Laboratory-based Tender X-ray Emission Spectroscopy: Instrumental, Experimental, and Theoretical Advances and Application to the Study of Phosphorus and Sulfur Electronic Structure

Abstract

Tender x-ray emission spectroscopy (XES) is a powerful, element-specific, atomically local probe of chemical and electronic structure. Taking advantage of advances in every component of spectrometer systems including crystal analyzers, color x-ray cameras, and bremsstrahlung x-ray tubes, I designed, built, and demonstrated a new, laboratory-based tender x-ray emission spectrometer. This apparatus creates an opportunity for more widespread access to tender XES measurements, which in recent years have been largely restricted to a limited number of beamlines at synchrotron facilities. Using the developed spectrometer, I performed lab-based XES studies on phosphorus and sulfur, whose emission lines lie in the energy range of optimal performance, and are of significant experimental value due to their chemical sensitivity and the ubiquity of phosphorus and sulfur in environmental, material, and fundamental science. I conducted analytical applications, demonstrating the speciation of phosphorus in indium phosphide quantum dots and the speciation of sulfur in biochars at low concentration. These studies illustrate the strength of P Kα XES as an alternative to solid-state nuclear magnetic resonance (SSNMR), and the ability for S Kα XES to yield information comparable and complementary to synchrotron x-ray absorption near edge structure (XANES). Supplementing these new experimental capabilities, I utilized linear-response time-dependent density functional theory (LR-TDDFT) for theoretical prediction and analysis of Kα core-to-core and Kβ valence-to-core emission lines of sulfur. The strong quantitative agreement between this theoretical approach and the observed results supports future applications in both analytical and theoretical investigations. With the establishment of these experimental and theoretical capabilities by the work in this thesis, tender XES is primed to grow into a powerful and routine analytical tool in both academia and industry.