Probing the structure of CuInS₂-ZnS core-shell and similar nanocrystals by Raman spectroscopy

CuInS₂/ZnS core-shell and alloyed nanocrystals (NCs) are promising candidates for applications in biolabeling, photocatalysis, solar energy conversion, and light emitting diodes. The growth mechanism and subsequent internal structure of such heterogeneous NCs are therefore of crucial importance, as it strongly affects their optical and electronic properties. Here, we investigated using resonant Raman spectroscopy the structure of CuInS₂/ZnS and Cu-Zn-In-S/ZnS core-shell NCs, as well as the evolution of Cu_2−xS NCs into CuInS₂via the heterogeneous Cu_2−xS/CuInS₂ phase. We demonstrate that the particular phases can be distinguished based on their characteristic Raman modes and tuning the exciting laser energy into resonance with the bandgap of the particular phase.