Pulsed laser deposition of thin carbon films in a neutral gas background

We studied carbon film deposition using a laser-produced plasma, in argon and helium background gas, at pressures between 0.5 and 700 mTorr. A Nd:YAG, 370 mJ, 3.5 ns, at 1.06 μm, operating at 10 Hz, with a fluence of 6.7 J cm ^-2 was used. The laser plasma was characterized using space resolved OES and a fast response Faraday cup. The resulting carbon films were analysed using AFM, Raman spectroscopy, XPS and SIMS. The structural properties of the carbon films were found to be strongly correlated with the laser carbon plasma composition. Films with a relatively high content of sp³, characteristic of DLC, were obtained at pressures below 200 mTorr. For these conditions the characteristic carbon ion energies in the expanding laser plasma were of the order of 100 eV. At higher pressures sp² bonds, associated with amorphous carbon, were dominant, which coincides with a high content of C₂ molecules in the laser plasma, and a characteristic carbon ion energy around 20 eV.