Fig. 2: Microstructure characterization of the AlGaN/CuO_x-based photoelectrode.

a The XPS peaks of Cu2p. b Top-view SEM images of the bare AlGaN (top; scale bar, 200 nm) and AlGaN/CuO_x NWs (bottom; scale bar, 200 nm). c–e HRTEM image (c, scale bar, 20 nm) and elemental mapping (d, scale bar, 20 nm) of AlGaN/CuO_x NWs (e, scale bar, 2 nm).