Browsing by Author "Ranjit, Smriti"
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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.