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  • March 21, 2019
  • Guo, Zhenkun
    • Affiliation: College of Arts and Sciences, Department of Chemistry
  • Zhenkun Guo: Application of Diffractive Optical Element on Spectroscopy and Imaging (Under the direction of Andrew Moran) Diffractive optical elements (DOE) are optical components that manipulate light by diffraction, interference, and other phase control methods. The application of DOE in multi-dimensional spectroscopy could significantly reduce the efforts required for conducting experiments and enhance the signal-to-noise ratio with high efficiency. In this dissertation, DOE-based two-dimensional resonance Raman spectroscopy was developed and implemented in two model systems, triiodide and myoglobin. This new technique uncovers new dimensions of information, which were not available with previous one-dimensional spectroscopy techniques. The DOE was also applied to the wide-field transient absorption microscopy. Conducting a large number of experiments simultaneously is possible in this configuration. Analysis of parallel measurements provides statistical information essential to comprehensively study heterogeneous samples. After absorbing an ultraviolet photon, triiodide undergoes photodissociation to produce diiodide and radical iodine on a time scale comparable to the period of triiodide’s nuclear motion, which could impulsively activate a vibrational coherence in the diiodide. In this dissertation, the ability of 2DRR to capture coherent reaction mechanisms is demonstrated by directly establishing a correlation, for the first time, between the nonequilibrium geometry of triiodide at photodissociation and the stretching frequency of diiodide. Ligand binding and dissociation processes are crucial to the functions of heme proteins. The recovery of the protein matrix involves fast energy dissipation from the heme group to solvent, facilitated by the propionic acid side chains as an effective “gateway”. In this dissertation, we found that the propionic chains possess significant structural heterogeneity, which could be induced by the thermal fluctuation in geometries. It is interesting to consider whether the variation in conformation could relate to the vibrational cooling rate distributions. Carrier diffusion is imaged in a perovskite film and crystal using a newly developed DOE-based wide-field transient absorption microscopy technique. The function of the instrument is illustrated with 41 parallel measurements conducted on methylammonium lead iodide perovskite films and single crystals in a single experiment. Obvious carrier diffusion is observed in the crystal. However, results indicate that the carrier dynamics in the film are dominated by many-body interactions instead. The grain boundaries in the film contribute to this difference in behavior.
Date of publication
Resource type
  • Moran, Andrew
  • Atkin, Joanna
  • Kanai, Yosuke
  • You, Wei
  • Cahoon, James
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2018

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