Extensive Raman-scattering studies have been performed in order to study the structure of ion-implanted GaAs, prior to any anneal. The spectroscopic evidence is consistent with a fine-scale mixture of amorphous and microcrystalline GaAs. Excessive bombardment with 120-keV SiF₃⁺ ions results in a 500-A thick surface layer which is completely amorphous (a-GaAs). A detailed chemical-etch damage depth profile has been completed for 45-keV Be⁺-implanted GaAs, which is not completely amorphized. The damage is characterized using the microcrystalline longitudinal-optical (LO) phonon frequency, line width, and intensity, and the intensity of the a-GaAs component of the Raman spectrum. The damage layer possesses a 1500-A thick surface layer of constant, high damage. This high-damage plateau is followed by a transition region in which the damage level smoothly decreases until the undisturbed crystal is reached near 4000 A. LO intensities were analyzed, within the amorphous/crystalline mixed-phase model, to obtain the volume fractions of the two components. Consistent estimates of the optical absorption in the high-damage plateau were obtained via two independent means. Resonance-Raman experiments were carried out, using laser lines between 1.5 and 2.71 eV. The intensity of the a-GaAs spectral component was found to depend on scattering volume (optical penetration), thus providing an internal intensity standard allowing the effects of scattering volume and scattering efficiencies to be separated. The LO phonon was found to resonate approaching the E₁ electronic transition at 2.9 eV. The strength of the resonance decreases with smaller crystallite size. A new Raman band was observed near 47 cm⁻¹ for photon energies below 2 eV. It resonates at 1.7 eV, near E₀ and not near E₁. I propose that this new feature arises from GaAs acoustic modes made Raman active by defectassisted scattering involving the crystalline/amorphous interface regions. A quantitative analysis is developed, with some success. Intensities of silicon local are observed to remain constant upon annealing, although conductivity increases by several orders of magnitude. The anneal primarily restores the mobility to that of crystalline GaAs. / Ph. D.

Polypyrrole is an electrochemically synthesized conductive polymer that has physical properties which impede efforts to develop structure-properties relationships. The extent of conjugation, as limited by the presence of structural disorders in the polymer, is important in determining its inherent conductivity. The extent of conjugation in thin electrochemically generated films of polypyrrole and poly-N-methylpyrrole has been examined with resonance Raman spectroscopy. The Raman experiment was performed within the electrochemical cell and does not suffer from exposure to the contaminants encountered when transfer techniques are employed. Electrochemically reduced films of polypyrrole exhibited intense resonance Raman spectra of the carbon-carbon stretching frequencies. The position of these bands is a function of the number of double bonds in conjugation. The conjugation length within the polymer chain was found to be between 3 and 4 rings for PP and slightly less in PNMP (2-3 rings). This is the first reported determination of the conjugation length in PP and PNMP. This data confirms the idea that PNMP is less conductive than PP due to reduced planarity within the chain, thus less conjugation. Reduced films of PP and PNMP yielded intense luminescence that disappeared upon oxidation. The luminescence is a broad featureless band that consumes the weakly enhanced Raman of PNMP. The intensity of the luminescence increased as the reduction potential increased and the highest intensities occurred at potentials far cathodic of the E₀ for the film. The explanation for this is still obscure but may involve either further reduction of highly luminescent segments or a decrease in the amount of quenching by solvent or counter-ion interactions with the luminescer. / Ph. D.

Fast, sensitive, quantitative, and low-cost analysis of environmental pollutants is highly valuable for environmental monitoring. Due to its single-molecule sensitivity and fingerprint specificity, surface-enhanced Raman spectroscopy (SERS) has been widely employed for heavy metal, organic compound, and pathogen detection. However, SERS quantitation is challenging because 1) analytes do not stay in the strongest enhancing region ("hot spots") and 2) SERS reproducibility is poor. In this dissertation, gold nanoparticle/bacterial cellulose (AuNP/BC) substrates were developed to improve SERS sensitivity by increasing hot spot density within the laser excitation volume. Environmentally relevant organic amines were fixed at "hot spots" by lowering solution pH below the analyte pKa and thus enabling SERS quantitation. In addition, a new SERS internal standard was developed based upon the electromagnetic enhancement mechanism that relates Rayleigh (elastic) and Raman (in-elastic) scattering. Rayleigh scattering arising from the amplified spontaneous emission of the excitation laser was employed as a normalization factor to minimize the inherent SERS signal variation caused by the heterogeneous distribution of "hot spots" across a SERS substrate. This highly novel technique, hot spot-normalized SERS (HSNSERS), was subsequently applied to evaluate the efficiency of SERS substrates, provide in situ monitoring of ligand exchange kinetics on the AuNP surface, and to reveal the relationship between the pKa of aromatic amines and their affinity to citrate-coated AuNPs (cit-AuNPs). Finally, colloidally stable stable pH nanoprobes were synthesized using co-solvent mediated AuNP aggregation and subsequent coating of poly(ethylene) glycol (PEG). These nanoprobes were applied for pH detection in cancer cells and in phosphate buffered aerosol droplets. The latter experiments suggest that stable pH gradients exist in aerosol droplets. / PHD / Traditional analytical methods, such as gas chromatography/mass spectroscopy, liquid chromatography/mass spectroscopy, etc., cannot meet the demand for rapid screening of target environmental pollutants in drinking water. This issue arises due to the requirements for time-consuming sample pre-treatment, well-trained experts, complex instrumental parameter optimization, and scale challenges that limit onsite measurement. Surface-enhanced Raman spectroscopy is a promising approach to overcome these limitations. To improve SERS quantitation, surface-enhanced elastic scattering was developed as a novel internal standard to account for the SERS signal variation caused by substrate heterogeneity (“hot spot” normalization). Compared with traditional SERS internal standards, using scattered light as an internal standard reduces cost, time, interference, and experimental complexity for SERS detection. With this novel approach, the kinetics of adsorption/desorption of guest ligands/citrate onto/from the AuNP surface were quantified in situ and in real time. In addition, the SERS intensities of organic amines acquired at different solution pH values were differentiated using “hot spot” normalization, which revealed the relationship between aromatic amine pK_a and their affinity to the AuNP surface. Finally, the chemistry in confined aqueous environments, such as aerosol droplets, membrane channels, and cells, is challenging to probe using conventional analytical tools due to their inaccessible small volumes. To address this problem, SERS pH nanoprobes were synthesized and used to detect the pH inside cancer cells and micrometer-sized aerosol droplets.

During the last decades, the continuing need for faster and smaller sensors has indeed triggered the rapid growth of more sophisticated technologies. This has led to the development of new optical-based sensors, able to detect and measure different phenomena using light. Furthermore, material processing technologies and micro fabrication methods have exponentially advanced, allowing engineers and scientists to develop new and more complex sensors on optical fibers platforms; specifically attractive for life science and biomedical research. All these substantial developments have brought biosensors to a point where multifunctionality is needed, this has led to envision the "Lab-on-Fiber" concept. Which promotes the integration of different sensing components into a single platform, an optical fiber. In this work, an integrated system with non-conventional polymer optical fibers and their further surface modification has been developed. With these different approaches, electrodes, hollow channels and plasmonic nanostructures can be incorporated into a single optical fiber-based sensor, allowing for both electrical and optical sensing with the capabilities of tuning and signal enhancement thanks to the metallic nanostructures. Different fiber substrates can be designed and modified in order to satisfy multiple requirements for a wide variety of applications. / MS / Silica optical fibers have been used since the 1960’s to guide optical signals, such as light, with low losses through long distances; making them an attractive platform to use in large communication systems. However, over the past couple of decades researchers have been trying to implement these low-loss platforms in sensing devices for many different fields, such as environmental and structural monitoring, and chemical and biomedical research. Unfortunately, their high brittleness has prompted researchers to introduce different materials in the same technology, leveraging the development of multimaterial non-conventional fibers. Where different polymers and even metals have replaced silica as the structural material, making these fibers more cost-affordable, flexible, and allow for multi-sensing capabilities of both electrical and optical signals. Although these multimaterial fibers are able to transmit light, they need to be functionalized or modified in order for them to be able to sense different phenomena occurring in their surrounding media. This can be achieved by integrating small particles or structures onto the fibers end-faces, these small structures are known as plasmonic nanostructures. When light (electromagnetic radiation) travels through a fiber and interacts with the free (conduction) electrons of a metallic nanostructure, it leads to a coupling that results in collective oscillations, which produce strong enhancement of the local electromagnetic fields surrounding the nanostructures. The latter can be easily detected with the help of an optical spectrum analyzer that iv stores the transmitted light as a function of the transmitted wavelength. Noble metals like gold and silver produce unprecedented electromagnetic field enhancements and are also biocompatible, making them very attractive in biosensing applications. In this research metallic plasmonic nanostructures were deposited on the end face of multimaterial polymer fibers to enhance the optical properties and potentially the electrical properties as well, creating new sensing devices. The enhancement produced by these structures was studied with both experimental measurements and theoretical simulations. The results demonstrate that the nanostructures investigated in this work can indeed enhance the optical properties of the used polymer fibers, enabling them to work as sensing probes for a many different applications, especially biosensing research.

Understanding the Earth’s interior requires exploring minerals under extreme pressures and temperatures, conditions often unattainable by experimental methods. Atomistic simulations provide a powerful tool to investigate these extreme environments, offering insights into minerals' physical and chemical behavior deep within the Earth. However, complex phase relations and pronounced anharmonic effects pose significant challenges to these simulations. To address these challenges, we developed advanced methodologies and employed cutting-edge atomistic simulation techniques. Our work focused on modeling phonon behavior, simulating X-ray, IR, and Raman spectroscopy, and evaluating key properties such as thermodynamics, compressive strength, and thermoelasticity. We extended the quasiharmonic approximation for thermoelasticity and introduced a new formalism for third-order elasticity to tackle the complexities inherent in these systems. Our research sheds light on phenomena like hydrogen bond disordering, tunneling, diffusion, and hydrogen bond-induced elastic anisotropy under extreme pressure. These advancements significantly enhance our understanding of the thermal and chemical structures of the Earth’s deep interior.

No / The Raman spectrum of budesonide is reported for the first time, and molecular assignments are proposed on the basis of ab initio BLYP DFT calculations with a 6-31 G* basis set and vibrational wavenumbers predicted on a quasi-harmonic approximation. Comparison with previously published infrared data has explained several spectral features, and the relative band intensities in the CO and CC stretching regions are interpreted. The results from this study provide data that can be used for the preparative process monitoring of budesonide, an important steroidal pharmaceutical in various dosage forms, and its interaction with excipients and other components.

No / Luticasone propionate is a synthetic glucocorticoid with potent anti-inflammatory activity that has been used effectively in the treatment of chronic asthma. The present work reports a vibrational spectroscopic study of fluticasone propionate and gives proposed molecular assignments on the basis of ab initio calculations using BLYP density functional theory with a 6-31G* basis set and vibrational frequencies predicted within the quasi-harmonic approximation. Several spectral features and band intensities are explained. This study generated a library of information that can be employed to aid the process monitoring of fluticasone propionate.

No / The Raman spectrum of terbutaline hemisulphate is reported for the first time, and molecular assignments are proposed on the basis of ab initio BLYP DFT calculations with a 6-31G* basis set and vibrational frequencies predicted within the quasi-harmonic approximation; these predictions compare favourably with the observed vibrational spectra. Comparison with previously published infrared data explains several spectral features. The results from this study provide data that can be used for the preparative process monitoring of terbutaline hemisulphate, an important ß2 agonist drug in various dosage forms and its interaction with excipients and other components.

No / Salbutamol hemisulphate is a relatively selective ß2-adrenergic agonist and is used as a bronchodilator. In this work, we present a detailed vibrational spectroscopic investigation of salbutamol hemisulphate using mid-infrared and near-infrared Fourier-transform (NIR-FT) Raman spectroscopies. These data are supported by quantum chemical calculations, which allow us to characterise the vibrational spectra of this compound reasonably. As such, this study could be viable for examining the way in which this drug interacts with its target molecules.

No / In this work the chemistry of the lichens Candelaria fibrosa and Pyxine coccifera have been investigated for the first time using FT-Raman spectroscopy with the help of quantum mechanical DFT calculations to support spectral band assignments. The non-destructive spectral vibrational analysis provided evidence for the presence of pulvinic acid derivatives and conjugated polyenes, which probably belong to a carotenoid with characteristic signatures at ca. 1003, 1158 and 1525 cm−1 assigned respectively to δ(C–CH3), ν(C–C) and ν(Cdouble bond; length as m-dashC) modes. The identification of features arising from chiodectonic acid in the Pyxine species and calycin and pulvinic dilactone pigments in C. fibrosa were assisted by the quantum mechanical DFT calculations. Raman spectroscopy can provide important spectroscopic data for the identification of the biomarker spectral signatures nondestructively for these lichen pigments without the need for chemical extraction processes.