Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

We present recent progress in the field of ion-implanted diamond-like carbon thin films. The phase transformation mechanism from an insulating sp3 matrix into a well-conducting sp2-rich graphite-like carbon phase by means of focused ion beam irradiation is investigated. The resistivity decrease is compared for the implantation of different ion species at 30 keV. It is shown that the sp3-to-sp2-conversion saturates at an Ga+ ion fluence of approximately 1 x 1015 cm-2. Nevertheless, further ion irradiation yields a continued drop of the film resistivity. Raman spectroscopy and transmission electron microscopy analysis show that ion-induced ordering proceeds at high fluences above the sp3-to-sp2-conversion saturation. This ordering can be considered as a microstructural transformation into a more graphite-like arrangement. We show that the increase of atomic ordering correlates with the local energy density deposited during the ion impact and furthermore, the resistivity lowering correlates with the degree of graphitization. The ion-induced phase transformation of diamond-like carbon layers is thus proposed to comprise a rehybridization stage (sp3-to-sp2-conversion), driven by nuclear collisions, and a rearrangement stage (graphitic ordering) that is thermally driven by the ion impact.