From CdSe Nanoplatelets to Quantum Rings by Thermochemical Edge Reconfiguration

The variation in the shape of colloidal semiconductor nanocrystals (NCs) remains intriguing. This interest goes beyond crystallography as the shape of the NC determines its energy levels and optoelectronic properties. While thermodynamic arguments point to a few or just a single shape(s), terminated by the most stable crystal facets, a remarkable variation in NC shape has been reported for many different compounds. For instance, for the well-studied case of CdSe, close-to-spherical quantum dots, rods, two-dimensional nanoplatelets, and quantum rings have been reported. Here, we report how two-dimensional CdSe nanoplatelets reshape into quantum rings. We monitor the reshaping in real time by combining atomically resolved structural characterization with optical absorption and photoluminescence spectroscopy. We observe that CdSe units leave the vertical sides of the edges and recrystallize on the top and bottom edges of the nanoplatelets, resulting in a thickening of the rims. The formation of a central hole, rendering the shape into a ring, only occurs at a more elevated temperature.

Automated summary

The variation in the shape of colloidal semiconductor nanocrystals is intriguing, and even though thermodynamic arguments suggest a few stable shapes, a remarkable variety in shape has been reported for different compounds. In the case of CdSe, shapes such as quantum dots, rods, nanoplatelets, and quantum rings have been observed. By monitoring the reshaping process in real time using structural characterization and spectroscopy, it has been found that CdSe nanoplatelets can reshape into quantum rings with a central hole at elevated temperatures.