Nanomechanical and Molecular Studies via Advanced Atomic Force Microscopy

Date of Award

Spring 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering & Materials Science (ENAS)

First Advisor

Schwarz, Udo

Abstract

This thesis explores the application of advanced atomic force microscopy (AFM) techniques to investigate the nanomechanical properties of bulk metallic glasses (BMGs) and the molecular characteristics of cobalt phthalocyanine (CoPc) molecules. By bridging materials science and molecular chemistry, the research contributes to understanding mechanical behavior in disordered materials and the catalytic potential of molecular systems for sustainable energy applications. In the first part, a commercial ambient AFM was employed to study the nanomechanical properties of platinum-based BMGs. Through nanoindentation experiments, stiffness distribution maps were generated from indentation force curves, providing insights into the structural homogeneity of BMGs prepared at varying fictive temperatures. These findings elucidate the relationship between thermal history and mechanical properties, offering pathways for optimizing BMGs for practical applications. The second part focuses on the molecular investigation of CoPc, a molecule with significant catalytic potential for CO2 reduction to liquid fuels such as methanol. Using a home-built tuning fork-based AFM under ultra-high vacuum and cryogenic conditions, several studies were conducted. A novel CO-functionalized tip enabled the visualization of CoPc's inner structure and the extraction of chemical information through 3D-AFM techniques. Further investigations revealed the rotational behavior of t-butyl groups in substituted CoPc when interacting with CO, highlighting their impact on catalytic efficiency. Finally, NH2-substituted CoPc molecules were analyzed to isolate interaction forces between CO and the molecule, excluding substrate and tip contributions. A comparative study with unsubstituted CoPc revealed the influence of NH2 ligands on binding strength and molecular properties. This work advances the use of AFM in probing nanomechanical and molecular interactions, providing a deeper understanding of material homogeneity in BMGs and the catalytic mechanisms of CoPc. The methodologies and findings presented here have implications for designing next-generation materials and catalysts, contributing to the fields of materials science and sustainable energy research.

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