Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [221]-233).

Thesis (M.Sc.(Chemistry))--University of Pretoria, 2001. / Includes abstract in English. Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D. in Mechanical Engineering)--Vanderbilt University, Dec. 2007. / Title from title screen. Includes bibliographical references.

Nanometallic structures efficiently convert light to surface plasmon-polaritons (SPPs) localized to ultra-small volumes. Such structures can provide highly enhanced fields and are of interest in applications involving plasmon-enhanced nonlinear optics. In this study, the devices consist of rectangular gold nanoantennas on a graphene layer on a SiO2/Si substrate. The nanoantennas are used to exploit SPPs to enhance the interaction between graphene and light. Specifically, plasmon-enhanced Raman scattering from graphene is of interest. Here, the nanoantennas are spectrally-aligned with a Stokes wavelength of graphene. With the addition of a second laser source, stimulated Raman scattering can be achieved. The first laser source pumps the sample’s atoms and molecules into virtual excited states and the second one stimulates emission of a photon and relaxation to a higher mode of the ground state. This work involves designing and constructing a stimulated and spontaneous Raman microscope and also a reflectance measurement tool. Within the framework of this thesis, Raman scattering enhancement in graphene based on plasmonic resonant enhancement of the Stokes emission is demonstrated, providing a maximum cross-sectional gain of approximately 500 per antenna. This work also shows the normalized reflectance response of the nanoantenna structures of different length and width and how their resonant wavelengths shift.

Tip-enhanced Raman spectroscopy (TERS) is a scanning probe technique that utiHscs a confined, ovanescent field at the tip apex to conduct optical characterisation of a surface at length-scales below the diffraction limit. This thesis details the development of a new TER.S system based upon a shear-force scanning probe microscope (SPM) which sits atop an inverted microscope configured for bottom illumination geometry and coupled to a Raman spectrometer. The system has been optimised for use with solid silver probes and 532 nm illumination. Measurement procedures, automated scripts and data analysis software have been developed that allow reliable alignment of the tip; complex automated mapped measurements; and post processing which produces visual summary sheets to facilitate rapid review of a TERS experiment. Enhanced TERS spectra have been demonstrated on ultra-thin Rhodamine 6G films, self assembled monolayers (SAM) of thiophenole molecules, ultra-thin graphitic films and on multilayered graphene. Improvements in fabrication and alignment procedures have reduced the setup time between fabrication and approach to 20 minutes and improved the reliability of TERS tips with ~ 50% of tips demonstrating TERS activity. Using TERS, heightened defect sensitivity was observed on graphene edges, folds and overlapping regions. The TERS contrast of the defect induced D band was ~ 7.5 times the contrast of the graphene G band. Calculations show that the phonons correlating to the D and G bands interact differently with the enhanced TERS field and that the for certain defect types the D band experiences greater enhancement. Defects play an important role in tailoring the electronic and chemical properties of graphene which is key to the development of graphene based devices. The localised structural and spectral information makes TERS a highly promising tool for the characterisation of defects in graphene. This work demonstrates the potential of TERS for this exciting and important application.

The project has been concerned with structure/property relationships in a series of different carbon nanotube (CNT) composite fibres. Raman spectroscopy has been proved to be a powerful technique to characterise the CNT-containing fibres. Electrospinning has been used to prepare poly(vinyl alcohol) (PVA) nanofibres containing single-wall carbon nanotubes (SWNTs). The effect of the processing conditions including the polymer concentration, electric voltage, tip-to-collector distance, nanotube concentration and the collection method upon the morphology, diameter and the alignment of the fibres have been investigated.Raman spectroscopy of individual SWNTs dispersed in PVA electrospun fibres have been studied systematically in terms of the Raman band frequency, intensity and linewidth. The G'-band shift per unit strain during tensile deformation has been found to be dependent on the nanotube chirality. A detailed study has been undertaken of the efficiency of reinforcement in PVA/SWNT nanocomposites. The stress-induced Raman band shifts in the nanocomposites have been shown to be controlled by both geometric factors such as the angles between the nanotube axis, the stressing direction and the direction of laser polarisation, and by finite length effects and bundling. A theory has been developed that takes into account all of these factors and enables the behavior of the different forms of nanocomposite, both fibres and films, to be compared.The effects of dispersion and orientation of nanotubes and the interfacial adhesion on mechanical properties of poly(p-phenylene terephthalamide) (PPTA)/SWNTs composite fibres have been investigated. It has been shown the change of orientation of the polymer molecules upon incorporating nanotubes had direct effect on mechanical properties of the PPTA fibres. An in-situ Raman spectroscopy study during fibre deformation has revealed good stress transfer from the matrix to nanotubes in low strain range, and the interface failed when the strain exceeded 0.5%.Raman spectroscopy has also been employed to investigate the microstructure and micromechanical process of neat carbon nanotube (CNT) fibres. It has been found the fibres consisted of both SWNTs and MWNTs and varied in composition at different locations. High efficiency of stress transfer both within the fibre and in composites has been observed, suggesting the promising potential of CNT fibres in reinforcing polymers.

The diploma thesis deals with the study of biotechnologically significant microorganisms, using the Raman spectroscopy. Content of the theoretical part is brief characteristic of Raman spectroscopy as a method, its use in practice and also use as a tool for monitoring of biotechnologically processes. Thesis was further focus on the biotechnologically significant microorganism Aureobasidium pullulans, its use in biotechnology and also for over-produced substances and in particular poly-L-maleic acid and pullulan. The content of the experimental part was study of selected strains A. pullulans, specifically stains as DSMZ, CCM F148 and CCM 8182, using Raman spectroscopy on the various types of culture media. Subject of practical part research was too production of extracellular polymers, acid poly-L-apple and pullulan, by selected strains A. pullulans. Objective of my thesis was described and determinate, spectra of individual strains as well as extracellular products, mainly pullulan, and then choose suitable production medium and optimal production strain A. pullulans. During experimental work was found, that optimal production strain was DSMZ strain culture on the mineral medium with the addition of yeast autolysate, which was optimal medium type. The content of the pullulan produced was for gravimetric determination, 6,3g/L, which also confirmed the results of the HPLC method. It was experimentally found, that Raman spectroscopy isn´t suitable method for quantification of extracellular products, but is appropriate and was used for PCA analysis of individual strains.

Thesis advisor: Kenneth Burch / In quantum materials, quantum mechanical effects survive over a wide range of temperatures and length scales, which leads to fascinating phenomena, such as charge density waves, spin liquids, and magnetism. These remarkable properties originate from a delicate balance among many interacting degrees of freedom. Even small perturbations such as temperature and doping can induce many diverse phases and colossal changes in the material's functionalities. It remains a mystery how to detect these novel phenomena without complicated fabrication and extreme conditions. This thesis contributed to this field by studying collective modes in quantum materials via inelastic light scattering. After fabricating the devices in a glovebox, we directly transfer them to the measurement platform under a high vacuum. Using Raman spectroscopy, a new quasi-particles--axial Higgs mode in charge density wave systems was discovered and further symmetry breaking accompanied with it suggests the charge density wave is unconventional. In addition to symmetry analysis breakthroughs, this thesis also provided direct evidence of the fractional nature as well as the energy and temperature limits of Kitaev interactions in quantum spin liquid candidate systems, which is the building block for topological quantum computers. Not limited to 2D Kitaev materials, the non-Fluery-Loudon single magnon scattering process was detected in a 3D Kitaev system. Other than using Raman to probe the fundamental nature, we also employed it to reveal, for the first time, a clean way to realize modulation doping in 2D materials, where the acceptor carrier density has reached 10$^{14}$ cm$^{-2}$. This method can be applied to dope magnetic materials or twisted heterostructures to find new phases. / Thesis (PhD) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Poly(N-isopropylacrylamide) (PNIPAM) is a thermo-responsive hydrogel; that is, it is a macromolecule which exists in a hydrated state beneath its lower critical solution temperature (LCST). Polymers such as PNIPAM undergo a phase transition in response to changes in temperature, pressure, pH, salt concentration, and the addition of co-solvents. Previously, visible-light microscopic measurements of the pressure-induced phase transition have been hindered by the lack of a pressurization apparatus with the short working distance and optical transmission properties necessary for high resolution microscopy. We employ a high pressure setup which uses a fused silica micro-capillary to contain the sample. Our experiment reveals differences in the spatial evolution of the phase change across the temperature and pressure thresholds, and Raman measurements allude to conformational differences in the evolution of the phase transitions. The Raman peaks positions are in agreement with previous FTIR measurements, and due to a difference in selection rules additional vibrational bands are observed in the Raman spectra.