Irradiation effects in a-SiC studied via RBS-C, Raman-scattering and surface profiling
We have investigated the defect accumulation and amorphization in -SiC (6H) during 50-900 keV bombardment with N-, Na-, Xe- and Au-ions at 80 K. A combination of Rutherford backscattering spectroscopy in channeling geometry, mechanical surface profiling and Raman spectroscopy was used to characterize the modified samples. The amorphization of a-SiC takes place in three regimes: point defects are accumulated in the lattice at low irradiation fluences until a critical damage level is reached and a coherent amorphous layer has formed. The critical energy density ranges from 0.3 eV/Å3 (N-ions) to 1.1 eV/Å3 (Au-ions). The corresponding displacement rates of only 0.12 to 0.2 dpa indicate that the chemical short-range order of the crystalline material is at least partly conserved during the crystalline-to-amorphous transition. This is supported by the results of Raman spectroscopy. After high fluence bombardment, the Raman spectre clearly indicate the presence of homonuclear Si-Si- and C-C-bonds, which are not present in the crystalline material. We attributed the appearance of these bonds to the transition from a sp3-bonded network of Si-C4– and C-Si4-tetrahedrons to an "atomically" amorphous structure without chemical short-range order.
