SIMBAD references

Hydrogenated amorphous carbons, a-C:H, can incorporate a variety of heteroatoms, which can lead to interesting effects. We investigate the doping of interstellar a-C:H grains with, principally, Si, O, N and S atoms within the astrophysical context. A search of the literature on doped a-C:H reveals a number of interesting phenomena of relevance to astrophysics. X dopants in a-C:H:X materials can affect the sp³/sp² ratio (X=Si, O and N), lead to blue photoluminescence (undoped or X=N), induce ferromagnetic-like behaviour (X=N and S) or simply be incorporated (depleted) into the structure (X=Si, O, N and S). Si and N atoms could also incorporate into fullerenes, possibly forming colour-centres that could mimic diffuse interstellar bands. Doped a-C:H grains could explain several dust-related conundrums, such as: ``volatile'' Si in photo-dissociation regions, S and N depletion in molecular clouds, blue luminescence, some diffuse interstellar bands and ferromagnetism in carbonaceous grains.