Fig. 2: Basic characterization of Cu2O and Cu2−xSe HNSs samples.

a Schematic illustrating the synthesis process of Cu2−xSe HNSs. b, c TEM images of Cu2O NPs and Cu2−xSe HNSs. d HRTEM image of Cu2−xSe HNSs. Inset: SAED pattern. e HAADF-STEM and corresponding elemental mapping of Cu2−xSe HNSs. f XRD spectra. g Crystal structure of Cu2−xSe HNSs. h EDS survey spectrum. i–k Survey XPS spectrum of Cu2−xSe HNSs (i), high-resolution XPS spectra of (j) Cu 2p and (k) Se 3d. Source data are provided as a Source Data file (arb. units, arbitrary units).