Recrystallization of hexagonal silicon carbide after gold ion irradiation and thermal annealing

Abstract

International audienceSilicon carbide (SiC) single crystals with the 6H polytype structure were irradiated with 4.0-MeV Au ions at room temperature (RT) for increasing fluences ranging from 1 x 10(12) to 2 x 10(15)cm(-2), corresponding to irradiation doses from ~0.03 to 5.3 displacements per atom (dpa). The damage build-up was studied by micro-Raman spectroscopy that shows a progressive amorphization by the decrease and broadening of 6H-SiC lattice phonon peaks and the related growth of bands assigned to Si-Si and C-C homonuclear bonds. A saturation of the lattice damage fraction deduced from Raman spectra is found for ~0.8 dpa (i.e. ion fluence of 3 x 10(14)cm(-2)). This process is accompanied by an increase and saturation of the out-of-plane expansion (also for ~0.8 dpa), deduced from the step height at the sample surface, as measured by phase-shift interferometry. Isochronal thermal annealing experiments were then performed on partially amorphous (from 30 to 90%) and fully amorphous samples for temperatures from 200 degrees C up to 1500 degrees C under vacuum. Damage recovery and densification take place at the same annealing stage with an onset temperature of ~200 degrees C. Almost complete 6H polytype regrowth is found for partially amorphous samples (for doses lower than 0.8 dpa) at 1000 degrees C, whereas a residual damage and swelling remain for larger doses. In the latter case, these unrelaxed internal stresses give rise to an exfoliation process for higher annealing temperatures

Characterization of the ion-amorphization process and thermal annealing effects on third generation SiC fibers and 6H-SiC

“…MSDA parameters for 6H-SiC amorphization kinetics are consistent with previous reported ones based in RBS and mRS data [25,27] hence confirming x (Si-Si) as a relevant indicative for the amorphization level of the sample.…”

“…Even though amorphous SiC (a-SiC) is known to be highly stable, irradiation-induced damage in SiC can be recovered and the a-SiC layer recrystallized by thermal annealing at high temperatures [25,35]. However, …”

“…it has been reported that thermal annealing has an undesirable side effect. As shown in Figure 8, it induces mechanical failure of the ion-amorphized layers in single crystals SiC [25,36] and in HNS fibers [37]. However, little information concerning thermal annealing-induced mechanical failure is available for SiC.…”

“…The latter is defined as the ratio of C2C homonuclear bonds to Si2C bonds and denoted as x (C-C) , ranging from zero for perfect short-range order to unity for random short-range disorder. Short-range order describes the degree of the chemical state with respect to the local arrangement of atoms, which can be partially preserved even when the LRO is completely lost [20,25].…”

Ion irradiation and radiation effect characterization at the JANNUS-Saclay triple beam facility

“…35 Recrystallization phenomena have been studied after thermal annealing. 18,36 Recently, ex situ Raman spectroscopy has evidenced the presence of molecular dihydrogen in an ODS steel (Fe-12wt% Cr-0.4wt% Y 2 O 3 ) after a triple beam irradiation conducted with Fe 81 , He 1 , and H 1 ions. 24 For in situ measurements, a dedicated device has been connected to the Raman spectrometer and to the triple beam chamber (Fig.…”