The impact of strain and chemical functionalization on two-dimensional materials

Two-dimensional (2D) materials, such as graphene and transition metal dichalcogenides (TMDCs), have emerged as promising candidates for flexible electronics, optoelectronics, and energy storage devices due to their exceptional electronic, optical, and mechanical properties. This dissertation investigates strain engineering and chemical functionalization of 2D materials, focusing on their impacts on electrical properties, surface energy, and device performance. Conventional silicon-based electronics face intrinsic challenges, including short-channel effects, high leakage currents, and limited mechanical flexibility, which restrict their scalability and adaptability for next-generation technologies. Similarly, organic semiconductors offer mechanical flexibility but suffer from low electron mobility and poor scalability. To overcome these limitations, 2D materials provide unique opportunities due to their atomic thinness, high elastic strain limits, and tunable electronic structures. This dissertation explores strain engineering as a tool to precisely modulate band structures, work functions, and carrier mobilities in 2D materials. It demonstrates the fabrication of a stretchable MoS2 transistor based on wrinkled 2D heterostructures, showcasing its mechanical flexibility and strain-tunable band gap without compromising performance. Raman and photoluminescence studies confirm strain-induced band gap modulations and threshold voltage shifts, enabling applications in wearable electronics. This study further explores the effects of strain on work function (WF) shifts in 2D materials using Kelvin Probe Force Microscopy (KPFM). The results reveal strain-tunable WF modulations in materials such as WSe2, WS2, and MoS2. The observed modulations exhibit distinct trends across materials, reflecting differences in their band structures and providing valuable insights into the development of straintronics based on 2D materials. Additionally, this work examines surface energy modulation of hydrogenated and fluorinated graphene through contact angle measurements and Fowkes’ theory. Results highlight how volatile organic compound (VOC) adsorption affects wettability, while chemical functionalization enables hydrophilic-to-hydrophobic transitions, supporting applications in biosensing, anti-corrosion coatings, and selective adsorption systems. This dissertation offers a comprehensive analysis of the effects of mechanical strain, chemical functionalization, and substrate interactions on the physical properties of 2D materials and their device performance. By integrating experimental observations with theoretical modeling, it establishes a framework for designing functional 2D interfaces tailored for quantum devices, energy-efficient electronics, and bio-integrated systems.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Kim, Hyunchul

Contributors dc:contributor

• van der Zande, Arend M
• Miljkovic, Nenad
• Tawfick, Sameh
• Diao, Ying

• 2D materials
• strain-engineering
• chemical functionalization
• stretchable electronics

Statement dc:rights

• Copyright 2025 Hyunchul Kim

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129527

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129527