications in Microwave Generation and Metrology.
Creator: Bagnell, Marcus, Delfyett, Peter, Schoenfeld, Winston, Li, Guifang, Peale, Robert, University of Central Florida
Abstract / Description: This work uses the photonic filtering properties of Fabry-Perot etalons to show improvements in the electrical signals created upon photodetection of the optical signal. First, a method of delay measurement is described which uses multi-heterodyne detection to find correlations in white light signals at 20 km of delay to sub millimeter resolution. By filtering incoming white light with a Fabry-Perot etalon, the pseudo periodic signal is suitable for measurement by combining and photodetecting...
Show moreThis work uses the photonic filtering properties of Fabry-Perot etalons to show improvements in the electrical signals created upon photodetection of the optical signal. First, a method of delay measurement is described which uses multi-heterodyne detection to find correlations in white light signals at 20 km of delay to sub millimeter resolution. By filtering incoming white light with a Fabry-Perot etalon, the pseudo periodic signal is suitable for measurement by combining and photodetecting it with an optical frequency comb. In this way, optical data from a large bandwidth can be downconverted and sampled on low frequency electronics. Second, a high finesse etalon is used as a photonic filter inside an optoelectronic oscillator (OEO). The etalon's narrow filter function allows the OEO loop length to be extremely long for a high oscillator quality factor while still suppressing unwanted modes below the noise floor. The periodic nature of the etalon allows it to be used to generate a wide range of microwave and millimeter wave tones without degradation of the RF signal.
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Date Issued: 2014
Identifier: CFE0005457, ucf:50396
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005457

Title: Multimaterial fibers in photonics and nanotechnology.
Creator: Tao, Guangming, Abouraddy, Ayman, Li, Guifang, Glebov, Leonid, Peale, Robert, University of Central Florida
Abstract / Description: Recent progress in combing multiple materials with distinct optical, electronic, and thermomechanical properties monolithically in a kilometer-long fiber drawn from a preform offers unique multifunctionality at a low cost. A wide range of unique in-fiber devices have been developed in fiber form-factor using this strategy. Here, I summary my recent results in this nascent field of 'multimaterial fibers'. I will focus on my achievements in producing robust infrared optical fibers and in...
Show moreRecent progress in combing multiple materials with distinct optical, electronic, and thermomechanical properties monolithically in a kilometer-long fiber drawn from a preform offers unique multifunctionality at a low cost. A wide range of unique in-fiber devices have been developed in fiber form-factor using this strategy. Here, I summary my recent results in this nascent field of 'multimaterial fibers'. I will focus on my achievements in producing robust infrared optical fibers and in appropriating optical fiber production technology for applications in nanofabrication.The development of optical components suitable for the infrared (IR) is crucial for applications in this spectral range to reach the maturity level of their counterparts in the visible and near-infrared spectral regimes. A critical class of optical components that has yet to be fully developed is that of IR optical fibers. Here I will present several unique approaches that may result in low-cost, robust IR fibers that transmit light from 1.5 microns to 15 microns drawn from multimaterial preforms. These preforms are prepared exploiting the newly developed procedure of multimaterial coextrusion, which provides unprecedented flexibility in material choices and structure engineering in the extruded preform. I will present several different 'generations' of multimaterial extrusion that enable access to a variety of IR fibers. Examples of the IR fibers realized using this methodology include single mode IR fibers, large index-contrast IR fibers, IR imaging fiber bundles, IR photonic crystal and potentially photonic band-gap fibers.The complex structures produced in multimaterial fibers may also be used in the fabrication of micro- and nano-scale spherical particles by exploiting a recently discovered in-fiber Plateau-Rayleigh capillary instability. Such multimaterial structured particles have promising application in drug delivery, optical sensors, and nanobiotechnology. The benefits accrued from the multimaterial fiber methodology allow for the scalable fabrication of micro- and nano-scale particles having complex internal architectures, such as multi-shell particles, Janus-particles, and particles with combined control over the radial and azimuthal structure.Finally, I will summarize my views on the compatibility of a wide range of amorphous and crystalline materials with the traditional thermal fiber drawing process and with the more recent multimaterial fiber strategy.
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Date Issued: 2014
Identifier: CFE0005555, ucf:50289
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005555

Title: Spin and Charge Transport in Graphene Based Devices.
Creator: Anguera Antonana, Marta, Del Barco, Enrique, Peale, Robert, Bhattacharya, Aniket, Schoenfeld, Winston, University of Central Florida
Abstract / Description: The present dissertation is comprehended in two main parts. The first part is focused on understanding the mechanisms behind spin current to charge current interconversion (i.e. the spin Hall angle), where the spin current is generated by means of spin pumping. The measurement of a positive spin Hall angle of magnitude 0.004 in Uranium is reported in Chapter 2. These results support the idea that the electronic configuration may be at least as important as the atomic number in governing spin...
Show moreThe present dissertation is comprehended in two main parts. The first part is focused on understanding the mechanisms behind spin current to charge current interconversion (i.e. the spin Hall angle), where the spin current is generated by means of spin pumping. The measurement of a positive spin Hall angle of magnitude 0.004 in Uranium is reported in Chapter 2. These results support the idea that the electronic configuration may be at least as important as the atomic number in governing spin Hall effects. In Chapter 3, the design of a spintronics device designed to interconvert charge and spin currents in CVD graphene is presented. The second part of the thesis is centered in the study of transport through single molecules with the use of three-terminal devices. The first evidence of a molecular double quantum dot is detailed in Chapter 5. The conclusions are supported by self-assembled monolayers (SAMs) and single-electron transistors (SETs) measurements. Using gold electrodes for SETs measurements has its disadvantages, two of the main ones being: the junctions are not stable at room temperature and it does not allow for transport measurements in the presence of light. Graphene electrodes, on the other hand, have been reported to be stable at temperatures above room temperature and have no absorption in the visible range. Along those lines, the development of a multilayer graphene-based SET is reported in Chapter 6. Finally, a new technique, based on CVD graphene transistors, that will allow three-terminal measurements on an STM is described in Chapter 7.
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Date Issued: 2017
Identifier: CFE0006715, ucf:51897
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006715

Title: Spray_Deposited Titanium-Oxide Films For Infrared Optics, Photonics, And Solar Cell Applications.
Creator: Alhasan, Sarmad, Peale, Robert, Sundaram, Kalpathy, Mikhael, Wasfy, Abdolvand, Reza, Kar, Aravinda, University of Central Florida
Abstract / Description: Self-assembled TiO2 foam-like films, were grown by the water based Streaming Process for ElectrodelessElectrochemical Deposition (SPEED). The morphology of the 1 m thick films consistsof a tangled ropy structure with individual strands of 200 nm diameter and open pores of 0.1to 3 micron dimensions. Such films are advantageous for proposed perovskite solar cell comprisingCH3NH3PbI3 absorber with additional inorganic films as contact and conduction layers,all deposited by SPEED. Lateral film...
Show moreSelf-assembled TiO2 foam-like films, were grown by the water based Streaming Process for ElectrodelessElectrochemical Deposition (SPEED). The morphology of the 1 m thick films consistsof a tangled ropy structure with individual strands of 200 nm diameter and open pores of 0.1to 3 micron dimensions. Such films are advantageous for proposed perovskite solar cell comprisingCH3NH3PbI3 absorber with additional inorganic films as contact and conduction layers,all deposited by SPEED. Lateral film resistivity is in the range 20 - 200 k-cm, increasing withgrowth temperature, while sheet resistance is in the range 2 ?? 20 108 /Sq. Xray diffractionconfirms presence of TiO2 crystals of orthorhombic class (Brookite). UV-vis spectroscopy showshigh transmission below the expected 3.2 eV TiO2 bandgap. Transmittance increases with growthtemperature. This is a Ropy TiO2 thin film.We also prepared a Smooth TiO2 thin film. Self-assembled TiO2 film deposited by aqueous-spraydeposition was investigated to evaluate morphology, crystalline phase, and infrared optical constants.The Anatase nano-crystalline film had 10 nm characteristic surface roughness sparselypunctuated by defects of not more than 200 nm amplitude. The film is highly transparent throughoutthe visible to wavelengths of 12 m. The indirect band gap was determined to be 3.2 eV. Importantfor long-wave infrared applications is that dispersion in this region is weak compared with themore commonly used dielectic SiO2 for planar structures. The low-cost, large-area, atmosphericpressure,chemical spray deposition method allows conformal fabrication on flexible substrates forlong-wave infrared photonics.For comparison TiO2 films deposited by electron-beam evaporation were evaluated to determinemorphology, crystalline phase, and optical transparency.The evaporated TiO2 film was amorphous but crystallized into Anatase phase after annealing.Such film is attractive as electron conductor of unprecedented thinness and flexibility for proposedperovskite solar cell comprising CH3NH3PbI3 absorber with additional inorganic films as contactand conduction layers. The spray deposition method would allow conformal solar cell fabricationon flexible substrates for wearable power generation. Band gap of Evaporated TiO2 film is 4.0 eV.We prepared BaTiO3 thin film to know infrared pyroelectric response.Self-assembled nano-crystalline BaTiO3 films on stainless steel foil substrates, were grown by thewater based Streaming Process for Electrodeless Electrochemical Deposition (SPEED). SPEED isan aqueous process that deposits self-assembled nano-crystalline inorganic thin films over largeareas, without a vacuum, providing a scalable and manufacturing friendly process to fabricatedurable films. The morphology of the 1m thick films comprises single crystals of micron dimensionsimbedded in a matrix of nanocrystals. XRD confirms presence of BaTiO3 crystals ofhexagonal phase for samples annealed at 500C. Subsequent annealing at 600C transforms thefilm to the cubic phase. Potential applications include dielectric layers, capacitors, waveguides,ferroelectric RAM, pyroelectric infrared detectors, and phosphors. Characterization of infraredpyroelectric response at 10m wavelength shows an initially good sensitivity that reversibly decaysover a period of days due to water vapor absorption. A short-lived photo-response due topoling of the hydrated sample is also observed. We studied BaTiO3 to know hysteresis loop.Pyroelectric photoresponse of aqueous spray deposited thin films containing BaTiO3 nano-crystalsis reported. X-ray diffraction data indicate the presence of hexagonal BaTiO3 nano-crystals with20 nm crystalline domains in a matrix of some as yet unidentified nano-crystalline material.When the film is annealed at 600C, the X-ray pattern changes significantly and indicates a conversionto one of the non-hexagonal phases of BaTiO3 as well as a complete change in the matrix.With suitable amplifier, the measured photoresponse was 40V/W.Ferroelectric hysteresis on a film with significant presence of hexagonal BaTiO3 shows saturatedpolarization which is about 5-times smaller than for the bulk tetragonal phase.
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Date Issued: 2017
Identifier: CFE0006710, ucf:51899
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006710

Title: A study of organo-phosphorous simulants thermal destruction using shock tube/laser diagnostics techniques and chemical kinetics modeling.
Creator: Neupane, Sneha, Vasu Sumathi, Subith, Kassab, Alain, Chow, Louis, Peale, Robert, University of Central Florida
Abstract / Description: High-fidelity chemical kinetic models are critical in predictive modeling during design and optimization of next generation energy systems. Shock tube provides an ideal tool to investigate high-temperature chemical kinetics. Non-intrusive laser absorption diagnostics provide in-situ measurements of quantitative, time-resolved species concentration data in this complex chemically reacting system. In this work, shock tube and laser absorption spectroscopy were utilized to measure species...
Show moreHigh-fidelity chemical kinetic models are critical in predictive modeling during design and optimization of next generation energy systems. Shock tube provides an ideal tool to investigate high-temperature chemical kinetics. Non-intrusive laser absorption diagnostics provide in-situ measurements of quantitative, time-resolved species concentration data in this complex chemically reacting system. In this work, shock tube and laser absorption spectroscopy were utilized to measure species concentration time-histories during pyrolysis and oxidation of organo-phosphorous compounds (OPCs). The experiments data obtained were used as benchmark to develop an improved kinetic model of OPCs combustion. Interest in combustion chemistry of OPCs is associated to their use as fire suppressants and as chemical weapons. Pyrolysis and oxidation of OPCs were carried out behind reflected shock wave and laser absorption spectroscopy utilizing quantum cascade laser at mid-IR wavelength region was used to measure time resolved intermediate CO concentration produced during the process. Utilizing the experiments data, an improved chemical kinetic model for combustion of an OPC (-) Triethyl Phosphate (TEP) was developed. Various steps taken to develop the improved model include: calculation of thermochemical properties; updating hydrocarbon kinetics; calculation of reaction rates and addition of alternative TEP decomposition pathways. The prediction of TEP combustion, in terms intermediate CO concentration yield during its pyrolysis and oxidation, made by the improved model is in much better agreement with the experiments. Such an accurate kinetic model is critical in predicting the effectiveness of OPCs as flame retardants when used as dopants in hydrocarbon fuels; and in devising counter weapon of mass destruction strategies to destroy chemical weapons.
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Date Issued: 2019
Identifier: CFE0007691, ucf:52444
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007691

Title: Hybrid integration of second- and third-order highly nonlinear waveguides on silicon substrates.
Creator: Camacho Gonzalez, Guillermo Fernando, Fathpour, Sasan, Likamwa, Patrick, Amezcua Correa, Rodrigo, Peale, Robert, University of Central Florida
Abstract / Description: In order to extend the capabilities and applications of silicon photonics, other materials and compatible technologies have been developed and integrated on silicon substrates. A particular class of integrable materials are those with high second- and third-order nonlinear optical properties. This work presents contributions made to nonlinear integrated photonics on silicon substrates, including chalcogenide waveguides for over an octave supercontinuum generation, and rib-loaded thin-film...
Show moreIn order to extend the capabilities and applications of silicon photonics, other materials and compatible technologies have been developed and integrated on silicon substrates. A particular class of integrable materials are those with high second- and third-order nonlinear optical properties. This work presents contributions made to nonlinear integrated photonics on silicon substrates, including chalcogenide waveguides for over an octave supercontinuum generation, and rib-loaded thin-film lithium niobate waveguides for highly efficient second-harmonic generation. Through the pursuit of hybrid integration of the two types of waveguides for applications such as on-chip self-referenced optical frequency combs, we have experimentally demonstrated fabrication integrability of chalcogenide and thin-film lithium niobate waveguides in a single chip and a pathway for both second- and third-order nonlinearities occurring therein. Accordingly, design specifications for an efficient nonlinear integrated waveguide are reported, showing over an octave supercontinuum generation and frequency selectivity for second-harmonic generation, enabling potentials of on-chip interferometry techniques for carrier-envelope offset detection, and hence stabilized optical combs.
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Date Issued: 2019
Identifier: CFE0007607, ucf:52560
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007607

Title: Prediction of survival of early stages lung cancer patients based on ER beta cellular expressions and epidemiological data.
Creator: Martinenko, Evgeny, Shivamoggi, Bhimsen, Chow, Lee, Peale, Robert, Brandenburg, John, University of Central Florida
Abstract / Description: We attempted a mathematical model for expected prognosis of lung cancer patients based ona multivariate analysis of the values of ER-interacting proteins (ERbeta) and a membranebound, glycosylated phosphoprotein MUC1), and patients clinical data recorded at the timeof initial surgery. We demonstrate that, even with the limited sample size available to use,combination of clinical and biochemical data (in particular, associated with ERbeta andMUC1) allows to predict survival of lung cancer...
Show moreWe attempted a mathematical model for expected prognosis of lung cancer patients based ona multivariate analysis of the values of ER-interacting proteins (ERbeta) and a membranebound, glycosylated phosphoprotein MUC1), and patients clinical data recorded at the timeof initial surgery. We demonstrate that, even with the limited sample size available to use,combination of clinical and biochemical data (in particular, associated with ERbeta andMUC1) allows to predict survival of lung cancer patients with about 80% accuracy whileprediction on the basis of clinical data only gives about 70% accuracy. The present work canbe viewed as a pilot study on the subject: since results conrm that ER-interacting proteinsindeed inuence lung cancer patients' survival, more data is currently being collected.
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Date Issued: 2011
Identifier: CFE0004134, ucf:49120
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004134

Title: Nonlinear Optical Response of Simple Molecules and Two-Photon Semiconductor Lasers.
Creator: Reichert, Matthew, Vanstryland, Eric, Hagan, David, Likamwa, Patrick, Peale, Robert, University of Central Florida
Abstract / Description: This dissertation investigates two long standing issues in nonlinear optics: complete characterization of the ultrafast dynamics of simple molecules, and the potential of a two-photon laser using a bulk semiconductor gain medium. Within the Born-Oppenheimer approximation, nonlinear refraction in molecular liquids and gases can arise from both bound-electronic and nuclear origins. Knowledge of the magnitudes, temporal dynamics, polarization and spectral dependences of each of these mechanisms...
Show moreThis dissertation investigates two long standing issues in nonlinear optics: complete characterization of the ultrafast dynamics of simple molecules, and the potential of a two-photon laser using a bulk semiconductor gain medium. Within the Born-Oppenheimer approximation, nonlinear refraction in molecular liquids and gases can arise from both bound-electronic and nuclear origins. Knowledge of the magnitudes, temporal dynamics, polarization and spectral dependences of each of these mechanisms is important for many applications including filamentation, white-light continuum generation, all-optical switching, and nonlinear spectroscopy. In this work the nonlinear dynamics of molecules are investigated in both liquid and gas phase with the recently developed beam deflection technique which measures nonlinear refraction directly in the time domain. Thanks to the utility of the beam deflection technique we are able to completely determine the third-order response function of one of the most important molecular liquids in nonlinear optics, carbon disulfide. This allows the prediction of essentially any nonlinear refraction or two-photon absorption experiment on CS2. Measurements conducted on air (N2 and O2) and gaseous CS2 reveal coherent rotational revivals in the degree of alignment of the ensemble at a period that depends on its moment of inertia. This allows measurement of the rotational and centrifugal distortion constants of the isolated molecules. Additionally, the rotational contribution to the beam deflection measurement can be eliminated thanks to the particular polarization dependence of the mechanism. At a specific polarization, the dominant remaining contribution is due to the bound-electrons. Thus both the bound-electronic nonlinear refractive index of air, and second hyperpolarizability of isolated CS2 molecules, are measured directly. The later agrees well with liquid CS2 measurements, where local field effects are significant. The second major portion of this dissertation addresses the possibility of using bulk semiconductors as a two-photon gain medium. A two-photon laser has been a goal of nonlinear optics since shortly after the original laser's development. In this case, two-photons are emitted from a single electronic transition rather than only one. This processes is known as two-photon gain (2PG). Semiconductors have large two-photon absorption coefficients, which are enhanced by ~2 orders of magnitude when using photons of very different energies, e.g., ??_a?10??_b. This enhancement should translate into large 2PG coefficients as well, given the inverse relationship between absorption and gain. Here, we experimentally demonstrate both degenerate and nondegenerate 2PG in optically excited bulk GaAs via pump-probe experiments. This constitutes, to my knowledge, the first report of nondegenerate two-photon gain. Competition between 2PG and competing processes, namely intervalence band and nondegenerate three-photon absorption (ND-3PA), in both cases are theoretically analyzed. Experimental measurements of ND-3PA agree with this analysis and show that it is enhanced much more than ND-2PG. It is found for both degenerate and nondegenerate photon pairs that the losses dominate the two-photon gain, preventing the possibility of a two-photon semiconductor laser.
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Date Issued: 2015
Identifier: CFE0005874, ucf:50871
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005874

Title: ELECTROMECHANICAL LIFTING ACTUATION OF A MEMS CANTILEVER AND NANO-SCALE ANALYSIS OF DIFFUSION IN SEMICONDUCTOR DEVICE DIELECTRICS.
Creator: Rezadad, Imen, Peale, Robert, Del Barco, Enrique, Tetard, Laurene, Prenitzer, Brenda, University of Central Florida
Abstract / Description: This dissertation presents experimental and theoretical studies of physical phenomena in micro- and nano-electronic devices. Firstly, a novel and unproven means of electromechanical actuation in a micro-electro-mechanical system (MEMS) cantilever was investigated. In nearly all MEMS devices, electric forces cause suspended components to move toward the substrate. I demonstrated a design with the unusual and potentially very useful property of having a suspended MEMS cantilever lift away from...
Show moreThis dissertation presents experimental and theoretical studies of physical phenomena in micro- and nano-electronic devices. Firstly, a novel and unproven means of electromechanical actuation in a micro-electro-mechanical system (MEMS) cantilever was investigated. In nearly all MEMS devices, electric forces cause suspended components to move toward the substrate. I demonstrated a design with the unusual and potentially very useful property of having a suspended MEMS cantilever lift away from the substrate. The effect was observed by optical micro-videography, by electrical sensing, and it was quantified by optical interferometry. The results agree with predictions of analytic and numerical calculations. One potential application is infrared sensing in which absorbed radiation changes the temperature of the cantilever, changing the duty cycle of an electrically-driven, repetitively closing micro-relay.Secondly, ultra-thin high-k gate dielectric layers in two 22 nm technology node semiconductor devices were studied. The purpose of the investigation was to characterize the morphology and composition of these layers as a means to verify whether the transmission electron microscope (TEM) with energy dispersive spectroscopy (EDS) could sufficiently resolve the atomic diffusion at such small length scales. Results of analytic and Monte-Carlo numerical calculations were compared to empirical data to validate the ongoing viability of TEM EDS as a tool for nanoscale characterization of semiconductor devices in an era where transistor dimensions will soon be less than 10 nm.
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Date Issued: 2015
Identifier: CFE0006228, ucf:51075
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006228

Infrared (4)	+ -
Plasmonics (4)	+ -
MEMS (3)	+ -
infrared (3)	+ -
Cathodoluminescence (2)	+ -

GaN (2)	+ -
THz (2)	+ -
absorber (2)	+ -
far-infrared (2)	+ -
gold black (2)	+ -
infrared detector (2)	+ -
integrated photonics (2)	+ -
nonlinear optics (2)	+ -
photometry (2)	+ -
semiconductor (2)	+ -
spectroscopy (2)	+ -
terahertz (2)	+ -
(Numerical) Algebraic Geometry (1)	+ -
(Super) Zeeman (1)	+ -
2deg (1)	+ -
AFM (1)	+ -
AFM-IR (1)	+ -
Acoustic Optic Modulator (1)	+ -
Active Region Temperature (1)	+ -
Adiankraic Tensor Product Decomposition (1)	+ -
Adinkra (1)	+ -
AlGaN/GaN (1)	+ -
Algebraic Paradigms (1)	+ -
Ansatz Templates (1)	+ -
Anti-reflective Coating (1)	+ -

ETD Collection (50)	+ -
Honors Collection (1)	+ -

University of Central Florida (51)	+ -
Peale, Robert (50)	+ -
Schoenfeld, Winston (7)	+ -
Del Barco, Enrique (6)	+ -
Chernyak, Leonid (5)	+ -

Ishigami, Masa (5)	+ -
Chow, Lee (4)	+ -
Delfyett, Peter (4)	+ -
Fathpour, Sasan (4)	+ -
Flitsiyan, Elena (4)	+ -
Klemm, Richard (4)	+ -
Likamwa, Patrick (4)	+ -
Britt, Daniel (3)	+ -
Chanda, Debashis (3)	+ -
Hagan, David (3)	+ -
Li, Guifang (3)	+ -
Shivamoggi, Bhimsen (3)	+ -
Abdolvand, Reza (2)	+ -
Abouraddy, Ayman (2)	+ -
Buchwald, Walter (2)	+ -
Cleary, Justin (2)	+ -
Coffey, Kevin (2)	+ -
Harrington, Joseph (2)	+ -
Kassab, Alain (2)	+ -
Lyakh, Arkadiy (2)	+ -
Mucciolo, Eduardo (2)	+ -
Panjwani, Deep (2)	+ -
Tetard, Laurene (2)	+ -
Vanstryland, Eric (2)	+ -
Vasu Sumathi, Subith (2)	+ -

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