New Understanding of Nanoscale Thermal Transport and Mechanical Properties Uncovered Using Coherent Extreme Ultraviolet Light

Knobloch, Joshua Lee

Graduate Thesis Or Dissertation

New Understanding of Nanoscale Thermal Transport and Mechanical Properties Uncovered Using Coherent Extreme Ultraviolet Light Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/kw52j921j

Abstract

Advances in nanofabrication capabilities have pushed feature dimensions of complex systems into the few-nanometer range and below; however, at these length scales, conventional macroscopic models fail to accurately describe their physical behavior and traditional metrology tools struggle to precisely measure their functional properties. Fortunately, tabletop sources of ultrafast, coherent extreme ultraviolet (EUV) pulses via high harmonic generation have nanometer wavelengths and femtosecond pulse durations which are well-matched to the intrinsic length- and time-scales of energy transport at the nanoscale. Here, I demonstrate that a novel dynamic scatterometry technique—based on these coherent EUV beams—is a versatile route for uncovering nanoscale influences on the thermal transport behavior and mechanical properties of nanostructured materials. Using this tool, I map non-diffusive thermal transport away from 1D- and 2D-confined nanoscale heat sources on bulk substrates, validating the counter-intuitive dependence of heat source geometry on the thermal dissipation efficiency. Moreover, these results made it possible to develop and benchmark a general mesoscopic model—based on a phonon hydrodynamic transport equation—and fundamental atomistic calculations, to form a more complete picture of phonon transport. Additionally, I use this EUV scatterometry tool to nondestructively extract the full elastic tensor of ultrathin, low-k dielectric films, down to 5nm in thickness, finding that both the amount of doping and presence of surfaces induces substantial alterations in the film’s mechanical properties. Additionally, I extend this EUV-based technique to probe the mechanical, structural, and thermal properties of complex, 3D nanostructured metalattices that exhibit controllable thermal, magnetic, and electronic properties. By measuring the acoustic wave dispersion, this technique extracts Young’s modulus, filling fraction, and thickness of metalattices, which agrees with results from other techniques and bulk theoretical calculations. However, these measurements simultaneously uncover that the thermal transport does not follow bulk predictions. Finally, I collaborated on extending this scatterometry technique to the novel modalities of dynamic EUV imaging and EUV transient grating excitation to capture spatial resolution in isolated structures and probe transport in a more general set of materials. These unique tools enrich our understanding of nanoscale behavior for applications in next-generation nano- and quantum technologies.

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