Fig. 2: Chemical state and elemental composition analysis of the SnO₂-CuO composite film.

a Sn 3d core level XPS spectra of SnO₂-CuO and pure SnO₂. b Cu 2p core level XPS spectra of SnO₂-CuO and pure CuO. c O 1s core level XPS spectra of SnO₂-CuO, pure SnO₂ and CuO. d Energy dispersive spectroscopy spectrum of SnO₂-CuO film