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(1 - 8 of 8)
- Title
- Multiscale simulation of laser ablation and processing of semiconductor materials.
- Creator
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Shokeen, Lalit, Schelling, Patrick, Kar, Aravinda, Vaidyanathan, Rajan, Su, Ming, Kara, Abdelkader, University of Central Florida
- Abstract / Description
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We present a multiscale model of laser-solid interactions in silicon based on an empirical potential developed under conditions of strong electronic excitations. The parameters of the interatomic potential depends on the temperature of the electronic subsystem Te, which is directly related to the density of the electron-hole pairs and hence the number of broken bonds. We analyze the dynamics of this potential as a function of electronic temperature Te and lattice temperature Tion. The...
Show moreWe present a multiscale model of laser-solid interactions in silicon based on an empirical potential developed under conditions of strong electronic excitations. The parameters of the interatomic potential depends on the temperature of the electronic subsystem Te, which is directly related to the density of the electron-hole pairs and hence the number of broken bonds. We analyze the dynamics of this potential as a function of electronic temperature Te and lattice temperature Tion. The potential predicts phonon spectra in good agreement with finite-temperature density-functional theory (DFT), including the lattice instability induced by the high electronic excitations. For 25fs pulse, a wide range of fluence values is simulated resulting in heterogeneous melting, homogenous melting, and ablation. The results presented demonstrate that phase transitions can usually be described by ordinary thermal processes even when the electronic temperature Te is much greater than the lattice temperature TL during the transition. However, the evolution of the system and details of the phase transitions depend strongly on Te and corresponding density of broken bonds. For high enough laser fluence, homogeneous melting is followed by rapid expansion of the superheated liquid and ablation. Rapid expansion of the superheated liquid occurs partly due to the high pressures generated by a high density of broken bonds. As a result, the system is readily driven into the liquid-vapor coexistence region, which initiates phase explosion. The results strongly indicates that phase explosion, generally thought of as an ordinary thermal process, can occur even under strong non-equilibrium conditions when Te (>)(>)TL. In summary, a detailed investigation of laser-solid interactions in silicon is presented for femtosecond laser pulse that yields strong far-from-equilibrium conditions.
Show less - Date Issued
- 2012
- Identifier
- CFE0004599, ucf:49206
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004599
- Title
- Enhanced Ablation by Femtosecond and Nanoseond Laser Pulses.
- Creator
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Kerrigan, Haley, Richardson, Martin, Baudelet, Matthieu, Shivamoggi, Bhimsen, University of Central Florida
- Abstract / Description
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Laser ablation of GaAs by a combination of femtosecond and nanosecond pulses is investigated as a means of enhancing material removal by a femtosecond pulse in the filamentation intensity regime. We demonstrate for the first time increased ablation of GaAs by ultrafast laser pulse plasmas augmented by nanosecond pulse radiation from a secondary laser. Material removal during laser ablation is a complex process that occurs via multiple mechanisms over several timescales. Due to different pulse...
Show moreLaser ablation of GaAs by a combination of femtosecond and nanosecond pulses is investigated as a means of enhancing material removal by a femtosecond pulse in the filamentation intensity regime. We demonstrate for the first time increased ablation of GaAs by ultrafast laser pulse plasmas augmented by nanosecond pulse radiation from a secondary laser. Material removal during laser ablation is a complex process that occurs via multiple mechanisms over several timescales. Due to different pulse durations, ablation by femtosecond and nanosecond pulses are dominated by different mechanisms. Ablation can be enhanced by optimally combining a femtosecond and nanosecond pulse in time. In this work, the craters generated by combinations of pulses are investigated for inter-pulse delays ranging from -50ns to +1?s, with the fs pulse preceding the ns pulse corresponding to a positive delay. The Ti:Sapph Multi-Terawatt Femtosecond Laser (MTFL) in the Laser Plasma Laboratory (LPL) provides 50fs pulses at 800nm with intensities of 1014W/cm^2 at the sample. An Nd:YAG laser (Quantel CFR200) provides 8ns pulses at 1064nm with intensities of 109W/cm^2. Crater profilometry with white-light interferometry and optical microscopy determine the structure and surface features of the craters and the volume of material removed. Ultrafast shadowgraphy of the ejected plasma provides insight to the dual-pulse ablation dynamics. Sedov-Taylor analysis of the generated shockwave reveals the energy coupled to the sample or preceding plasma. It was found that inter-pulse delays between +40 and +200ns yielded craters 2.5x greater in volume than that of the femtosecond pulse alone, with a maximum enhancement of 2.7x at +100ns. Shadowgraphy of -40 to +40ns delays revealed that enhancement occurs when the nanosecond pulse couples to plasma generated by the fs pulse. This work provides a possible means of enhancing ablation by femtosecond filaments, which propagate long distances with clamped intensity, advancing long-range stand-off ablation
Show less - Date Issued
- 2017
- Identifier
- CFE0006889, ucf:51734
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006889
- Title
- Laser Filamentation Interaction with Materials for Spectroscopic Applications.
- Creator
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Weidman, Matthew, Richardson, Martin, Schulzgen, Axel, Christodoulides, Demetrios, Sigman, Michael, University of Central Florida
- Abstract / Description
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Laser filamentation is a non-diffracting propagation regime consisting of an intense core that is surrounded by an energy reservoir. For laser ablation based spectroscopy techniques such as Laser Induced Breakdown Spectroscopy (LIBS), laser filamentation enables the remote delivery of high power density laser radiation at long distances. This work has shown a quasi-constant filament-induced mass ablation along a 35 m propagation distance. The mass ablated was sufficient for the application of...
Show moreLaser filamentation is a non-diffracting propagation regime consisting of an intense core that is surrounded by an energy reservoir. For laser ablation based spectroscopy techniques such as Laser Induced Breakdown Spectroscopy (LIBS), laser filamentation enables the remote delivery of high power density laser radiation at long distances. This work has shown a quasi-constant filament-induced mass ablation along a 35 m propagation distance. The mass ablated was sufficient for the application of laser filamentation as a sampling tool for plasma based spectroscopy techniques. Within the scope of this study, single-shot ablation was compared with multi-shot ablation. The dependence of ablated mass on the number of pulses was observed to have a quasi-linear dependence on the number of pulses, advantageous for applications such as spectroscopy. Sample metrology showed that both physical and optical material properties have significant effects on the filament-induced ablation behavior. A relatively slow filament-induced plasma expansion was observed, as compared with a focused beams. This suggests that less energy was transferred to the plasma during filament-induced ablation. The effects of the filament core and the energy reservoir on the filament-induced ablation and plasma formation were investigated. Goniometric measurements of the filament-induced plasma, along with radiometric calculations, provided the number of emitted photons from a specific atomic transition and sample material.This work has advanced the understanding of the effects of single filaments on the ablation of solid materials and the understanding of filament-induced plasma dynamics. It has laid the foundation for further quantitative studies of multiple filamentation. The implications of this work extend beyond spectroscopy and included any application of filamentation that involves the interaction with a solid material.
Show less - Date Issued
- 2012
- Identifier
- CFE0004616, ucf:49940
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004616
- Title
- CARDIAC CONSEQUENCES OF SELECTIVE ADRENERGIC CELL ABLATION IN MICE.
- Creator
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Tumuluri, Lahari, Ebert, Steven, University of Central Florida
- Abstract / Description
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Phenylethanolamine-N-methyltransferase (Pnmt), is the enzyme that catalyzes the conversion of noradrenaline to adrenaline. It has been found in the embryonic heart and in certain adult heart cells, including intrinsic cardiac adrenergic cells, intracardiac neurons, and cardiomyocytes, but their physiological role in the heart is not well understood. To determine the function of Pnmt-expressing cells in the developing heart, a novel genetically-targeted mouse model that causes selective...
Show morePhenylethanolamine-N-methyltransferase (Pnmt), is the enzyme that catalyzes the conversion of noradrenaline to adrenaline. It has been found in the embryonic heart and in certain adult heart cells, including intrinsic cardiac adrenergic cells, intracardiac neurons, and cardiomyocytes, but their physiological role in the heart is not well understood. To determine the function of Pnmt-expressing cells in the developing heart, a novel genetically-targeted mouse model that causes selective cellular suicide of Pnmt-expressing cells was created by mating Pnmt-Cre Recombinase knock-in mice (Pnmt Cre/Cre) with ROSA26-eGFP-DTA (R26R+/DTA). The �cellular suicide� allele is the Diptheria Toxin A (DTA) gene fragment. Activation of the DTA suicide allele is dependent upon Cre expression, which is under the control of the endogenous Pnmt gene locus (i.e., expression is restricted to adrenaline-producing �adrenergic� cells). Ongoing studies in Dr. Ebert�s laboratory have shown that Pnmt-Cre/DTA mice have a loss of adrenergic cells in the adrenal gland and begin developing serious cardiac and neurological deficits within one month after birth. The purpose of my project is to examine the potential cardiac consequences of selective adrenergic cell ablation in this model. Aim 1 of this study is to analyze echocardiography data from mice with genetic ablation of adrenergic cells compared to age-matched (littermate) controls over the first 6-months after birth. Preliminary evidence indicates that there is substantial loss of function that progressively worsens with age in the ablation group compared to controls. Aim 2 of this study seeks to uncover evidence of adrenergic cell ablation in the heart using histological and immunofluorescence staining techniques. We predict that these experiments will provide physiological and anatomical evidence showing that Pnmt-expressing cells in the heart make significant contributions to cardiac development and function. This knowledge is expected to increase our basic understanding about the specific roles adrenergic cells play during heart, and could lead to the development of novel treatment strategies for certain types of cardiac defects in the future.
Show less - Date Issued
- 2016
- Identifier
- CFH2000045, ucf:45512
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000045
- Title
- HIGH-INTENSITY ULTRA-FAST LASER INTERACTION TECHNOLOGIES.
- Creator
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Bernath, Robert, Richardson, Martin, University of Central Florida
- Abstract / Description
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To our knowledge this is the first comprehensive study of laser-induced effects generated at intermediate distances using self-channeled femtosecond laser pulses. Studies performed were made both experimentally and theoretically with the use of novel modeling techniques. Peak laser pulse powers above 3 GW allow beam propagation without divergence for up to several kilometers. In this regime, experiments were performed at 30 meters from the laser system in a custom propagation and target range...
Show moreTo our knowledge this is the first comprehensive study of laser-induced effects generated at intermediate distances using self-channeled femtosecond laser pulses. Studies performed were made both experimentally and theoretically with the use of novel modeling techniques. Peak laser pulse powers above 3 GW allow beam propagation without divergence for up to several kilometers. In this regime, experiments were performed at 30 meters from the laser system in a custom propagation and target range, utilizing the Laser Plasma Laboratory's Terawatt laser system. Experiments included investigations of laser ablation; electromagnetic pulsed (EMP) radiation generation over the 1-18 GHz region; shockwave formation in air and solid media; optical coupling of channeled pulses into transparent media; and, conservation of energy in these interactions. The use of bursts of femtosecond pulses was found to increase the ablation rate significantly over single-pulse ablation in both air and vacuum. EMP generation from near-field focused and distance-propagated pulses was investigated. Field strengths upwards of 400 V/m/λ for vacuum focusing and 25 V/m/λ for self-channeled pulses were observed. The total field strengths over 1-18 GHz measured at distance surpassed 12 kV/m. Shockwaves generated in transparent media at 30 meters were observed as a function of time. It was found that the interaction conditions control the formation and propagation of the shock fronts into the medium. Due to the processes involved in self-channeling, significant fractions of the laser pulse were coupled into the target materials, resulting in internal optical and exit-surface damage. Basic estimations on the conservation of energy in the interaction are presented. The results of the experiments are supported by hydrodynamic plasma physics code and acoustic modeling.
Show less - Date Issued
- 2007
- Identifier
- CFE0001902, ucf:47497
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001902
- Title
- ALTERNATIVE FOAM TREATMENTS FOR THE SPACE SHUTTLE'S EXTERNAL TANK.
- Creator
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Dreggors, Kirsten, Nayfeh, Jamal, University of Central Florida
- Abstract / Description
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The Space Shuttle Columbia accident and the recent excitement surrounding Discovery's return to space brought excessive media attention to the foam products used on the External Tank (ET). In both cases, videos showed chunks of foam or ablative material falling away from the ET during lift off. This led to several years of investigation and research into the exact cause of the accident and potential solutions to avoid the problem in the future. Several design changes were made prior to the...
Show moreThe Space Shuttle Columbia accident and the recent excitement surrounding Discovery's return to space brought excessive media attention to the foam products used on the External Tank (ET). In both cases, videos showed chunks of foam or ablative material falling away from the ET during lift off. This led to several years of investigation and research into the exact cause of the accident and potential solutions to avoid the problem in the future. Several design changes were made prior to the return to flight this year, but the ET still shed foam during lift off. Since the Columbia accident, the loss of foam on ETs has been a significant area of interest for NASA, United Space Alliance, and Lockheed Martin. The Columbia Accident Investigation Board did not evaluate alternative materials but certainly highlighted the need for change. The majority of the research previously concentrated on improving the design and/or the application process of the current materials. Within recent years, some research and testing has been done to determine if a glass microsphere composite foam would be an acceptable alternative, but this work was overcome by the need for immediate change to return the shuttle to flight in time to deliver supplies to the International Space Station. Through a better understanding of the foam products currently used on the ET, other products can be evaluated for future space shuttle flights and potential applications on new space vehicles. The material properties and the required functionality of alternative materials can be compared to the current materials to determine if suitable replacement products exist. This research also lends itself to the development of future space flight and unmanned launch vehicles. In this paper, the feasibility of alternative material for the space shuttle's external tank will be investigated. Research on what products are used on the ET and a set of functional requirements driving the selection of those materials will be presented. The material properties of the current ET foam products will be collected and an evaluation of how those materials' properties meet the functional requirements will be accomplished. Then significant research on polymeric foams and ablative materials will be completed to learn how these various products can be applied in this industry. With this research and analysis, the knowledge gained will be used to select and evaluate the effectiveness of an alternate product and to determine feasibility of a product change with the current ET and the importance of maintaining the shuttle launch schedule. This research will also be used to evaluate the potential application of the alternative product on future platforms. There are several possible outcomes to this research. This research could result in a recommended change to the ET foam material or a perfectly acceptable alternative material that could result in a cost or schedule impact if implemented. It is also possible that there exists no suitable alternative material given the existing functional requirements. In any case, the alternative material could have future applications on new space vehicles. A set of results from the research and analysis will be provided along with a recommendation on a future material for use on space vehicles.
Show less - Date Issued
- 2005
- Identifier
- CFE0000787, ucf:46566
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000787
- Title
- DEVELOPMENT AND APPLICATION STUDY OF NANOSCALE THIN FILM MATERIALS AND POLYMER NANOCOMPOSITES.
- Creator
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Chen, Hui, Huo, Qun, University of Central Florida
- Abstract / Description
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This dissertation demonstrated that the manipulation of substances at the molecular or nanometer level can lead to the discovery and development of new materials with interesting properties and important applications. Chapter 1 describes the development of a nanoscale molecular thin film material for corrosion protection. By using a self-assembled monolayer film with a thickness of only about 1 nanometer as a linkage, a covalent bonding was achieved between a polyurethane top coating and an...
Show moreThis dissertation demonstrated that the manipulation of substances at the molecular or nanometer level can lead to the discovery and development of new materials with interesting properties and important applications. Chapter 1 describes the development of a nanoscale molecular thin film material for corrosion protection. By using a self-assembled monolayer film with a thickness of only about 1 nanometer as a linkage, a covalent bonding was achieved between a polyurethane top coating and an aluminum alloy substrate. This covalent bonding between polymer top coating and the aluminum alloy substrate significantly improved the corrosion resistance of the substrate. Chapter 2 and Chapter 3 describe the development of a gold nanoparticle-polymer composite material in different forms with a number of applications. Gold nanoparticles are among one of the most extensively studied nanomaterials. When the size of gold is shrunk to the nanometer scale, many interesting and new physical properties start to appear from gold nanoparticles. The optical properties of gold nanoparticles, particularly the surface plasmon resonance absorption, have been investigated in this dissertation for the development of multifunctional nanocomposite materials. Chapter 2 presents the preparation of a gold nanoparticle/poly(methyl methacrylate) (PMMA) nanocomposite film and the application of such films for microstructure fabrication using a direct laser writing technique. Gold nanoparticles are excellent photon-thermal energy converters due to their large absorption cross section at the surface plasmon resonance region. Upon laser irradiation of the nanocomposite film, the thermal energy converted from the absorbed photon energy by gold nanopaticles induced a complete decomposition of PMMA, leading to the formation of various microstructures on the nanocomposite films. Chapter 3 reports the further development of a nanoparticle/polymer composite nanofiber material fabricated through an electrospinning process. The matrix of the nanofiber is made of two polyelectrolytes, poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH). Three methods were developed to incorporate gold nanoparticles into the polymer matrix. The composite nanofiber materials developed in this study demonstrate multifunctional properties, including good electrical conductivity, photothermal response, and surface-enhanced IR absorption. This material may be used for many important applications including catalysis, chemical and biological sensors, and scaffold materials for tissue engineering. In Chapter 4, another most important nanomaterial, carbon naotubes (CNTs), were introduced as fillers to prepare polymer nanocomposites. A dispersion method for multi-walled carbon nanotubes (MWCNTs) using a conjugated conducting polymer, poly(3-hexylthiophene) (P3HT) as the third component and trifluoroacetic acid (TFA) as a co-solvent was developed. Due to the excellent dispersion of carbon nanotubes in PMMA and enhanced conductivity of the nanocomposites by the conjugated conducting polymers, the prepared composite materials has an extremely low percolation threshold of less than 0.006 wt% of MWCNT content. The potential use of MWCNT/conducting polymer composites for energy storage applications such as suppercapacitors was further investigated by Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and charging-discharging cycles. Compared to pure carbon nanotubes, the nanocomposite materials have significantly improved properties and are promising for supercapacitor applications.
Show less - Date Issued
- 2008
- Identifier
- CFE0002265, ucf:47825
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002265
- Title
- Genetically-programmed suicide of adrenergic cells in the mouse leads to severe left ventricular dysfunction, impaired weight gain, and symptoms of neurological dysfunction.
- Creator
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Owji, Aaron, Ebert, Steven, King, Stephen, Sugaya, Kiminobu, University of Central Florida
- Abstract / Description
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Phenylethanolamine-N-methyltransferase (Pnmt) catalyzes the conversion of noradrenaline to adrenaline and is the last enzyme in the catecholamine biosynthetic pathway. Pnmt serves as a marker for adrenergic cells, and lineage-tracing experiments have identified the embryonic heart and hindbrain region as the first sites of Pnmt expression in the mouse. Pnmt expression in the heart occurs before the adrenal glands have formed and prior to sympathetic innervation, suggesting that the heart is...
Show morePhenylethanolamine-N-methyltransferase (Pnmt) catalyzes the conversion of noradrenaline to adrenaline and is the last enzyme in the catecholamine biosynthetic pathway. Pnmt serves as a marker for adrenergic cells, and lineage-tracing experiments have identified the embryonic heart and hindbrain region as the first sites of Pnmt expression in the mouse. Pnmt expression in the heart occurs before the adrenal glands have formed and prior to sympathetic innervation, suggesting that the heart is the first site of catecholamine production in the mouse. The function of these Pnmt+ cells in heart development remains unclear. In the present study, we test the hypothesis that (i) a genetic ablation technique utilizing a suicide reporter gene selectively destroys Pnmt cells in the mouse, and (ii) Pnmt cells are required for normal cardiovascular and neurological function.To genetically ablate adrenergic cells, we mated Pnmt-Cre mice, in which Cre-recombinase is under the transcriptional regulation of the Pnmt promoter, and a Cre -activated diphtheria toxin A (DTA) mouse strain (ROSA26-eGFP-DTA), thereby causing activation of the toxic allele (DTA) in Pnmt-expressing (adrenergic) cells resulting in selective (")suicide(") of these cells in approximately half of the offspring. The other half serve as controls because they do not have the ROSA26-eGFP-DTA construct. In the Pnmt+/Cre; R26+/DTA offspring, we achieve a dramatic reduction in Pnmt transcript and Pnmt immunoreactive area in the adrenal glands. Furthermore, we show that loss of Pnmt cells results in severe left ventricular dysfunction that progressively worsens with age. These mice exhibit severely reduced cardiac output and ejection fraction due to decreased LV contractility and bradycardia at rest. Surprisingly, these mice appear to have a normal stress response, as heart rate and ejection fraction increased to a similarextent compared to controls. In addition to baseline cardiac dysfunction, these mice fail to gain body weight in a normal manner and display gross neurological dysfunction, including muscular weakness, abnormal gaiting, and altered tail suspension reflex, an indicator of neurological function.This work demonstrates that selective Pnmt cell destruction leads to severe left ventricular dysfunction, lack of weight gain, and neurological dysfunction. This novel mouse is expected to shed insight into the role of Pnmt cells in the heart, and suggests a role for Pnmt cells in neurological regulation of feeding behavior, metabolism, and motor control.
Show less - Date Issued
- 2015
- Identifier
- CFE0006048, ucf:50984
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006048
