Fig. 1.

Illustration of the masked cation-exchange process in single CdSe nanowires. The layer of surface ligands of a pristine CdSe NW (a) gets locally exposed to an electron beam that renders it impenetrable for cations (b). The CE reaction initiates in the unexposed regions and proceeds laterally until it reaches the interface with the e-beam irradiated region (c), which results in a heterojunction with an epitaxial sharpness (d). Cu⁺ (Cd²⁺) cations are sketched by blue (magenta) circles, and the arrows illustrate the diffusion directions