Maximizing Solid-state NMR Sensitivity for Materials Science Characterization

• Author / Creator

  Ha, Michelle

• A major challenge that plagues nuclear magnetic resonance (NMR) spectroscopists is the inherently low sensitivity of this workhorse characterization technique. This low sensitivity results in long acquisition times and/or costly isotopic-labelling to obtain good resolution and signal-to-noise (S/N) ratios. Therefore, in this thesis, different approaches used to maximize NMR sensitivity are explored. While increasing the magnetic field strength or experimental time can aid in this dilemma, this is not always feasible. Thus, spectroscopic techniques can be used to alleviate these problems. Firstly, variable temperature NMR spectroscopy is explored to manipulate the different phases of organic/inorganic perovskite materials such that ordering about the 119Sn centre can be achieved. As more ordered samples provide better S/N with fewer number of experimental scans in comparison to amorphous (disordered) material, we can maximize NMR sensitivity, as well as remove anisotropic interactions which would result in spectral distortions. Another technique to improve sensitivity is to manipulate the magnetization of a highly abundant nucleus and transfer this magnetization to the insensitive nucleus of interest, namely cross-polarization (CP). This technique can be used to experimentally probe structural layers of a material, as well as minimize the time needed between each experiment. This is beneficial when studying 29Si nuclei in silicon nanoparticles as 29Si has very long relaxation delays. While CP can help with boosting NMR sensitivity, a sister technique, namely dynamic nuclear polarization (DNP) NMR spectroscopy, has become more popular in the recent decade due to its sensitivity enhancements over conventional methods. Thus, DNP NMR is utilized in the later part of this research to demonstrate the evolution of magnetic resonance techniques. One of the most challenging aspects for NMR-active nuclei are their natural abundances (for example: oxygen-17 has a natural abundance of < 0.037% even though oxygen makes up 21% of the air in the Earth’s atmosphere). Additionally, it can be quite challenging to obtain maximum labelling with minimal costs. In this thesis, a fast and cost-effective labelling protocol is introduced for labelling oxygen atoms in amino acids with optimal incorporation of 17O, reducing cost from ~ $110 USD/100 mg of amino acid to ~ $25 USD/100mg. An emerging NMR instrumentation called cross-polarization magic-angle spinning (CPMAS) cryoprobe technology is also introduced to boost sensitivity gains. Overall, this research explores the traditional and emerging NMR technology for pushing the limits of sensitivity gains for studying next-generation materials.

• Subjects / Keywords

  • Chemistry
  • NMR

• Graduation date

  Fall 2022

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-yfjx-hb49

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.