High-temperature neutron irradiation effects on CVD-diamond, silicon and silicon carbide

Diamond films on single-crystal silicon and polycrystalline silicon carbide substrates were neutron-irradiated in JMTR up to a fluence of 8.1 × 1024 n/m2 (E > 0.1 MeV) at 725 °C. Lattice parameter expanded 0.39%, 0.20–0.27%, 0.001%, in diamond, silicon carbide and silicon, respectively. Raman peaks of diamond at 1335 cm−1 was weakened and shifted 8 cm−1 after the irradiation, but after annealing up to 1500 °C relatively large peak at 1329 cm−1 and the peaks corresponding to disordered graphite were observed. Lattice parameter of diamond slightly decreased from the irradiation temperature and up to 1300 °C, but was not recovered completely after annealing at 1400 °C. Sp2 clusters may be induced during irradiation and grow by annealing. The change in lattice parameter of silicon was negligible but broad scattering around 25° (2θ/Cu Kα) was observed, indicating the presence of amorphous region. Mobility of monovacancy at room temperature, different from those of diamond and silicon carbide, should be a cause of different irradiation response of silicon.