Browsing by Author "Hauser, Adam J."
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Item Demonstration of nearly pinhole-free epitaxial aluminum thin films by sputter beam epitaxy(Nature Portfolio, 2020) Law, Ka Ming; Budhathoki, Sujan; Ranjit, Smriti; Martin, Franziska; Thind, Arashdeep S.; Mishra, Rohan; Hauser, Adam J.; University of Alabama Tuscaloosa; Washington University (WUSTL)Superconducting resonators with high quality factors have been fabricated from aluminum films, suggesting potential applications in quantum computing. Improvement of thin film crystal quality and removal of void and pinhole defects will improve quality factor and functional yield. Epitaxial aluminum films with superb crystallinity, high surface smoothness, and interface sharpness were successfully grown on the c-plane of sapphire using sputter beam epitaxy. This study assesses the effects of varying substrate preparation conditions and growth and prebake temperatures on crystallinity and smoothness. X-ray diffraction and reflectivity measurements yield extensive Laue oscillations and Kiessig thickness fringes for films grown at 200 degrees C under 15 mTorr Ar, indicating excellent crystallinity and surface smoothness; moreover, an additional substrate preparation procedure which involves (1) a modified substrate cleaning procedure and (2) prebake at 700 degrees C in 20 mTorr O-2 is shown by atomic force microscopy to yield nearly pinhole-free film growth while maintaining epitaxy and high crystal quality. The modified cleaning procedure is environmentally friendly and eliminates the acid etch steps common to conventional sapphire preparation, suggesting potential industrial application both on standard epitaxial and patterned surface sapphire substrates.Item Determining the Thermal Properties of Buckypapers Used in Photothermal Desorption(American Chemical Society, 2021) Shedd, Jacob S.; Kuehster, Wyatt W.; Ranjit, Smriti; Hauser, Adam J.; Floyd, Evan L.; Oh, Jonghwa; Lungu, Claudiu T.; University of Alabama Birmingham; University of Alabama Tuscaloosa; University of Oklahoma Health Sciences CenterVolatile organic compounds (VOCs) pose an occupational exposure risk due to their commonplace usage across industrial and vocational sectors. With millions of workers annually exposed, monitoring personal VOC exposures becomes an important task. As such, there is a need to improve current monitoring techniques by increasing sensitivity and reducing analysis costs. Recently, our lab developed a novel, preanalytical technique known as photothermal desorption (PTD). PTD uses pulses of high-energy, visible light to thermally desorb analytes from carbonaceous sorbents, with single-walled carbon nanotube buckypapers (BPs) having the best overall performance. To apply this new technology most effectively for chemical analysis, a better understanding of the theoretical framework of the thermal phenomena behind PTD must be gained. The objectives of the present work were 3-fold: measure the thermal response of BPs during irradiation with light; determine the best method for conducting such measurements; and determine the thermal conductivity of BPs. BPs were exposed to four energy densities, produced by light pulses, ranging from 0.28 to 1.33 J/cm(2), produced by a xenon flash lamp. The resulting temperature measurements were obtained via fast response thermocouple (T/C) mounted to BPs by three techniques (pressing, adhering, and embedding). Temperature increase measured by T/C using the adhering and pressing techniques resulted in similar values, 29.2 +/- 0.8 to 56 +/- 3 degrees C and 29.1 +/- 0.9 to 50 +/- 5 degrees C, respectively, while temperature increase measured by embedding the T/C into the BP showed statistically larger increases ranging from 35.2 +/- 0.9 to 76 +/- 4 degrees C. Peak BP temperatures for each mounting technique were also compared with the temperatures generated by the light source, which resulted in embedded BPs demonstrating the most temperature conversion among the techniques (74-86%). Based on these results, embedding T/Cs into the BP was concluded to be the best way to measure BP thermal response during PTD. Additionally, the present work modeled BP thermal conductivity using a steady-state comparative technique and found the material's conductivity to be 10.6 +/- 0.6 W/m(2). The present work's findings will help pave the way for future developments of the PTD method by allowing calculation of the energy density necessary to attain a desired sorbent temperature and providing a means for comparing BP fabrication techniques and evaluating BP suitability for PTD before conducting PTD trials with analytes of interest. Sorbents with greater thermal conductivity are expected to desorb more evenly and withstand higher energy density exposures.Item Effects of Environmental Factors on Functional Properties of Particulate Matter(University of Alabama Libraries, 2022) Ranjit, Smriti; Hauser, Adam J.; University of Alabama TuscaloosaThe properties of the material are determined by its structure and the functional motif, understanding the structure of a material can explain its behavior under certain conditions. The effects of environmental factors on the functional properties of thin films of particulate matter due to fabrication method or exposure to the environment are investigated. Understanding the mechanism behind material defects/degradation provides insight to optimize the functional properties of the film, suitability for the application, or robustness for a potential application. This dissertation explores the effect on the functional properties of the material due to aerosol deposition method, interaction with chemical warfare agents, and environmental exposure. Barium Hexaferrite (BaM) films deposited on a-plane sapphire substrate by aerosol deposition are investigated in a subtractive wedge series to determine the extent of energetic substrate damage and indentation. The Al2O3 particulates ejected from the substrate surface during growth and the estimate of indentation depth is ~600 nm. The magnetic moment of the deposited film is lower than the bulk and thickness dependence is consistent with the fractional increase of Al2O3 content in the film.Fe2O3 nanoparticles exhibit chemical changes due to contact with the four chemical warfare agents simulants. Due to the exposure, a redox reaction occurs and Fe2O3 nanoparticles show lowered magnetic moment. The differentiable, frequency-dependent responses to the simulants are observed due to changes in the sensor material that opens the possibilities for the use of Fe2O3 nanoparticles for frequency-dependent impedance fingerprinting. The effects of UV and visible light exposure in dry air and humid environments have been investigated using the Zr-based metal-organic framework, UiO-66-NH2. The metal-organic framework undergoes irreversible photochemical change due to prolonged UV light and blue light exposure. These changes happen more rapidly and grow larger in total cumulative magnitude as the atmospheric humidity increases. However, humidity introduced in dark or with lower energy photons than blue light results in no material change to the MOF. Impedance data modeling suggests that humidity increases the ionic conductivity of the material and that the degradation occurs at grain boundaries, to a depth that increases with humidity. Importantly, the result of the degradation is the loss of chemical sensitivity, defining the conditions for applications in both aqueous and airborne filtration and sensing applications.Item Electro-thermal circuit modeling in atomic clock mechanical structures(University of Alabama Libraries, 2017) Miskell, Kyle; Lemmon, Andrew N.; University of Alabama TuscaloosaAs electrical and electronics engineers have striven to create more energy-dense and efficient designs, thermal non-idealities have risen to the forefront of such design endeavors as impediments to miniaturizing and densifying electrical products. In order to overcome these thermal design barriers, engineers require detailed prediction of their circuits' thermal characteristics. Modern electrical engineers must often understand the thermal dynamics of their systems equally as well as the electrical characteristics. In this thesis, an overview of electrical design areas affected by thermal concerns is given, and a literature review of thermal modeling techniques commonly utilized in electrical designs is provided. Furthermore, the thermal modeling of atomic clock mechanical structures is identified as the primary focus of this thesis, and the well-known Cauer electro-thermal circuit framework for thermal modeling is identified as an optimal modeling solution for atomic clock geometries. Subsequently, a full description of the Cauer model and its associated conductive, convective, and radiant physics is given with specific emphasis on atomic clock thermal modeling. Additionally, experimental and numerical techniques utilized in the extraction of Cauer network parameters are discussed, and background on the practical implementation and physical behavior of thermal sensors is given. Last, experimental validation of the Cauer model and its applicability to atomic clock geometries is shown through the application of the techniques and theories discussed in this thesis.Item Experimental Investigation of Thermodynamic Stability, Phase Evolution, and Structure-Property Relationships in X2YZ Heusler and Heusler-Like Alloys(University of Alabama Libraries, 2026) Grier, Tecia; Hauser, Adam J.; Leclair, PatrickHeusler and Heusler-like intermetallic alloys are widely predicted to exhibit useful magnetic, electronic, and mechanical properties, but many theoretically favorable X2YZ compounds are difficult to stabilize experimentally because of competing phases, chemical disorder, and processing-dependent microstructural evolution. This dissertation investigates the thermodynamic stability, phase stability, atomic ordering, magnetic response, and mechanical behavior of selected bulk Heusler and Heusler-like alloys, with emphasis on Cr2FeAl, Cr2TiAl, and off-stoichiometric Ni-Fe-Al alloys. Experimental studies were conducted using arc-melted bulk samples followed by controlled annealing treatments. Phase constitution and microstructure were evaluated using X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD), while functional properties were assessed using vibrating sample magnetometry (VSM) and Vickers hardness testing. Experimental observations were compared with density functional theory (DFT)-based predictions, Slater–Pauling behavior, the "4-2" rule, CALPHAD calculations, and available phase diagram data.Cr2FeAl remained compositionally homogeneous and BCC-derived after annealing at 900 °C for up to 21 days, but laboratory X-ray diffraction did not reveal clear long-range B2 or inverse-Heusler XA ordering. These results indicate that disorder stabilization and sluggish atomic exchange can suppress the experimentally accessible ordered state. In contrast, Cr2TiAl showed clear thermodynamic instability during annealing, decomposing into Cr-rich intermetallic constituents and Ti/Al-rich BCC-derived phases, with increasing temperature and dwell time promoting chemical partitioning, coarsening, and lamellar microstructure formation. Off-stoichiometric Ni-Fe-Al alloys showed strong sensitivity to composition near the β/γ phase boundary. Across the investigated compositions, B2 ordering dominated over fully ordered L21 Heusler formation, and small compositional changes strongly affected secondary phase formation, magnetization, Curie behavior, and hardness. Overall, this work demonstrates that electronic stability alone is insufficient to predict experimentally accessible Heusler phases. Incorporating CALPHAD-based phase stability analysis with first-principles and electron-counting approaches provides a more reliable framework for screening, synthesizing, and understanding Heusler and Heusler-like intermetallic alloys.Item Influence of Microstructural Properties of Thin Films on Their Magnetic Properties(University of Alabama Libraries, 2022) Nakarmi, Prabandha; Mewes, Tim; University of Alabama TuscaloosaMagnetic materials are of great importance for a wide range of applications from daily usage to industrial scale equipment. Different devices require different classes of magnetic materials based on the required magnetic properties. Magnetic properties of these materials are influenced by the microstructure of the material. Therefore, a detailed understanding of the microstructures of magnetic material and their influence on the magnetic properties are extremely crucial to optimize materials for particular applications. This dissertation provides theoretical and experimental studies of the influence of the microstructural properties of ferromagnetic materials on the dynamic magnetic properties using numerical simulations and ferromagnetic resonance experiments.A theoretical investigation of the influence of the magnetic properties of multiple constituents of a material on the presence of multiple resonances observed in magnetization dynamics studies is presented in the second chapter of this dissertation. In addition, this chapter also provides insights regarding the consequences of erroneous model assumptions on extraction of material parameters from studies of the magnetization dynamics. The understanding gained from the studies of the second chapter is used in chapter three to study the presence of two strong resonances in cobalt-based nanocomposites and its derivatives synthesized by addition of cobalt and boron. Furthermore, detailed structural and magnetic analyses of cobalt and boron added nanocomposites under the influence of annealing are presented in the third chapter of this dissertation. In chapter four, the influence of defects on the Gilbert damping in polycrystalline iron is investigated. Detailed ferromagnetic resonance studies of the polycrystalline iron samples showed a surprising insensitivity of the damping parameter to defects present in the samples at room temperature.Item Metal organic frameworks as sorbents for volatile organic compounds(University of Alabama Libraries, 2021) Shankwitz, Jennifer Elizabeth; Szulczewski, Gregory J.; University of Alabama TuscaloosaMetal organic frameworks (MOFs) are a class of highly porous materials with large surface areas, large pore volumes, and chemical tunability. These features make MOFs desirable as sorbents for applications such as gas storage, gas separation, and gas sensing. In this work, MOF thin films of UiO-66-R, where R = -H, -NH2, and-NO2, were fabricated onto Au-coated Si wafers and Au-coated quartz crystal microbalance surfaces using a vapor-assisted conversion method. The films were then characterized by scanning electron microscopy, powder x-ray diffraction, x-ray photoelectron spectroscopy, reflection absorbance infrared spectroscopy, and Raman spectroscopy. The spectroscopy reveals that the films of UiO-66-H, UiO-66-NH2, and UiO-66-NO2 are polycrystalline and 1 – 3 µm thick. The diffraction patterns reveal that the UiO-66-NO2 film potentially has the most missing linker defects. The UiO-66-R films grown on quartz microbalance crystals were activated by heating under high vacuum and exposed to a known pressure of benzene, toluene, ethyl benzene, and the xylene isomers (BTEX). The Henry’s constant, which describes the adsorption capacity for each MOF, was calculated from the mass change during the adsorption isotherm at 30°C, 25°C, and 20°C. The enthalpy of adsorption and entropy change was determined by plotting the logarithm of Henry’s constants versus the reciprocal of temperature. The results reveal the Henry’s constant for BTEX increased in the following order: UiO-66-H < UiO-66-NH2 < UiO-66-NO2. The results suggest that the functional groups on the organic linker and missing linkers influence adsorption behavior. The Henry’s constant of the films UiO-66-H were an order of magnitude smaller than those obtained for UiO-66-NH2 and UiO-66-NO2 films, largely due to the large pore size and lack of any functional group. The results suggest that UiO-66-NO2 films contain more missing linker defects than UiO-66-NH2 films. As a result, the heat of adsorption and entropy change for BTEX molecules in UiO-66-NH2 films is more negative than UiO-66-NO2. In contrast, due to a large pore size caused by the missing linkers, the adsorption capacity of UiO-66-NO2 films is larger than UiO-66-NH2 films.Item The spin Seebeck effect in magnetic insulating oxides(University of Alabama Libraries, 2019) Li, Zhong; Gupta, Arunava; Mankey, Gary J.; University of Alabama TuscaloosaThe spin Seebeck effect (SSE), the generation of a spin current from a thermal gradient, is a novel effect which involves the interaction between charge, spin and heat. Insulating magnetic materials, like yttrium iron garnet (YIG, Y₃Fe₅O₁₂) and nickel ferrite (NFO, NiFe₂O₄), are ideal for the study of this new effect due to avoiding other magnetic effects. Thin films of Y₃Fe₅O₁₂, Ce₀.₇₅Y₂.₂₅Fe₅O₁₂ and NiFe₂O₄ have been grown and optimized on different substrates (MgAl₂O₄, MgGa₂O₄, CoGa₂O₄) using the pulsed laser deposition (PLD) technique, and their crystal structures were investigated using X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). For the magnetocrystalline anisotropy in the thin films, vibrating sample magnetometry (VSM) and ferromagnetic resonance (FMR) measurements are done. We further did spin Seebeck effect measurements on optimized samples. First, for thin films of Ce₀.₇₅Y₂.₂₅Fe₅O₁₂, homogeneous substitution of Ce in YIG results in the enhancement of the signal in magneto-optic Kerr effect (MOKE) without forming CeO₂ when at lower O₂ atmosphere. The spin Seebeck effect measurements on Ce:YIG films show similar trends and comparable results with pure YIG films suggesting potential applications for thermoelectric generation. Second, an increase in the spin Seebeck voltage is observed with decreasing lattice mismatch between NFO thin films and substrates, which also correlates well with the decrease in the Gilbert damping parameter from FMR measurements. Furthermore, we have developed a vector measurement of the spin Seebeck effect in epitaxial NiFe₂O₄ thin films, which were grown by pulsed laser deposition on (011)- or (001)-oriented MgGa₂O₄ and CoGa₂O₄ substrates with varying lattice mismatches. This new method for SSE measurement shows the existence of a magnetic strain anisotropy in NiFe₂O₄ thin films significantly impacts the shape and magnitude of the SSE voltage hysteresis loops, which demonstrates that voltage signals from bidirectional SSE measurements can be utilized as a new vectorial magnetometry technique to reveal the complete magnetization reversal process.Item Supramolecular interactions as a basis for differential sensing applications(University of Alabama Libraries, 2021) Ihde, Michael Henry; Bonizzoni, Marco; University of Alabama TuscaloosaIn this work, we used supramolecular interactions to construct systems that respond to analytical stimuli and report on specific chemical species in solution using optical spectroscopic techniques (e.g. absorbance and fluorescence spectroscopy), affording low cost and high sensitivity. To obtain selectivity, we used cross reactive sensors (organic dyes, conjugated polymers) to generate differential response patterns when exposed to families of subtly different analytes of interest. The differential responses produced large data sets that were interpreted using well established pattern recognition algorithms, such as linear discriminant analysis (LDA) and principal component analysis (PCA). We first report on conditions and methods based on linear discriminant analysis to predict the identity and composition of samples containing metal ion mixtures without prior physical separation, a common shortcoming of these systems. We also report on a higher sensitivity metal ion sensing array composed of novel fluorene based conjugated polymers with high affinity groups to detect nine divalent metal cations down to 500 pM in freshwater, and to 100 nM in seawater samples collected from the Gulf of Mexico. This robust system was sufficiently sensitive for detection below the maximum mandated concentrations set by the US Environmental Protection Agency (EPA) for toxic metals in drinking water and aquatic ecosystems. Similar highly sensitive, fluorene based conjugated polymers were used again to detect pollutants with intrinsic characteristic light absorption such as polycyclic aromatic hydrocarbons (PAHs) and azo textile dyes. Instead of chemical interaction with these analytes, the polymers displayed good spectral overlap with the absorbance spectra of the targets, leading to changes in their optical spectrum caused by the inner filter effect, where the analytes themselves acted as “chemical filters”. Finally, we investigated the nature of the binding interactions between PAH probes and amine terminated poly(amidoamine) (PAMAM) dendrimers. Using time resolved fluorescence, fluorescence anisotropy, and selective quenching experiments, we used two probes, anthracene and pyrene, to highlight distinct binding modes and locations to the polycationic, macromolecular PAMAM hosts, paving the way for future applications of such charged polymers with interesting affinity towards hydrophobic guests.