Carbonization of polyimide using CO2 laser and femtosecond laser for sensor applications
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Date
2023-10-05Author
Biswas, Ratul Kumar
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Abstract
Laser carbonization is the process of photothermal conversion of polymers rich in aromatic
carbons such as Polyimide (PI) into graphene, via a process called Laser Induced Graphene
(LIG) using a laser as the source of heat and pressure. This process allows the printing of
conductive graphene-circuits on flexible polymeric substrates without chemicals in liquid or
gaseous state and transfer printing process used in other graphene deposition methods. The
Carbon-di-oxide (CO2) laser is most commonly for this process due to the strong absorption of
PI at 10.6 µm. Femtosecond lasers reduce the interaction with the material and include
multiphoton absorption process in dielectrics and polymers allowing both carbonization and
ablation using a single IR laser source.
In this project, the interaction of both CO2 laser and femtosecond laser radiation with PI is
studied and techniques such as laser graphitization and plasma treatment of PI surface were
applied to improve the electrical conductivity of LIG by ~2.6 times and ~51% respectively.
Photothermal models were solved using Finite Element Method to estimate the irradiation
temperatures (400-900 K) of PI and were experimentally validated from threshold conditions.
The temperature estimated was used to study the thin film growth kinetics of LIG using the
Arrhenius model and the activation temperature and energy of formation of LIG from PI were
calculated as 2.35±0.30 x 103 K and 0.20±0.03 eV respectively. Finally, the carbonization of
PI using femtosecond laser radiation was modelled using heat accumulation model and the
multiphoton absorption of laser radiation by PI was used to create ablation which enables
precise cutting without any thermal damage. This technique was used to print a Kirigami inspired strain sensor using a single laser source. Kirigami patterning of PI was used to improve
the sensitivity of strain sensors. Kirigami cuts showed ~3 times better sensitivity to body motions when compared to planar sensors, and femtosecond laser processed LIG showed that
the Gauge Factor was improved by ~4 times than that obtained using CO2 laser due to different
morphology of LIG.