Pulsed laser deposition of carbon films in low pressure neutral gas background

We have investigated Pulsed Laser Deposition (PLD) of thin carbon films using a graphite target, in a low pressure Argon gas background. Raman spectroscopy based structural analysis of the films shows a correlation between films properties and pressure of the buffer gas background. The morphology of the resulting thin films was characterized with Raman spectroscopy. Time resolved Optical Emission Spectroscopy (OES) observations indicate that, at the substrate position, and for background pressures above 80 mTorr, the dominant species in the expanding carbon plasma are C2 molecules. This is also consistent with Faraday cup observations, which show a strong decrease in the carbon ions content, as the pressure is increased. Our main result is the observation of a sharp transition in the film morphology, around 300 mTorr, from Diamond like Carbon (DLC) at lower pressures, to amorphous Carbon at higher pressures.