ELECTRONIC-PROPERTIES OF ION-IMPLANTED HYDROGENATED AMORPHOUS-CARBON

It has been recently demonstrated that ion bombardment affects the med ium range order parameters in hydrogenated amorphous carbon (HAC), ind ucing graphitic clustering and reducing the hydrogen content. In this frame, the aim of the present work is to put in evidence the strong co rrelations existing between the electronic properties of this type of material and both hydrogen concentration and sp2 to sp3 ratio. The cha nges in the above ratio have been monitored by analysing the complex d ielectric function as obtained by electron Energy Loss Spectroscopy (i n reflection mode) in the range 0-100 eV and by optical spectroscopy i n the range 0-5 eV and comparing the results with those obtained on Ar -implanted HOPG samples. As a consequence of the damage induced by the ion-implantation, the dielectric function shows a strong rearrangemen t of the sigma --> sigma transitions together with a change in the re lative oscillator strengths on going from pure amorphous carbon to the most hydrogenated (40%) one.