Graduate Thesis Or Dissertation

 

Ultrafast, Cryogenic, and Hyperspectral Nano-Imaging of Quantum Materials Public Deposited

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https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/z603qz52z
Abstract
  • Quantum materials have been moving into the focus of research for several decades.In these materials, fundamental particles and excitations strongly interact with each other, are confined to low dimensional structures, or couple and delocalize across large spatial distances, leading to a myriad of novel phenomena and properties.However, these complex interactions are influenced by defects and heterogeneities on similar length scales as their own physical size and spatial extent.With the spatial resolution of scanning probe microscopy and the chemical specificity of optical spectroscopy, scattering scanning near-field optical microscopy (s-SNOM) can directly access the natural time, energy and length scales of nanoscale heterogeneity and coupling.In this thesis, I will describe my work in advancing s-SNOM by developing and implementing additional modalities, designing and commissioning new instrumentation and demonstrating these new capabilities on specific quantum systems.

    After a brief introduction, I will give a summary on relevant background information to scanning probe microscopy and optical nano-imaging and -spectroscopy as a basis for s-SNOM.

    Then, I will focus on developments in ultrafast pump-probe nano-imaging. By optically inducing the insulator to metal phase transition in VO2 with far from equilibrium excitation, I was able to resolve nanometer spatial heterogeneities in the ultrafast phase transition of VO2 that are not observable in the thermally induced transition. Further, I will discuss adaptations to the technique that are necessary to extend its applicability more broadly, including the development and implementation of a new tabletop ultrabroadband laser source for nano-imaging and -spectroscopy.

    Next, I will describe my work in designing and building a variable temperature cryogenic s-SNOM instrument based on a closed cycle cryocooler. This part of my thesis highlights the challenges in successfully combining a highly sensitive nano-optical experiment with a permanent source of vibrations. Together with a performance evaluation of the instrument, I will present preliminary nano-imaging data of the insulator to metal phase transition behavior in bilayer Ca3Ru2O7.

    Lastly, I will present hyperspectral nano-imaging correlated with density functional theory (DFT)-based vibrational exciton modelling and scanning transmission electron microscopy. These results suggest the coexistence of domains with varying levels of molecular coupling within individual and nominally homogeneous poly-tetrafluoroethylene (PTFE) nano-crystals.On the basis of my nano-spectroscopy measurements, I will also discuss the interplay between local structure and highly delocalized vibrational modes in PTFE.

    I will close with a short summary of my work, and an outlook to future experimental efforts.

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  • 2020-10-08
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  • 2021-03-08
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