Date of Award

Summer 8-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Program/Concentration

Physics

Committee Director

Yuan Zhang

Committee Member

Alex Gurevich

Committee Member

Hani Elsayed-Ali

Committee Member

Sylvain Marsillac

Committee Member

Guijun Wang

Abstract

Emerging molecular electronics, molecular devices, and carbon-based nanotechnologies increasingly rely on the precise control of molecular structures and interfaces at the atomic scale. Advancing these systems requires experimental techniques capable of resolving atomic structures, quantifying molecular behavior, and revealing the mechanisms governing nanoscale assembly. Scanning probe microscopy uniquely provides these capabilities by combining atomic-resolution imaging with local spectroscopy and manipulation. This dissertation employs ultra-high-vacuum low-temperature scanning tunneling microscopy (UHV-LT-STM) and qPlus atomic force microscopy (qPlus AFM) to address three complementary challenges: (i) atomic-scale characterization of complex supramolecular architectures, (ii) quantitative investigation of mechanically induced conformational switching of individual molecules, and (iii) elucidation of the growth mechanisms governing graphene nanoribbons (GNRs) on surfaces.

The first study demonstrates the capability of UHV-LT-STM to directly characterize giant metallo-macrocycles and their surface organization with atomic resolution. As molecular systems become increasingly complex, conventional characterization methods provide primarily ensemble-averaged information. UHV-LT-STM overcomes these limitations by resolving individual supramolecular structures, establishing single-molecule microscopy as an essential tool for validating sophisticated molecular architectures.

The second study establishes a quantitative framework for understanding the mechanical response of individual TBrPP-Co(II) molecules on Au(111). Using three-dimensional force spectroscopy with qPlus AFM at 4.6 K, complete force and interaction energy landscapes governing molecular switching were reconstructed. Quantitative thresholds of 38 ± 4 meV and 96 ± 8 pN demonstrate that long-range tip-induced van derWaals interactions alone can mechanically deform a molecule and induce conformational switching while preserving its adsorption site.

The final study elucidates the atomic-scale growth mechanism of 15-armchair graphene nanoribbons (15-AGNRs) on Au(111). By tracking the evolution from molecular precursors to fully formed nanoribbons, the study reveals that the Au(111) herringbone reconstruction governs nanoribbon orientation, while the anisotropic geometry of the nanoribbons directs pentacene (5 P) adsorption, providing insight into hybrid organic-carbon interfaces.

Together, these studies establish scanning probe microscopy as a comprehensive platform for investigating functional molecular systems and provide a foundation for the rational design of future molecular materials, nanoscale electronic devices, and molecular technologies.

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DOI

10.25777/nbwc-8863

ISBN

9798193216223

ORCID

0000-0002-6003-6801

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