Theses and Dissertations - Department of Physics & Astronomy
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Browsing Theses and Dissertations - Department of Physics & Astronomy by Author "Araujo, Paulo T."
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Item Mechanical and Thermal Properties of Linear Carbon Chains Encapsulated by Multi- and Double -Walled Carbon Nanotubes(University of Alabama Libraries, 2021) Sharma, Keshav; Araujo, Paulo T.; University of Alabama TuscaloosaAs a field of study, optics have been a critical to the development of material’s science. The interaction between light and matter is often non-destructive and non-invasive; making it powerful in the determination of materials’ compositions, and their properties at the electronic and vibrational levels. In the present work, we have broadened the use of light spectroscopy as a technique to determine, accurately, mechanical and thermal properties of molecular systems. More specifically, pressure (P) and temperature (T)-dependent Raman spectroscopy allowed us to access elusive mechanical (Young’s modulus (E), Grüneisen parameter (γ), and mechanical strain (ε)) and thermal properties (coefficient of thermal expansion (α), specific heat capacity (c_v), and thermal strain (ε_T)) of linear carbon chains (LCCs), which are one-atom thick linear carbon molecules. The results show that all these quantities follow universal relations that are solely dependent on P, T, and on the number of carbon atoms (N). In Appendix 01 we also describe how spectral derivative analysis combined with absorption and photo-luminescence spectroscopies allowed for unravelling elusive electronic and vibronic transition in free base 5,10,15,20-meso-tetra(pyridyl)-21H,23H-porphyrin (H2TPyP).Item Raman spectroscopy of double- and triple-walled carbon nanotubes: fundamental, combination, and overtone modes(University of Alabama Libraries, 2020) Hue, Jia Wern; Araujo, Paulo T.; University of Alabama TuscaloosaA single-walled carbon nanotube (SWNT) is a graphene sheet rolled up into a tube. Double-walled (DWNT) and triple-walled carbon nanotubes (TWNT) are two and three coaxial SWNTs respectively. Isolated species of DWNTs and TWNTs were only recently probed and it can be considered as a new branch in carbon nanotube science. Phonons, and the combination of phonons and overtones are fundamental to understanding optical processes, transport and thermoelectricity in carbon nanotubes. To study these phonons, resonance Raman spectroscopy is employed on DWNT and TWNT bundles, as well as isolated TWNTs. The phonon modes of interest to this dissertation are the radial breathing mode (RBM), the G-band, and the M-band. From the RBM, it is learnt that for inner tubes with a tube diameter less than 1.2 nm, the curvature effects are dominant. Evidence for intertube interactions was found, although for outer tubes the environmental effects dominate. There was also evidence for commensurate and incommensurate tubes. Studying the G-band allowed for possible chiral indices to be identified for the middle and outer tubes of isolated TWNTs. In addition, the frequency shifts of TWNT G-band frequencies relative to SWNT G-band frequencies were studied and compared to TWNT G-band frequency shifts. As for the M-bands, phonon mode assignments for peaks between 1680 cm-1 to 1850 cm-1 were attempted.Item Stokes spectroscopy: the development of a novel method to acquire and interpret polarized emission spectra - applications to poly(3hexylthiophene and p(ndi2od-t2)(University of Alabama Libraries, 2018) Ulrich, Steven V.; Araujo, Paulo T.; University of Alabama TuscaloosaOptics, as a field of study, has been a critical tool within the discipline of material science for over one hundred years. Through lights interaction with matter, researchers can determine information such as material composition, electronic and physical properties. This information is then used to guide research for specific applications. From the outside, it may seem as though optics as a field is complete; all possible experiments known and possible outcomes interpreted. However, one such property of light, specifically polarization, has proven difficult to measure and subsequently analyze in a meaningful way. Current techniques for measuring polarization information involve simple rotations of a linear polarizer, or analyzer, to get a loose understanding of an emitting sources polarization state. However, this technique and others like it are far from complete and much of the polarization information is still unavailable to researchers. One way to elucidate more polarization information is to implement a method proposed by Stokes in the late 1800s, in which four parameters are used to describe a sources intensity and polarization states. The goal of this work is to show how the addition of the Stokes technique to a typical spectroscopic setup, along with computational fitting, produces direct measurements of these polarization states. Further, we show the capabilities of these adaptations by applying the technique to two organic semi-conducting polymers, Poly(3-hexothilophene) and P(NDI2OD-T2). Doing so has allowed for further elucidation of material properties, including aggregate formation and energy transfer, which is typically unavailable for such materials at high temperature.