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EFFECT OF GERMANIUM DOPING ON ERBIUM SENSITIZATION IN THE ERBIUM DOPED SILICON RICH SILICA MATERIAL SYSTEM
Title
EFFECT OF GERMANIUM DOPING ON ERBIUM SENSITIZATION IN THE ERBIUM DOPED SILICON RICH SILICA MATERIAL SYSTEM.
Creator
Ruhge, Forrest, Kik, Pieter, University of Central Florida
Abstract / Description
The continued size reduction in electronic integrated circuits has lead to a demand for on-chip high-bandwidth and low loss communication channels. Optical interconnects are considered an essential addition to the silicon electronics platform. A major challenge in the field of integrated Si photonics is the development of cost effective silicon compatible light sources. This thesis investigates the sensitization of group IV doped silica films emitting at 1.535μm for applications as...
Show moreThe continued size reduction in electronic integrated circuits has lead to a demand for on-chip high-bandwidth and low loss communication channels. Optical interconnects are considered an essential addition to the silicon electronics platform. A major challenge in the field of integrated Si photonics is the development of cost effective silicon compatible light sources. This thesis investigates the sensitization of group IV doped silica films emitting at 1.535μm for applications as silicon compatible light sources. Thin erbium-doped silica films containing excess silicon and germanium were deposited using a multi-gun sputter system. The composition of the deposited materials was verified by Rutherford Backscattering Spectrometry. Samples from each deposition were annealed in a controlled atmosphere tube furnace at temperatures between 500ºC and 1100ºC for 30 minutes. The photoluminescence spectra from the visible to the near-infrared region were acquired while pumping either near or far from the Er3+ absorption lines. Under both excitation conditions all samples annealed at temperatures below 1000ºC show clear emission at 1.535μm from Er3+ ions in the host material. In the current literature this is attributed to exciton mediated excitation of the Er3+. By contrast, in these studies indirect excitation was observed for samples annealed at temperatures well below the onset of nanocrystal nucleation and growth (between 500ºC and 1000ºC), suggesting excitation via small clusters or lattice defects. These findings could have significant implications in the further development of group IV sensitized silicon compatible gain media.
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Date Issued
2006
Identifier
CFE0001439, ucf:47066
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001439
PLASMON ENHANCED NEAR-FIELD INTERACTIONS IN SURFACE COUPLED NANOPARTICLE ARRAYS FOR INTEGRATED NANOPHOTONIC DEVICES
Title
PLASMON ENHANCED NEAR-FIELD INTERACTIONS IN SURFACE COUPLED NANOPARTICLE ARRAYS FOR INTEGRATED NANOPHOTONIC DEVICES.
Creator
Ghoshal, Amitabh, Kik, Pieter, University of Central Florida
Abstract / Description
The current thrust towards developing silicon compatible integrated nanophotonic devices is driven by need to overcome critical challenges in electronic circuit technology related to information bandwidth and thermal management. Surface plasmon nanophotonics represents a hybrid technology at the interface of optics and electronics that could address several of the existing challenges. Surface plasmons are electronic charge density waves that can occur at a metal-dielectric interface at...
Show moreThe current thrust towards developing silicon compatible integrated nanophotonic devices is driven by need to overcome critical challenges in electronic circuit technology related to information bandwidth and thermal management. Surface plasmon nanophotonics represents a hybrid technology at the interface of optics and electronics that could address several of the existing challenges. Surface plasmons are electronic charge density waves that can occur at a metal-dielectric interface at optical and infrared frequencies. Numerous plasmon based integrated optical devices such as waveguides, splitters, resonators and multimode interference devices have been developed, however no standard integrated device for coupling light into nanoscale optical circuits exists. In this thesis we experimentally and theoretically investigate the excitation of propagating surface plasmons via resonant metal nanoparticle arrays placed in close proximity to a metal surface. It is shown that this approach can lead to compact plasmon excitation devices. Full-field electromagnetic simulations of the optical illumination of metal nanoparticle arrays near a metal film reveal the presence of individual nanoparticle resonances and collective grating-like resonances related to propagating surface plasmons within the periodic array structure. Strong near-field coupling between the nanoparticle and grating resonances is observed, and is successfully described by a coupled oscillator model. Numerical simulations of the effect of nanoparticle size and shape on the excitation and dissipation of surface plasmons reveal that the optimum particle volume for efficient surface plasmon excitation depends sensitively on the particle shape. This observation is quantitatively explained in terms of the shape-dependent optical cross-section of the nanoparticles. Reflection measurements on nanoparticle arrays fabricated using electron-beam lithography confirm the predicted particle-grating interaction. An unexpected polarization-dependent splitting of the film-mediated collective resonance is successfully attributed to the existence of out-of plane polarization modes of the metal nanoparticles. In order to distinguish between the excitation of propagating surface plasmons and localized nanoparticle plasmons, spectrally resolved leakage radiation measurements are presented. Based on these measurements, a universally applicable method for measuring the wavelength dependent efficiency of coupling free-space radiation into guided surface plasmon modes on thin films is developed. Finally, it is shown that the resonantly enhanced near-field coupling the nanoparticles and the propagating surface plasmons can lead to optimized coupler device dimensions well below 10 microns.
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Date Issued
2010
Identifier
CFE0003091, ucf:48322
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003091
SILICON-SENSITIZED ERBIUM EXCITATION IN SILICON-RICH SILICA FOR INTEGRATED PHOTONICS
Title
SILICON-SENSITIZED ERBIUM EXCITATION IN SILICON-RICH SILICA FOR INTEGRATED PHOTONICS.
Creator
Savchyn, Oleksandr, Kik, Pieter, University of Central Florida
Abstract / Description
It is widely accepted that the continued increase of processor performance requires at least partial replacement of electronic interconnects with their photonic counterparts. The implementation of optical interconnects requires the realization of a silicon-based light source, which is challenging task due to the low emission efficiency of silicon. One of the main approaches to address this challenge is the use of doping of silicon based matrices with optical centers, including erbium ions....
Show moreIt is widely accepted that the continued increase of processor performance requires at least partial replacement of electronic interconnects with their photonic counterparts. The implementation of optical interconnects requires the realization of a silicon-based light source, which is challenging task due to the low emission efficiency of silicon. One of the main approaches to address this challenge is the use of doping of silicon based matrices with optical centers, including erbium ions. Erbium ions incorporated in various hosts assume the trivalent state (Er3+) and demonstrate a transition at 1.54 μm, coinciding with optical transmission windows in both silicon and silica. Due to the low absorption cross-section and discrete energy levels of the Er3+ ion, indirect excitation is necessary. In late 90s it was demonstrated that the incorporation of excess silicon in erbium-doped silica results in strong erbium sensitization, leading to an increase of the effective absorption cross-section by orders of magnitude. The sensitization was considered to occur via silicon nanocrystals that formed at high annealing temperatures. While a large increase of the absorption cross-section was demonstrated, the incorporation of Si nanocrystals was found to result in a low concentration of excited erbium, as well as silicon related free-carrier absorption. The focus of this dissertation is the investigation of the nature of the sensitization mechanism of erbium in silicon-rich silica. The results presented in the dissertation demonstrate that erbium in silicon-rich silica is predominantly excited by silicon-excess-related luminescence centers, as opposed to the commonly considered silicon nanocrystals. This is a remarkable conclusion that changes the view on the exact origin of erbium sensitization, and that resolves several technical challenges that exist for nanocrystal-based sensitization. The work shows that the density of indirectly excited erbium ions is significantly larger in samples without silicon nanocrystals (annealed at T < 1000oC) as opposed to samples with silicon nanocrystals (annealed at T > 1000oC). The density of indirectly excited erbium ions, defining the maximum achievable gain, was demonstrated to be approximately excitation wavelength independent, while the effective erbium absorption cross-section was shown to significantly depend on the excitation wavelength. The excitation mechanism of erbium by luminescence centers was shown to be fast (< 30 ns) and capable of erbium sensitization to different energy levels. This multilevel nature of erbium excitation was demonstrated to result in two different mechanisms of the excitation of the first excited state of erbium: fast (< 30 ns) direct excitation by the luminescence centers, and slow (> 2.3 μs) excitation due to the relaxation of erbium ions excited into higher energy levels to the first excited state. Based on photoluminescence studies conducted in the temperature range 15 - 300K it was shown that the relaxation efficiency of erbium from the second excited state to the first excited state (responsible for the slow excitation mechanism) is temperature independent and approaches unity. The relative stability of the optical properties demonstrated in the temperature range 20 - 200oC, implies that relatively stable optical gain can be achieved under realistic on-chip operating conditions. The optimum Si excess concentration corresponding to the highest density of sensitized Er3+ ions is shown to be relatively insensitive to the presence of Si nanocrystals and is ~ 14.5 at.% and ~ 11.5 at.% for samples without and with Si nanocrystals respectively. The presented results and conclusions have significant implications for silicon photonics and the industrial application of Er-doped SiO2. The work shows that in order to sensitize erbium ions in silicon-rich silica there is no need for the presence of silicon nanocrystals, and consequently lower fabrication temperatures can be used. More importantly, the results strongly suggest that higher gain values can be acquired in samples annealed at lower temperature (without silicon nanocrystals) as compared to samples annealed at high temperatures (with silicon nanocrystals). In addition, the maximum gain is predicted to be relatively independent of excitation wavelength, significantly relaxing the requirements on the pump source. Based on the experimental results it is predicted that relatively stable performance of erbium-doped silicon-rich silica is possible up to typical processor operating temperatures of ~ 80 - 90oC making it a viable material for on-chip devices. The results suggest that low temperature annealed erbium-doped silicon-rich silica is a preferable material for on-chip photonic devices as compared with its high temperature annealed counterpart.
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Date Issued
2010
Identifier
CFE0003312, ucf:48492
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003312
Nanoscale Control of Gap-plasmon Enhanced Optical Processes
Title
Nanoscale Control of Gap-plasmon Enhanced Optical Processes.
Creator
Lumdee, Chatdanai, Kik, Pieter, Dogariu, Aristide, Kuebler, Stephen, Huo, Qun, University of Central Florida
Abstract / Description
Surface plasmon resonances of metal nanostructures have been studied intensely in recent years. The strong plasmon-mediated electric field enhancement and field confinement well beyond the diffraction limit has been demonstrated to improve the performance of optical devices including ultrasensitive sensors, light emitters, and optical absorbers. A plasmon resonance mode of particular recent interest is the gap plasmon resonance that occurs on closely spaced metallic structures. In contrast to...
Show moreSurface plasmon resonances of metal nanostructures have been studied intensely in recent years. The strong plasmon-mediated electric field enhancement and field confinement well beyond the diffraction limit has been demonstrated to improve the performance of optical devices including ultrasensitive sensors, light emitters, and optical absorbers. A plasmon resonance mode of particular recent interest is the gap plasmon resonance that occurs on closely spaced metallic structures. In contrast to plasmon resonances supported by isolated metal nanostructures, coupled nanostructures provide additional spectral and spatial control over the plasmon resonance response. For example, the resonance frequencies of metal nanoparticle dimers depend strongly on the gap size between the nanoparticles. Gap plasmons can produce local electric field enhancement factors that are several orders of magnitude stronger and more confined than surface plasmon resonances of isolated plasmonic nanospheres. The reliance of gap plasmons on few-nanometer separation between nanostructures makes it difficult to prepare gap-plasmon supporting structures with predictable resonance frequency and field enhancement. A structure that avoids this challenge is the film-coupled nanoparticle (NP). Similar to nanoparticle dimers, a nanoparticle on a supporting metallic film (or NP-on-a-mirror) can offer a strong coupling between the particle and its local environment, in this case the supporting film instead of adjacent nanoparticles, enabling strongly confined gap-plasmon modes. The NP-on-a-mirror geometry has been shown to produce reproducible gap plasmon resonances in a chemically and thermally robust, easy to fabricate structure. In this Thesis, we first present a scheme for controlling the gap plasmon resonance frequency of single gold nanoparticles using aluminum oxide coated metal films. We demonstrate experimentally and numerically that the gap-plasmon resonance of single gold nanoparticles can be tuned throughout the visible range by controlling the aluminum oxide thickness via anodization. In a separate study of Au NP on Al2O3 coated gold films it is shown that the oxide coating improves the stability of the structure under intense laser irradiation. An combined experimental and numerical analysis of the spectral response of Au NP on rough Au films shows that a film roughness of a few nanometer can affect the gap plasmon resonance in the absence of an oxide spacer layer. A photoluminescence study of single gold nanoparticles on an Al2O3 coated gold film shows that the gap-plasmon resonance of this type of plasmonic structure can increase gold photoluminescence by more than four orders of magnitude. Related numerical simulations reveal that the local photoluminescence enhancement of a gold nanoparticle on an Al2O3 coated gold film can be as high as one million near the particle-film junction. Finally, a new plasmonic sensing element was proposed based on our findings in the previous chapters. This proposed hole-in-one structure offers several attractive features including an easily optically accessible gap plasmon mode, while maintaining a relatively simple fabrication method. Taken together, the research presented in this Thesis demonstrates how the resonance frequency, field enhancement, mode polarization, structural stability, and structure reliability can be controlled at the nanoscale. The knowledge gained in the course of this work could lead to further development of nanophotonic devices that utilize extremely confined optical fields and precisely controlled resonance frequencies.
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Date Issued
2015
Identifier
CFE0005972, ucf:50772
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005972
Conservation Laws and Electromagnetic Interactions
Title
Conservation Laws and Electromagnetic Interactions.
Creator
Kajorndejnukul, Veerachart, Dogariu, Aristide, Abouraddy, Ayman, Kik, Pieter, Rahman, Talat, University of Central Florida
Abstract / Description
Aside from energy, light carries linear and angular momenta that can be transferred to matter. The interaction between light and matter is governed by conservation laws that can manifest themselves as mechanical effects acting on both matter and light waves. This interaction permits remote, precise, and noninvasive manipulation and sensing at microscopic levels. In this dissertation, we demonstrated for the first time a complete set of opto-mechanical effects that are based on nonconservative...
Show moreAside from energy, light carries linear and angular momenta that can be transferred to matter. The interaction between light and matter is governed by conservation laws that can manifest themselves as mechanical effects acting on both matter and light waves. This interaction permits remote, precise, and noninvasive manipulation and sensing at microscopic levels. In this dissertation, we demonstrated for the first time a complete set of opto-mechanical effects that are based on nonconservative forces and act at the interface between dielectric media. Without structuring the light field, forward action is provided by the conventional radiation pressure while a backward movement can be achieved through the natural enhancement of linear momentum. If the symmetry of scattered field is broken, a side motion can also be induced due to the transformation between spin and orbital angular momenta. In experiments, these opto-mechanical effects can be significantly amplified by the long-range hydrodynamic interactions that provide an efficient recycling of energy. These unusual opto-mechanical effects open new possibilities for efficient manipulation of colloidal microparticles without having to rely on intricate structuring or shaping of light beams. Optically-controlled transport of matter is sought after in diverse applications in biology, colloidal physics, chemistry, condensed matter and others.Another consequence of light-matter interaction is the modification of the optical field itself, which can manifest, for instance, as detectable shifts of the centroids of optical beams during reflection and refraction. The spin-Hall effect of light (SHEL) is one type of such beam shifts that is due to the spin-orbit transformation governed by the conservation of angular momentum. We have shown that this effect can be amplified by the structural anisotropy of random nanocomposite materials.
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Date Issued
2015
Identifier
CFE0005961, ucf:50818
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005961
High Efficiency and Wide Color Gamut Liquid Crystal Displays
Title
High Efficiency and Wide Color Gamut Liquid Crystal Displays.
Creator
Luo, Zhenyue, Wu, Shintson, Kik, Pieter, Schoenfeld, Winston, Fang, Jiyu, University of Central Florida
Abstract / Description
Liquid crystal display (LCD) has become ubiquitous and indispensable in our daily life. Recently, it faces strong competition from organic light emitting diode (OLED). In order to maintain a strong leader position, LCD camp has an urgent need to enrich the color performance and reduce the power consumption. This dissertation focuses on solving these two emerging and important challenges. In the first part of the dissertation we investigate the quantum dot (QD) technology to improve the both...
Show moreLiquid crystal display (LCD) has become ubiquitous and indispensable in our daily life. Recently, it faces strong competition from organic light emitting diode (OLED). In order to maintain a strong leader position, LCD camp has an urgent need to enrich the color performance and reduce the power consumption. This dissertation focuses on solving these two emerging and important challenges. In the first part of the dissertation we investigate the quantum dot (QD) technology to improve the both the color gamut and the light efficiency of LCD. QD emits saturated color and grants LCD the capability to reproduce color vivid images. Moreover, the QD emission spectrum can be custom designed to match to transmission band of color filters. To fully take advantage of QD's unique features, we propose a systematic modelling of the LCD backlight and optimize the QD spectrum to simultaneously maximize the color gamut and light efficiency. Moreover, QD enhanced LCD demonstrates several advantages: excellent ambient contrast, negligible color shift and controllable white point. Besides three primary LCD, We also present a spatiotemporal four-primary QD enhanced LCD. The LCD's color is generated partially from time domain and partially from spatial domain. As a result, this LCD mode offers 1.5(&)#215; increment in spatial resolution, 2(&)#215; brightness enhancement, slightly larger color gamut and mitigated LC response requirement (~4ms). It can be employed in the commercial TV to meet the challenging Energy star 6 regulation. Besides conventional LCD, we also extend the QD applications to liquid displays and smart lighting devices. The second part of this dissertation focuses on improving the LCD light efficiency. Conventional LCD system has fairly low light efficiency (4%~7%) since polarizers and color filters absorb 50% and 67% of the incoming light respectively. We propose two approaches to reduce the light loss within polarizers and color filters. The first method is a polarization preserving backlight system. It can be combined with linearly polarized light source to boost the LCD efficiency. Moreover, this polarization preserving backlight offers high polarization efficiency (~77.8%), 2.4(&)#215; on-axis luminance enhancement, and no need for extra optics films. The second approach is a LCD backlight system with simultaneous color/polarization recycling. We design a novel polarizing color filter with high transmittance ((>)90%), low absorption loss (~3.3%), high extinction ratio ((>)10,000:1) and large angular tolerance (up to (&)#177;50?). This polarizing color filter can be used in LCD system to introduce the color/polarization recycling and accordingly boost LCD efficiency by ~3 times. These two approaches open new gateway for ultra-low power LCDs. In the final session of this dissertation, we demonstrate a low power and color vivid reflective liquid crystal on silicon (LCOS) display with low viscosity liquid crystal mixture. Compared with commercial LC material, the new LC mixture offers ~4X faster response at 20oC and ~8X faster response at ?20oC. This fast response LC material enables the field-sequential-color (FSC) driving for power saving. It also leads to several attractive advantages: sub-millisecond response time at room temperature, vivid color even at ?20oC, high brightness, excellent ambient contrast ratio, and suppressed color breakup. With this material improvement, LCOS display can be promising for the emerging wearable display market.
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Date Issued
2015
Identifier
CFE0006225, ucf:51078
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006225
High Performance Three-Dimensional Display Based on Polymer-Stabilized Blue Phase Liquid Crystal
Title
High Performance Three-Dimensional Display Based on Polymer-Stabilized Blue Phase Liquid Crystal.
Creator
Liu, Yifan, Wu, Shintson, Kik, Pieter, Likamwa, Patrick, Zhai, Lei, University of Central Florida
Abstract / Description
Autostereoscopic 2D/3D (two-dimension/three-dimension) switchable display has been attracting great interest in research and practical applications for several years. Among different autostereoscopic solutions, direction-multiplexed 3D displays based on microlens array or parallax barrier are viewed as the most promising candidates, due to their compatibility with conventional 2D display technologies. These 2D/3D switchable display system designs rely on fast switching display panels and...
Show moreAutostereoscopic 2D/3D (two-dimension/three-dimension) switchable display has been attracting great interest in research and practical applications for several years. Among different autostereoscopic solutions, direction-multiplexed 3D displays based on microlens array or parallax barrier are viewed as the most promising candidates, due to their compatibility with conventional 2D display technologies. These 2D/3D switchable display system designs rely on fast switching display panels and photonics devices, including adaptive focus microlens array and switchable slit array. Polymer-stabilized blue phase liquid crystal (PS-BPLC) material provides a possible solution to meet the aforementioned fast response time requirement. However, present display and photonic devices based on blue phase liquid crystals suffer from several drawbacks, such as low contrast ratio, relatively large hysteresis and short lifetime. In this dissertation, we investigate the material properties of PS-BPLC so as to improve the performance of PS-BPLC devices. Then we propose several PS-BPLC devices for the autostereoscopic 2D/3D switchable display system designs. In the first part we evaluate the optical rotatory power (ORP) of blue phase liquid crystal, which is proven to be the primary reason for causing the low contrast ratio of PS-BPLC display systems. Those material parameters affecting the ORP of PS-BPLC are investigated and an empirical equation is proposed to calculate the polarization rotation angle in a PS-BPLC cell. Then several optical compensation methods are proposed to compensate the impact of ORP and to improve the contrast ratio of a display system. The pros and cons of each solution are discussed accordingly. In the second part, we propose two adaptive focus microlens array structures and a high efficiency switchable slit array based on the PS-BPLC materials. By optimizing the design parameters, these devices can be applied to the 2D/3D switchable display systems. In the last section, we focus on another factor that affects the performance and lifetime of PS-BPLC devices and systems: the UV exposure condition. The impact of UV exposure wavelength, dosage, uniformity, and photo-initiator are investigated. We demonstrate that by optimizing the UV exposure condition, we can reduce the hysteresis of PS-BPLC and improve its long term stability.
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Date Issued
2014
Identifier
CFE0005370, ucf:50466
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005370
Liquid Crystal-Based Biosensors for the Detection of Bile Acids
Title
Liquid Crystal-Based Biosensors for the Detection of Bile Acids.
Creator
He, Sihui, Wu, Shintson, Kuebler, Stephen, Kik, Pieter, Fang, Jiyu, University of Central Florida
Abstract / Description
Bile acids are physiologically important metabolites, which are synthesized in liver as the end products of cholesterol metabolism and then secreted into intestine. They are amphiphilic molecules which play a critical role in the digestion and absorption of fats and fat-soluble vitamins through emulsification. The concentration of bile acids is an indicator for liver function. Individual suffering from liver diseases has a sharp increase in bile acid concentrations. Hence, the concentration...
Show moreBile acids are physiologically important metabolites, which are synthesized in liver as the end products of cholesterol metabolism and then secreted into intestine. They are amphiphilic molecules which play a critical role in the digestion and absorption of fats and fat-soluble vitamins through emulsification. The concentration of bile acids is an indicator for liver function. Individual suffering from liver diseases has a sharp increase in bile acid concentrations. Hence, the concentration level of bile acids has long been used as a biomarker for the early diagnosis of intestinal and liver diseases.Conventional methods of bile acid detection such as chromatography-mass spectrometry and enzymatic reactions are complex and expensive. It is highly desired to have a simple, fast, and low-cost detection of bile acids that is available for self-testing or point-of-care testing. To achieve this goal, we develop a liquid crystal-based biosensor for the detection of bile acids. The sensor platform is based on the anchoring transition of liquid crystals (LCs) at the sodium dodecyl sulfate (SDS)-laden LC/aqueous interface for the detection of bile acids in aqueous solution. The first part of this dissertation focuses on the detection mechanism of bile acids. Our studies show that the displacement of SDS from the LC/aqueous interface by the competitive adsorption of bile acids induces a homeotropic-to-planar anchoring transition of the LC at the interface, providing an optical signature for the simple and rapid detection of bile acids. The adsorption of bile acids on the interface was found to follow Langmuir-Freundlich isotherm. The adsorption kinetics of different bile acids is compared. We find that both the number and position of hydroxyl groups of bile acids affect their adsorption kinetics. The different optical patterns of LC films formed by the adsorption of bile acids are also discussed. The second part of this dissertation studies the effect of solution conditions, surfactants, and liquid crystals on the detection limit of the LC-based biosensor for bile acids. Low pH and high ionic strength in the aqueous solution can reduce the electrostatic interaction between SDS and bile acids, which leads to a decreased detection limit. Surfactants with smaller headgroup and lower packing density also help to reduce the detection limit. To further reduce the detection limit, we investigate the effect of LC structures and find that LCs with a shorter chain length give lower detection limits. Also, by substituting a phenyl ring with a cyclohexane ring, we find that the detection limit is further reduced due to the decrease of the interaction between the phenyl rings of LCs. By mixing different LCs together, the detection limit can be linearly tuned from 160 (&)#181;M to 1.5 (&)#181;M, which is comparable to the traditional methods. But the LC-based biosensors have much simpler design and manufacture process.The third part of this dissertation is to apply this LC-based biosensor to the detection of urinary bile acids. We test the influence of several potential interfering species such as urea, creatinine, uric acid and ascorbic acid by conducting experiments in synthetic urine. By adjusting the concentration of SDS, we are able to eliminate the impact of those interfering species, and demonstrate that the LC-based biosensors can selectively detect urinary bile acids in human urine, suggesting its potential for screening liver dysfunctions. The final part of this dissertation is to investigate the application of LC-based biosensors in detecting the lipolysis process by porcine pancreatic lipase (PPL). It has been a long-standing argument over the role of bile salts on the activity of PPL. Thus, we study the time course of the hydrolysis of phospholipid L-dipalmitoylphosphatidylcholine (L-DPPC) by PPL at LC/aqueous interface. The hydrolysis of L-DPPC leads to a homeotropic-to-tilted anchoring transition of the LC at the interface, which allows the hydrolysis process to be monitored by a polarizing optical microscope. The microscopy image analysis reveals a lag-burst kinetics where a lag phase is followed by a burst phase. The effect of bile acids on these two phases is studied. We find that the activity of PPL both in the presence and absence of colipase can be improved by increasing the concentration of bile acids. The improvement becomes more distinct in the presence of colipase.
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Date Issued
2015
Identifier
CFE0005804, ucf:50028
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005804
Fabrication of Metallic Antenna Arrays using Nanoimprint Lithography
Title
Fabrication of Metallic Antenna Arrays using Nanoimprint Lithography.
Creator
Lin, Yu-wei, Kik, Pieter, Schoenfeld, Winston, Fathpour, Sasan, University of Central Florida
Abstract / Description
This Thesis describes the development of a cost-effective process for patterning nanoscale metal antenna arrays. Soft ultraviolet (UV) Nanoimprint Lithography (NIL) into bilayer resist was chosen since it enables repeatable large-scale replication of nanoscale patterns with good lift-off properties using a simple low-cost process. Nanofabrication often involves the use of Electron Beam Lithography (EBL) which enables the definition of nanoscale patterns on small sample regions, typically (
Show moreThis Thesis describes the development of a cost-effective process for patterning nanoscale metal antenna arrays. Soft ultraviolet (UV) Nanoimprint Lithography (NIL) into bilayer resist was chosen since it enables repeatable large-scale replication of nanoscale patterns with good lift-off properties using a simple low-cost process. Nanofabrication often involves the use of Electron Beam Lithography (EBL) which enables the definition of nanoscale patterns on small sample regions, typically (<) 1 mm2. However its sequential nature makes the large scale production of nanostructured substrates using EBL cost-prohibitive. NIL is a pattern replication method that can reproduce nanoscale patterns in a parallel fashion, allowing the low-cost and rapid production of a large number of nano-patterned samples based on a single nanostructured master mold.Standard NIL replicates patterns by pressing a nanostructured hard mold into a soft resist layer on a substrate resulting in exposed substrate regions, followed by an optional Reactive Ion Etching (RIE) step and the subsequent deposition of e.g. metal onto the exposed substrate area. However, non-vertical sidewalls of the features in the resist layer resulting from an imperfect hard mold, from reflow of the resist layer, or from isotropic etching in the RIE step may cause imperfect lift-off. To overcome this problem, a bilayer resist method can be used. Using stacked resist layers with different etch rates, undercut structures can be obtained after the RIE step, allowing for easy lift-off even when using a mold with non-vertical sidewalls. Experiments were carried out using a nanostructured negative SiO2 master mold. Various material combinations and processing methods were explored. The negative master mold was transferred to a positive soft mold, leaving the original master mold unaltered. The soft mold consisted of a 5 ?m thick top Poly(methyl methacrylate) (PMMA), or Polyvinyl alcohol (PVA) layer, a 1.5 mm thick Polydimethylsiloxane (PDMS) buffer layer, and a glass supporting substrate. The soft mold was pressed into a bilayer of 300 nm PMMA and 350 nm of silicon based UV-curable resist that was spin-coated onto a glass slide, and cured using UV radiation. The imprinted patterns were etched using RIE, exposing the substrate, followed by metal deposition and lift-off. The experiments show that the use of soft molds enables successful pattern transfer even in the presence of small dust particles between the mold and the resist layer. Feature sizes down to 280 nm were replicated successfully.
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Date Issued
2013
Identifier
CFE0005026, ucf:49990
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005026
The Impact of Growth Conditions on Cubic ZnMgO Ultraviolet Sensors
Title
The Impact of Growth Conditions on Cubic ZnMgO Ultraviolet Sensors.
Creator
Boutwell, Ryan, Schoenfeld, Winston, Likamwa, Patrick, Kik, Pieter, Chernyak, Leonid, University of Central Florida
Abstract / Description
Cubic Zn1-xMgxO (c-Zn1-xMgxO) thin films have opened the deep ultraviolet (DUV) spectrum to exploration by oxide optoelectronic devices. These extraordinary films are readily wet-etch-able, have inversion symmetric lattices, and are made of common and safe constituents. They also host a number of new exciting experimental and theoretical challenges. Here, the relation between growth conditions of the c-Zn1-xMgxO film and performance of fabricated ultraviolet (UV) sensors is investigated....
Show moreCubic Zn1-xMgxO (c-Zn1-xMgxO) thin films have opened the deep ultraviolet (DUV) spectrum to exploration by oxide optoelectronic devices. These extraordinary films are readily wet-etch-able, have inversion symmetric lattices, and are made of common and safe constituents. They also host a number of new exciting experimental and theoretical challenges. Here, the relation between growth conditions of the c-Zn1-xMgxO film and performance of fabricated ultraviolet (UV) sensors is investigated. Plasma-Enhanced Molecular Beam Epitaxy was used to grow Zn1-xMgxO thin films and formation conditions were explored by varying the growth temperature, Mg source flux, oxygen flow rate, and radio-frequency (RF) power coupled into the plasma. Material review includes the effect of changing conditions on the film's optical transmission, surface morphology, growth rate, crystalline phase, and stoichiometric composition. Oxygen plasma composition was investigated by spectroscopic analysis under varying oxygen flow rate and applied RF power and is correlated to device performance. Ni/Mg/Au interdigitated metal-semiconductor-metal detectors were formed to explore spectral responsivity and UV-Visible rejection ratio (RR). Zn1-xMgxO films ranged in Mg composition from x = 0.45 - 1.0. Generally, x increased with increasing substrate temperature and Mg source flux, and decreased with increasing oxygen flow rate and RF power. Increasing x was correlated with decreased peak responsivity intensity and increased RR. Device performance was improved by increasing the ratio of O to O+ atoms and minimizing O2+ in the plasma. Peak responsivity as high as 500 A/W was observed in visible-blind phase-segregated Zn1-xMgxO devices, while cubic phase solar-blind devices demonstrated peak responsivity as high as 12.6 mA/W, and RR of three orders of magnitude. Optimal conditions are predicted for the formation of DUV Zn1-xMgxO sensors.
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Date Issued
2013
Identifier
CFE0005087, ucf:50735
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005087
Density-Functional Theory+Dynamical Mean-Field Theory Study of the Magnetic Properties of Transition-Metal Nanostructures
Title
Density-Functional Theory+Dynamical Mean-Field Theory Study of the Magnetic Properties of Transition-Metal Nanostructures.
Creator
Kabir, Alamgir, Rahman, Talat, Kara, Abdelkader, Del Barco, Enrique, Kik, Pieter, University of Central Florida
Abstract / Description
In this thesis, Density Functional Theory (DFT) and Dynamical Mean-Field Theory (DMFT) approaches are applied to study the magnetic properties of transition metal nanosystems of different sizes and compositions. In particular, in order to take into account dynamical electron correlation effects (time-resolved local charge interactions), we have adopted the DFT+DMFT formalism and made it suitable for application to nanostructures. Preliminary application of this DFT+DMFT approach, using...
Show moreIn this thesis, Density Functional Theory (DFT) and Dynamical Mean-Field Theory (DMFT) approaches are applied to study the magnetic properties of transition metal nanosystems of different sizes and compositions. In particular, in order to take into account dynamical electron correlation effects (time-resolved local charge interactions), we have adopted the DFT+DMFT formalism and made it suitable for application to nanostructures. Preliminary application of this DFT+DMFT approach, using available codes, to study the magnetic properties of small (2 to 5-atom) Fe and FePt clusters provide meaningful results: dynamical effects lead to a reduction of the cluster magnetic moment as compared to that obtained from DFT or DFT+U (U being the Coulomb repulsion parameter). We have subsequently developed our own nanoDFT+DMFT code and applied it to examine the magnetization of iron particles containing10-147 atoms. Our results for the cluster magnetic moments are in a good agreement with experimental data. In particular, we are able to reproduce the oscillations in magnetic moment with size as observed in the experiments. Also, DFT+DMFT does not lead to an overestimation of magnetization for the clusters in the size range of 10-27 atoms found with DFT and DFT+U. On application of the nanoDFT+DMFT approach to systems with mixed geometry (-) Fe2O3 film, which are periodic (infinitely extended), in two directions, and finite in the third. Similar to DFT+U, we find that the surface atom magnetic moments are smaller compared to the bulk. However, the absolute values of the surface atoms magnetic moments are smaller in DFT+DMFT. In parallel, we have carried out a systematic study of magnetic anisotropy in bimetallic L10 FePt nanoparticles (20-484 atoms) by using two DFT-based approaches: direct and the torque method. We find that the magnetocrystalline anisotropy (MCA) of FePt clusters is larger than that of the pure Fe and Pt ones. We explain this effect by a large hybridization of 3d Fe- and 5d Pt-atom orbitals, which lead to enhancement of the magnetic moment of the Pt atom, and hence to a larger magnetic anisotropy because of large spin-orbit coupling of Pt atoms. In addition, we find that particles whose (large) central layer consists of Pt atoms, rather than Fe, have larger MCA due to stronger hybridization effects. Such 'protected' MCA, which does not require protective cladding, can be used in modern magnetic technologies.
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Date Issued
2015
Identifier
CFE0006038, ucf:50971
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006038
Nano and nanostructured materials for optical applications
Title
Nano and nanostructured materials for optical applications.
Creator
Chantharasupawong, Panit, Thomas, Jayan, Hagan, David, Kik, Pieter, Gaume, Romain, Chanda, Debashis, University of Central Florida
Abstract / Description
Nano and nanostructured materials offer unique physical and chemical properties that differ considerably from their bulk counterparts. For decades, due to their fascinating properties, they have been extensively explored and found to be beneficial in numerous applications. These materials are key components in many cutting-edge optic and photonic technologies, including photovoltaics, waveguides and sensors. In this dissertation, the uses of nano and nanostructured materials for optical...
Show moreNano and nanostructured materials offer unique physical and chemical properties that differ considerably from their bulk counterparts. For decades, due to their fascinating properties, they have been extensively explored and found to be beneficial in numerous applications. These materials are key components in many cutting-edge optic and photonic technologies, including photovoltaics, waveguides and sensors. In this dissertation, the uses of nano and nanostructured materials for optical applications are investigated in the context of optical limiting, three dimensional displays, and optical sensing. Nanomaterials with nonlinear optical responses are promising candidates for self-activating optical limiters. In the first part of this study, optical limiting properties of unexplored nanomaterials are investigated. A photoacoustic detection technique is developed as an alternative characterization method for studying optical nonlinearities. This was done with an indigenously developed setup for measuring the photoacoustic signals generated from samples excited with a pulse laser. A theoretical model for understanding the experimental observations is presented. In addition, the advantages of this newly developed technique over the existing methods are demonstrated. Blending optical sensitizers with photoconducting polymers and chromophores results in a polymer composite that is able to record a light grating. This composite can be used as recording media in 3D holographic display technology. Here, 2D nano materials, like graphenes, are used as optical sensitizers to improve the response time of a photorefractive polymer. The addition of graphenes to a PATPD/ECZ/7-DCST composite results in a three-fold enhancement in response time and therefore faster recording speed of the medium. The faster build-up time is attributed to better charge generation and mobility due to the presence of graphenes in the composite. Lastly, a facile nanofabrication technique is developed to produce metallic nanostructures with a tunable plasmonic response. The enhancement of the light-matter interactions due to these nanostructures in sensing an analyte is demonstrated.
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Date Issued
2015
Identifier
CFE0006029, ucf:51016
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006029
Fabrication and Characterization of Spatially-Variant Self-Collimating Photonic Crystals
Title
Fabrication and Characterization of Spatially-Variant Self-Collimating Photonic Crystals.
Creator
Digaum, Jennefir, Kuebler, Stephen, Kik, Pieter, Schoenfeld, Winston, Likamwa, Patrick, Gesquiere, Andre, University of Central Florida
Abstract / Description
Spatially-variant photonic crystals (SVPCs) created using materials having a low refractive index are shown to be capable of abruptly controlling light beams with high polarization selectivity. SVPCs are photonic crystals for which the orientation of the unit cell is controllably varied throughout the lattice to control the flow of light. Multi-photon lithography in a photo polymer was used to fabricate three-dimensional SVPCs that direct the flow of light around a 90 degree bend. The optical...
Show moreSpatially-variant photonic crystals (SVPCs) created using materials having a low refractive index are shown to be capable of abruptly controlling light beams with high polarization selectivity. SVPCs are photonic crystals for which the orientation of the unit cell is controllably varied throughout the lattice to control the flow of light. Multi-photon lithography in a photo polymer was used to fabricate three-dimensional SVPCs that direct the flow of light around a 90 degree bend. The optical performance of the SVPCs was characterized using a scanning optical-fiber system that introduced light onto the input face of a structure and measured the intensity of light emanating from the output faces.As a proof-of-concept, SVPCs that can bend a beam at a wavelength of ?0 = 2.94 ?m were fabricated in the photo-polymer SU-8. The SVPCs were shown to direct infrared light of one polarization through a sharp bend, while the other polarization propagated straight through the SVPC, when the volumetric fill-factor is near 50%. The peak-to-peak ratio of intensities of the bent- and straight-through beams was 8:1, and a power efficiency of 8% was achieved. The low efficiency is attributed to optical absorption in SU-8 at ?0 = 2.94 ?m.SVPCs that can bend a beam at telecommunications wavelengths near ?0 = 1.55 ?m were fabricated by multi-photon lithography in the photo-polymer IP-Dip. IP-Dip was chosen over SU 8 to enable fabrication of finer features, as are needed for an SVPC scaled in size to operate at shorter wavelengths. Experimental characterization shows that these particular SVPCs provide effective control of the vertically polarized beam at ?0 = 1.55 ?m, when the volumetric fill-factor is around 46%. The beam bending peak efficiency was found to be 52.5% with a peak-to-peak ratio between the bent- and straight-through beams of 78.7. Additionally, these SVPCs can bend a light beam with a broad bandwidth of 153 nm that encompasses both the C- and S-bands of the telecommunications window. Furthermore, the SVPCs have high tolerance to misalignment, in which an offset of the input beam by as much as 6 ?m causes the beam-bending efficiency to drop no more than 50%. Finally, it is shown that these particular SVPCs can bend beams without significantly distorting the mode profile. This work introduces a new scheme for controlling light that should be useful for integrated photonics.The penultimate chapter discusses nonlinear phenomena that were observed during the optical characterization of the SVPCs using a high peak-power amplified femtosecond laser system. The first of these effects is referred to as "super-collimation", in which the beam bending peak efficiency of certain SVPCs increases with input intensity, reaching as high as 68%. The second effect pertains to nonlinear imaging of light at ?0 = 1.55 ?m scattered from an SVPC and detected using a silicon-CCD camera. This effect enables beam bending within the device to be imaged in real time. The dissertation concludes with an outlook for SVPCs, discussing potential applications and challenges that must be addressed to advance their use in photonics.
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Date Issued
2016
Identifier
CFE0006527, ucf:51371
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006527
Cascaded plasmon resonances for enhanced nonlinear optical response
Title
Cascaded plasmon resonances for enhanced nonlinear optical response.
Creator
Toroghi, Seyfollah, Kik, Pieter, Vanstryland, Eric, Kuebler, Stephen, Hagan, David, Belfield, Kevin, University of Central Florida
Abstract / Description
The continued development of integrated photonic devices requires low-power, small volume all-optical modulators. The weak nonlinear optical response of conventional optical materials requires the use of high intensities and large interaction volumes in order to achieve significant light modulation, hindering the miniaturization of all-optical switches and the development of lightweight transmission optics with nonlinear optical response. These challenges may be addressed using plasmonic...
Show moreThe continued development of integrated photonic devices requires low-power, small volume all-optical modulators. The weak nonlinear optical response of conventional optical materials requires the use of high intensities and large interaction volumes in order to achieve significant light modulation, hindering the miniaturization of all-optical switches and the development of lightweight transmission optics with nonlinear optical response. These challenges may be addressed using plasmonic nanostructures due to their unique ability to confine and enhance electric fields in sub-wavelength volumes. The ultrafast nonlinear response of free electrons in such plasmonic structures and the fast thermal nonlinear optical response of metal nanoparticles, as well as the plasmon enhanced nonlinear Kerr-type response of the host material surrounding the nanostructures could allow ultrafast all-optical modulation with low modulation energy. In this thesis, we investigate the linear and nonlinear optical response of engineered effective media containing coupled metallic nanoparticles. The fundamental interactions in systems containing coupled nanoparticles with size, shape, and composition dissimilarity, are evaluated analytically and numerically, and it is demonstrated that under certain conditions the achieved field enhancement factors can exceed the single-particle result by orders of magnitude in a process called cascaded plasmon resonance. It is demonstrated that these conditions can be met in systems containing coupled nanospheres, and in systems containing non-spherical metal nanoparticles that are compatible with common top-down nanofabrication methods such as electron beam lithography and nano-imprint lithography. We show that metamaterials based on such cascaded plasmon resonance structures can produce enhanced nonlinear optical refraction and absorption compared to that of conventional plasmonic nanostructures. Finally, it is demonstrated that the thermal nonlinear optical response of metal nanoparticles can be enhanced in carefully engineered heterogeneous nanoparticle clusters, potentially enabling strong and fast thermal nonlinear optical response in system that can be produced in bulk through chemical synthesis.
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Date Issued
2014
Identifier
CFE0005556, ucf:50272
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005556
Large Area Conformal Infrared Frequency Selective Surfaces
Title
Large Area Conformal Infrared Frequency Selective Surfaces.
Creator
Darchangel, Jeffrey, Schoenfeld, Winston, Boreman, Glenn, Likamwa, Patrick, Kik, Pieter, Lail, Brian, University of Central Florida
Abstract / Description
Frequency selective surfaces (FSS) were originally developed for electromagnetic filtering applications at microwave frequencies. Electron-beam lithography has enabled the extension of FSS to infrared frequencies; however, these techniques create sample sizes that are seldom appropriate for real world applications due to the size and rigidity of the substrate. A new method of fabricating large area conformal infrared FSS is introduced, which involves releasing miniature FSS arrays from a...
Show moreFrequency selective surfaces (FSS) were originally developed for electromagnetic filtering applications at microwave frequencies. Electron-beam lithography has enabled the extension of FSS to infrared frequencies; however, these techniques create sample sizes that are seldom appropriate for real world applications due to the size and rigidity of the substrate. A new method of fabricating large area conformal infrared FSS is introduced, which involves releasing miniature FSS arrays from a substrate for implementation in a coating. A selective etching process is proposed and executed to create FSS particles from crossed-dipole and square-loop FSS arrays. When the fill-factor of the particles in the measurement area is accounted for, the spectral properties of the FSS flakes are similar to the full array from which they were created. As a step toward scalability of the process, a square-patch design is presented and formed into FSS flakes with geometry within the capability of ultraviolet optical lithography.Square-loop infrared FSS designs are investigated both in quasi-infinite arrays and in truncated sub-arrays. First, scattering-scanning near-field optical microscopy (s-SNOM) is introduced as a characterization method for square-loop arrays, and the near-field amplitude and phase results are discussed in terms of the resonant behavior observed in far-field measurements. Since the creation of FSS particles toward a large area coating inherently truncates the arrays, array truncation effects are investigated for square-loop arrays both in the near- and far-field. As an extension of the truncation study, small geometric changes in the design of square-loop arrays are introduced as a method to tune the resonant far-field wavelength back to that of the quasi-infinite arrays.
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Date Issued
2014
Identifier
CFE0005476, ucf:50348
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005476
Optically Induced Forces in Scanning Probe Microscopy
Title
Optically Induced Forces in Scanning Probe Microscopy.
Creator
Kohlgraf-Owens, Dana, Dogariu, Aristide, Christodoulides, Demetrios, Kik, Pieter, DeWilde, Yannick, University of Central Florida
Abstract / Description
The focus of this dissertation is the study of measuring light not by energy transfer as is done with a standard photodetector such as a photographic film or charged coupled device, but rather by the forces which the light exerts on matter. In this manner we are able to replace or complement standard photodetector-based light detection techniques. One key attribute of force detection is that it permits the measurement of light over a very large range of frequencies including those which are...
Show moreThe focus of this dissertation is the study of measuring light not by energy transfer as is done with a standard photodetector such as a photographic film or charged coupled device, but rather by the forces which the light exerts on matter. In this manner we are able to replace or complement standard photodetector-based light detection techniques. One key attribute of force detection is that it permits the measurement of light over a very large range of frequencies including those which are difficult to access with standard photodetectors, such as the far IR and THz. The dissertation addresses the specific phenomena associated with optically induced force (OIF) detection in the near-field where light can be detected with high spatial resolution close to material interfaces. This is accomplished using a scanning probe microscope (SPM), which has the advantage of already having a sensitive force detector integrated into the system. The two microscopies we focus on here are atomic force microscopy (AFM) and near-field scanning optical microscopy (NSOM). By detecting surface-induced forces or force gradients applied to a very small size probe ( diameter), AFM measures the force acting on the probe as a function of the tip-sample separation or extracts topography information. Typical NSOM utilizes either a small aperture ( diameter) to collect and/or radiate light in a small volume or a small scatterer ( diameter) in order to scatter light in a very small volume. This light is then measured with an avalanche photodiode or a photomultiplier tube.These two modalities may be combined in order to simultaneously map the local intensity distribution and topography of a sample of interest. A critical assumption made when performing such a measurement is that the distance regulation, which is based on surface induced forces, and the intensity distribution are independent. In other words, it is assumed that the presence of optical fields does not influence the AFM operation. However, it is well known that light exerts forces on the matter with which it interacts. This light-induced force may affect the atomic force microscope tip-sample distance regulation mechanism or, by modifying the tip, it may also indirectly influence the distance between the probe and the surface. This dissertation will present evidence that the effect of optically induced forces is strong enough to be observed when performing typical NSOM measurements. This effect is first studied on common experimental situations to show where and how these forces manifest themselves. Afterward, several new measurement approaches are demonstrated, which take advantage of this additional information to either complement or replace standard NSOM detection. For example, the force acting on the probe can be detected while simultaneously extracting the tip-sample separation, a measurement characteristic which is typically difficult to obtain. Moreover, the standard field collection with an aperture NSOM and the measurement of optically induced forces can be operated simultaneously. Thus, complementary information about the field intensity and its gradient can be, for the first time, collected with a single probe. Finally, a new scanning probe modality, multi-frequency NSOM (MF-NSOM), will be demonstrated. In this approach, the tuning fork is driven electrically at one frequency to perform a standard tip-sample distance regulation to follow the sample topography and optically driven at another frequency to measure the optically induced force. This novel technique provides a viable alternative to standard NSOM scanning and should be of particular interest in the long wavelength regime, e.g. far IR and THz.
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Date Issued
2013
Identifier
CFE0004705, ucf:49829
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004705