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REACTION VELOCITIES IN FREE STANDING ALUMINUM AND COPPER OXIDE THIN FILMS
Title
REACTION VELOCITIES IN FREE STANDING ALUMINUM AND COPPER OXIDE THIN FILMS.
Creator
Erickson, Matthew, Coffey, Kevin, University of Central Florida
Abstract / Description
In this work we investigate the reaction propagation velocity of aluminum and copper oxide Metastable Intermolecular Composites (MIC's). All samples were deposited in a magnetron sputtering system using 2 aluminum targets and 2 copper targets. The copper is sputtered in an oxygen rich environment in order to obtain copper oxide rich films. Three different layer structures are used for various measurements that are composed of alternating 20 layer pairs, 30 layer pairs, and 40 layer pairs....
Show moreIn this work we investigate the reaction propagation velocity of aluminum and copper oxide Metastable Intermolecular Composites (MIC's). All samples were deposited in a magnetron sputtering system using 2 aluminum targets and 2 copper targets. The copper is sputtered in an oxygen rich environment in order to obtain copper oxide rich films. Three different layer structures are used for various measurements that are composed of alternating 20 layer pairs, 30 layer pairs, and 40 layer pairs. All layer pairs maintain a constant total thickness of 3.2 microns. Each layer structure can be prepared independent of a substrate and is measured with the use of photodiodes or with direct device contact. Aluminum and copper oxide structures have potential use as propellants and additives to explosives, thus, accurate propagation velocity or burn rate measurements are important. The developed measurement system for burn rate measurements of Al/CuO MIC's can achieve and accuracy of 0.1 m/s. In order to determine the velocity limiting characteristics, MIC's on glass and silicon substrates were measured as well as free standing Al/CuO MIC's. Separate burn rate measurement devices were created in order to handle the variety of substrates. In addition, the ignition energy of the Al/CuO MIC was studied to further characterize the samples. This was done using both voltage and current probes of a reacting sample. Rutherford backscattering spectroscopy (RBS) was used for sample composition calibration. The pre- and post-reaction Al/CuO MIC's were also characterized by transmission electron microscopy (TEM).
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Date Issued
2009
Identifier
CFE0002786, ucf:48093
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002786
EFFECT OF ANNEALING ON COPPER THIN FILMS:THE CLASSICAL SIZE EFFECT AND AGGLOMERATION
Title
EFFECT OF ANNEALING ON COPPER THIN FILMS:THE CLASSICAL SIZE EFFECT AND AGGLOMERATION.
Creator
Gadkari, Parag, Sundaram, Kalpathy, University of Central Florida
Abstract / Description
With continued shrinking of CMOS technology to reduce the gate delay times, an increase in the resistivity of the metal corresponding to the wire dimension is a concern. This phenomenon of increase in resistivity with decreasing dimension of the thin metallic film or interconnect is known as the "classical size effect". Various theories have been postulated to explain the phenomenon of classical size effect; these theories can be broadly classified as resistivity due to scattering arising...
Show moreWith continued shrinking of CMOS technology to reduce the gate delay times, an increase in the resistivity of the metal corresponding to the wire dimension is a concern. This phenomenon of increase in resistivity with decreasing dimension of the thin metallic film or interconnect is known as the "classical size effect". Various theories have been postulated to explain the phenomenon of classical size effect; these theories can be broadly classified as resistivity due to scattering arising from surface and grain boundaries. The total resistivity of metals depends on the electron scattering due to impurities, phonons, surfaces, grain boundaries, and other crystal defects. Managing the size effect in a practical and manufacturing way is of major concern to the microelectronics industry. Since each of the processes (phonon, surface and grain boundary scattering) adds to the resistivity and are interrelated, it further complicates managing the size effect. However, these effects have been separately studied. In this work, the effect of annealing on the classical size effect in Cu thin films deposited on SiO2 substrate is investigated. Polycrystalline Cu thin films having thicknesses in the range of 10nm to 200nm were ultra high vacuum sputter deposited on thermally grown SiO2 surfaces. The films were annealed at temperatures in the range of 150°C to 800°C in argon and argon+3% hydrogen gases. The un-annealed Cu thin films exhibit higher resistivity than the annealed films. The resistivities of un-annealed films were in good agreement with Mayadas and Shatzkes model. When annealed the films undergoes grain growth resulting in lowering the resistivities by about 20%-30% thereby confirming the role of grain size on resistivity of the film. However, there is a limit to annealing, i.e. agglomeration phenomenon. Agglomeration is a thermally activated process resulting in a reduction of the free energy of the film–substrate system and can occur well below the melting point of the material by surface and interfacial diffusion. The reduction of film-substrate interfacial energy, film-surface interfacial energy and stresses within the film are possible driving forces for agglomeration. This work also includes the study of agglomeration phenomenon. The agglomeration behavior of Cu is investigated and compared with that of Ru, Au and Pt thin films with thicknesses in the range of 10 nm to 100 nm UHV deposited on thermally grown SiO2 substrate. The films were annealed at temperatures in the range of 150°C to 800°C in argon and argon+3% hydrogen gases. Scanning electron microscopy was used to investigate the agglomeration behavior, and transmission electron microscopy was used to characterize the microstructure of the as-deposited and annealed films. The agglomeration sequence in all the films is found to follow a two step process of void nucleation and void growth. However, void growth in Au and Pt thin films is different from Cu and Ru thin films. Residual stress and adhesion were observed to play important part in deciding the mode of void growth in Au and Pt thin films. Lastly, it is also observed that the tendency for agglomeration can be reduced by encapsulating the metal film with an oxide overlayer, which in turn improves the resistivity of the thin film due to prolonged grain growth without film breakup.
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Date Issued
2005
Identifier
CFE0000496, ucf:46363
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000496
CLASSICAL SIZE EFFECT IN CU THIN FILMS: IMPACT OF SURFACE AND GRAIN BOUNDARY SCATTERING ON RESISTIVITY
Title
CLASSICAL SIZE EFFECT IN CU THIN FILMS: IMPACT OF SURFACE AND GRAIN BOUNDARY SCATTERING ON RESISTIVITY.
Creator
Sun, Tik, Coffey, Kevin, University of Central Florida
Abstract / Description
Surface and grain boundary electron scattering contribute significantly to resistivity as the dimensions of polycrystalline metallic conductors are reduced to, and below, the electron mean free path. A quantitative measurement of the relative contributions of surface and grain boundary scattering to resistivity is very challenging, requiring not only the preparation of suitably small conductors having independent variation of the two relevant length scales, namely, the sample critical...
Show moreSurface and grain boundary electron scattering contribute significantly to resistivity as the dimensions of polycrystalline metallic conductors are reduced to, and below, the electron mean free path. A quantitative measurement of the relative contributions of surface and grain boundary scattering to resistivity is very challenging, requiring not only the preparation of suitably small conductors having independent variation of the two relevant length scales, namely, the sample critical dimension and the grain size, but also independent experimental quantification of these two length scales. In most work to date the sample grain size has been either assumed equal to conductor dimension or measured for only a small number of grains. Thus, the quantification of the classical size effect still suffers from an uncertainty in the relative contributions of surface and grain boundary scattering. In this work, a quantitative analysis of both surface and grain boundary scattering in Cu thin films with independent variation of film thickness (27 nm to 158 nm) and grain size (35 nm to 425 nm) in samples prepared by sub-ambient temperature film deposition followed by annealing is reported. Film resistivities of carefully characterized samples were measured at both room temperature and at 4.2 K and were compared with several scattering models that include the effects of surface and grain boundary scattering. Grain boundary scattering is found to provide the strongest contribution to the resistivity increase. However, a weaker, but significant, role is also observed for surface scattering. Several of the published models for grain boundary and surface scattering are explored and the Matthiessen's rule combination of the Mayadas and Shatzkes' model of grain boundary scattering and Fuchs and Sondheimer's model of surface scattering resistivity contributions is found to be most appropriate. It is found that the experimental data are best described by a grain boundary reflection coefficient of 0.43 and a surface specularity coefficient of 0.52. This analysis finds a significantly lower contribution from surface scattering than has been reported in previous works, which is in part due to the careful quantitative microstructural characterization of samples performed. The data does suggest that there is a roughness dependence to the surface scattering, but this was not conclusively demonstrated. Voids and impurities were found to have negligible impact on the measured resistivities of the carefully prepared films.
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Date Issued
2009
Identifier
CFE0002959, ucf:47949
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002959
Terahertz Emission from the Intrinsic Josephson Junctions of High-Symmetry Thermally-Managed Bi2Sr2CaCu2O8+d Annular Microstrip Antennas
Title
Terahertz Emission from the Intrinsic Josephson Junctions of High-Symmetry Thermally-Managed Bi2Sr2CaCu2O8+d Annular Microstrip Antennas.
Creator
Bonnough, Sheila, Klemm, Richard, Peale, Robert, Shivamoggi, Bhimsen, University of Central Florida
Abstract / Description
The intrinsic Josephson junctions in the high transition temperature superconductor Bi2Sr2CaCu2O8+? (BSCCO) have shown great potential for oscillators emitting in the terahertz frequency. The radiation frequency satisfies the conditions for both the ac Josephson effect and for a mesa cavity resonance mode. The observed angular dependence of the emissions from some mesa imply that the ac Josephson effect plays the primary role in a dual source radiation mechanism. But the integrated emission...
Show moreThe intrinsic Josephson junctions in the high transition temperature superconductor Bi2Sr2CaCu2O8+? (BSCCO) have shown great potential for oscillators emitting in the terahertz frequency. The radiation frequency satisfies the conditions for both the ac Josephson effect and for a mesa cavity resonance mode. The observed angular dependence of the emissions from some mesa imply that the ac Josephson effect plays the primary role in a dual source radiation mechanism. But the integrated emission power had generally been significantly below the 1 mW level suitable for many applications. This output power can be enhanced by a suitable design of an array of suitably shaped mesas that are all within a wavelength of each other so that their combined output is coherent. One such tightly packed array consists of concentric annuli. Here we calculate the angularly independent modes of thin annular microstrip antennas, with the ratio of the inner to the outer radii varying from 0.1 to 0.9. We then calculate the angular distribution of the emission power arising from the annular cavity modes and from the uniform ac Josephson current source at the frequencies of the cavity modes. We also calculate the five leading wavefunctions with the lowest order angular dependence for those annuli.
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Date Issued
2018
Identifier
CFE0007314, ucf:52137
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007314
Electronic Structure of Metal (Al, Cu) Doped Carbon Nanotubes and the Resultant Conduction of the Hybrid Materials
Title
Electronic Structure of Metal (Al, Cu) Doped Carbon Nanotubes and the Resultant Conduction of the Hybrid Materials.
Creator
Jiang, Jingyin, Chen, Quanfang, Zhai, Lei, Fang, Jiyu, Bai, Yuanli, Stolbov, Sergey, University of Central Florida
Abstract / Description
Due to the exceptional strength, stiffness and excellent electrical and thermal properties, carbon nanotubes (CNTs) have been regarded as promising candidates for advanced nanoelectronics and multifunctional nanocomposites. In this dissertation, the interaction of CNTs with metals have been investigated and the resultant electrical conduction have been analyzed, aiming to develop innovative avenues to best utilize CNTs' potential. In order to do so, quantum mechanics calculations have been...
Show moreDue to the exceptional strength, stiffness and excellent electrical and thermal properties, carbon nanotubes (CNTs) have been regarded as promising candidates for advanced nanoelectronics and multifunctional nanocomposites. In this dissertation, the interaction of CNTs with metals have been investigated and the resultant electrical conduction have been analyzed, aiming to develop innovative avenues to best utilize CNTs' potential. In order to do so, quantum mechanics calculations have been carried out to study that how to obtain greater electrical conduction by doping metals (Cu, Al) which tailor the electronic structure of three different types of metal-CNT interactions, : 1) encapsulation of atoms inside the CNTs, 2) adsorption of atoms onto CNT surface, and 3) substitutional doping. Models of different doping methods were built and optimized with Density Functional Theory (DFT). And in conjunction with non-equilibrium Green's function, the electronic structure and the conducting properties were then calculated.Through this study, both metallic and semiconducting CNTs have been used. Metallic CNT (5, 5) encapsulated with copper chains have been first investigated with an emphasis on the electronic structure and the resultant conductance. The Density of States (DOS) have showed that the encapsulation of Cu effectively introduced more states around the fermi level. And due to the interaction between copper and CNTs, the conductance of the metallic CNTs-Cu system can be significantly increased.In addition to copper, aluminum has been also introduced for the study. The electronic structure and transport properties of hybrid nanowires consisting of aluminum chains adsorbed on a single-wall semiconducting CNT (10, 0) have been calculated. The band structure and DOS of the hybrid nanowires have showed that the adsorption of Al can effectively reduce the band gap. And with more than 4 Al chains adsorbed, the CNT has transformed from semiconducting to conducting. The transmission eigenstates further indicated that both Al chains and the modified nanotube were responsible for the increased conduction in the hybrid nanowires. The resultant conductance of CNT (10, 0)/Al hybrid nanowire is about 40% greater than that of pure Cu nanowire with the same diameter. In order to utilize the extraordinary conductance in CNT(10,0)/Al hybrid nanowire, it is also important to investigate the end-contact between the hybrid nanowire with Al electrodes. During this work the transmission spectrum at different bias voltage were calculated to study the I-V characteristics and the electrical contact resistances at the interfaces. The results have suggested that the electrical contact resistances between Al electrodes and the hybrid nanowire is significantly lower than that of Al-pure CNT contacts, although the actual contact resistance is directional dependent that the contact resistance is reduced to 20% of that Al-pure CNT along the longitudinal direction.The possibility of substitutional doping of Cu and Al in both metallic and semiconducting CNTs were also investigated. The formation energies have showed that Al doping was more energy favorable than Cu doping in both cases. And by doping of Al or Cu, a metallic tube experienced a higher conductance and a semiconducting tube has transited to conducting.In summary, different doping methods could modify the conducting property of nanotubes. Encapsulation of Cu in metallic CNT results in a significant conductance increment. Adsorption of Al transforms semiconducting CNT to conducting and reduces the contact resistance between the nanowire and Al electrode. Substitutional doping of Cu or Al transits semiconducting nanotube to conducting and enhance the conductance of metallic nanotube.
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Date Issued
2017
Identifier
CFE0006607, ucf:51274
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006607
Plasticity of Central and Peripheral Nervous System: Effects of Oxygen-Glucose Deprivation (OGD), Chronic Intermittent Hypoxia (CIH) and hSOD1 Overexpression
Title
Plasticity of Central and Peripheral Nervous System: Effects of Oxygen-Glucose Deprivation (OGD), Chronic Intermittent Hypoxia (CIH) and hSOD1 Overexpression.
Creator
Chen, Jin, Cheng, Zixi, Naser, Saleh, Singla, Dinender, University of Central Florida
Abstract / Description
Transient receptor potential canonical 6 (TRPC6) channels are permeable to Na+ and Ca2+ and are widely expressed in the brain. In this study, we investigated the role of TRPC6 following ischemia/reperfusion (I/R) and oxygen-glucose deprivation (OGD). We found that TRPC6 expression was increased in wild type (WT) mice cortical neurons following I/R and in primary neurons with OGD, and that deletion of TRPC6 reduced the I/R-induced brain infarct in mice and the OGD- /neurotoxin-induced neuronal...
Show moreTransient receptor potential canonical 6 (TRPC6) channels are permeable to Na+ and Ca2+ and are widely expressed in the brain. In this study, we investigated the role of TRPC6 following ischemia/reperfusion (I/R) and oxygen-glucose deprivation (OGD). We found that TRPC6 expression was increased in wild type (WT) mice cortical neurons following I/R and in primary neurons with OGD, and that deletion of TRPC6 reduced the I/R-induced brain infarct in mice and the OGD- /neurotoxin-induced neuronal death. Using live-cell imaging to examine intracellular Ca2+ levels ([Ca2+]i), we found that OGD induced a significant higher increase in glutamate-evoked Ca2+ influx compared to untreated control and such an increase was reduced by TRPC6 deletion. Enhancement of TRPC6 expression using AdCMV-TRPC6-GFP infection in WT neurons increased [Ca2+]i in response to glutamate application compared to AdCMV-GFP control. Inhibition of N-methyl-d-aspartic acid receptor (NMDAR) with MK801 decreased TRPC6-dependent increase of [Ca2+]i, indicating that such a Ca2+ influx was NMDAR dependent. Furthermore, TRPC6-dependent Ca2+ influx was blunted by blockade of Na+ entry. Finally, OGD-enhanced Ca2+ influx was reduced, but not completely blocked, in the presence of voltage dependent Na+ channel blocker tetrodotoxin (TTX) and dl???amino?3?hydroxy?5?methyl?4?isoxazole propionic acid (AMPA) blocker CNQX. Altogether, we concluded that I/R-induced brain damage was, in part, due to upregulation of TRPC6 in cortical neurons. We postulate that overexpression of TRPC6 following I/R may induce neuronal death partially through TRPC6-dependent Na+ entry which activated NMDAR, thus leading to a damaging Ca2+ overload. These findings may provide a potential target for future intervention in stroke-induced brain damage. Obstructive sleep apnea (OSA) is a highly prevalent sleep disorder that is associated with many cardiovascular complications, such as autonomic dysfunctions, stroke and heart failure. Chronic intermittent hypoxia (CIH) is a prominent feature of OSA. In CIH exposed rodents (a model for OSA), CIH induces the similar cardiovascular complications as seen in OSA patients. In particular, OSA impairs baroreflex control of the heart rate (HR), which is used as an independent indicator for heart failure. Since the baroreflex control arc includes the aortic depressor nerve (ADN), vagal efferent and central components, we hypothesize that CIH induces dysfunctions of all three components. Since mice can be genetically manipulated, an understanding of the effects of CIH on multiple neural components in the baroreflex arc in wild type mice may lead to a future study of treatments. In this study, we have examined the effects of CIH on baroreceptor afferent, central and vagal efferent components of the baroreflex circuitry in normal wild type C57BL/6J mice. Mice (4-5 months) were exposed to room air (RA) or CIH for 35-50 days and were then anesthetized with isoflurane, ventilated and catheterized for measurement of mean arterial blood pressure (MAP) and HR. Baroreceptor function was characterized by measuring percent changes of integrated ADN activity (Int ADNA) relative to the baseline value in response to the vasodilator sodium nitroprusside and the vasoconstrictor phenylephrine-induced changes in MAP. Data were fitted to a sigmoid logistic function curve. HR responses to electrical stimulation of the left ADN and the right vagus nerve were assessed under anesthesia. Compared with RA controls, CIH significantly increased maximum baroreceptor gain or maximum slope, maximum Int ADNA, and Int ADNA range (maximum-minimum Int ADNA). In addition, CIH maintained the maximum amplitude of the bradycardic response to vagal efferent stimulation. In contrast, CIH significantly reduced the maximum amplitude of bradycardic response to left ADN stimulation. Thus, CIH decreased central mediation of the baroreflex, but augmented the baroreceptor afferent function and maintained vagal efferent control of HR in mice. Excessive reactive oxygen species (ROS) (such as the superoxide radical) is commonly associated with cardiac autonomic dysfunctions. Though superoxide dismutase 1 (SOD1) overexpression may protect against ROS damage to the autonomic nervous system, superoxide radical reduction may change normal physiological functions. Previously, we demonstrated that human SOD1 (hSOD1) overexpression did not change baroreflex bradycardia and tachycardia, but increased aortic depressor nerve activity (ADNA) in responses to arterial pressure changes in C57B6SJL-Tg (SOD1)2 Gur/J mice. Since the barorelfex arc includes afferent, central and efferent components, the objective of this study was to determine whether hSOD1 overexpression alters the central and vagal efferent mediation of the heart rate (HR) responses. Our data indicate that SOD1 overexpression decreased HR responses to vagal efferent nerve stimulations but did not change HR responses to aortic nerve stimulation. Along with the previous study, we suggest that SOD1 overexpression preserves the normal baroreflex function but may alter the functions of aortic depressor nerve, vagal efferent and central components differently. While SOD1 overexpression likely enhanced aortic depressor nerve function and central mediation of bradycardia, it decreased vagal efferent control of HR. Currently, we are using the hSOD1 overexpressing mouse model to determine whether hSOD1 overexpression can preserve normal afferent, efferent, and central components of the baroreflex arc in the CIH model of sleep apnea.
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Date Issued
2017
Identifier
CFE0006576, ucf:51334
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006576
X-ray Scattering Investigations of Metallic Thin Films
Title
X-ray Scattering Investigations of Metallic Thin Films.
Creator
Warren, Andrew, Coffey, Kevin, Sohn, Yongho, Suryanarayana, Challapalli, Heinrich, Helge, Barmak, Katayun, Toney, Michael, University of Central Florida
Abstract / Description
Nanometric thin films are used widely throughout various industries and for various applications. Metallic thin films, specifically, are relied upon extensively in the microelectronics industry, among others. For example, alloy thin films are being investigated for CMOS applications, tungsten films find uses as contacts and diffusion barriers, and copper is used often as interconnect material. Appropriate metrology methods must therefore be used to characterize the physical properties of...
Show moreNanometric thin films are used widely throughout various industries and for various applications. Metallic thin films, specifically, are relied upon extensively in the microelectronics industry, among others. For example, alloy thin films are being investigated for CMOS applications, tungsten films find uses as contacts and diffusion barriers, and copper is used often as interconnect material. Appropriate metrology methods must therefore be used to characterize the physical properties of these films. X-ray scattering experiments are well suited for the investigation of nano-scaled systems, and are the focus of this doctoral dissertation. Emphasis is placed on (1) phase identification of polycrystalline thin films, (2) the evaluation of the grain size and microstrain of metallic thin films by line profile analysis, and (3) the study of morphological evolution in solid/solid interfaces.To illustrate the continued relevance of x-ray diffraction for phase identification of simple binary alloy systems, Pt-Ru thin films, spanning the compositional range from pure Pt to pure Ru were investigated. In these experiments, a meta-stable extension of the HCP phase is observed in which the steepest change in the electronic work function coincides with a rapid change in the c/a ratio of the HCP phase.For grain size and microstrain analysis, established line profile methods are discussed in terms of Cu and W thin film analysis. Grain sizes obtained by x-ray diffraction are compared to transmission electron microscopy based analyses. Significant discrepancies between x-ray and electron microscopy are attributed to sub-grain misorientations arising from dislocation core spreading at the film/substrate interface. A novel "residual" full width half max parameter is introduced for examining the contribution of strain to x-ray peak broadening. The residual width is subsequently used to propose an empirical method of line profile analysis for thin films on substrates.X-ray reflectivity was used to study the evolution of interface roughness with annealing for a series of Cu thin films that were encapsulated in both SiO2 and Ta/SiO2. While all samples follow similar growth dynamics, notable differences in the roughness evolution with high temperature ex-situ annealing were observed. The annealing resulted in a smoothing of only one interface for the SiO2 encapsulated films, while neither interface of the Ta/SiO2 encapsulated films evolved significantly. The fact that only the upper Cu/SiO2 interface evolves is attributed to mechanical pinning of the lower interface to the rigid substrate. The lack of evolution of the Cu/Ta/SiO2 interface is consistent with the lower diffusivity expected of Cu in a Cu/Ta interface as compared to that in a Cu/SiO2 interface. The smoothing of the upper Cu/SiO2 interface qualitatively follows that expected for capillarity driven surface diffusion but with notable quantitative deviation.
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Date Issued
2013
Identifier
CFE0004770, ucf:49784
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004770