STRUCTURE OF CAPPED CDSE CLUSTERS BY EXAFS

Clusters of CdSe and CdS capped with -SeC6H5 or -SC6H5 terminations were produced by synthesis in micellar solution. These clusters were studied by Se K-edge EXAFS. Substitution of S for Se in the bulk and cap were done in order to separate the structural information about the cluster interiors from that pertaining to their surfaces. We find that the cluster interiors have bulklike Cd coordinations about the Se, with distances reduced from the bulk by a marginally detectable amount. There is a static strain (dispersion of interatomic distances at low temperatures) of up to 0.0015 angstrom-2, depending on the type of sample. The temperature dependance of the EXAFS Debye-Waller factor is the same as in the bulk, except for the addition of the static contribution. Se atoms on the surfaces are coordinated to interior Cd and chalcogen atoms, to other surface Se atoms, and to C atoms of the capping ligands.