Atomic-scale engineering of 2D materials via scanning tunneling microscopy: Bridging synthesis, characterization, and device integration for post-silicon electronics

The semiconductor industry faces fundamental limitations as silicon-based technologies approach their physical and economic thresholds. Two-dimensional (2D) materials, including graphene nanoribbons (GNRs), coronoids, and transition metal dichalcogenides (TMDs), offer transformative potential for next-generation electronics due to their atomically thin nature, and tunable electronic and optical properties. This dissertation investigates the synthesis, atomic-scale characterization, and device integration of these materials using scanning tunneling microscopy (STM) and spectroscopy (STS) techniques. Graphene nanoribbons are engineered via various liquid phase synthesis methods to attempt precise control over width and edge structure for desirable electronic properties. STM/STS studies reveal that defects are a major issue in standard liquid phase synthesis of GNRs, while integrated iterative strategies demonstrate potential for structural uniformity for scalable device integration. GNR stacks of ribbons with randomly alternating widths and nitrogen endcaps provide an alternative device structure based on 2D materials. Coronoids, cyclic nanographenes with various cavity sizes, are synthesized via programmable head-to-tail cyclization. STM imaging highlights their strain-dependent bandgap modulation and emergent phenomena such as locallized metallic edges and lateral p-n junctions. In a move towards mixed-dimensional systems, the charge density wave (CDW) was observed in the 2D materials 1T-TaS2 was observed and studied at room temperature. Central to this work is the use of STM not only as a characterization tool but as a bridge between atomic scale understanding of 2D materials and functional device engineering based on these materials. The findings provide a roadmap for leveraging STM supported insights to the optimization of material preparation, correlation between structural and electronic properties, and the potential of 2D materials in post-silicon electronics.

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

• Wang, Hanfei

Contributors dc:contributor

• Lyding, Joseph W
• Rakheja, Shaloo
• Zhu, Wenjuan
• Sinitskii, Alexander

• Low-dimensional materials
• post-silicon electronics
• graphene nanoribbons
• coronoids
• transition metal dichalcogenides.

Statement dc:rights

• © 2025 Hanfei Wang

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129767

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129767