Studying the reactions of CdTe nanostructures and thin CdTe films with Ag⁺ and AuCl₄^-

The reactions between Ag⁺ and AuCl₄^- ions with three different CdTe systems, that is, thermally evaporated thin CdTe films, CdTe nanoparticles (NPs) stabilized by thioglycolic acid (TGA), and 20 layers of these CdTe NPs embedded in poly(diallyldimethylammonium) chloride (CdTe-201bl), were studied. We found that AuCl₄^- oxidized the CdTe, in all investigated systems, to form metallic gold. However, the kinetics of the reaction was substantially sluggish for the thin CdTe films than with the CdTe NPs systems. On the other hand, the reaction with Ag⁺ was rather complex, and our findings alluded to different reaction for each system. Although it is possible that a Ag-SR bond was formed between Ag ⁺ and the thiol group of the TGA-stabilized NPs, cation exchange between Ag⁺ and Cd²⁺ is evidenced when these CdTe NPs were embedded in a polymer (CdTe-201bl). Furthermore, Ag⁺ reacted with thin CdTe films to form a precipitate consisting of silver. In addition, we investigated the reactions between locally generated Ag⁺ and AuCl₄^- and CdTe surfaces using scanning electrochemical microscopy (SECM). A flux of silver and gold chloride ions was electrochemically generated from their respective microelectrodes upon applying a positive potential close to thin CdTe films and CdTe-201bl. The flux of AuCl ₄^- resulted in the local formation of Au NPs on the CdTe surface, whreas local quenching of CdTe-201bl was achieved by the flux of Ag⁺ ions. Finally, the current transients recorded during the SECM experiments provided invaluable information regarding the reactions at the CdTe surface below the microelectrodes.