The study focused on developing synthetic routes for the colloidal synthesis of ZnSe/CdS semiconductor heterostructures, various in size and geometry, and evaluating their applicability to practical realizations. Such composite semiconductor nanocrystals (NCs) with core/shell morphology can be designed to drive an efficient separation of photoinduced charges.
As a preliminary, high-quality ZnSe/CdS core/shell quantum dots (QDs), exhibiting a type II carrier localization regime, were fabricated via a traditional pyrolysis of organometallic precursors. An efficient spatial separation of electrons and holes between the core and the shell was observed for heterostructures containing more than 3 monolayers of CdS, which allows for their potential applications in areas of biomedical imaging, solar cells, and QD based lasers.
Furthermore, colloidal synthesis of ZnSe/CdS barbell-shaped NCs, comprising a type II heterojunction of ZnSe and CdS domains, showed compelling evidence of photoinduced charge separation at the interface of semiconductor materials. The nanobarbells were fabricated in a two-step procedure by growing ZnSe caps onto polar facets of CdS nanorods.
Finally, time-resolved spectroscopy and electrochemistry techniques were used to demonstrate that the attachment of a hole-scavenging surfactant to ZnSe/CdS nanocrystals promotes an efficient transfer of holes to the surface. Specifically, the effect of the shell thickness in core/shell NCs on the ability of core-localized charges to perform oxidative reactions was determined. More importantly, it was observed that holes can be extracted from the core much faster than they recombine with shell-localized electrons, indicating that most of photoinduced holes in these nanostructures can be made available to drive catalytic reactions.