Monocrystalline samples were bombarded with clusters of C (1 to 8 atoms) and Ge (1 to 3 atoms), to fluences of up to 3 x 1016/cm2. The energy varied from 0.2 to 4MeV/atom. The resultant defect concentration profiles were measured by means of channelling Rutherford back-scattering spectrometry. The damage at the end-of-range of the particles (where the cluster fragments had straggled far apart) was independent of the cluster size. However, the defect concentration in the first few 100nm below the sample surface depended sensitively upon the size of the molecule. Up to a size of about 6, the swift C clusters (where electronic stopping predominated) produced fewer defects per incident constituent than did single C atoms with the same velocity. In the case of larger C clusters, the defect production per atom was increased. The slower polyatomic Ge particles exhibited a marked increase in defect production close to the sample surface. This enhancement increased strongly with cluster size, but decreased at higher energies. A radius of interaction (between individual fragment tracks) of one cluster could be deduced from the shape of the defect profile.

M.Doebeli, F.Ames, R.M.Ender, M.Suter, H.A.Synal, D.Vetterli: Nuclear Instruments and Methods in Physics Research B, 1995, 106[1-4], 43-6