Raman microspectroscopic imaging and multivariate analysis to investigate the chemical properties of novel geological and planetary materials
Date
2017
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Developing and applying analytical methodology, including the collection and subsequent analysis of chemical data, is critical for the scientific community at large. In this dissertation, innovative analytical methods, including microspectroscopy and microspectroscopic imaging, in conjunction with multivariate analysis methods and chemometric techniques are employed to fundamentally study the chemical properties of diverse, novel materials. Specifically, this dissertation will focus on three collaborative, multidisciplinary studies. First, the high-pressure, α-PbO2-structured polymorph of titanium dioxide, termed TiO2-II, was investigated to understand ancient impact events on Earth. Raman microspectroscopy was used to identify, for the first time, TiO2-II in grains recovered from four Neoarchean (~2.5 billion years old) spherule layers—a discovery that has eluded researchers for nearly 30 years until now. By further investigating these grains using Raman microspectroscopic imaging with multivariate analysis methods, spatially-resolved chemical images and resolved Raman spectra of the individual chemical species within these complex grains were generated. The spatial resolution of the chemical images was increased using a pioneering strategy, and a Raman spectrum for pure TiO2-II was estimated for the first time. Second, a novel analytical methodology was utilized to enhance the search for life on Mars. In 2020, both the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) have planned rover missions to Mars. The primary objective for both missions is the search for evidence of extant or past life. Using multivariate analysis methods with Raman microspectroscopic imaging, the identification, differentiation, and resolution of chemical species relevant to Martian exploration was achieved. For the first time, organic carbon was spatially and spectrally resolved from hematite (α-Fe2O3), a chemical species abundant on Mars and highly relevant for Martian exploration and discovery. Third, innovative analytical methodology was used to study extraterrestrial materials. The chemical properties of lunar meteorites, provided by the NASA Johnson Space Center, were elucidated using microspectroscopic imaging techniques with multivariate analysis. Spatially-resolved chemical maps with resolved Raman spectra of the pure chemical species within these heterogeneous meteorites were produced. Overall, this dissertation aims to move analytical chemistry in a transformative and innovative direction in ways that can benefit and interest the broader scientific community.
Description
Keywords
Pure sciences, Chemical imaging, Chemometric, Multivariate curve resolution, Raman, Raman microspectroscopic imaging, Spectroscopy