Finite Element Analysis of Conductive Carbon-Based Thin Films Modified by Ultrashort Pulsed Laser Processing
Abstract
A COMSOL Multiphysics simulation study on the relationship between ultrashort pulsed laser process parameters and the thermal modification of conductive carbon-based (e.g., graphite, graphene) thin films is presented in this thesis. The research objective is to utilize the theoretical models of heat transfer in thin films with finite element analysis (FEA) techniques to understand the impact of laser process parameters on the heat affected zone (HAZ) profile when an ultrashort pulsed laser beam strikes a thin conductive carbon film deposited on a polymer substrate. The goal is to be able to anneal or ablate the carbon-based films without causing thermal or structural damage to the underlying substrate. The laser process parameters include wavelength, pulse width, pulse energy, and beam diameters. In this study, the two-temperature model (TTM) and multi-temperature model (MTM) are examined in detail for different types of graphene layered films. The simulation experiments demonstrate that TTM is a suitable model for highly oriented pyrolytic graphite (HOPG) and reduced graphene oxide (rGO) films, whereas MTM is more appropriate for modeling single layer graphene. The impact of laser wavelength on surface annealing and ablation on graphite (HOPG) and graphene derivative (rGO) films on different substrates is explored in greater detail. The simulation results are compared with experimental observations reported in the published literature and found to be a realistic reflection of the physical processes. The FEA study provides the groundwork for using ultrashort laser pulses to anneal carbon-based conductive films and electrodes, micromachine printed films to remove excess material, and to reduce the thickness of functional layers. Furthermore, laser thermal processing represents an environmentally benign method of creating a wide variety of single-use disposable electrical and electrochemical sensors for healthcare, food safety inspection, intelligent packaging, environmental monitoring, and public security.