Instability of hydrogenated amorphous carbon films towards defect creationat high disorder

We report a complete characterization of hydrogenated amorphous carbon (a-C :H) thin films through Raman spectroscopy, photothermal deflection spectros copy, and mechanical studies. The interpretation of the optical absorption data within the Dasgupta's model offers an estimate of the disorder intensi ty through a characteristic energy scale of the model. The vibrational data (Raman spectra) and the stress data together with the optical absorption d ata give strong evidence for a sharp transition between a low disorder stat e dominated by aromatic rings and a strong disorder state likely in keeping with the creation of some topological defects, such as odd rings. (C) 2001 American Institute of Physics.