Analysis of the extended defects in 3C-SiC.pdf - Nelson Mandela ...

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with direction. Values published by Perlado et al. (2000) range from 42 – 112 eV for
Si and 26 – 58 eV for C depending on the direction. Heinisch et al. (2004), in a study
on displacement damage in SiC in fission reactors, stated that the displacement value
for Si could be taken as 35 eV and for C as 20 eV since these are the average values
taken over all directions in the SiC the also stated that there are actually four
minimum recoil damage energies that should be considered to create displacements in
SiC, depending on the projectile/target combinations: 41 eV (C/Si), 35 eV (Si/Si), 24
eV (Si/C) and 20 eV (C/C). Vladimirov et al. (1998) used values of 93 eV for Si and
16.3 eV for C in their calculations as well as Ryazanov et al. (2002).
Thus it is obvious that there is still a lot of uncertainty about the correct values for
TDE to be used in calculations for SiC and is as mentioned before, a result of the
anisotropy within the material. Hence the method of computer simulation is used to
determine the displacement mechanisms and TDE in the material.
Gao et al. (2001) used molecular dynamics (MD) software to simulate Si
displacement cascades in SiC. Their simulation showed that during a high energy Si
primary knock on atom (PKA), multiple sub-cascades were generated. This prevented
both a compact structure of displaced atoms to form during the collision phase and a
high-energy density during the thermal spike. They attributed this to the light masses
of the SiC system and small scattering cross-sections of the Si and C atoms.
Furthermore the high melting temperature of the SiC also inhibits the development of
a liquid like cascade which results in a very short lifetime of the thermal spike. This
along with the formation energies of defects provide a physical basis for defect
production and clustering in the material. They found that at the peak of the thermal
spikes the number of displaced Si and C atoms are essentially the same but that the Si
sublattice partially recovers as the energy of the cascades dissipate into the lattice,
while the damage in the C sublattice does not. The number of Si interstitials surviving
after the cascade was on average three times smaller than for C. This is possible since
most silicon atoms are only displaced a short distance from their lattice positions and
recombine during the thermal spike phase. They explain that as a consequence of the
above facts, the formation of a dispersed cascade is seen with defects spread over the
simulation box, and most interstitials remain as single defects. Only a small fraction
of interstitials form clusters, the biggest being four atoms. Furthermore Perlado et al.