Figure 7.

Schematic depiction of the Cu⁺ for Ga³⁺ cation exchange reaction in Cu_2–xS nanocrystals. (a) Free GaCl₃ reacts as a Lewis acid, extracting S^2–, leading to etching of the nanocrystals. (b) Extraction of S^2– is inhibited when GaCl₃ is complexed with a phosphine ligand. (c) Successful cation exchange involves four steps: (i) cleavage of the Ga–P bond at the Cu_2–xS nanocrystal surface, at which point Ga–S and P–Cu bonds are made simultaneously; (ii) extraction of Cu⁺ by the phosphine; (iii) subsequent incorporation of Ga³⁺ into the nanocrystal; and (iv) reaction of remaining Cl^– with Cu⁺, extracting two additional Cu⁺ ions, completing the exchange.