The electronic characterization of a type 9A graphene nanoribbon using scanning tunneling microscopy and spectroscopy

This dissertation presents the electronic characterization of a type 9A graphene nanoribbon (GNR) synthesized through a bottom-up solution-based approach and analyzed using scanning tunneling microscopy (STM) and spectroscopy (STS). The study focuses on the structural and electronic properties of this novel GNR variant, which features functionalized end groups designed to facilitate controlled interactions and potential device integration. The GNRs were exfoliated onto hydrogen-passivated silicon (H:Si(100)) substrates using the dry contact transfer (DCT) method in an ultra-high vacuum (UHV) environment. High-resolution STM imaging revealed distinct morphological features, including an average length of 18.25 nm and occasional structural defects attributed to missing phenyl groups. The electronic properties were further investigated using STS, which showed an average bandgap of 2.13 eV, with spatial variations due to quantum confinement effects and the influence of functional end groups. Density functional theory (DFT) calculations predicted a bandgap of 1.4 eV, which increased to 3.71 eV after GW correction, closely aligning with experimental observations. Notably, bilayer GNRs were observed for the first time, demonstrating an unexpected increase in bandgap compared to monolayer counterparts, contrary to theoretical predictions. This phenomenon suggests additional interlayer interactions that warrant further investigation. Moreover, hydrogen depassivation nanolithography (NL) was employed to modify the substrate beneath the GNRs, resulting in selective pinning and local metallic behavior. These findings contribute to the broader understanding of GNR-based nanoelectronics by elucidating the impact of structural modifications on electronic properties. The observed electronic behavior, combined with the stability of the GNRs under nanolithographic modification, underscores their potential for future applications in nanoscale devices. Further research into mixed-dimensional systems incorporating GNRs and transition metal dichalcogenides (TMDs) could yield novel heterostructures with tailored electronic properties for next-generation semiconductor technologies.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Electrical & Computer Engr

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Berg, Abigail W

Contributors dc:contributor

• Lyding, Joseph W
• Zhu, Wenjuan
• Choquette, Kent D
• Sinitskii, Alexander

• graphene
• graphene nanoribbon
• carbon-based materials
• low-dimensional materials
• 2D materials
• scanning tunneling microscopy
• spectroscopy

Statement dc:rights

• Copyright 2025 Abigail W. Berg

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129743

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129743