Spectroscopic characterization and photoactivity of SiOx-based films electrochemically grown on Cu surfaces

Electrodeposited SiOx electrodes were shown to be photoactive and exhibit n- and p-type effects for electrodes placed in aqueous and organic solutions, respectively. As seen by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron (XPS) spectroscopy, the mechanism of the electrodeposition included reactions with the used electrolyte as well as with traces of water as sources of oxygen and hydrogen. The lowest band gap energy (E-g) of the films of approximately 1.6 eV was observed for the film electrodeposited at -2.5 V in comparison to 1.9 eV for the films obtained at -2.25 and -2.75 V. The depth profiles of Si and O in the films were registered by XPS, secondary ion mass spectrometry (SIMS), and glow discharge optical emission spectroscopy (GD-OES), which showed that Si and O were relatively uniformly distributed across the entire layer of the film. The n-type photoactivity was associated with the evolution of oxygen from the aqueous solution, and the p-type was attributed to the reductive deterioration of the amorphous SiOx deposit and simultaneous photodecomposition of the electrolyte.