An investigation was made of defect accumulation and amorphization in -phase (6R) material during bombardment with 50 to 900keV ions of N, Na, Xe or Au at 80K. Rutherford back-scattering spectroscopy in the channelling geometry, mechanical surface profiling and Raman spectroscopy were used to characterize the samples. It was found that amorphization occurred in stages. Point defects first accumulated in the lattice, at low fluences, until a critical damage level was reached and a coherent amorphous layer formed. The critical energy density ranged from 300eV/nm3 for N ions to 1100eV/nm3 for Au ions. The corresponding displacement rates, of only 0.12 to 0.2dpa, indicated that the chemical short-range order of the crystalline material was at least partly conserved during the crystalline-to-amorphous transition. This assumption was supported by Raman spectroscopic results. At high fluences, the Raman spectra clearly indicated the presence of homo-nuclear Si-Si and C-C-bonds which were not present in the crystalline material. The appearance of these bonds was attributed to a transition, from a sp3-bonded network of Si-C4- and C-Si4- tetrahedra, to a so-called atomically amorphous structure which had no chemical short-range order.

J.Conrad, T.Roedle, T.Weber, W.Boise: Nuclear Instruments and Methods in Physics Research B, 1996, 118[1-4], 748-52