Monitoring laser-induced microstructural changes of thin film hydrogenated amorphous carbon (a-C : H) using Raman spectroscopy

Thin films (10 - 150 nm) of a-C:H on glass and silicon substrates have been studied utilizing a confocal micro Raman system using an argon ion laser (514.5 nm) and helium-neon (He-Ne) laser (637.8 nm) for sample excitation. The relationship between the measured Raman spectrum and the film thickness, substrate material, laser intensity and exposure time, have been assessed. From this, the dominant variables have been identified. Microstructural changes in the form of the growth of graphitic crystallites, similar to that of thermally annealed samples, have been observed. For longer laser irradiation exposure times this graphitic component decreases, revealing an amorphous carbon structure, possibly containing some tt tetrahedrally-bonded carbon. Optical microscopy and topographical atomic force microscopy also highlight the range of laser ablated conditions that result. (C) 1998 Elsevier Science S.A. All rights reserved.