IMAGING CHARGE CARRIER AND ACOUSTIC PHONON DYNAMICS IN SEMICONDUCTOR NANOMATERIALS USING ULTRAFAST PUMP-PROBE MICROSCOPY

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  • March 20, 2019
Creator
  • Van Goethem, Erika
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • Future advancement of nanotechnology is dependent on our capabilities to design novel and ever increasingly complex nanomaterials. In order to manipulate the electronic and optical properties of these materials in an efficient way, we need a fundamental understanding of the physics of how structural features alter the properties of these nanomaterials. Nanostructures that are produced under identical conditions can have vastly different properties, and they can even have variations among different spatial locations within the same structure. This heterogeneity can have a significant impact on the properties, dynamics, and performance of nanoscale devices. As a result, it is important to understand dynamics in individual nanostructures. Most analytical techniques, however, probe dynamics in an ensemble of structures and thereby obscuring dynamics and making quantitative conclusions difficult. Pump-probe microscopy overcomes these limitations by combining the high-temporal resolution of pump-probe spectroscopy and the high-spatial resolution of optical microscopy. With combined spatial and temporal resolution, the microscope collects data from spatially distinct locations on individual nanostructures with a high throughput. Additionally, using computer controlled scanning mirrors with the microscope allows us to spatially separate the excitation and probe spots at the sample to allow the direct visualization of charge carrier and acoustic lattice motion on the nanoscale without the need for physical contact or active electrical connection. Here, this microscope has been used to image electron diffusion and thermal transport, as well as acoustic phonon propagation in germanium nanowires. Additionally, it has been employed to study exciton and free charge carrier dynamics in tungsten disulfide and tungsten diselenide nanoflakes. The propagation of a shear mode is captured in suspended tungsten diselenide nanoflakes using the spatially-separated pump-probe imaging configuration.
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  • In Copyright
Advisor
  • Moran, Andrew
  • Cahoon, James
  • Warren, Scott
  • Atkin, Joanna
  • Papanikolas, John
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2018
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