Graphene-based heterostructures for strain-tunable and mechanically flexible electronic sensors

Zhang, Zhichao

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https://hdl.handle.net/2142/124622 Copy

Description

Title

Graphene-based heterostructures for strain-tunable and mechanically flexible electronic sensors

Author(s)

Zhang, Zhichao

Issue Date

2024-01-26

Director of Research (if dissertation) or Advisor (if thesis)

Nam, SungWoo

Doctoral Committee Chair(s)

Nam, SungWoo

Committee Member(s)

• van der Zande, Arend
• Cai, Lili
• Diao, Ying

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Graphene
• Thin films
• Heterostructure
• Sensors

Abstract

Since its isolation in 2004, graphene has introduced a new field of research in 2D materials. It attracted wide attention among researchers due to its exceptional properties, including its ultrathin thickness, outstanding mechanical properties, remarkable electrical properties with high conductivity, and excellent optical transparency. Consequently, graphene has found widespread application in various sensing technologies, such as photodetectors, temperature sensors, gas sensors, pressure sensors and biosensors. However, its relatively low tunability in molecular structure, lack of active sites, and low optical absorption have constrained its use as a sensing medium. Decorating the surface of graphene with another functional layer or creating a composite based on graphene is an effective way to enhance the sensitivity of graphene-based sensors and expand their applications. In this thesis, I investigate graphene heterostructures with active layers, including organic conjugated polymers and metal nanoparticles, and developed various types of sensors based on the hybrid materials. I first created a heterostructure based on graphene and a thin film of organic conjugated polymer, and demonstrated its application in a stretchable photodetector. The built-in electrical field at the interface between graphene and polymer was proven to contribute to a high photoresponsivity and a fast photoresponse. The stretchability and flexibility of the photodetector were achieved by transferring the heterostructure onto a pre-stretched elastomer substrate. After releasing the pre-strain, wrinkles formed in the heterostructure. The devices not only possess good mechanical stretchability and stability, but also exhibit enhanced photoresponsivity after wrinkling. The modulation of heterostructure energy diagram and polymer backbone alignments by local mechanical strain were investigated, where it was found to have a positive effect by reducing barriers for charge transfer. I then developed a sensor array based on metal nanoparticles-functionalized graphene for gas sensing. Metal nanoparticles were formed on top of graphene film by thermal dewetting of metal thin films, and were proven to tune the conductivity of the graphene channel through electrical doping. The mechanism of the sensors in response to a variety of analytes was investigated in detail, and it was attributed to both electrical sensitization and chemical sensitization effects. The device showed competitive sensitivity and response time, along with excellent repeatability and selectivity. In the last section, I demonstrated a wireless temperature and humidity sensor based on metal nanoparticles-decorated graphene channel. Different types of metal nanoparticles were selected to ensure the effective adsorption and dissociation of water molecules. The size of the metal nanoparticles was optimized by controlling the deposition conditions through evaporation. I also applied a specific design of the graphene channels to separate the signals from temperature changes and humidity changes. The sensor was integrated with a wireless circuit board and was packaged for real in-line measurement in a drying testbed. This thesis illustrates various types of heterostructures based on graphene and their related applications in sensors. I believe that our approaches to depositing functional layers on graphene and forming heterostructures with different topographies contribute to the research community, providing new platforms for enhancing the performance of graphene sensors.

Graduation Semester

2024-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2024 Zhichao Zhang

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