Elsevier

Materials Letters

Volume 307, 15 January 2022, 131097
Materials Letters

Graphene growth kinetics for CO2 laser carbonization of polyimide

https://doi.org/10.1016/j.matlet.2021.131097Get rights and content

Highlights

  • The crystallite size of graphene obtained from laser carbonization of Polyimide was controlled by varying laser fluence and scan speed.

  • Laser irradiation temperature was calculated by photothermal model in COMSOL and controlled by varying laser fluence.

  • Laser irradiation time was controlled by varying laser scan speed.

  • Growth rate of graphene was formulated using Arrhenius classic kinetic model from which the activation energy of laser carbonization from Polyimide was calculated.

Abstract

The study of growth kinetics of graphene on Polyimide upon carbon-dioxide (CO2) laser irradiation enables optimisation of crystal size for maximum electrical conductivity. We report the first study on growth kinetics of graphene produced by laser carbonization of polyimide using the Arrhenius equation. The peak irradiation temperature (Tirr) for each laser fluence was calculated from the photothermal model, solved by Finite Element Analysis in COMSOL software. Studies of the Raman spectra of the laser induced graphene revealed that the crystallite size increases with decreasing scan-speed at constant laser fluence. The barrier activation energy for graphene growth was found to be 0.20 ± 0.03 eV.

Introduction

Laser carbonization is a promising method for large scale patterning of graphene on Polyimide (PI), for manufacturing which involves photothermal conversion of PI to graphene, called Laser Induced Graphene (LIG), by irradiation of Carbon-di-oxide (CO2) laser [1], [2], [3], [4]. LIG has been used in flexible sensor devices such as urea, glucose sensors, and energy storage applications such as supercapacitors [3], [4]. However, LIG is mostly limited to nanoflakes having edge-defects [5] inhibiting its intrinsic electrical conductivity and limiting its application in flexible electronics. Each laser pulse at a constant fluence, should thermalize PI with controlled kinetics, and graphene growth from PI follows the Arrhenius classic kinetic equation as a function of temperature and time [6]. Since both irradiation temperature and time are governed by the laser fluence and scan-speed, the Arrhenius kinetic parameters such as growth barrier activation energy and pre-exponential coefficient can also be calculated for this process to control LIG crystallite size. Kinetic parameters for graphene growth have been calculated previously, for other thermally activated processes such as Chemical Vapour Deposition, where the barrier energy for growth on copper calculated from the Arrhenius plot is 2.6 ± 0.5 eV [7]. A Molecular Dynamics study of laser carbonization has shown that the formation of crystalline graphene clusters from PI occurs without a catalyst at very low activation temperature (>2400 K or 0.207 eV), due to generation of high pressure (∼3 GPa) [8], [9]. Here, we have estimated the peak laser irradiation temperature (Tirr) from photothermal model using the Finite Element Method in COMSOL software, laser irradiation time (tirr) from scan-speed [10], and the average crystallite size (La) from the defect ratio in the Raman spectra of LIG [11] produced at varying scan-speed under constant laser fluences. Such parameters will enable the appropriate scan-speed to be derived for varying laser fluence to obtain maximum crystallite size of graphene.

Section snippets

Experimental procedure

Laser carbonization was performed with GEM 6O Coherent DEOS CO2 laser system of wavelength (λ) 10.6 µm, integrated with a DEI PDG-2510 Digital Pulse Generator. 127 µm PI film (Dupont KaptonR HN) with dimension 25 mm × 10 mm was cleaned with ethanol and de-ionized (DI) water in an ultrasonic apparatus and rinsed for 10 min followed by drying. The laser was focused by a lens of focal length 100 mm onto the film.

Single laser pulse carbonization was performed to measure the spot-radius (ɷ0) of

Structural characterization of carbonized tracks

The diameter of single pulse carbonized features and LIG linear tracks were measured using a Olympus BX60M optical microscope by averaging along two perpendicular axes. The average crystallite size was calculated from Raman spectroscopy of LIG measured over 5 points through the central positions of each track (Fig. S2) measured by RENISHAW inVia Raman Spectrometer using 532 nm excitation laser.

Modelling of laser irradiation temperature (Tirr)

Tirr was estimated using a Finite Element Analysis (FEA) software package-COMSOLR for a time-variant Gaussian equation for laser source at position (x, y) written as [12]:Qx,y=2F·αλπ/ln2τp.1-R.[exp-2xω02-4ln2t-tctP2]expα(λ)yWhere, absorption coefficient (α(λ)) and reflectivity (R) are given by [12]:αλ=4πκλ,R=1-n2+κ21+n2+κ2Where n and κ are refractive index and extinction coefficient of Polyimide, respectively shown in Table 1, and reference time, tc = 2tp. Single pulse fluence (F) given by [13]:

Calculation of spot-size, threshold laser fluence, and irradiation temperature

Single pulses of CO2 laser created carbonized spots with diameter increasing with laser power (Fig. 1 a–f). The relation between ω0 and P is given by equation [13]:D2=2ω02[lnP-lnPTh]Where PTh is threshold laser power for single pulse. ω0 and PTh were calculated from the slope and x-intercept of plot D2 vs ln(P) (Fig. 1g) and were found to be 240.167 µm and 0.489 W respectively.

The single pulse threshold fluence (FTh) was calculated using equation (3) and evaluated as 5.4 × 103 mJ/cm2.

The peak

Conclusion

This article describes the first study of growth kinetics of graphene from laser carbonization of polyimide using the Arrhenius equation. The peak temperature for each laser fluence was calculated using a photothermal model implemented by Finite Element Analysis and irradiation time was controlled by varying scan-speed. The peak activation energy for graphene crystal growth was found to be 0.20 ± 0.03 eV and peak activation temperature was found to be 2.35 ± 0.30 × 103 K which is close to the

CRediT authorship contribution statement

Ratul Kumar Biswas: Writing – original draft, Investigation, Methodology, Formal analysis. Rajani K. Vijayaraghavan: Investigation. Patrick McNally: Investigation. Gerard M. O’Connor: Supervision, Resources, Writing – review & editing. Patricia Scully: Supervision, Visualization, Writing – review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This publication has emanated from research conducted with the financial support of Science Foundation Ireland under Grant number 16/RC/3872 and 20/FFP-P/8627. For the purpose of Open Access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission. Ratul Biswas acknowledges the receipt of a Fellowship from the College of Science & Engineering at NUI Galway. The contribution from EU INTERREG project EAPA 384 2016,

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