+In contrast, investigations of strained Si$_{1-y}$C$_y$/Si heterostructures form
+ed by MBE~\cite{strane94,guedj98}, which incidentally involve the formation of SiC nanocrystallites, suggest an initial coherent precipitation by agglomeration of substitutional instead of interstitial C.
+Coherency is lost once the increasing strain energy of the stretched SiC structure surpasses the interfacial energy of the incoherent 3C-SiC precipitate and the Si substrate.
+These two different mechanisms of precipitation might be attributed to the respective method of fabrication.
+While in CVD and MBE surface effects need to be taken into account, SiC formation during IBS takes place in the bulk of the Si crystal.
+However, in another IBS study, Nejim et~al.~\cite{nejim95} propose a topotactic transformation that is likewise based on the formation of substitutional C, which is accompanied by the emission of Si self-interstitial atoms that previously occupied the lattice sites and a compensating reduction of volume due to the lower lattice constant of SiC compared to Si.
+
+For several reasons, solving the controversial view of SiC precipitation in Si is of fundamental interest.