Controlling electron beam-induced structure modifications and cation exchange in cadmium sulfide-copper sulfide heterostructured nanorods

The atomic structure and interfaces of CdS/Cu₂S heterostructured nanorods are investigated with the aberration-corrected TEAM 0.5 electron microscope operated at 80kV and 300kV applying in-line holography and complementary techniques. Cu₂S exhibits a low-chalcocite structure in pristine CdS/Cu₂S nanorods. Under electron beam irradiation the Cu₂S phase transforms into a high-chalcocite phase while the CdS phase maintains its wurtzite structure. Time-resolved experiments reveal that Cu⁺-Cd²⁺ cation exchange at the CdS/Cu₂S interfaces is stimulated by the electron beam and proceeds within an undisturbed and coherent sulfur sub-lattice. A variation of the electron beam current provides an efficient way to control and exploit such irreversible solid-state chemical processes that provide unique information about system dynamics at the atomic scale. Specifically, we show that the electron beam-induced copper-cadmium exchange is site specific and anisotropic. A resulting displacement of the CdS/Cu₂S interfaces caused by beam-induced cation interdiffusion equals within a factor of 3-10 previously reported Cu diffusion length measurements in heterostructured CdS/Cu₂S thin film solar cells with an activation energy of 0.96eV.