Doctor of Philosophy (Ph.D.)
M. Mumtaz Qazilbash
Infrared phenomena at the micro and nanoscales can elucidate fundamental physics of highly correlated and complex systems. However, accessing these length scales require high resolution microscopic instrumentation and novel analysis methods to extract meaningful information. Initially this work describes the implementation of a far-field microscope and subsequent study of single strands of spider silk and temperature dependent behavior of Li2RuO3.
Little is known about the internal structure of protein fibrils, the basic building blocks of spider silk. Polarized Fourier-transform infrared micro transmittance on single strands of native spider silk was performed to determine the concentrations and orientations of seven protein secondary structures. Through decomposition of these secondary structures a high crystallinity was observed and corroborated by Raman and XRD analysis. The totality of results will help researchers develop structure-property relationships for the production of artificial silks.
Next, the temperature dependent phonon and electronic properties of Li2RuO3(LRO) are presented. LRO forms a valence bond crystal at room temperature and undergoes a high temperature phase transition that involves structural, magnetic, and electronic changes. The orbital degrees of freedom are thought to be fundamental to the evolution of LRO properties across the phase transition. Above the transition temperature (Tc ≈ 500 K), an orbital selective metallic state emerges, which to our knowledge has not been previously reported in LRO.
Visible polarized microscopy and scattering-type near-field infrared microscopy(S-SNIM) reveals the existence of domain in LRO. S-SNIM can circumvent the diffraction limit and access the nanoscale through the interaction between an illuminated atomic force microscope tip and sample of interest. Backscattered fields provide information about the local interaction between the tip apex (~20 nm) and sample. Fully unpacking the complicated backscattered fields to unravel the local optical properties is a difficult task though. A numerical model of scattering type near-field infrared microscopy (S-SNIM) was developed and is presented. Numerically modeling the tip-sample interaction allows a universal modeling methodology which is free of tunable phenomeno-logical parameters. Application of this model to describe numerous experimental systems is presented including polaritonic resonant materials, nanostructures, ultrathin, multilayered structures and anisotropic materials. Lastly the developed model is used to describe the observed contrast in LRO.
© The Author
McArdle, Patrick, "Broadband Infrared Microspectroscopy and Nanospectroscopy of Local Material Properties: Experiment and Modeling" (2022). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1638386965.
Available for download on Monday, May 20, 2024