In Situ Study of the Temperature Dependence of Irradiation-Induced Amorphization in A-Sic
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ABSTRACT Ion-beam-induced amorphization in single crystal a-SiC has been studied as a function of temperature. Specimens have been irradiated with 1.5 MeV Xe' ions over the temperature range from 20 to 475 K using the HVEM-Tandem Facility (ANL), and the evolution of the amorphous state has been followed in situ in the HVEM. Specimens also have been irradiated at 170, 300, and 370 K with 360 keV Ar' ions, and the damage accumulation process followed in situ by Rutherford backscattering spectroscopy/channeling using the dual beam facilities at the Ion Beam Materials Laboratory (LANL). At 20 K, the displacement dose for complete amorphization is 0.25 dpa and increases with temperature in two stages. The activation energy associated with the simultaneous recovery processes above 100 K is 0.12 ± 0.02 eV. The critical temperature above which amorphization does not occur is 485 K under the 1.5 MeV Xe' irradiation conditions. Ion channeling results suggest that the rate of simultaneous recovery increases with temperature only above a critical damage level. Raman spectroscopy indicates that rapid chemical disordering occurs during irradiation. INTRODUCTION Silicon carbide (SiC) is an important technological material with high-temperature semiconducting properties, high thermal conductivity, high-temperature stability, extreme hardness, and chemical inertness. Because of its small neutron capture cross-section, it also is a candidate material for structural components in fusion reactor systems. Electronic device fabrication, long-term performance in nuclear environments, and ion-beam modification of hightemperature structural components will require detailed understanding of the kinetics of defect accumulation and amorphization in SiC. There are over 100 polymorphs of SiC that exist; however, cc-SiC (6H polytype) and 3-SiC (3C polytype) are of the most technological interest and readily amorphize under ion-beam irradiation at room temperature [1]. Electron-beam-induced amorphization in ct-SiC [2-4] and 13-SiC [5] also has been studied, and chemical disordering apparently plays an important role in amorphization under electron irradiation [4,5]. In investigations of the temperature dependence of amorphization in a-SiC [2,3] and P3-SiC [5] under electron irradiation, the dose for complete amorphization increases with temperature in two stages. Above 200 K in cc-SiC and 250 K in 13-SiC, the dose for complete amorphization rises rapidly, and the critical temperature, T,, above which amorphization cannot be induced is estimated to be 290 K [2] and 340 K [5], respectively. We recently studied amorphization in P3-SiC under 1.5 MeV Xe+ ion irradiation and reported T. to be 498 K [6]. The activation energy for simultaneous recovery processes in P3-SiC was estimated to be 0.1 eV [6]. The present paper extends this investigation to the temperature dependence of amorphization in ct-SiC under ion irradiation and to studying the disordering 351
Mat. Res. Soc. Symp. Proc. Vol. 398 ©1996 Materials Research Society
process using in situ R
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