Colloidal Synthesis of Hollow Cobalt Sulfide Nanocrystals


  • Y. Yin and C. K. Erdonmez contributed equally to this work. This work was supported by the Air Force Office of Scientific Research under award no. FA9550-04-1-0065 and by the Director, Office of Energy Research, Office of Science, Division of Materials Sciences, of the U.S. Department of Energy under contract no. DE-AC02-05CH11231. A. Cabot acknowledges financial support from the Generalitat de Catalunya, Departament d'Universitats, Recerca i Societat de L'Informacio.


Formation of cobalt sulfide hollow nanocrystals through a mechanism similar to the Kirkendall Effect has been investigated in detail. It is found that performing the reaction at > 120 °C leads to fast formation of a single void inside each shell, whereas at room temperature multiple voids are formed within each shell, which can be attributed to strongly temperature-dependent diffusivities for vacancies. The void formation process is dominated by outward diffusion of cobalt cations; still, the occurrence of significant inward transport of sulfur anions can be inferred as the final voids are smaller in diameter than the original cobalt nanocrystals. Comparison of volume distributions for initial and final nanostructures indicates excess apparent volume in shells, implying significant porosity and/or a defective structure. Indirect evidence for fracture of shells during growth at lower temperatures was observed in shell-size statistics and transmission electron microscopy images of as-grown shells. An idealized model of the diffusional process imposes two minimal requirements on material parameters for shell growth to be obtainable within a specific synthetic system.