Fig. 3.
a Schematic illustration of the cation exchange transformation of Cu1.8S NCs into sandwich-like heterostructures with ZnS caps. b–f TEM images show the composition change from the initial Cu1.8S NCs b into ZnS f with a thin layer of Cu1.8S. The Cu1.8S disk thickness (t) is indicated. Reproduced with permission from Ref. [89]. Copyright 2014, American Chemical Society. g Scanning transmission electron microscopy (STEM) image of a single partially exchanged hexagonal Cu2Se NC. Two PbSe stripes in the middle of the NC were observed. Reproduced with permission from Ref. [90]. Copyright 2017, American Chemical Society. h TEM image of partially exchanged CdS QD consisting of a heterostructure of CdS and PbS. i TEM image of partially exchanged CdSe QD. Reproduced with permission from Ref. [91]. Copyright 2015, American Chemical Society