Surface characterisation of Ga+ ion implanted ta-C thin films

Abstract

Samples of thin film (d∼40nm) tetrahedral amorphous carbon (ta-C), deposited by filtered cathodic vacuum arc (FCVA), have been implanted with Ga+ at ion energy E = 20 keV and ion doses D=3.1014÷3.1015 cm-2. The induced structural modification of the implanted material results in a considerable change of its optical properties, best manifested by a significant shift of the optical absorption edge to lower photon energies. This shift is accompanied by a considerable increase of the absorption coefficient (photo-darkening effect) in the measured photon energy range (0.5÷3.0 eV). These effects could be attributed both to additional defect introduction and increased graphitization, as well as due to Ga colloids formation, as confirmed by electron microscopy analysis. Further nano-scale structural and electronic properties characterisation of the Ga+ implanted films has been carried out here using conductive atomic force microscopy (C-AFM) measurements. The observed properties modification results from the high concentration of introduced Ga+ atoms, which is of the order of those for the host element. The obtained optical contrast (between implanted and unimplanted film material) could be made use of in the area of high-density optical data storage by using focused Ga+ ion beams.