Applied Surface Science, Vol.493, 1278-1285, 2019
Synthesis of Ag/AgCuS/CuInS2 hybrid nanoparticles by reductive cation exchange and their asymmetric heterostructure
Ag/AgCuS/CuInS2 hybrid nanoparticles (HNPs) were synthesized via a reductive cation exchange method. In this reaction, selective formation of Ag+ vacancies was achieved via direct reduction of Ag +/- ions in AgCuS using a mixture of 1-dodecanethiol and tri-n-octylamine. AgCuS underwent a phase transition from orthorhombic (beta-) to superionic delta-AgCuS phase with a face-centered cubic sulfur sublattice. This phase transition increased cation mobility during the cation exchange process. Below the phase transition temperature, the lower ionic conductivity of the orthorhombic phase prevents cation and hole diffusions through the interface between AgCuS and CuInS2 to stabilize a AgCuS/CuInS2 heterostructure. Transmission electron microscopy analyses revealed that the beta-AgCuS/CuInS2 interface was composed of (010) or (001) beta-AgCuS and (112) CuInS2. Because of the band alignment of Ag/AgCuS/CuInS2, the Ag NP tended to deposit on the surface of the AgCuS domain of the HNP. This selective redox reaction on the AgCuS domain may induce an electromotive force that plays an important role in the formation of the asymmetric heterostructure. Our proposed method may provide a novel strategy for the synthesis and precise structural tuning of metal/semiconductor hetero-nanostructures.