BULK SEMICONDUCTORS FROM MOLECULAR-SOLIDS - A MECHANISTIC INVESTIGATION

We report on the mechanism of the solid-state conversion of a series of II/VI precursors of general formula (R4N+)4[S4M10(SPh)16]4- (R = Me, Et; M = Cd, Zn) to the bulk metal sulfide structure. On heating in vacuum or inert atmosphere, we find that the solid-state conversion proceeds in two discrete reaction steps. The first step, approximately 200-degrees-C, can be characterized as a nucleophilic substitution or elimination initiated by the attack of a fragment of the anion cluster on the tetraalkylammonium counterion. The intermediate solid produced in this step consists of charge neutral M10S16Ph12 clusters that retain the primary cluster size present in the starting material but appear to aggregate to varying degrees in the solid or solution. The intermediate cluster has very different chemical and physical properties from the starting material and, therefore, suggests some new possible routes to the preparation of bulk II/VI semiconductor films and powders from molecular precursors.