Formation of nanoscale cracks and fractoluminescence upon destruction of carbon ceramics

We obtained a Raman spectrum for a surface layer of porous carbon ceramic (porosity $\approx$ 5%) of $\approx$ 80 nm thick. The analysis of the spectrum showed that the ceramics contain crystals of silicon carbide 6$H$-SiC and silicon. The destruction of ceramics by diamond microcrystals resulted in fractoluminescence (FL). Its spectrum contained two bands at 1.6 and 1.9 eV. The first is emerged at the destruction of silicon crystals, and the second is emerged at 6$H$-SiC crystals. We obtained the time dependence of the intensity of the fractoluminescence signals with a time resolution of 2 ns. Three types of signals were observed: one is formed when the 6$H$-SiC crystals are destroyed; the second is formed when silicon crystals are destroyed; the third is formed when these crystals are simultaneously destroyed. The appearance of signals is associated with the formation of cracks arising from the breakthrough of barriers formed at the intersection of slip planes of dislocations in silicon carbide and silicon crystals. The size of cracks in 6$H$-SiC has been estimated: the smallest is 5.5 nm, and the largest is $\approx$ 18 nm.