Depth profiling free carbon in silicon carbide

A fingerprint for free carbon was identified from the negative ion mass spectra of various carbon and silicon carbide standards. It was found that high-mass carbon molecular species can be used to distinguish free carbon in silicon carbide. Secondary ion mass spectrometry (SIMS) depth profiling (12 keV Cs⁺ primary beam, negative SIMS mode) was used to calculate the useful yield of negatively charged molecular carbon ions from carbon (in various forms) and silicon carbide. The useful yield ratio of C_n^-molecules from carbon to SiC increased with increasing n, meaning higher mass molecular carbon species are more likely to originate from free carbon than silicon carbide. ⁷²C₆- and ⁹⁶C₈^-species were used to depth profile free carbon in chemically vapor deposited SiC/C coatings on SCS-0 and SCS-6 silicon carbide fibers.