Extreme Ultraviolet Measurements of Thermal and Elastic Dynamics in Nanostructured Media

Nanofabrication today spans from atomic level precision to hierarchically organized structures reaching up to microns. Nanoscale material properties are profoundly different from their bulk counterparts, and when combined with metamaterial approaches, systems can be engineered with properties unavailable in naturally occurring substances. These effects have applications from nanoelectronics, to thermoelectrics, to nanoparticle-based cancer therapies. However, the full capabilities of these materials have not yet been realized due to the difficulty of studying functional nanosystems. In this thesis, I study the properties of nanoscale materials at their intrinsic length and time scales, via the diffraction of extreme ultraviolet (EUV) beams, generated coherently using tabletop high harmonic generation. First, using periodic nanoline gratings, I systematically explore size- and spacing-dependence in the ultrafast cooling of nanoscale heat sources. We find that, though nanoscale heat sources generally cool much slower than the bulk diffusive prediction, they can be brought within a factor of two of the efficient, diffusive prediction simply by bringing them closer together. I then use similar nanoline transducers to study nanoscale acoustic waves, and thus extract the elastic tensor of isotropic, amorphous films, down to 11nm thickness. We find that hydrogenating these films to a critical level of broken bonds causes a divergence towards incompressible behavior, which could also mitigate thickness-dependent changes in the films’ mechanical properties. I next demonstrate our technique can measure thermal and elastic dynamics in 3D silicon metalattices, a promising thermoelectric material. To measure even more general samples, I finally extend this EUV nanometrology technique into a non-contact modality. First, I implement an optical transient grating excitation to study micron-scale thermal transport in 2D nanoparticle-molecular arrays. We measure an effective thermal conductivity for the arrays that is three orders of magnitude lower than bulk gold. Second, I participate in EUV transient grating experiments at the FERMI free electron laser to directly excite deep nanoscale thermal and elastic dynamics, and design a similar experiment for tabletop EUV light sources.
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Department of Physics
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University of Colorado Boulder
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