In the present study, we have observed silicon-carbon cluster ions (SinCm+) emitted from a Si(1 0 0) surface under irradiation of reactive molecular ions, such as C6F5+, at 4 keV, 1 muA/cm(2). The cluster Si-n up to n = 8 and "binary" cluster SinC up to n = 6 are clearly detected for the C6F5+ irradiation. Stoichiometric clusters (SinCm n = m) except SiC+ and other binary clusters which contain more than two carbon atoms (m greater than or equal to 2) were scarcely observed. The observed clusters show a yield alternation between odd and even n. The intensities of Si-4, Si-6 and Si5C clusters are relatively higher than those of the neighboring clusters. In the case of Si5C, it is considered that doped carbon atom acts as silicon atom. These results imply that the recombination through the nascent cluster emission and subsequent decomposition takes place during the cluster formation.