Optical Monitoring of Laser-Induced Plasma Derived from Graphite and Characterization of the Deposited Carbon Film

Abstract

Mechanisms of the deposition of carbon thin films by the laser ablation of graphite were investigated by monitoring the plasma emission. Parameters such as electron density, ionization temperature, and vibrational temperature during plasma growth were evaluated as a function of the laser power density and the surrounding atmosphere. Also, Raman spectra of the deposited films were measured so that the particle size can be estimated from the intensity ratio of the Raman bands around 1360 and 1580 cm−1. The increase in power density caused an increase in ionization temperature and vibrational temperature of carbon species in the plasma but a decrease of particle size of the deposited thin films. The existence of 10 Torr of helium as a surrounding atmosphere caused drastic changes in the plasma parameters. The films deposited with helium atmosphere showed a low optical band gap, which indicates heat restructuring of ablated graphite particles in the hot plasma. The results can be explained with a simple model of laser ablation and the subsequent interaction of ablated particles with the laser-induced plasma.