Doctor of Philosophy, The Ohio State University, 2024, Chemistry

Understanding the fundamental interactions within and at the surface of atmospheric aerosol is of the utmost importance as they drive the properties of aerosol that influence global climate and public health. The first work presented herein explores the highly perturbed structure of water within systems inspired by phase separated organic aerosol. An approach is taken that combines polarized Raman spectroscopy and molecular dynamics to reveal the structural changes that occur as water is added incrementally to propylene carbonate (PC), a polar, aprotic solvent that is relevant in the environment and in electrochemical systems. Polarized Raman spectra of PC solutions were collected for water mole fractions 0.003 ≤ Χwater ≤ 0.296, which encompasses the solubility range of water in PC. The novel approach taken to the study of water-in-PC mixtures herein provides additional hydrogen bond and solvation characterization of this system that has not been achieveable in previous studies. Analysis of the polarized carbonyl Raman band in conjunction with simulations demonstrated that the bulk structure of the solvent remained unperturbed upon the addition of water. Experimental spectra in the O-H stretching region were decomposed through Gaussian fitting into sub-bands and studies on dilute HOD in H2O. With the aid of simulations, we identified these different bands as water arrangements having different degrees of hydrogen bonding. The observed water structure within PC indicates that water tends to self-aggregate, forming a hydrogen bond network that is distinctly different from the bulk and dependent on concentration. For example, at moderate concentrations, the most likely aggregate structures are chains of water molecules, each with two hydrogen bonds on average. The interaction of NO2 with organic interfaces is critical in atmospheric processing of marine and continental aerosol as well as in the development of NO2 sensing and trapping technologies. Recen (open full item for complete abstract)

Committee: Heather Allen (Advisor); Zachary Schultz (Committee Member); Bern Kohler (Committee Member) Subjects: Chemistry; Physical Chemistry

Master of Science (MS), Wright State University, 2020, Physics

A recently constructed novel analytical tabletop terahertz (THz) chemical sensor capable of detecting a wide range of gases with high sensitivity and specificity was characterized to assess its performance over a range of operational parameters. The sensor was designed with an objective of quantifying composition of exhaled human breath, where target concentrations span part per trillion (ppt) to part per billion (ppb) level of dilutions. The sensor utilizes terahertz rotational spectroscopy of sampled gases for quantification of dilutions. The sensor occupies a volume of ~ 2 ft3 and incorporates a coiled absorption cell, thermal desorption tubes, and all necessary electronic components necessary for autonomous operation. Coiled absorption cell minimizes the sensor footprint while maintaining a large path length for sensitive spectral measurements. Preconcentration aides the detection of compounds by removing the background gases which would negatively affect the absorption signal if present during spectral analysis. Spectral parameters of the sensor were studied to optimize its sensitivity. Efficiencies of preconcentration over a range of gas sampling parameters were determined by comparing concentrations measured by the sensor to concentrations of a reference gas mixture. The sensor was characterized in its ability to detect acetaldehyde, acetone, ethanol, isoprene, and methanol – all known breath analytes. These gases were chosen for their range of volatility and absorption strength. Minimum detectable sample concentrations are well suited for breath sampling making this sensor a valuable new tool for environmental sensing and biosensing.

Committee: Ivan Medvedev Ph.D. (Advisor); Brent Foy Ph.D. (Committee Member); Jason Deibel Ph.D. (Committee Member) Subjects: Physics

Master of Science, The Ohio State University, 2020, Aero/Astro Engineering

Non-self-sustained hybrid plasmas are formed by the overlap of two separate voltage waveforms with significantly different reduced electric field values (E/N), one of them below the ionization threshold, to produce excited species and radicals selectively. In this work, a stable, capacitively coupled ns pulse – RF waveform hybrid discharge is operated in nitrogen and mixtures of nitrogen with other molecular gases at 50 – 100 Torr pressure, using a single pair of electrodes mounted externally to the reactor cell. The purpose of the ns pulse discharge is to generate ionization and electronic excitation of the mixture components, while the below-breakdown RF voltage couples additional energy to the vibrational modes of the mixture components. Based on the broadband plasma emission imaging, the plasma volume appears to be enhanced by the RF waveform, compared to ns pulse discharge, due to the drift oscillations of electrons induced by the RF waveform. Coherent Anti-Stokes Raman Spectroscopy (CARS) measurements in the hybrid discharge operated in nitrogen show that the RF waveform significantly enhances the vibrational excitation of N2 in the ground electronic state, populating vibrational levels up to at least v=3, and increasing the vibrational temperature of N2 from TV = 1210 ± 110 K in the ns pulse train plasma to TV = 1810 ± 170 K in the ns-RF hybrid discharge. The translational- rotational temperature at these conditions remains low, TR = 315 ± 15 K. To evaluate the potential of this plasma to operate in other gas mixtures, 1% of H2 is added to nitrogen. CARS measurements reveal a moderate N2 vibrational relaxation by hydrogen, reducing the vibrational temperature in the hybrid plasma to TV = 1700 ± 150 K and increasing in the translational-rotational temperature to TR = 396 ± 10 K. Time-resolved measurements of the number density of the first electronically excited state of nitrogen, N2(A3Σ), obtained using Tunable Diode Laser Absorption Spectroscopy (TDLAS) in n (open full item for complete abstract)

Committee: Igor Adamovich (Advisor); Jeffrey Sutton (Committee Member) Subjects: Chemistry; Energy; Engineering; Environmental Engineering

Doctor of Philosophy, The Ohio State University, 2020, Chemistry

Solar energy has a great potential to meet the growing global energy demand. However, at present sunlight contributes less than 1% to the total energy economy. To enable conversion and storage of solar energy for practical applications, several scientific challenges remain to be addressed. Absorption of sunlight produces energetic negative and positive charges, which can be utilized to generate electrical or chemical energy. However, in many materials these charges recombine within femtoseconds after forming, which significantly limits the efficiency of a material. Note that a femtosecond is 10^-15 seconds (i.e. only a millionth of a billionth of a second), indicating that if the energy conversion process is not well controlled at the very early times following absorption of sunlight, then these charges will recombine before they can be used. With the goal of better understanding and controlling electron motion in energy conversion materials, my work focuses on watching electrons move in solar materials in order to understand the material chemistry that controls energy conversion efficiency. Towards this goal I have assisted to develop a lab-based extreme ultraviolet reflection-absorption (XUV-RA) spectrometer which can provide an element specific chemical fingerprint of materials and can track motion of charges on the femtosecond time scale. The details of XUV-RA spectrometer and the capability of this instrument has been described in the chapter 1 of this thesis. Additionally, I was involved in developing an algorithm of data interpretation for XUV-RA spectra based on ligand field multiplet calculation and classical electromagnetism. A summary of the algorithm has been provided in the chapter 1 of the thesis. Understanding the site specific ultrafast localization of charges in semiconductor materials is important to determine the efficiency of photocatalytic energy conversion processes. To demonstrate the capability of XUV-RA in this respect, I have stud (open full item for complete abstract)

Committee: L. Robert Baker (Advisor); Bern Kohler (Committee Member); Heather Allen (Committee Member); Dongping Zhong (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2016, Chemistry

Sea spray aerosols (SSA) impact Earth's climate directly and indirectly by scattering and absorbing solar radiation and influencing cloud formation, respectively. SSA are formed through the wind-drive wave action at the ocean surface, and their chemical composition is impacted by the biological activity in the sea surface microlayer (SSML), the thin organic layer present at the air-ocean interface. Physical and optical properties of SSA are influenced by the structure and organization of their surfaces. Organic films are known to form at the surface of SSA, and therefore a molecular-level understanding of the organic species that make up these films and their subsequent impact on interfacial properties is necessary to gain insight into climate change. In this dissertation Langmuir monolayers are utilized as proxies for organic-coated SSA. Phase behavior, rigidity, and stability of monolayers are assessed with surface pressure-area isotherms. Surface morphology of monolayers was imaged with Brewster angle microscopy (BAM). Infrared reflection-absorption spectroscopy (IRRAS) and vibrational sum frequency generation (VSFG) spectroscopy were used to examine the molecular-level structure and intermolecular interactions of the monolayers. VSFG was additionally used to probe the organization and structure of water molecules in the interfacial region. As SSA are chemically complex, several different types of atmospherically-relevant lipid-aqueous interfaces are investigated. The effect of ion enrichment for marine-relevant cations (Na+, Mg2+, Ca2+, and K+) on the interfacial properties of the phospholipid dipalmitoylphosphatidylcholine (DPPC) was investigated. All cations were found to impact monolayer properties, with divalent cations having a greater effect than monovalent ions. Refractive index of the monolayer was found to decrease with increasing cation concentration. In the case of Ca2+, significant dehydration of the phosphate headgroup was observed. Bindin (open full item for complete abstract)

Committee: Heather Allen (Advisor) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2011, Chemistry

Molecule based electronics and devices are an increasingly popular area of research in chemistry. These molecular-based devices largely rely on the separation of charge from (solar cell, LED) or movement of charge through (wires) a molecular unit. Largely, it is desirable for these materials to be easily fabricated, absorb throughout the visible/NIR spectrum or emit certain wavelengths. Organic systems generally provide good fabrication properties while the incorporation of metals can provide more easily tunable physical properties. Metallo-organic paddlewheel compounds involving quadruple bonds have previously been made into soluble, linear polymers with tunable absorption and have been incorporated into an LED to show electroluminescence. In terms of device performance, it is important to know how well charge can be expected to flow through the material. In devices that rely upon photon absorption, charge transport ability is dependent on charge delocalization and rates of transport. As a first step in these regards a series of complexes which represent simple monomeric analogs to the individual repeating units of the polymer have been studied. They serve as model complexes to the polymeric and a better understanding of their fundamental properties should relate to better design of polymeric materials. This dissertation uses both electronic and vibrational spectroscopies to characterize photoexcited states, determine their lifetimes, and evaluate the electronic delocalization within these states. Theoretical calculations also supported the results. Four molecules constitute limiting cases across a wide set of properties and are the focus of this work. Chapters 2 describes the molecules M2(O2CTiPB)2(O2C-C6H4-C≡N)2 (2a and 2b) and 3 describes the molecules M2(O2CCH3)2(NiPr)2C-C≡C-C6H5]2 (3a and 3b), where M = Mo (a) or W (b), each focusing on results from electronic spectroscopy. In particular, assignments for the photophysical excited states were made as well as s (open full item for complete abstract)

Committee: Malcolm Chiholm Prof. (Advisor); Terry Gustafson Prof. (Advisor); Claudia Turro Prof. (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2010, Chemical Physics

Interest in SMM/THz spectroscopy is partly driven by its potential as an analytic method. Briefly, rotational spectroscopy in the SMM/THz is a high resolution technique capable of absolute specificity due to the fact that each molecule has a unique rotational spectrum (fingerprint) that for most molecules of interest fills only a small portion of the available resolution elements (< 0.1%). Further, because the field has traditionally used low-power devices, very sensitive detector systems are available for making trace measurements. We have designed and built a solid-state Multi-Purpose Spectrometer based on recently available broadband amplifier/multiplier chains and new X-Band electronic synthesizers. The frequency precision and agility of the synthesizers allow the Multi-Purpose Spectrometer to implement many analytic strategies, including fast-scanning, frequency modulation, Stark modulation and cavity absorption without changes to the spectrometer hardware. The Multi-Purpose Spectrometer was built to investigate the effects of making analytical measurements on larger molecules that contain highly congested spectra (> 1000 lines/GHz). At question is to what extent increasing spectral congestion will impact the ability to identify trace elements of a gas mixture in an otherwise congested spectrum. We report our tests of the effectiveness of the frequency modulation technique in congested environments and whether Stark modulation and cavity absorption techniques are effective alternatives to frequency modulation in these environments. To this end, the frequency modulation spectrum of a series of large, planar molecules based on the benzonitrile backbone (benzonitrile, all six difluorobenzonitriles and pentafluorobenzonitrile) have been measured between 180 - 270 GHz with an FM spectrometer and the ground-state spectra of all but pentafluorobenzonitrile were assigned, followed by companion measurements of some of the molecules with the Stark modulation and cavity (open full item for complete abstract)

Committee: Frank C. De Lucia (Advisor); James V. Coe (Committee Member); Douglass W. Schumacher (Committee Member) Subjects: Chemistry; Physics

Doctor of Philosophy, Case Western Reserve University, 2007, Chemistry

The ultrafast electronic and vibrational dynamics of a model five-coordinate, high-spin heme FeIIOEP-2MeIm, following excitation in the Soret band, have been studied in a coordinated fashion using ultrafast transient absorption, time-resolved Stokes and anti-Stokes resonance Raman spectroscopies. Electronic excitation on the blue side of the Soret band region led to sub-100 fs S2→S1, followed by 800 fs nonradiative decay to a vibrationally hot, nonthermal ground state species S0*. S0* then evolved to the thermally equilibrated ground state species S0 on ~10 ps timescale. The initial accepting modes during the S1→S0 internal conversion underwent rapid vibrational relaxation evidenced by 1-3 ps decay of transient anti-Stokes signals. Comparison to other studies in heme proteins where the initial excited electronic state was prepared by ligand photolysis led to insight into the state dependence of vibrational dynamics in hemes. The ultrafast dynamics of a six-coordinate low-spin heme FeIIOEP-(Im)2 were studied following photolysis of one of the imidazole ligands upon electronic excitation. No detectable vibrationally hot six-coordinate ground state heme is observed, indicating the intrinsic quantum yield of the photolysis to be close to unity. The intramolecular vibrational relaxation is the major contribution to the photoproduct cooling on the order of 0.6 to 4.5 ps time scale. The intermolecular vibrational cooling has a lifetime of approximately 10 ps. On average 75% of the photolysed ligand geminately recombines on the time scale of 10-20 ps strongly overlapping with the vibrational cooling dynamics. In addition to the two heme compounds, the effect of methyl groups on the vibrational relaxation processes of para-nitroaniline (PNA) was studied. Minimal impact upon electronic dynamics, significant impact upon vibrational dynamics was observed in 2-methyl, 2, 6-dimethyl and N, N-dimethyl PNA compounds. NO2 group wagging overtone (~1495 cm-1) acts as the coupling and (open full item for complete abstract)

Committee: Miriam Simpson (Advisor) Subjects: Chemistry, Physical

Doctor of Philosophy, The Ohio State University, 2024, Chemistry

Eumelanin is a black-brown pigment and is the most studied type of melanin, which acts as a sunscreen and antioxidant in human organisms. Despite decades of studies, the macromolecular structure of this pigment is still unknown. Past researchers were able to identify the initial steps of eumelanogenesis, which starts with the oxidation of L tyrosine to 5,6 dihydroxyindole (DHI) and 5,6 dihydroxyindole carboxylic acid (DHICA). The rapid and spontaneous oxidation and polymerization of DHI and DHICA results in insoluble black product formation. While these compounds are the last relatively stable precursors that have been isolated for studies, theoretical studies have highlighted the critical role of their respective oxidized forms, indole-5,6-quinone (IQ) and indole-5,6-quionone carboxylic acid (IQCA). However, until now the study of these oxidized molecules was not possible due to their instability. The first part of this dissertation focuses on the stabilized IQ molecules (IQ Me) studied through various spectroscopic techniques, including steady-state absorption and photoluminescence measurements and transient absorption (TA) spectroscopy. IQ-Me reveals unprecedented properties like broad absorption extending into the near-infrared (NIR) region, ultrafast nonradiative decay to the ground state without the formation of harmful intermediates in polar environment like acetonitrile. These unexpected properties are unique to a small molecule like IQ-Me and they resemble eumelanin's light-induced sunscreening behavior. These spectroscopic studies provide the first experimental characterization of the photophysical and photochemical properties of the oxidized monomer (IQ-Me). The following chapter investigates the role of the microenvironment on the excited-state decay channel of eumelanin subunits. The oxidized IQ molecule has a ditopic character with H-bond accepting and donating moieties, which drives intermolecular hydrogen bonding in nonpolar solvents like cyclohe (open full item for complete abstract)

Committee: Bern Kohler (Advisor) Subjects: Physical Chemistry

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2023, Photochemical Sciences

The very initial photoprocesses of relevant chromophores and organic molecular probes can provide important mechanistic insight into designing more robust and useful compounds for targeting in vivo applications, drug delivery, as well as an overall understanding of significant biological functions. Therefore, examining and comprehending these ultrafast processes is critical. In this dissertation, the elucidation of excited state dynamics of several molecular probes and organic systems is obtained from the results of multiple femtosecond transient absorption experiments. Chapters I and II detail the theoretical and experimental aspects, respectively, of this dissertation as fundamental and practical methods are addressed. The first chapter will cover laser spectroscopy and associated theories surrounding the technique relevant to the work discussed herein in general, while the second chapter will discuss specifics of experimental design and practices used for data analysis. The third chapter focuses on a photochromic system, trans-4,4'-azopyridine, capable of undergoing trans-cis isomerization upon irradiation and how similar and different this compound's dynamics are compared to trans-azobenzene and other azo dyes in general. An unusual trend in the quantum yield increasing upon exciting with higher excitation photon energies is linked to vibrational coherence observed for an in-plane bending mode. Chapter IV delves into a project on two polymethine cyanine dyes, which are utilized for deep tissue imaging due to their absorption and emission in the shortwave infrared region. The excited state dynamics in the fluorescent state and non-radiative relaxation mechanisms in this state, discovered to be competing photoisomerization and the energy gap law relaxation pathways, are analyzed and discussed. Finally, Chapter V describes work on a series of enaminones where the question of if and how excited state intramolecular proton transfer plays a role in the excited state m (open full item for complete abstract)

Committee: Alexander Tarnovsky Ph.D. (Committee Chair); Yuning Fu Ph.D. (Other); John Cable Ph.D. (Committee Member); Peter Lu Ph.D. (Committee Member) Subjects: Chemistry; Physical Chemistry

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2023, Photochemical Sciences

Ultrafast time-resolved pump-probe spectroscopy is an ultimate method for revealing fundamental photophysical and photochemical processes that govern the evolution of molecular systems. This method can be used to study organic, inorganic, biological molecules, as well as materials, unraveling the response of the sample to photoexcitation on very rapid timescales from femtoseconds (10-15 s) to picoseconds (10-12 s), which response frequently defines molecular properties and functions. Excited-state relaxation dynamics of a paradigm ruthenium nitrosyl complex, an important sub-class of nitric oxide carriers, is studied by means of ultrafast dispersed, broadband transient absorption spectroscopy. A computational extension is performed for related NO-releasers such as trans [RuNOL2Cl3] complexes which possess coordinated derivatives of biologically-relevant nicotinic and isonicotinic acids. Further studies to develop NO releasers, including those involving covalent linkage sites as isonicotinic/nicotinic derivatives for potential application as photochemical drugs, can rely on the findings in the ultrafast study of [RuNOCl5]2- dynamics as involvement of the triplet states rather than linkage isomers. Further, molecular properties of compounds related to the perovskite-based photovoltaic were computationally investigated. The electron-rich series of [I3]-, [TeI4]2-, and [BiI6]3- compounds were discussed in detail with a focus on three-center four-electron bond, which plays an important role in the compounds containing heavy-atoms. Excited-state relaxation dynamics in a polyhalogenated compound (CH2BrI) were investigated by means of computational dynamics on the earliest timescale of 100 fs following excitation of this molecule into two electronic states of spectroscopic interest. The computed pump probe spectra yield the time occurrence and spectral position of the absorption and stimulated emission transitions of the involved product states. The results are instrument (open full item for complete abstract)

Committee: Alexander N. Tarnovsky Ph.D. (Committee Chair); Amelia Carr Ph.D. (Other); John R. Cable Ph.D. (Committee Member); Alexis D. Ostrowski Ph.D. (Committee Member) Subjects: Chemistry

Master of Arts (MA), Bowling Green State University, 1965, Chemistry

Committee: Hanns K. Anders (Advisor) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2022, Astronomy

The composition and evolution of galaxies have been an elemental but long-standing mystery in Astronomy. In the last century, the advent of telescopes across the electromagnetic spectrum has revolutionized our perception of galaxies from a mere assembly of stars to a complex ecosystem. Both observational and theoretical studies have pointed towards the existence of a gaseous medium beyond the stellar component of galaxies, aka, the circumgalactic medium (CGM). The CGM is a multi-phase gas surrounding the stellar disk of a galaxy, filling up its dark-matter halo. The CGM is simultaneously the fuel tank, waste dump, and recycle hub of galaxies. It is expected to harbor the baryons, metals, and feedback that are missing from the stellar disk. I have studied the two extreme phases of the CGM to investigate how the feeding (accretion) and the feedback (outflow) at the galactic scale govern the evolution of the Milky Way and similar nearby galaxies. The ≥106 K hot CGM, despite being challenging to detect, is a treasure trove of galaxy evolution. By probing the hot CGM of the Milky Way (MW) using X-ray absorption lines of multiple metal ions, I have discovered a super-virial 107 K phase coexisting with the well-known virialized 106 K phase, featuring non-solar abundance ratios of light elements, α-enhancement, and non-thermal line broadening. I have also detected this super-virial phase of MW CGM in X-ray emission analyses. Detection of these surprising properties of the CGM along multiple directions in the sky suggests a strong connection between the hot CGM and past Galactic outflow(s). Observations of MW-like galaxies complement our observations of the Milky Way. I have discovered the hot CGM emission of an MW-mass galaxy NGC 3221 that is extended (~150-200 kpc) and is massive enough to account for its missing baryons. The CGM is not isothermal, with the CGM within 100 kpc of NGC 3221 being super-virial, and fainter along the minor axis than the global a (open full item for complete abstract)

Committee: Smita Mathur (Advisor); Paul Martini (Committee Member); Annika Peter (Committee Member); Adam Leroy (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2022, Photochemical Sciences

Our overall goal here in this dissertation is to develop silicon-based hybrid materials that are potential high stability materials replacements for those in current electronics systems. To design the hybrid structures, a unique class of silicon-based compounds, silsesquioxanes (SQ) was used as the building block. SQs are three dimensionally compact Si-O bonded, cage-type compounds that can be synthesized to contain a variety of functional groups on each of the cage vertices. They offer useful properties such as thermal and photo stability, a high degree of functionalization, solution processability, and facile synthesis. The works in this dissertation focus on mixed functional (vinyl/phenyl) SQs of different sized cages containing 8, 10, and 12 silicon atoms. They are synthesized by fluoride catalyzed rearrangement reaction in a statistically controlled manner to achieve the desired vinyl groups for oligomerization. Spectroscopic measurements in picosecond/subpicosecond timeframes were performed before evaluating their potential applications. In chapter 2, vinyl/phenylSQs are cross-coupled by 4-di-bromo-aromatic linkers: Benzothiadiazole (BT), Phenanthrenequinone (PQ), Ethyl-carbazole (EC) and Phenyl-carbazole (PC). To compare photophysical properties between caged and non-caged structures, bis-tri-alkoxysilyl (linker) model compounds are synthesized. Luminescence quantum yields for oligomers are generally lower than the corresponding model compounds (except for PQ) which denotes non-radiative energy transfer possibility in oligomer. In addition, rapid transient absorption anisotropy decay (10's ps in oligomers) provide signatures for excitation energy transfer between linker chromophores in oligomers. In chapter 3, we have designed hybrid oligomers with a vinyl/phenylSQ cage backbone linked with cross-linkers including 2,7-dibromo-9-fluorenone, 2,7-dibromo-9,9-dimethylfluorene, 1,4-dibromo-2,5-dimethoxybenzene, 2,5-dibromopyridine, 2,6-dibromopyridine, 2, (open full item for complete abstract)

Committee: Joseph Furgal Ph.D. (Committee Chair); Robyn Miller Ph.D. (Other); H. Peter Lu Ph.D. (Committee Member); Xiaohong Tan Ph.D. (Committee Member) Subjects: Organic Chemistry; Physical Chemistry

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2021, Photochemical Sciences

This dissertation work is focused on the deposition of gallium oxide (Ga2O3) thin films by metal organic chemical vapor deposition (MOCVD) method. This material belongs to a special group of wide bandgap oxide semiconductors with high optical transmittance and high levels of conductivity. The importance of this material is generated by the wide range of applications of electronic and optoelectronic devices such as MOSFET's, photo diodes, solar cells, LED's, laser diodes, sensors etc. Through MOCVD technique, an implementation of a Si4+ dopant was incorporated in the monoclinic β-Ga2O3 crystal structure on homoepitaxial and heteroepitaxial β-Ga2O3 single crystal wafers. The MOCVD process allowed us to deposit at a growth rate of 1 μm/hour while controlling the electrical transport properties with this dopant. These films were carefully characterized by surface morphology, crystal structure, levels of conductivity and trapping defects. The work shows that the electron density and conductivity of MOCVD Ga2O3 films are mainly governed by the interplay between dopant concentration, C concentration and the presence of trapping defects in the films, which is most likely applicable for other oxide films grown by MOCVD. Conductive films of Ga2O3 with resistivity in the order of 0.07 Ω.cm were successfully grown. The electron density in most of these films was in the range of 1019 cm−3 but the mobility was limited to 1.5 cm2/V⋅s. Higher mobility of 30 cm2/V⋅s was obtained in some films at the expense of carrier concentration by reducing Si doping level resulting in resistivity in the order of 0.3 Ω.cm. This range of conductivity and mobility is relevant for field-effect transistors (FET) and the applications of Ga2O3 as transparent FET in Deep Ultra-Violet (DUV) technology. The second part of this work focuses on investigating the electronic and crystal structure properties of an indium gallium oxide alloy (IGO) doped with Si4+ ions through MOCVD technique on c-sapph (open full item for complete abstract)

Committee: Farida Selim Dr. (Advisor); Marco Nardone Dr. (Committee Member); Alexander Tarnovsky Dr. (Committee Member); Ellen Grosevski Dr. (Other) Subjects: Materials Science; Physics

Doctor of Philosophy, The Ohio State University, 2021, Chemistry

The ability of DNA to resist photodamage has led to extensive study of its excited state properties. Most recently interest in metal coordinated DNA materials have led to a surge in study of the spectroscopic properties of Metallo-DNAs. In particular, Ag+ interactions with DNA have been of great interest to due to the non-canonical base pairs, such as cytosine-cytosine, formed through Ag+ binding and the ability to form reduced silver nanoclusters which could potentially operate as biosensors. In this text the relationship between structure and photophysics is explored for a Ag+ bound all-cytosine oligonucleotide dC20 as well as Ag+ bound cytosine and Ag+ bound cytidine monomers. Using circular dichroism and UV-Vis-NIR transient absorption spectroscopy, in conjunction with TDDFT calculations carried out by our collaborator Prof. Lara Martinez-Fernandez, it is shown that addition of silver nitrate to dC20 (Ag+-dC20) solutions leads to the formation of parallel duplexes which contains Ag+ mediated cytosine-cytosine base pairs with a high degree of propeller twist. The Ag+-dC20 duplexes are found to form an unusually long-lived state which persists beyond our time window (>4 ns). This state is unobserved in i-motif and single stranded forms of dC20. Furthermore, the state is absent in solutions of Ag+ bound cytosine monomers which are expected to form planar base pairs than can potentially form sheets or ribbons, indicating that propeller twisting is leading to the formation of this long-lived state. iii The identity of this long-lived species in Ag+-dC20 was investigated using FTIR and time resolved infrared spectroscopy (TRIR) with aid from QM/MM calculations carried out by our collaborator Prof. Lara Martinez-Fernandez. In addition to Ag+-dC20, Ag+ bound cytidine monomers (Ag+-Cyd) and cytosine monomers (Ag+-Cyt) were studied which are expected to form propeller twisted and sheet like structures, respectively. The long-lived state, which is found to also form in A (open full item for complete abstract)

Committee: Bern Kohler (Advisor); Robert Baker (Committee Member); James Coe (Committee Member) Subjects: Biophysics; Physical Chemistry

Doctor of Philosophy, The Ohio State University, 2021, Chemistry

The global need for clean renewable fuels has led to a high degree of interest in using photocatalytic processes that can form useful fuels. Semiconducting metal oxide materials have been extensively studied in this field due to their ability to generate highly reactive charge carriers upon photoexcitation, nontoxicity, and inexpensive fabrication. CeO2 has recently garnered interest as a photocatalytic material due to its redox mutability and relative abundance. In order to understand and improve the behavior of CeO2 as a photocatalyst, a thorough investigation into the dynamics of photoexcited charge carriers is needed. Herein, transient absorption spectroscopy was used to study the lifetime of photogenerated electrons and holes within CeO2 nanoparticles with varying diameters and crystalline domain sizes. Through tuning the size, the surface-to-bulk ratio is altered, allowing for a finer study of the surface and bulk hole dynamics in the nanoparticles. Through hole scavenging experiments, spectral assignments of surface and bulk holes were made and the behavior of these carriers vs electron small polarons (self-trapped electrons) was compared. The faster decay dynamics of ESPs in comparison with hole dynamics, both bulk and surface, reveals that the latter charge carrier is able to migrate away from its geminate partner and likely trap elsewhere within the particle. This observation suggests CeO2 nanoparticles should be considered photocatalysts for oxidation half reactions in which holes are employed. The surface holes were found to decay slower than the bulk holes, indicating that the latter trap/recombine more quickly. This long-lived decay for surface holes shows promise for the use of CeO2 as a photocatalytic oxidant. Signals from both holes and electrons small polarons decay slower in larger nanoparticles comprised of larger crystalline domains. This observation suggests the larger distance the electron small polaron must migrate or “hop” to within CeO2 a (open full item for complete abstract)

Committee: Bern Kohler (Advisor); Heather Allen (Committee Member); Robert Baker (Committee Member) Subjects: Chemistry; Materials Science

Doctor of Philosophy, The Ohio State University, 2021, Chemistry

Marine aqueous interfaces constitute one of the most prevalent surfaces in the biosphere and the atmosphere, and understanding the physicochemical processes at these interfaces is of significant importance for informing Earth system models. In the following chapters, surfactant organization and morphology on aqueous solutions of high ionic strength are explored as a proxy for the organic films coating sea spray aerosol (SSA) surfaces and the sea surface microlayer (SSML). First, a proxy film mixture comprised of the saturated fatty acids myristic acid (C14), palmitic acid (C16), and stearic acid (C18) was selected to study sea spray aerosol film morphology as a function of atmospheric acidification. The nascent SSA proxy film is fluid and flexible, whereas the acidified film is more rigid; as a result, the nascent SSA proxy film folds upon collapse, and the acidified film fractionates into three-dimensional structures with compression. Next, the influence of surfactant organization on one-dimensional surface-sensitive infrared spectroscopy was examined. Decreasing intermolecular distances between a soluble perfluorooctanoic acid film and an insoluble arachidic acid (C20) monolayer cause vibrational exciton delocalization across the surfactants, manifesting in alkyl and fluoroalkyl signal reduction and deviations from the Beer-Lambert law. The aqueous electrolyte composition in part modulates surfactant intermolecular spacing, affecting the extent of vibrational delocalization. Consequently, quantitative analyses involving alkyl and fluoroalkyl one dimensional vibrational peak intensities must be approached with caution. Lastly, surfactant-mediated cooperative adsorption of a soluble polysaccharide to a proxy sea surface microlayer is studied. Seawater divalent cations facilitate ionic bridges between the marine-relevant, anionic polysaccharide alginate and a partially deprotonated palmitic acid monolayer. Calcium promotes the strongest bridging interactions, and pal (open full item for complete abstract)

Committee: Heather Allen (Advisor); Bern Kohler (Committee Member); Sherwin Singer (Committee Member); Donald Yau (Committee Member) Subjects: Atmospheric Chemistry; Biogeochemistry; Chemistry; Physical Chemistry

Doctor of Philosophy, The Ohio State University, 2021, Physics

In this thesis, we lay the groundwork for performing attosecond transient absorption spectroscopy (ATAS) measurements in the condensed phase using mid-infrared (MIR) lasers. This was accomplished by designing, building and testing several pieces of home-built experimental equipment, including a MIR / extreme ultraviolet (XUV) Mach-Zehnder interferometer and a two-dimensional XUV spectrometer. A home-made bright XUV light source was designed and demonstrated to be nearly two orders of magnitude brighter than existing sources. Finally, the equipment was used to study ultrafast dynamics in germanium, a technologically important indirect bandgap semiconductor. This thesis is organized as follows. Chapter 1 introduces the relevant background, including ultrafast dynamics and the tools required to observe them. Chapter 2 details the commercial laser system, the home-built transient absorption beamline (TABLe) and the XUV spectrometer. In Chapter 3, we design and optimize the XUV light source for high flux, which is a general requirement for ATAS measurements and especially needed at longer wavelengths with poor high harmonic generation (HHG) quantum efficiency. Also covered in Chapter 3 are basic diagnostics of the XUV & IR optics, as well as our XUV detector. In Chapter 4, we present the results of a MIR ATAS experiment in germanium, an experimental first. Chapter 5 concludes the dissertation with a roadmap for future condensed matter studies. An appendix provides instructions on how to operate some aspects of the home-built experimental apparatus.

Committee: Louis DiMauro (Advisor); Robert Baker (Committee Member); Jay Gupta (Committee Member); Yuri Kovchegov (Committee Member) Subjects: Condensed Matter Physics; Optics; Physics

Doctor of Philosophy, Case Western Reserve University, 2020, Chemistry

The need for alternative energy sources has been growing in the last decade or so. With an ever-increasing population and a strong consumer culture, particularly in the United States, the current energy sources are becoming difficult to obtain and are filling the Earth's atmosphere with pollutants. My work has been focused on investigating structure-function relationships in photovoltaic materials, specifically their optoelectronic response. One of the materials I have studied is methylammonium lead iodide, a hybrid organic-inorganic perovskite that finds application in many fields, such as light emitting diodes, laser dyes, and superconductors. As photovoltaics, they are usually deposited onto a substrate to form a thin, polycrystalline film, sandwiched by electron and hole transport materials. Perovskites can be formed using many different compositions, which affect its ultimate surface morphology and electronic performance. I created a set of perovskite morphologies and compositions with the aim to learn more about how a different surface morphology and an additive will influence the charge carrier movement in perovskite films. Two different morphologies, granular and fibrous, showed that film morphology is not as important in material performance as is the compositional homogeneity throughout the film and that long photoluminescence lifetime is influenced by sub-band edge states. Addition of chloride into the methylammonium lead iodide films results in films with very low concentrations of chloride, but still produces a change in the morphology of the film. The optoelectronic behavior did not change homogenously or drastically throughout the film, but appeared as trap states in localized areas. This supports other's findings that chloride does not directly influence perovskite's performance, and is instead a morphological influence. I have also investigated a benzannulated iron(II)-based complex showing exceptionally long-lived charge transfer states. Additional (open full item for complete abstract)

Committee: Clemens Burda (Advisor); Carlos Crespo-Hernández (Committee Chair); Geneviève Sauvé (Committee Member); Shane Parker (Committee Member); Lydia Kisley (Committee Member) Subjects: Chemistry; Materials Science; Physical Chemistry