Raman properties stoichiometry and the hardness of hydrogenated amorphous carbon

Abstract

Results of a systematic investigation of the Raman, hardness, and resistivity properties of sputtered amorphous carbon films on silicon substrates for hydrogen stoichiometries between 14% and 39% are presented. Frequency shift and line broadening effects of the Raman active graphite-like vibrations are consistent with a model of both harness and strain present in the amorphous network being independently controlled by the unprotonated sp3 carbon-carbon bonding fraction and the hydrogen concentration. Comparison to constraint counting models for covalent random networks indicates that the hardness of hydrogenated amorphous carbon follows the degree of network strain. We find no evidence for phonon confinement effects in micro crystals consistent with a random network structure without predominating microcrystals. Resistivity data indicate that the vibrational properties are largely independent of strong variations in the electronic properties with stoichiometry.