Abstract
Graphene is a two-dimensional carbon material with excellent conductivity, flexibility, and strength. It is widely used in electronics, energy, and sensing. However, traditional fabrication methods face limitations in efficiency, scalability, and substrate compatibility. Mechanical exfoliation yields high quality but low output. CVD offers large-area graphene but is slow, requires high temperatures, and weakens durability after transfer. Liquid-phase exfoliation is scalable but struggles with dispersion and layer control. Laser-induced graphene (LIG) provides a direct, low-cost, and repeatable method for fabricating graphene on carbon-rich, flexible substrates, with strong bonding and improved durability. Nevertheless, LIG quality is highly dependent on substrate selection and processing parameters. Inappropriate substrates can compromise mechanical strength and thermal resistance, while poor laser settings may lead to structural damage or reduced conductivity. Various substrates have been explored, including polyimide (PI), Kevlar composites, cellulose-based materials, and Nomex paper—the latter proving ideal due to its superior mechanical and thermal stability. The machining parameters includes laser properties and scanning strategies, while the laser power, scanning speed, and scanning paths are the most important parameters when the beam and focus characteristics are optimal for a defined continuous-wave CO2 laser source.To address this, this study starts with a theoretical reference of the graphitization threshold of the Nomex paper during LIG production. A series of experiments were conducted to verify this theoretical reference and further study the effect of laser parameters on LIG formation. The experiments evaluated the effects of different laser powers and scanning speeds on material behaviours. Since laser power and scanning speed together determine the laser energy density, the material behaviors were further classified into four types based on variations in energy density: Partly LIG, Desired LIG, Protruded LIG, and Broken LIG. However, laser energy density is not enough to fully characterize the laser processing. Although different combinations of laser power and scanning speed can result in the same energy density, they may lead to distinct physical effects. Therefore, we further investigate the respective effects of scanning speed and laser power on surface morphology, void size, defect level, and conductivity. In addition, the effects of laser scanning path strategies (0°,45°,90°, linear scanning) are investigated in terms of electrical, thermal, and mechanical performances. To validate the effectiveness of the proposed strategy, a Nomex-paper based LIG sensor is produced and integrated with fracture correction tools for simultaneous temperature and swelling monitoring. The sensor has superior performance in terms of surface morphology, conductivity, defects, and mechanical stability.
The findings not only illustrate the potential of Nomex-paper-based LIGs for flexible electronic devices, but also provide practical references for future LIG-based sensor studies. Besides, the sensor prohibits high durability and solvent-free fabrication, which can reduce the material waste, enable eco-friendly flexible electronics, and support the concept of sustainable manufacturing. In summary, this work offers a simple, cost-effective, and efficient solution for graphene-based device manufacturing. Its integration with flexible electronics highlights its potential for applications in wearable devices and human health monitoring.
| Date of Award | 15 Nov 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Sze Shin Low (Supervisor) & Haonan Li (Supervisor) |