Structural dissimilarities between small II-VI compound clusters: MgO and CaO

Mass spectra and collision-induced-fragmentation (CIF) data for sputtered MgO and CaO cluster ions are presented. Two predominant cluster species are found: stoichiometric (MO${)}_{\mathrm{n}}^{+}$ and metal excess M(MO${)}_{\mathrm{n}}^{+}$, with M representing Mg or Ca. Regular pronounced features are observed in the mass spectra, including enhanced abundances of the M(MO${)}_{13}^{+}$ clusters and strong enhancement of the (MgO${)}_{\mathrm{n}}^{+}$ clusters with N=6, 9, 12, and 15. The CIF data indicate a structural dissimilarity between small (n≲8) CaO and MgO clusters. The stable MgO clusters appear to be based on (MgO${)}_3$ subunits, while for CaO clusters, the basic subunit is (CaO${)}_2$. .AE