Colloidal synthesis of metastable AuCuS phase nanocrystals and in-situ TEM heating study of their transformation

Introduction: Post-synthetic transformation of as synthesized nanocrystals leads to the novel nanoscale heterostructures that contain multiple distinct material domains coupled together through well-defined solid−solid... [ view full abstract ]

Introduction:

Post-synthetic transformation of as synthesized nanocrystals leads to the novel nanoscale heterostructures that contain multiple distinct material domains coupled together through well-defined solid−solid interfaces which are inaccessible by conventional synthesis methods. Herein we report  a novel, metastable ternary phase, with composition AuCuS, resulting from a colloidal synthesis protocol. Au⁺ ions from solution diffuse into stoichiometric Cu₂S (high chalcocite) disk-shaped nanocrystals obtained by formerly reported procedures (Figure 1a) [1]. Inward diffusion of Au⁺ ions is accompanied by outward migration of an equal number of Cu⁺ ions, resulting in a sort of cation exchange reaction [2]. Independent of the Au concentration in solution, the resulting particles are preferentially Janus-type structures, with the novel phase domain and the remaining Cu₂S one separated by sharp interfaces (Figure 1b). Only in few cases, the nanocrystals evolve entirely into the ternary phase, in which case the energetically favored structure is composed by multiple domains. In addition, the thermal stability of the AuCuS phase has been examined by in-situ heating TEM experiments, during which outwards diffusion of Au and metallic Au domain formation was observed at about 150°C. This is due to the high diffusivity of Au through the Cu₂S template structure, eventually leading to Au-decorated Cu_2-xS nanocrystals (Figure 1c). The initial ternary phase, the mechanisms leading to it starting from the parent high chalcocite phase and its thermal stability will be discussed in detail in this contribution.

References

1. F. Wang et al., J. Am. Chem. Soc. 137 (2015) 12006−12012.

2. D. H. Son et al., Science 306 (2004) 1009-1012.

3. We acknowledge funding from the European Union under grant agreement n. 614897 (ERC Grant TRANS-NANO).