New carbon nitride phase by high-dose N ion implantation in glassy carbon

The possibility for the synthesis of CN compounds by high-dose N implantation of glassy carbon is investigated. The changes in volume and surface morphology and the retained N concentration as a function of ion dose are reported. For both N and C (used as a control), implantation initially induces compaction in the surface region that saturates at a density above 2.6 g/cm3. After formation of this dense surface layer, additional implantation causes the material to expand to accommodate the implanted ions and vacancies formed during the implantation process. For N the swelling is initially linear in fluence up to 5×1017/cm2 with a volume increase of 16 Å3 per added N atom; this is twice the volume per atom in the compacted substrate. Above a dose of 5×1017 N/cm2 the swelling behavior is more complex. A phase change is observed to occur at a dose between 5×1017 and 1×1018/cm2, which is concomitant with at least some of the implanted N being driven to the surface. In addition, micron-sized surface features are seen by scanning electron microscopy, and a significant surface roughening occurs. Ion backscattering spectra have been used to characterize the implanted N profile. The maximum retained concentration was found to be 30 at. %.