Control of the Morphology of Complex Semiconductor Nanocrystals with a Type II Heterojunction, Dots vs Peanuts, by Thermal Cycling

Type II CdSe/CdTe core/shell nanocrystals with a dot shape were synthesized using a modified SILAR technique that incorporates cycling of the reaction temperature (thermal cycling). Conversely, experimental results revealed that the standard SILAR alone produced type II core/shell nanocrystals in a peanut shape (1D). Despite their differences in shape, the optical properties observed for the type II dot- and peanut-shaped core/shell nanocrystals were similar. The dot-shaped nanocrystals were confirmed as core/shell structures with an abrupt type II heterojunction within the experimental accuracy, and the peanut-shaped ones were found to be consistent with CdSe and CdTe separated on the two ends of the rods. Similar techniques were used for the synthesis of CdS/CdSe/CdTe type II colloidal quantum well heterostructures with dot and peanut shapes. For these type II colloidal quantum well structures, the PL peak positions were shown to be readily tunable by varying the CdSe and CdTe shell thickness, something not typically seen for the quantum dots. The PL quantum yield of these nanocrystals were found to range between 30 and 60%.